wmo_337.pdf

WORLD METEOROLOGICAL ORGANIZATION

Operational HydrologyReport No.2

AUTOMATIC COLLECTIONAND TRANSMISSION OF

HYDROLOGICAL OBSERVATIONSprepared hy

the Working Group on Instruments and Methods ofObservation of the Commission for Hydrology

IMO-WMOCENTENARY

I WMO - No. 337 ISecretariat of the World Meteorological Organization Geneva Switzerland

1973

1973, World Meteorological Organization

NOTE

The designations employed and the presentation of the material in this publication do notimply the expression of any opinion whatsoever on the part of the Secretariat of the WorldMeteorological Organization concerning the legal statns of RUy country or territory or of itsauthorities, or concerning the delimitation of its frontier.s.

FOREWORD

SUMMARY

CONTENTS

..................................................................

(English, French, Russian, Spanish) ............................

V

VII

CHAPTER 1 AUTOMATION OF HYDROLOGICAL OBSERVING STATIONS 1

1.1

1.21.2.1

1.2.2

1.3

1.3.11.3.21.3.31.3.41.3.51. 3.61.3.71.4

1.4.1

1.4.2

1.4.31.5

Introduction .................................... 0

Reasons for introducing automation ...........Adequacy af present data collection programme Manual versus automatic ..........................................

Factors affecting choice of instruments and type of installationfor automatic hydrological observing stations .........

Local conditions ..............................................

Sources of power ................................................

Accuracy requirements ..........................................

Proposed life of station .....................................

Maintenance .................................................

Transmission requirements ........................................

Treatment of data ................................................

Selection of instruments ........................................

Network design .

Aids for selection of instruments .

Questionnaire on instruments of proven reliability .Special considerations .

1

222

4577889

10

1010

10

11

11

CHAPTER 2 TRANSMISSION OF HYDROLOGICAL OBSERVATIONS ............. 13

2.1

2.22.32.4

2.4.1

2.4.2

Introduction .

Systems of data transmission .

General considerations in selection of systems .

Transmission links ...............................................

Dedicated land lines .

Commercial telephone lines .

131316171718

IV

2.4.32.4.42.4.52.5

AUTOMATIC HYDROLOGICAL OBSERVATIONS

Commercial telegraph lines ................................. 10 Direct radio links - .

Satelli te links. IO" .Receiving system ........................... 0

18191919

CHAPTER 3 EXAMPLES OF AUTOMATIC TRANSMISSION SYSTEMS FOR HYDROLOGICALPURPOSES. . . . . . . . . . . 21

3.13.23.3

3.43.53.6

Example I (Canada) ............................................Example II (U.S.A.). The Hy-Tel remote rodio telemetry system Example III (U.S.S.R.). Automatic hydrological recording station(AHRS) .Example IV (U.S.S.R.). Mudflow radio warner (MRW) .Example V (France). Tele-snow-gauge with moving horizon to1 beam.Example VI (Hungary). Hydra II automatic digital telemetering

2126

30

3236

system 41

BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . 45

ANNEX 1 Questionnaire on hydrometeorological instruments of provenreliabili ty. . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . 47

ANNEX 2 List of instruments of proven reliability and instruments forautomation of hydrological observations ....... 49

FOR E W0 R D

At its third sessioIT the WMO Commission for Hydrology (CHy) established aWorking Group on Instruments ond Methods of Observation. One of the tasks of theGroup was to complete a report on automatic equipment for observing and transmittinghydrological elements. The G~oup consisted of Messrs. E. Walser (Switzerland)(Chairman), M~ Hendler (Canada), M. F. E. Hinzpeter (Federal Republic ofGermany), E. L. Peck (U.S.A.), K. D. Zavjalov (U.S.S.R.) and H. Schtlfer (IAHS).Dr. K. D. Zavjalov was later replaced by Mr. N. Ja Solov'ev (U.S.S.R.). The reportwas accordingly prepared and is reproduced in this present publication entitledIIAutomatic collection and transmission of hydrological observations".

It is believed that it will be of particular value to national services andin particular to experts who have to install automatic stations and to select for thispurpose the most useful instrumental equipment.

The terms of reference of the CHy Rapporteur on Instruments, Dr. E. L. Peck,required him to collect recommendations from Members on hydrometeorological instru-ments which they have found reliable in specified environments, and to consolidatethese recommendations in a report for the use of Members and others in establishingnetworks. The group therefore maintained close collaboration with him especially incollecting information from Members. Analysis of the information he collectedrevealed that most of it could with advantage be included in the present. report,which is, therefore, the result of the common efforts of the Working Group and of theRapporteur on Instruments.

Taking into account the rapid developments in the field of equipment foroperational hydrology, the report core fully combines the new advanced data collectionand transmission systems with the present conventional approaches, thus increasing itsapplicobility to different stages of development ond modernization in differentcountries. The report is a timely contribution which provides 0 useful link betweensimple, classical instrumentation and the complex modern installations for transmitt-ing data by satellites.

I am pleased to have this opportunity of expressing to Mr. Walser and theother members of the Working Group, and to Dr. Peck, the sincere appreciation of theWorld Meteorological Organization for the time and effort they have devoted to thepreparation of this publication.

~.. .

D. A. DaviesSecretary-General

SUM MAR Y

Most hydrological observation networks and collection systems have developedin response to particular, localized problems or scientific interests without takinginto account future requirements. For various reasons the quality, quantity andtimely availability of hydrological dato are inadequate for present development needsin general, and in particular, for the timely preparation and issuing of hydrologicalforecasts and warnings.

Taking into account the present needs, this report discusses the advantagesand disadvantages of updating, modernizing and automating the data collection systemsin the light of the recent technological progress in automatic instrumentation andtransmission systems for hydrological purposes. Detailed guidance is included con-cerning the choice of automatic instruments and types of installation for variousclimatic and geographical conditions.

A description of basic systems of transmission of hydrological abservationsond guidance for their selection are followed by examples of operational automatictransmission systems for hydrological purposes in various countries. Technical in-formation on instruments of proven reliability is tabulated in a systematic and con-venient form in an annex.

RES U M E

La plupart des reseaux d'observation hydrologiques et des systames de ras-semblement des donnees obtenues grace a cas reseaux ant ete mis au point pour resou-dre des problemes particuliers, d'interet local, au pour repondre a des besoinsscientifiques t sans qulil soit tenu compte des necessites futures. Pour diversesraisons, les donnees hydrologiques one sant pas d'ossez bonne qualite, pas ossez nom-breuses et pos disponibles assez tot pour l'ensemble des besoins de developpementactuels at, en particulier, pour qulil soit possible de preparer at de diffuser atemps des previsions et des avis hydralogiques.

En 56 fondant sur les necessites actuelles, Ie present rapport expose lesQvantages at les inconvenients qulil y aurait a mattre a jour, moderniser at Qutoma-tiser les systemes de rassemblement des donnees, compte tenu des perfectionnementstechniques apportes recemment aux instruments et aux systemes de transmission auto-matiques utilises a des fins hydrologiques. Le rapport contient des indicationsdetaillees sur le choix d'instruments et de types d'installations automatiques adap-tes a diverses conditions climatiques et geographiques.

Une description des systemes fondamentaux de transmission d'observationshydrologiques et quelques directives concernant Ie choix de ces derniers sont suiviesd'exemples de systemes operationnels de transmission automatique utilises a des finshydrologiques dans divers pays. Le lecteur trouvera en annexe un tableau OU sontpresentes de fa~on systematique et commode des renseignements techniques sur lesinstruments dont la fiabilite est etablie.

PE3IDME

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RES U MEN

La mayoria de las redes hidro16gicas de observaci6n y la mayor parte de lossistemas de concentraci6n de datos se han creado para so!ucionar problemas especificosy localizados 0 para responder a intereses cientIficos, pera sin tener en cuento lasnecesidades futures. Por diverses rezones, 10 calidad, cantidad y oportuna disponibi-lidad de los datos hidro16gicos no son adecuadas para satisfacer las actuales necesi-clades en general ni, en particular, para pader preparar y publicar a su debido tiempopredicciones y avisos hidro16gicos.

Teniendo en cuenta las actuales exigencies, en este in forme se examinen lasventajos y desventajas que presenta 10 actualizaci6n, modernizaci6n y automatizacionde los sistemas de concentracion de datos, fund6ndose en 10$ recientes progresos tec-no16gicos en materia de instrumentos automaticos y sistemas de transmisi6n para fineshidro16gicos. Igualmente, se facilitan directrices detalladas para la selecci6n delos instrumentos automaticos y de los tipos de instalaci6n correspondientes a diver-50S condiciones climaticos y geograficaso

A 10 descripci6n de los sistemas b6sicos de transmisi6n de observacioneshidro16gicas y a las directrices para su selecci6n se ocompanan ejemplas de sistemasde transmisi6n automaticos y operativos para fines hidro16gicos en diversos paIses.En un onexo se facilita informacion tecnica sabre instrumentos de reconocida fiabili-dad, presentada en forma tabular, sistem6tica y adecuada.

C HAP T E K 1

AUTOMATION OF HYDROLOGICAL OBSERVING STATIONS

1.1 Introduction

Hydrologicol observing statians measure the primary elements of the hydro-logical cycle. There is an interrelationship between the primary elements andother, predominantly meteorological, parameters. For this reason, hydrologicalobserving stations ore normally equipped with auxiliary facilities for measuringthese parameters.

Automatic observing systems are now in widespread use in different fieldsof geophysics. New generations of these systems are capable of operatinq for moreand more extended periods of time unattended. Highly sophisticated automaticstations have been developed, to correspond to modern demands for transmission includ-ing satellite interrogation and data processing.

There is a need for classification of automatic hydrological observingsystems into a meaningful framework defined in the light of the overall functions ofsystems or stations. Such a classification should be simple because of the complexcharacter of outomatic hydrological systems. When defining a classification,descriptive terms such as "fully-" or II semi-automotic systems" should not be osedbecause they are too qualitative.

FQr the purpose of this report, the following three categories of hydro-logical observing stations are defined:

Automatic hydrological observing station

A hydrological station at which instruments make and record theobservations automatically.

Telemetering hydrological observing station

A hydrological station at which instruments make, but do not record,the observations automatically, and transmit them automatically tothe receiving centre.

Telemetering automatic hydrological observing station

A hydrological station at which instruments make and record theobservations automatically and transmit them automatically to thereceiving centre.

21.2

1.2.1


Reasons for introducing automation

The primary reason for changing to, or increasing the degree of, Qutomationin a data callection network is the need to improve the quality, quantity and/ortimely receipt of the data. Most present day hydrological networks were developedin response to particular, localized problems or scientific interests and not with aspecific objective of satisfying the future requirements for all hydrological purposes.

Many networks depend on manual, in-situ observations by observers. This isa slow and laborious way of collecting data. Consequently, there is often inadequatespatial information for those areas where observers are not readily available. Datafrom such networks are sufficient for simple general hydrological resource studies,but are of only limited value for project planning and operation. In most cases thedata collection programme does not meet the requirements for timely preparation andissuing ofhydrolagical forecasts and warnings or for synoptic monitoring.

As the demands for hydrological planning and forecasting services increase,the agency or agencies responsible for providing such services will be faced with adecision on the need for modernizing the data collection network.

1.2.2 Manual versus automatic

It is often frustrating to maintain a network of stations manned by observerswhen there may be a serious need to change to an automoted system. Changingobservers to improve the quality and/or reliability of reporting is a continualproblem. Although the trend for people to be more mobile has resulted in more fre-quent changes in observers than has been possible in the' past, it is becomingincreasingly difficult to obtain observers who are willing to make measurements onweekends. Moreover, there is a steady rise in the cost of observers, their recruit-ment and training and the processing of data collected from hydrological networksmanned by observers.

Although such factors may make a change to a more fully automated systemappear attractive l there are problems and costs associated with automated systemsthat should be carefully evaluated before a final decision is taken. A cost/benefitapproach should be the primary basis for such a decision. It is, however, extremelydifficult to determine the actual value of either the old or new system or even thecomparative figures. This is especially true when the data are utilized for severalpurposes and costs must be allocated accordingly. In addition to cost comparisons,the following questions should be given careful consideration.

(a) Is there a real need to improve the quality of the data?(b) Is there a real need to increase the quantity of data

(i.e. improve the areal coverage)?(c) Is there a real need to reduce the time required for

receipt of data?

AUTOMATION OF OBSERVING STATIONS

In considering the above questions it should be recognized thot the problem is adynamic one. Rapid chonges in the field of hydrology, instrumentation and means oftransmission of data as well as in the demand for services make it imperative thatanticipated future conditions be given proper evaluation.

3

The automation of data collection systems may reduce or eliminate most humanobservational errors. However, this advontage moy be offset by the introduction ofinaccuracies caused by instability in the sensing, recording or transmission system.Errors resulting from such instability in electronic systems may be much moredifficult to identify and correct than the human ones and quolity control of dot~then becomes highly dependent upon the quolity of maintenance.

A distinct advantage in most automated systems is the continuous recordingcompared to the point measurements obtained by manual observations. For example,continuous flow hydrographs, required for mony hydrologicol analyses, permit thedetermination of maximum and minimum values, which are essential for the developmentand application of mathematical and physical hydrological models that are now incommon use.

The quality of the data may be improved by data collection techniques otherthan the automation of the present system. Remote sensing technology moy providemeans to obtain acceptable areal averages for certain elements. Many such improvedtechniques ore now being developed ond these should be evoluated for the present andfuture requirements before automation of a point measurement network is undertaken.

One of the most obvious advantages of automation is the obility to obtoindata for locations where observers are not available. However, this should not be abasis for a decision to automate the entire network. From a cost consideration themost valuable data collection programme may be one in which automation is used foronly a portion of the area or for only those areas for which data are required on a"real time" basis.

The rapid advancement that is taking place in the fields of instrumentationand data transmission may provide ways and means for improved collection of data inthe near future that would be of great use, at less overall cost than those atpresent in use. Information on considerations that should be given to selection ofa transmission sy~tem is given in Chapter 2.

Careful consideration should be given to the possible advantages to begoined by automating only that portion of the . system required for present andforeseeable needs. However, the initial plans for any automatic system shouldinclude provisions for expansion and for the incorporation of neW technology wheneverpossible. Since the demands for improved data, quality and quantity, normallyincrease with time, a constant effort must be devoted to improve instrumentation.

4 AUTOMATIC HYDROLOGICAL OBSERVATIONS

A description of the various possible procedures as well as different equip-ment used in the handling and processing of' hydrological data is given in WHOTechnical Note No.115, Machine processing of hydrometeorological data. Any decisionregarding the eventual treatment of recorded observations will have a very importanteffect an the type of instruments to be used to obtain the data.

The use of the computer is most, profitable when handling either_ largequantities or very complicated series of observations. It is usually not justifiableto consider this means of handling the data from a small number of stations. Inthese cases, a relatively small staff can handle the treatment of data with 0 minimumof expense. On the other hand, if expansion of the observation network is envisagedin the near future, it wauld probably be reasonable to immediately start developinga system for automatic processing based on the information collected from the initialsmall number of stations.

It should be noted that any existing network, either for hydrological observa-tions or for other parameters, will have an impact on any decision. If, in the opera-tion of the hydrological network, much money has been invested in the past to installanalogue recorders, it could be more economical not to convert to digital recorders,but to continue using the analogue apparatus and available equipment to convert the ana-logue recording to machine input form such as cards and magnetic tapes. Some hydro-logists prefer this latter procedure of having as a basic record an analogue recordingbecause they feel that this type of record permits the person handling the data to havean overall visual check on the information. The existing network should olso be takeninto account to assure that existing interface apparatus be used as much as possible.This would eliminate the purchase of special individual translating equipment to con-vert paper tape to cards, magnetic tape to cards, paper tape to magnetic tape etc. Ifa system does not already exist and the number of installed analogue recorders is mini-mal, it would probably be preferable to initiate digital recorders which can eliminateall human processing of the record.

The treatment of hydrological data in itself does not necessarily justify thepurchase or rental of expensive computers so that, before taking a~y decision, astudy should be made of the computer facilities availoble and their cost, and thepossibility of either adding to these facilities or instolling completely new mochineprocessing equipment.

If the use of computers is contemplated it isrecording instruments should have an output compatiblefacilities.

verywith

importantavailable

that newcomputer

1.3 Factors affecting choice of instruments and type of installationfor automatic hydrological observing stations

In the previous sections the odvantages and disadvantages ofbeen discussed. Once the decision has been made to automate the

automation havehydrological

AUTOMATION OF OBSERVING STATIONS 5

observations at an individuo~ station or 0 network of stations, careful considerationshould be given to the vorious foctors which will offect decisions on the type ofequipment to be instolled. In the following porogrophs, some of the constroints aredescribed. It is understood thot, where different instruments meet the users'requirements, the final decision will be based on the relative pric~ of the equipmentand its availability.

1.3.1 Local conditions

Among the more important and sometimes most difficult constraints whichusually have to be overcome are the local climate and physiographic characteristics atthe proposed observing sites. In many cases the final choice of equipment will, ineffect, be made solely on the capability of the instruments to operate underparticular local conditions.

Climate

The local climate, especially where extreme conditions are found, will havea considerable effect on the choice of instruments and types of installations. Forexample, in polar regions or cold mountainous areas, ice cover on rivers, frozenground, heavy precipitation l deep snow cover, high winds and low t~mperatures mayrequire the use of specially designed equipment and non-standard installations.

Instruments to be installed in such areas would have to be designed to assurecontinuous operation and recording under conditions where temperatures will descend to-400 C and often lower. Moving ports should not contract appreciably with the fallingtemperature; special lubrication should be used (in some cases designs necessitatingno lubrication at all have proved satisfactory); inks should be of non-freezing type(recording devices eliminating the use of liquids are usually preferable); and clock-works or other methods of chart movement have to be of special design to assurecontinuous operation. This latter problem is usually one of the most serious whichhas to be overcome in the operation of automatic equipment in the polar regions. Highwinds which are usually prevalent in these areas will necessitate extremely well con-structed installations because blowing snow can completely fill the instrument shelterif even the smallest of openings is left in the walls of a shelter. Where instru-ments are partially in the water or on the river bed, the presence of ice cover willobviously affect the choice of equipment. In addition, as repair work during winteris practically impossible, this section of the equipment has to be extremely reliableand very well installed thereby minimizing failures.

In order to overcome some of the difficulties caused by low temperatures,various methods for heating shelters have been developed. Where electricity isavailable, electric heating has proved quite successful. On the other hand, ininaccessible areas, different systems using propane gas heaters have been used withsome degree of success either to heat the interior of the shelter or an insulated areaaround the instrument. These heaters have not always proved completely reliable forlong periods of unattended operation. In addition, this type of heater usuallyrequires relatively large amounts of gas so that in remote areas they are fairlyexpensive to operate because of transportation costs. Condensation forming inshelters as a result of the gas combustion has also been a problem.


These are same of the factors which must be considered in the colder partsof the world. Similarly, extremely hot, arid or humid climates give rise to theirown peculiar sets of instrumentation problems. In all extreme climotes, on analysisshould be mode of the conditions which would affect the operation of proposed outo-matic equipment. A valuable aid in this regard is the experience which has beengained by users of various types of : automatic equipment in similar locationDiscussion with these people or reference to the literature may eliminate costlyerrors in the choice of instruments.

The characteristics of the terrain in the immediote vicinity of the observ-ing station play an important role in the selection of equipment. For example, itwould be extremely costly to build wells to house water-level recorders near riverswhere waier-level fluctuations are quite large and the river banks are mostly bedrock.Wells will also be impractical where the river transports great amounts of sedimentwhich will continually block intake pipes. In these cases, a float-type gauge wouldnot be practical and instruments using the hydrostatic principle for detecting water-level chonges should be used.

On the other hand, for rivers having moving beds, it mightany instrument having the detecting section in the stream itself ascarried away. An installation using a well and a float-type gaugepractical.

be unwise to useit might be

would be more

Factors such as the geology of the local terrain and the presence of excessvegetation will affect the selection of the type of installation. Many instruments,in order to operate properly, have to be level, in which case the foundation of theshelter may have to be foirly elaborate in order to ensure that the structure is notaffected by changes in temperature, erosion or plant growth.

In mountainous areas the installation of radio relay stations may be necessaryto provide for the transmission of the data. The initial and mointenance costs may bea significant factor in a decision on automation.

Other conditions

In urban and in certain remote areas, the problem of vandals can beserious and often may necessitate the use of special housing and equipment.addition, wherever possible, exterior portions of any installation should beto avoid tampering.

veryIn

buried

When considering sites in inaccessible areas, difficulties and cost of trans-portation, in some cases, exclude the use of heavy equipment. In these c~ses, boththe type of installation and the instruments themselves should b: chosen w~th dueconsideration to weight and possible difficulties in tronsportat~on.


Animals may prave to be a problem in certain areas and, if so, suitableprotection should be included in the installations.

7

1.3.2

Many of the installations which will be considered in connexion with theautomation of hydrological obser/otions will imply the use of electric power forsensor purposes, chart movement, heating or data transmission. This is one of themost important and sometimes most difficult considerotions in the choice of equipment.If power is available locally, the choice will be relatively simple but, even so, astandby system of batteries may be necessary. This will be the case when, forexample, the observations are being used for flood forecasting and where, duringextreme floods, power lines could often be broken. In order to assure uninterruptedobservation of data during these critical periods, a standby battery system isessential.

If no commercial power is available other sources such as wind-generators,fuel-driven generatars and batteries should be considered. As a first step, a care-ful evaluation of the energy consumption of the observation system should be made.ObviouslYt continuous transmission of data will appreciably increase the power con-sumption. As the use of more sophisticated power supplies, such as generators,involves the possibility of mechanical failure, it is generally preferable, whereverpossible, to employ low-consumption equipment which would permit the use of batteries.The batteries should be carefully chosen to ensure reliable operation under differentclimatic conditions, especially in extremely hot or cold temperatures. Rechargeablebatteries usually involve a large initial expenditure as well as relatively frequentinspections. For most recording instruments, non-rechargeable batteries are avail-able, if required, which guarantee approximately two years of operation beforereplacement.

At present, it is very difficult to obtain recording and transmitting equip-ment as well as power supplies which will completely answer 011 the problemsencountered at ony one site. It should be understood by the network planner thatlocal modifications will almost invariably be nec~ssary to meet the particularcombination of problems arising from both local conditions and power demands.

1.3.3

As hydrological observing stations are installed primarily to obtain data tohelp ensure proper use of water resources, it is evident that the accuracy of themeasurements should meet the standards of those who use the information. Cost ofequipment usually varies directly with its accuracy. Therefore, excessive demandsover and above the accuracy needed by the data users would, in effect l be a waste offinancial resources. This is elso true when the G~curacy demanded from one part ofan observation programme is out of proportion with the results obtained in the overallprogramme.

During the design of an observing proglomme it is therefore obvious that astudy should be made regarding the accurocy needed by the users, both present and

8 AUTOMATIC HYDROLOGICAL 08SERVATIONS

future, as well as of the overall accuracy possible in the various components of theprogramme. Two basic elements should be considered in this regard; firstly,instrumental accuracy in the measurement of the parameter, and seco~dly, timeaccuracy and resolution. The former would affect the choice of sensor and recordingsystem while the latter will govern the selection of the type of clockwork and chartmovement.

When considering water-level~tqg~observationsfor eventual conversion intodischarge data by means of a stage-discharge relationship to be determined by streamgauging, thought should be given to the following points. As the effects ofinaccuracies in water level are relatively less significant at high stages than atlow stages, it is important to decide whether the station is to be operated to supplylow-flow or high-flow information. In addition, it would be useless to considerhigh accuracy equipment for the water-level measurement if local conditions da natpermit precise stream discharge measurement.

This does not preclude the possibility that data users, by justifying theneed for more precise data, would make it necessary to develop more acc~rate streamdischarge measurement (even at a relatively high cost). In view of this, betterquality stage records should be part of the initial programme.

If, far certain reasons such as back water from ice and weeds in the controlsection, precise calculation of discharges using water-levels is impractical,excessive disbursements of money and effort to obtain very accurate levels are notjustified. In general, the highest accuracy (at least 0.003 metres) is usuallyneeded where the aim of the observation is to obtain short duration low-flow data onrelatively small streams. Data requirements such as monthly means or flood flows onvery large rivers do not need extremely precise water-level data (better than 0.03metres), although for establishing peak flows for use in numerical analysis greaterprecision for measuring flood flows may be necessary. If equipment is to cover thecomplete range of stage, it must obviously satisfy the most demanding conditions.

1.3.4

If a station is to be operated for a relatively short period of time, sayone or two years, it would be desirable to select equipment and a type of installa-tion which can be easily moved. In other words, if possible, permanent structuressuch as wells and expensive shelters should only be used where long-term observationsare planned.

1.3.5 Maintenance

In order to derive maximum benefits fromcomplete maintenance of instruments is essential.proper maintenance each have their own effects on

any observing programme, regularVarious problems associated with

the choice of equipment.

The interval between inspections will largely depend uponthe type of equipment and the seriousness of any loss of record.

local conditions,The length of

AUTOMATION OF OBSERVING STATIONS 9

unattended aperation will in turn have its effect on the choice of clockwork and typeof recording (ink, pencil, special paper, etc.). Instruments where charts will bechanged once a week can have a relatively simple clockwork while stations visited ona six-monthly basis would require instruments with relatively complicated andexpensive clockwork. As to the problem of loss of record, it is. sometimes moreeconomical in extremely inaccessible areas to have duplicate installation to permitless frequent expensive inspections and at the same time ensure a minimum loss.

It is preferable that there be uniformity in the type of instruments used ina network. This would simplify the work of the technicians who have to make repairsand would make the stocking of spare parts less complicated. In this _egard, itwould be preferable to use relatively simple and standard equipment so that spareparts are available on demand.

It is also desirable to select an instrument that may be repaired in thefield if necessary with makeshift tools and parts.

It is important that the availability of spare parts is assured for thewhole life of the stations. In certain cases, in the past, because a type of instru-ment has become obsolete, it has become extremely difficult and expensive to obtainreplacement parts for those already installed.

Personnel

It is essential that competent technicians are available to perform theregular maintenance needed. If such personnel are not available a training programmeshould be started as soon as a decision is made to install the relatively complex 'equipment associated with automation. The competence of the actual or proposedpersonnel will be a factor in deciding upon the complexity of the equipment to beobtained. It would not be sensible to acquire instruments which, because of theircomplicated workings, could not be repaired by the available personnel.

It must be stressed that the decisions made have to be long-term; that is,maintenance must be part of the programme as long as it exists. As automatic instru-ments will not operate indefinitively without proper care, no matter what. type ofequipment is chosen, a breakdown in maintenance will result in a high capital expendi-ture with little useful return.

1.3.6

Any decision regarding the type of recorder to be used will have to take intoconsideration the speed with which the data is wanted by the user. If there is noneed for immediate information, an instrument can be installed and the recorded datacollected at any interval, either by a local observer ar by a visiting technician.On the other hand, if data are required immediately as the parameter varies or when itreaches predetermined limits, this might necessitate automatic transmission of thedata. This aspect af autamation is discussed more fully in Chapter 2, especially asta the decisions affecting the choice of mode of transmission. These decisions will


naturally influence the choice of automatic detecting and, if necessary, recordingequipment. There are cases where no local recording is deemed necessary as theinformation is fed continuously into a central computer.

It should b~ noted that even.though immediate transmission of data may notseem essential at the moment, future needs should be considered carefully to avoidhaving to change equipment if and when the need does arise. On the other hand, theuse of automatic recording equipment compatible with automatic transmission generallymeans using more complex instrumentation. As this equipment requires highly skilledtechnicians for maintenance as described in the previous paragraph, this could provea serious constraint in any selection.

1.3.7 Treatment of data

Treatment of data as a factor affecting the choice of instruments andinstallations for the automation of hydrological observing stations has beendescribed in paragraph 1.2.2 above.

1.4 Selection of instruments

1.4.1 ~:!~~:~_~:~~2~The design of a hydrological network must provide for the collection of all

pertinent data to satisfy the purposes of the programme. Thus a key element in theselection of instruments is the network design. Regrettably, design of hydro-logical networks has received comparatively little attention and definitive approachesto the problem are not generally available. To help overCome this deficiency, theWMO Commission for Hydrology has prepared a "Casebook on hydrological network designpractice" (WMO - No.324) which includes theoretical and practical examples of net-works together with explanatory notes on objectives and principles used. The WMOhas also sponsored and collaborated on several papers on network design, including:

Hydrologic networks and methods. Flood Control Series ReportNo. 15, WMO/ECAFE, Bangkok, 1960.

Design of hydrological networks, WMO-No.82.TP.32, 1958.Proceedings, WMO/IASH Symposium on the Design of Hydrological

Networks, Quebec. lASH Pub. No. 68, 1965.Hydrological network design - Needs, problems and approaches.

WMO/IHD Report No. 12, 1969.

1.4.2 Aids for selection of instruments

General guidance pertaining to instruments and methods of observations iscontained in WMO "Guide to hydrometeorological practices" and WMO "Guide tometeorological instruments and observing practices". Although the material in theGuides is specific as to the type of instruments required, no information oncommercially available instruments is included. Another source of general informa-tion is WMO/ECAFE Publication No. 22, "Field methods and equipment used in hydrologyand hydrometeorology".

are available inMast companies have

instruments to meet


The most complete reports on commercial : instrumentsbrochures published by the various instrument manufacturers.representatives who, upon request, will submit proposals fordesign specifications by a planning agency.

11

1.4.3 Questionnaire on instruments of proven reliability--------------------~-----------------------------The WMO Commission for Hydrology also directed its Rapporteur on Instruments

to solicit information from Members on instruments of proven reliability that couldbe consolidated into a report for use by Members and others as an aid in selectinginstruments for establishing hydrological networks.

The Members furnished information as specified by the questionnaire (seeAnnex 1) for those instruments which have been tested and proven reliable underactual operational conditions. Requested information included the name and addressof the reporting organi~ation, detailed information on the reported instrument,operational experience, environmental conditions under which it has been operated andcost data for the basic instrument and for equipment required for transmission ofreports. Details of new instrument development were also reported.

Some 220 responses were received from 31 Members. The replies were fairlyrepresentative for all requested categories except (c) instruments for meteorologicalelements at floating stations for energy balance or mass transfer estimates ofevaporation (see Annex 1).

The responses did not include some instruments that are known to be of provenreliability. However, they did include many of the instruments in use in the basicdata networks of Members.

Tables prepared by the Rapporteur containing selected information on theinstruments of proven reliability are contained in Annex 2 for all categories except(c) mentioned above. Included in the tables are data on some instruments which werereported as under development or in limited use.

Additional information, if desired, on any of the reported instruments maybe obtained upon request to the WMO Secretariat.

1.5 Special considerations

The rapid development in the fields of instrumentation and transmissionsystems makes it extremely difficult for even those most active in the fields to keepabreast of recent improvements and innovations. Direct contact_ with the manu-facturers and agencies conducting research and development is the most reliable ~ethodof keeping informed but potential users should be aware that many new instruments andtransmission systems are generally plagued by technical difficulties during the firstfew years of field test and use. Unless a user is willing to accept the possibilityof economic loss and a delay in achieving operational status, he should rely on thoseinstruments and systems which have proven to be reliable in field use or in nationalnetworks under environmental conditions similar to those anticipated for his area.


Those who consider the development of new instruments or transmission systemsof their own design should recognize the high cost generally ossociated with suchresearch, test and evoluation activities. Initial estimates of costs for suchdevelopment are often much less thon the finol cost to perfect an operationallyacceptable instrument or system.

C HAP T E R 2

TRANSMISSION OF HYDROLOGICAL OBSERVATIONS

2.1 Introduction

During recent yeors, the demonds of users of hydrolgicol data have becomemore and more sophisticated so that the system where an observer makes manualmeasurements of rainfall, water-levels etc. and then mails the results to the analystis becoming more and more obsolete. The need for data has extended to inaccessibleareas where up to now no information has been available. In addition the insistenceon higher quality information as well as rapid receipt of this information has result-ed in drastic changes both in the methods of measuring as well as the means of trons-mitting data.

It is well to note that these recent innovations are relatively expensiveand, in cases where daily readings by a local resident meet the requirements, this maystill be the least expensive operation. On the other hand, as stated above, moderndata requirements eliminate this procedure as an alternative in many cases t and callfor more complicated and expensive measuring stations. It is therefore essentialthat the network planner determine at the outset precisely the type of data he wishesto collect as well as the delay he can tolerate in the use of the information. Theserequirements should be examined attentively when comparing the cost and the outputof different possible systems before making any final decision as to the type ofinstallation to be used.

2.2 Systems of data transmission

The possible methods of transmitting hydrological data are given below in avery ba~ic form, together with comments on their advantages and disadvantages.

SYSTEM 1

Form of telemetered data.radio or telephone call toand supplies instantaneous

Observer at station mails data or initiatescentral office based on pre-arranged criteriareadings only

Advantages. Simple sensoring equipment may be used and malfunctionof sensor is known immediately. Inexpensive (communications paidfor only when used). If necessary can be interrogated from centraloffice

Disadvantages. No automatic recording so that continuousnot available. Quality of observer extremely important.or radio link overloaded at certain critical periods

record of eventsCentral phone

Remarks. Phone calls can be received and recorded automatically on anlIe l ec tronic secretary" and transcribed at any time.


SYSTEM 2

Form of telemetered data. Central affice interrogates by phone, radioor radio telephone, remote automatic station and receives single discretevalues as often as interrogated. It is possible to have an automatic dial-ling device in the control office which could interrogate and record responsesat regular intervals

Advantages. Instantaneaus infarmation can be obtained as required even inisolated areas

Disadvantages. No continuous record. Difficult to determine malfunctionof sensors. In addition to radio or telephone, equipment at station re-quires a device to answer calls for information automaticallyRemarks. Method of answering can be voice recording, short tones forhundredths, tenths, units etc. or one continuous tone the length of which isa function of the value (less accurate). In some instruments a memory canbe included so that upon interrogation continuous or extreme data can bereceived for a pre-determined period prior to the call. Cost can vary from$1 000 to $5 000 depending on complexity of system. When using FM radio thecost of radio antennae is normally the main portion of total cost particu~larly at remote and distant sites.

SYSTEM 3Form of telemetered data. Automatic equipment.at station programmed toinitiate phone or radio call to supply particular single instantaneousobservation

Advantages. Immediate alert of extraordinary hydrologic conditions

Disadvantages. No continuous record.sensors. Specia~ device necessary tocriteria

Difficult to determine malfunction ofinitiate calls based an predetermined

Remarks. As this system is normally an alert-oriented unit, it is usuollyon a private line to a receiver who is always on call.

SYSTEM 4Form of telemetered data. An impulse is transmitted automatically by phoneor radio for specified unit of change of porameter (each centimetre of changeof water-level for example)

Advantages. Complete record of change of events as they occur

Disadvantages. Malfunction of sensors can be detected only after a certaininterval of time (for example; due to malfunction no change detected inparameter and therefore no signal emitted). Reliable power supply very im-portant

TRANSMISSION OF HYDROLOGICAL OBSERVATIONS 15

Remarks. Infarmation received usually recorded on a graphical or digitalrecorder at central station. Cost of equipment (using rental telephone lines)approximately $3 000 plus telephone line rental usually based on distance.

SYSTEM 5

Form of telemetered ,data. An impulse is transmitted automatically by phoneor radio'at predetermined 'intervals of time

Advantages. A total record is obtained

Disadvantages. Reliable supply power very important

Remarks.teletype

SYSTEM 6

This form of in-formation transmissionor satellite re-tronsmission.

is especially suited for

Form of telemetered data. A combination of systems 4 and 5 is possible;that is, unit changes in the measured parameter are stored and transmittedat set intervals of time.

SYSTEM 7

Form of telemetered data. Data are transmitted and recorded on a continuausbasis through electrical wires fram a device that' produces an electricalsignal in proportion to the value of the parameter being monitored (analoguetransmission)

Advantages. A total record is obtained immediately

Disadvantages. Distance from sensor to user is limited to a few thousandfeet maximum

Remarks.

SYSTEM 8

Normally each sensor is connected to a separate receiver.

Form of telemetered data. Data ore transmitted on a continuous basis overradio or telephone by equipment that converts observations to a continuoustone or frequency. This information is reconverted at the receiving site(frequency modulation)

Advantages. A total record is abtained immediately

Remarks. Systems using telephone line can cover any distance through theuse of signal repeaters (amplifiers) along the way. FM radio usuallyapplies to line-of-sight distance only. AM radia can be used over greaterdistances but is more subject to atmospheric interference.


SYSTEM 9

Form of telemetered data. Remote field sites equipped with data sensors,encoder and radio transceiver transmit coded information to a central officewhere information is decoded and fed to a computer which has initiated thesequential calls

Advantage. System is completely automatic

Disadvantages. Very expensive and complex to service

Remarks. S~stem usually included programme where . predeterminedobservations are brought to the attention of the system operator.links or orbiting Earth satellites can be used for transmission ormission.

extreme. FM radio

re-trans~.

2.3 General considerations in selection of systems

When considering the possibility of including automatic transmission of datain any measuring system, consideration should be given to the following:

(i) Accessibility or inaccessibility of the measurement sites}Obviously where a statian is located in an area where accessibility

is extremely difficult and expensive, it would probably be preferableto have automatic recording as well as telemetering of the data.

(ii) Reliability of alternative recording device;In certain cases, because of rigorous local climatic conditions, the opera-

tion of on-site mechanical equipment is difficult and it is more reliable simplyto transmit information electronically to be recorded in a central climate con_trolled office. In addition, this type of system permits a continuous check ofthe operation of the sensors. .

(iii)Speed with which data is required;

(a) Time between observations and receipt of the data by the analyst(b) Time required to procees and analyse the data(c) Speed with which changes in the parameter take place and what

effect these parameters have on the regime in question(d) Accrued benefits of forecasts from telemetered data as well as

cost due to lack or delay of knowledge.

(iv) Staffing and logistic problems;Localobservations or a surveillance of. on-site recording equipment

requires qualified personnel in the vicinity of the measuring station whichimplies a relatively large number of qualified personnel. On the other hand,a centrally controlled telemetering system would necessitate the use of a very

TRANSMISSION OF HYDROLOGICAL OBSERVATIONS 17

much smaller proportion of technicians versus number of measuring stations, eventhough this latter personnel would have to be very highly qualified.

These are some of the more important criteria to beplanning process but each individual project will have its owncareful attention should be given to all the alternatives withfits before any final decision is made.

considered inparticularitiestheir costs and

theandbene-

When designing a system for the automatic transmission of measured data, thethree main components to develop are:

(a) Measuring and encoding equipment;(b) The transmission link;(c) Receiving, decoding and analysing.

While developing each of these units separately, it is necessary to considerthe three together in the design stage. This is essential as the special character-istics of anyone of these components can have serious Gonsequences on the decisionsregarding the others.

The type of installation for measuring and transmitting the data will dependgreatly on the parameter or parameters to be measured especially as regards theirvariability with time and space, the climate in the area which would affect the choiceof sensor, power supply etc. and the type of transmission to be used witb considera~tion given to the distances to be covered.

2.4 Transmission links

The type of transmission link used is determined by the frequenQY bondrequirements and economics. Availability locally of anyone of the alternate choicesis a constraint. Possible choices for transmission links include: dedicated landlines, commercial telephone or telegraph lines, direct radio links, satellite re-transmission systems.

2.4.1 Dedicated land lines

These are perhaps the easiest to install when relatively short distances areinvolved and no commercial lines already exist. Land lines are typically able totransmit frequencies of up to 3 000 Hertz* without special techniques. Time divisionand frequency multiplexing** can be used to provide more economic use of the trons-mission line.

* Hertz is a unit of frequency.

** The process of using one transmission line to transmit several measurements iscalled multiplexing.

18

2.4.2


When the distances invalved are lang and existing telephane systems exist,usecan be made af these. Equipment exists to enable the instrument to simulate thebehaviour of a relatively normal subscriber to the telephone service. Measurementsand commands can be transmitted to and from the remate site.

2.4.3

The use of commercial telegraph lines to transmit data on request from a re-mote site is illustrated in Figure 2.1.

Commercial teletype network

Tope advance . 3control lines

Paper tape loopextended outof recorder

2

".";-3

Leaend

1 _ Punch paper tope water-level recorder, float operated2 - Teletype tape reader head3 _ Teleprinter4 - Punch tope 'output5 - Hard copy printout

Figure 2.1 - Teletype equipment system. The system works asfollows: the operator activates the recorder tape advance tobring the last data punch within range of the reader; then thetape reader is activated; data on tape are transmitted viateletype lines to the receiving equipment; autput appears as aduplicate of the punched paper tape record gathered unattendedon site as well as a print out of the data

2.4.4

TRANSMISSION OF HYDROLOGICAL OBSERVATIONS

Direct radia links

19

These must be used when the data frequency requirements exceed thase avail-able over land lines.or when distances ar natural obstacles prevent the economicinstallation of wires. Distonces of kilometres to hundreds of kilometres may bespanned by radio transmitters, depending upon the frequency and power avoilable: Atthe higher frequencies, the tronsmitter and receiver must have a cleon line-of-sighttronsmission path. This limits the range without repeater stations.

In all cases, installation and operation of radio transmission links isgoverned by national and international regulations.

2.4.5 Satellite links

Data transmission from satellites can take place in two ways;of data as observed by sensors in the satellite (including photogrophs)data observed at remote ground stations to central receiving locations.

transmissionor by relaying

At present, the science of observation and transmission or retransmissionfrom satellites is developing rapidly and during the next few years, enormous amountsof data will be available either directly from the space craft or through central databanks. The Geostationory Operational Environmental Satellite (GOES) System scheduledfor launch in 1972 is an important addition to the World Weather Watch network. Thissystem is a good example of the two types of transmission mentioned above, and moredetailed information is available from the Director, National Environmental SatelliteService, National Oceanic and Atmospheric Administration, Washington, D.C. 20031,U.S.A.

It should be noted that the METEOR meteorological space system has alreadybeen established and is operating successfully in the Soviet Union. In the METEORsystem orientations are used in relation to the centre of the Earth and the course ofthe satellites. The satellites contain apparatus for collect ian and tronsmission ofinformation; the system also comprises a surface network for the collection, process-ing and dissemination of information obtained from the satellites including receivingstations, recording apparatus and data-processing machines, including electroniccomputers.

More detailed information about this system and the results of its utiliza-tion are available in the report IIProgress in the use of data from satellites in theHydrometeorological Service of the U.S.S.R.'~which can be obtained from the WMO Secre-tariat.

2.5 Receiving system

The eventual use of the data will govern the type of equipment needed for thereceiving end of any automatic transmission system. In a relatively simple system,regular calls- by the analyst to the measurement site coupled with simple analyses couldbe sufficient. On the other hand, in complex situations where complicated analysesprecede rapid decisions, it might be necessary to couple continuous transmissionsthrough the necessary decoding system to a computer which would be programmed to makethe required decisians. Added to this could be a system for alerting certain desig-nated peaple in such cases as flood or typhoon alerts for example. Figure 2.2 is


that af a system where anly extraardinary events are telemetered.order to eliminate continuous transmission on telephone lines thevery expensive.

This is done inrental of which is

-------1IIIIIIIIIIII

___ l ~

IJ\MnnJLJUlIlIL-------,

---.-'--

t

~-

81-Legend

1 _ Data transmitter. Analogue water-level do to are converted into electric-al digits

2 _ Memory unit which con store minimum ormaximum water-level information and tensuccessive water levels

3 _ Dialing unit which automatically callsa predetermined party in the event of anunusual water_level condition

4 _ Announcing unit which when addressed,announce5 the existing water-level,the rising or falling tendency, thelost high or low water or any of theother stored doto

5 _ Tilller6 _ Punch paper tope recorder7 - Power supply unit8 _ Telephone

Figure 2.2 - Tele-announcing system. The system works as follows:the tele-announcer is installed in place of an ordinary telephoneset and addressed by dialling the number of the telephone line. Inthe case of an unusual water-level change, the dialling unit pro-duces a series of pulses corresponding to a codified call numberand switches on the tele-announcer. On receiving a call in thecase of an unusual event! a punch paper tape recorder is activatedto store over a pre-set time period the water level changes at one-minute intervals. These data are available to the authorities con-cerned, or shortly after the event

C HAP T E R 3

EXAMPLES OF AUTOMATIC TRANSMISSION SYSTEMS FOR HYDROLOGICAL PURPOSES

3.1 Example I (Canada)

The following is an excerpt from a report written in 1969 by H. C. Belhouse,D. W. Colwell and J. S. Dickson, Meteorological Service of Canada, describing theapproach taken by this organization in the development of hydrometeorological auto-matic telemetering stations in the Columbia River basin of Canada.

At the beginning of our study, very little work wos being done in outomaticreporting of hydrometeorological parameters. The sensors available were principallydesigned for local recording. Also, in the commercial equipment available, a gapexisted between heavy industrial and sophisticated space-oriented techniques, neitherof which was suited to our needs.

Without available equipment specifically designed for our requirements, therewas little choice but to undertake the task of filling this gap ourselves. This meantthat it would be necessary to set out from basic principles in assessing our mountainenvironment and in discovering what equipment would be most reliable under these con-ditions.

The approach taken was to begin with existing, simple equipment, with no il-lusions of immediate success. At best what was hoped for was a fuller understandingof the environment and related equipment problems, to yield more specific objectivesfor later development phases.

In basic concept, the system would consist of a self-powered and unattendedremote station on a mountain observing site which would automatically measure andtransmit data by radio link to an attended base station where the report would be auto-matically recorded.

Assumed requirements

Environmental implications~ Certain assumptions had to be made about themountain environment, as a basis for initial design: operating ranges were establish-ed for temperature (-400 F to + 1200 F), wind (120 miles per hour), snow loads (100inches of water equivalent) and icing of radio antennae and towers (2 inches).

Reporting of parameters. The system was intended to report precipitationand temperature data which could be used to estimate mountain runoff into the Columbia


River watershed. The requirement was for up to eight reports per day of accumulatedsnowfall (water equivalent to ~ 0.1 inches) and of ambient temperature ( 10F).

Siting implications. A primary objective was that the observing site berepresentative of the' snowpack oreo in question. The measurements were to be madein a mountain meadow below the tree line with good drainage, minimum drifting of snowand low avalanche hazard. Since line-of-sight radio transmission to the base stationwas almost surely a necessity, a remote location meeting all these conditions wouldprobably be hard to find, and .not easily accessible. Installations would thereforebe difficult if the equipment was not easily portable, at least by helicopter. Asfrequent maintenance visits would be costly and impractical, the remote station wouldbe required to operate reliably and unattended for periods of four to six months.

Base station. It was assumed that a base station, suitably located forline-of-sight radio reception, would be served by telegraph or other primary communica-tions, for manual relay by the local operator of the automatically recorded data trans-mitted from the mountain site.

In parallel with the undertaking of long-term design and development, arecording precipitation gauge was installed on Mt. Fidelity in British Columbiaduring the winter of 1963-64 for an initial assessment of environmental problems.The gauge, with an Alter shield attached, was placed twelve feet above the groundon a metal tower.

The outcome of this experiment was an unquestionable verification of ourfears that wet snow clings tenaciously to rough surfaced gauge housings and chainedAlter shields, causing IImus hroom" overcopping of the gauge orifice and rendering thegauge completely inoperative.

Having a technique with which we hoped to overcome this problem, we then pro-ceeded to assemble existing sensors, encoders, radio and power supply equipment intoa first prototype telemetering system.

The dial pointer position of a Taylor mercury-in-steel thermometer and therecorder pen arm position of a Leupold and Stevens telemetering precipitation gaugewere detected by follower devices, servo-driven by Telemark drum encoders. Data fromthese encoders were transmitted by IItaxi ll radio equipment to a strip-chart eventrecorder.

The power consumption of the radio transmitter was such thatbattery would not be sufficient. A thermo-electric generator consumingpropane per year was added to replenish the battery charge continuously.

a lead-acid400 pounds of

This equipment was housed in a sectional fibreglass dome eight feet in heightand diameter, which was complete with ventilation pipes for the generator and a four-foot stack protruding through the roof to allow precipitation to fall into the gauge.

EXAMPLES OF TRANSMISSION SYSTEMS 23

The stack was tapped by a three foot metal cone, blackened and ~ silicone-treated toavoid snow adhesion, and having a ten-inch orifice at the top.

The entire ossembly was to be installed above the maximum snow level on awooden platform, to allow access for servicing.

In a pre-assessment of this configuration, the complete system was evaluatedat our Toronto test site, while a second dome, with stack and catch cone and a pre-cipitation gauge were installed on Mt. Fidelity to provide ~information on environ~mental effects.

Results. This strategy proved worthwhile in the early identification ofserious shortcomings of the system, making possible major redesign of these criticalareas before engaging in an arduous mountain test programme.

The propane power supply was cumbersome and in fact unreliable, and all laterequipment was redesigned for minimum power consumption to allow the exclusive use ofbatteries.

The precipitation gauge did not adequately represent the snow on the groundand was inaccurate even when an Alter shield was employed. More promising snow-on-ground sensors were later used to replace the gauge.

While the silicone-treated catch cone appeared to remain free of snow, theaccumulation on the dome itself and on the support tower threatened to overcap thegauge orifice. The deletion of the power generator and the precipitation gauge laterallowed a great reduction in shelter and support size.

To aid the full system redesign which was progressing at the Toronto labora-tory this first telemetering prototype with a few important changes, was installedduring the winter 1965-66 on a mountain meadow near Enderby, British Columbia.

A low power solid state radio transmitter allowed operation of the remotestation with a lead-acid battery, and further mountain environment and telemetry linkchecks were possible.

The Enderby tests showed that radio telemetry and battery power were feasible.The precipitation gauge however underweighed the snow as it had done at Toronto, andhigh snowfall rates caused some pile-up in the gauge because of surface dilution of theantifreeze.

March,cone.

wooden

The silicone treatment of the catch cone again avoided snow adhesion, but bybuild-up on the dome itself had reached to within six inches of the top of theComplete overcapping of the orifice was only averted when the collapse of the

tower under the extreme snow load terminated the winter's test.

Following the investigation of experimental problems with available hardware,the next two years were devoted to the identification of more suitable instrumentationfor a final prototype. Various sensor alternatives were explored, component models


were constructed and mountain tested. In this process there were several failures,but each led to a better understanding and subsequent approach to the problems involv-ed. More favourable sub-units slowly emerged, were refined and adapted into agradually improving prototype system. Some of the approaches used in this process,and the results and experience gained thereby, are worthy of note.

Tubular steel anemometer towers, suitably guyed, were used for basic support-ing structures, with functional equipment mounted in weatherproof boxes well aboveground to be clear of, or easily accessible through, the higher winter snow level.It was found however that forces were exerted on the 3/8 inch stranded steel guys byadherence, compaction and steeling of the snowpack itself, to the extent that some guysbroke, and others caused local bending of the tower as much as a foot off the vertical.It was faund that linear thermal contraction af the guy wires accentuated this problemgreatly and that leaving sufficient slack at the time of installation removed thefault.

Nickel-cadmium batteries and lead acid cells both proved unsuitable as powersupplies, because of current leakage to ground and high degree of susceptibility todamage even with careful handling. It was nevertheless felt that batteries of suit-able durability and performance still remained the only feasible answer to the powerproblem.

With electronic equipment, three major problems arose. Ever-present humid-ity caused extreme corrosion of normal contracts and connexions, calling for bettermaterials and protection, and electronic design less .. sensitive to this problem.Several components considered and even specified as suitable for particular applica-tions such as low temperatures were in fact found to be very critical for theseapplications and had to be re-selected. Fail safe devices installed for systemreliability resulted in some cases in causing system shut-down themselves, and had tobe refined for proper performance and better indication of system malfunction.

On the more positive side, the introduction of solid state programming andcontrol and use of binary-coded-decimal transmission showed immediate benefits inreliability, flexibility and lower power drain.

~u:r:n! ~p~r~a:hThe pratotype equipment now under test at the Enderby site represents a

feasibility model of final system design, based on the concepts evolved during ourstudy. The prototype incorporates our best solutions thus far to the problems en-countered, and is designed to provide not only a reliable but also a versatile system,capable of wide application to remote sensing needs.

Components which survived the evolution stage have been retained, such as thesnow pillow, the tipping bucket raingauge, the radio equipment and the chronometricclock which iriitiated transmission.

Sub-units which have been refined or completely modified include: supportstructures, sensors, analogue-to-digital devices, telemetry control and programming,power supplies and recording methods.


Support structures. The remote station equipment other thon sensors andantennae is enclosed in weatherproof metal boxes, which are presently mounted at thebases of the most resilient, unguyed, ground-rooted towers we were able to supply athand-toPPed-and unlimbed trees. The above snow sensors and the radio antenna aremounted above the maximum expected snow level.

Two coi1CejJf:s here are 'worthy of note. _. 'Firstly, the- placing of equipment onor even in the ground reduces tower loading and the snow cover provides good protec-tion from the environment. Secondly, while our use of trees os towers is notnecessarily advocated for long-term application, we feel that permonent structuresshould be designed with parollel characteristics and performance.

Sensors and encoders. While the raingauge and snow pillow have been retoin~ed from earlier models, the thermistor and its onalogue-to-digital encoder, and thepressure detector and encoder for the snow pillow are new designs and show greatpromise.

The temperature encoder is a simple electronic device. for digitizing ofresistance and appears to be reliable. Accuracy and linearity of this unit will beimproved before inclusion in the final system.

The snow pillow pressure digitizing encoder in this model is very good. Thedesign is essentially based on that of an open mercury manometer, employing a servo-driven micrometer lead screw to detect mercury level.

Programmer control. The readout of sensors, digitizing and scanning of dataand format of sequential transmission of information is directly controlled or accom-plished by a solid state programmer, the design of which is based on digital computerlogic functions.

Power supply. Alkaline "dry" electrolyte primary cells make up the batteryused to supply the remote station. These batteries are efficient at low temperatures,and are capable of operating the system for up to two years, depending on the fre-quency of reports and the number of batteries used.

Recording. An automatic electric typewriter equipped for computer-typedata input is employed at the base station to record both telemetered data and date/time information provided locally. The design of the telemetry link/recorder inter-face equipment is based on the same logic functions as the remote station programmer,and effectively reverses the role of that equipment by converting the sequentialbinary-coded-decimal transmission of data into parallel output for the typewriter.

Results. Outside of one period when records were interrupted by failure ofthe printer input power supply at the base station, operation of the system has beenvery satisfactory. The remote station did fail to transmit data for one two-dayperiod, but it was found that the ambient temperature had dropped below the designoperating minimum of _300 Fahrenheit. As soon as the temperature rose above thatpoint, normal operation was resumed automatically.

From our point of view, however, the most encouraging feature of theis the proving of the inherent reliability of the remote station equipment.

systemAt the


time of writing, no basic failure has occurred after over four months of continuousoperation.

Conclusion

At this stage, the specific purpose is to report snowpack parameters, fromremote mountain areas in the Columbia River watershed, to a manned base station. Thesystem as it stands will report up to three parameters, and will produce a record onelectric typewriter or punched paper tape.

The telemetry system is simple and versatile, however, and is adaptable toalmost any dedicated communications link: direct radio transmission, landline, tele-phone, or any combination of these. It will also be possible to provide thefacility for operation with existing land-line or radio teletype networks.

As the system is modular, it is possible to add other parameters to itsreport: wind speed and direction and total precipitation are examples where existingsensors can be incorporated, along with suitable encoders. Reporting of other paro-meters will be feasible when reliable - low-power sensors become available. Forexample, a simple humidity sensor not susceptible to contamination would be a verywelcome addition for many purposes.

The aim of such system versatility is to provide wide applicability to meetother needs. Few, if any, of these will . impo~e such formidable constraints ofenvironment and long term reliability as those of the mountain stations for theColumbia network, and in most cases the modular equipment will then constitute on easyand direct solution to the problem. Design features and components of this equip-ment have already been adopted in the development of a remote wind reporting stationon the Queen Charlotte Islands. Distinct opplications are foreseen for forestrypurposes as well.

Such equipment should now easily meet the needs expressed to MeteorologicalBranch for hydrometeorological reporting from other major river basins. The equip-ment could also accept hydrological inputs such as water-level sensors, and could infact be used to upgrade existing hydrological recording networks into telemeteringnetworks of both hydrological and hydrometeorological data.

3.2 Example II (U.S.A.). The Hy-Tel remote radio telemetry system

Since September 1968, the Notional Weather Service of the United States hasoperated experimentally a hydrological telemetry network in the American River Basinof California. This system, known as Hy-Tel (Hydrologic Telemetering), is manu-factured by the Astro-Met Division of Thiokol Chemical Corporation of Ogden, Utah,U.S.A.

The network provides precipitation, temperature and snow water equivalentdata for use in river, flood and water management forecasting. Sensors for otherparameters such as wind direction and speed, dew point, radiation, etc. are beingdeveloped. The system is designed to read up to 22 separate sensors.


The basic philosophy in planning the Hy-Tel system was that the remotestations b~ kept as simple, inexpensive and as reliable as possible. The basestation at Sacramento, California consists of a console with digital readout, a radiowith antenna and a radio remote unit. The base station, which will normally be in aconvenient location and a controlled environment, will contain the bulk of thesophisticated equipment.

The present readout is manually controlled. Code buttons are punched foreach remote data station and the data is presented visually by numbers which light upon the control console, after the call button is pushed. A more sophisticated read-out is available at added cost which will call up the data stations automaticallyon a programmed time basis and print out the data on a teletype machine.

Hy-Tel is a complete system. It includesbut all the components of a data collecting system;d~cers, antennae and towers -(se~ Figure 3.1).

not only the radioincluding gauges,

telemetry link,sensors,- trans-

To maintain the simplicity of the remote station, the data is kept in ana-logue form until it is received at the base station. The data at the remote stationis represented by the frequency of an audio tone. As the measured parameter changes,the frequency of the tone changes. The audio tone, in turn, frequency modulates theradio frequency carrier. Thence, the system is a VHF FM-FM telemetry system (UHF isavailable as an option). The data is conveyed to the base station on an r-f carrierwhich is frequency-modulated by a subcarrier which is in turn frequency-modulated bytransducers at the remote data station. The r-f carrier is demodulated by the basestation receiver, and the frequency modulated subcarrier is presented to the sub-carrier discriminator. The output of the subcarrier discriminator is a DC voltagewhich is digitized by a Digital Voltmeter (DVM) and visually displayed as a numberbetween 000.0 and 100.0. The number is interpreted as a- percentage of the fullscale of the parameter being measured; i.eo, if temperature is the parameter beingmeasured (suppose the temperature range is _15 0F to 1100F) then a base station displayof 000.0 would correspond to _15 0F, and a display of 100.0 would correspond to 1100F;readings in between would be determined from the transducer calibration curve.

Remote stations are called up by a two-tone sequential code (address) trans-mitted from the base station. A remote station address is selected by depressing onetone button in each of the two rows of ten buttons located on the front panel. Thestation is then called by pressing the front panel CALL button. Up to 100 stationscan be called from the base station.

A microphone is included with the base station, permitting voice communica-tion with the remote data stations.

Operational specifications include:

Environmental-operating temperature

Electrical-power

600F to 1100F (Base station)-200F to 1250F (Remote station)117 VAC/60 Hz (Base station)15V Battery (Remote station)

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l>=i

~....

n

~'"o....

~oOJUl1"'1

'"~;::j

~Ul

Interfacemod,uleI

II

Sensors

'-

III

I I1 ,r- I 1L ..,. __ , "End.-of-messog .1I generator II 11 II , Voltage I II . Controlled I 1I Oscillotor " II II ',. II I I Permeobili ty I1 "r


This system has proved to be highly reliable through three seasons of opera- .tion under very adverse conditions of rain, snow and sub-zero weather. Very littlemaintenance has been required other than the usual preventive and annual maintenancevisits. .

Battery operation at remote stations has been more than satisfactory. Thestations have operated for periods of up to a year without battery replacement. Thisis true in spite of hourly interrogation during pro19nge~ r~iny periods. Normaloperation calls for daily call-up shifting to hourly during critical storm periods.

Double mass plots comparing the Hy-Tel catch with nearby:gauges has shownvery close correlation throughout the season.

Radio reliability has been outstanding. The only problems have been at~hose sit:s where the ra~io path is marginal, and these could be improved by the,nstallat,on of a mounta,n-top relay assuring a clear path from sensor site to basestation.

. The Hy-Tel 9ystem has the advantages of low initial cost as well as lowmalntenan~e cost. In ar~as where no AC power is available, its ability to operateon battenes for long penods unattended is a definite advantage.

In the western United States, during the past several years, a large numberof telemetered hydrological networks have been established. This is due mainly tothe large number of agencies engaged in water management that require hydrological andmeteorological data from remote areas, In the State of California alone there arethirty-six such data collection networks operated by use of either radio or telephonecall-up.

A major development currently in the planning and procurement stage is theuse of a synchronous orbiting satellite as a reloy for hydrological and meteorologicaldata.

A multi-year (1967-69) test using the ATS I satellite has proved the feasi-bility of such a system to - telemeter streamgauge and precipitation data. Three..stations in California, Oregon and Arkansas were used. Data were relayed through t\~faxed satellite to the readout at Mohave, California.

The new system using the GOES satellite will interrogate a network of streamand precipitation gauges in the western U.S. The reports will then be relayed, fromthe data collection platforms to the National Weather Service River Forecast Centers.

It is possible, using such a satellite relay system, that the lorge numberof independent data collection networks could be consolidated into one. Data call-up could be programmed by computer and transmitted by land lines to the individualuser.


3.3 Example III (U.S.S.R.). Automatic hydrological recording station (AHRS)

The automatic hydrological recording station developed in the U.S.S.R. is in-tended to perform routine observations at hydrological stationB when systematic stor-age of observed data is required for a given period (not less thon a month) and whenthe data has 'to be presented in a form suitable for further processing by electroniccomputers for hydrologicaf;1:ud'ies.

AHRS consists ofa standard tape puncher.The information from eacho digital impulse code.

Sensors

a sensor unit and an automation unit which has a memory andThere are ten sensors for measuring hydrological elements,

sensor is transmitted to the automation unit in the form of

The first two sensors measure woter-level and temperature. A hydrostoticwater-level gauge is used as a water-level sensor. Its operation is based on trans-ducing hydrostatic water pressure into a mercury column movement in a manometer. Thechange in the mercury column is, in its turn, transformed into a digital impulse code.With some modifications, the instrument can measure water~levels from 0 to 3, 6, 9,or 12 metres.

An automatic temperature gauge consisting of a thermometer with a platinumresistor is used as a temperature sensor. Measured temperature is transformed intoa digital impulse code. The device allows water temperature measurements within therange from 0 to +400 C.

The automation unit

The automation unit is designed for automatic'datahydrological sensors according to the prearranged programme.gramming device, an information coding and storage device, aFigure 3.2). '

storage supplied byIt consists of 0 pro-

memory and a feeder (see

The programming device is a combination of circuits controlling successiveprogrommed operotions of the whole system. In it signals of time are coded into abinary decimal code to be punched on a paper tape. The device consists of a masterclock (1), timing generator (2), intermediate frequency divider (3) and time-keeper(4).

The e device consists of input devices (50 9depending on electronic counters (60 9)' storage -,(7), digital formation check circuit (8), intermediate storage - (9), matching'device (10), sensor of operational combinations (11), a sensor number dialling set(12) and a control device (13).

The memory (14) stores the information during the unattended period. Atape puncher serves os a memory and a standard paper tape, 17.5 mm wide, is used asthe information carrier.


I

The feeder (15) guarantees power supply by alternate current circuit and byaccumulators.

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50 oQ : I 8 I---

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L .....I I I 6 I I /2 I I 11 II 5u I I 9 I I

15 I I 13 If I I 3 I l /,21I I .-

Figure 3.2 - Block diagram of the AHRS automotion unit

AHRS specificatians.---.~ _.- - - - - -

(i) The AHRS system permits the automotic recording of 10 hydrologicol parameterssupplied by the sensors.

(ii) The information is supplied to the automation unit: by all sensors simul-taneously in a digital impulse code.

(iii) The time and measurements are recorded on a punched tape in a binary decimalcode.


(vii)

(iv) The whole measurement cycle is 5 minutes.(v) The measurement frequency may be varied by an aperatar and may be performed

on-an hourly, two-hourly, or once or twice a day basis.(vi) The accuracy of measurements:

Water-level (1-2) cm.Water temperature t 0.2C.

Hydrological sensors may be at a distance of up to 2 000 m from the auto-mation unit.

(viii)

(ix)

(x)

The automation unit operates satisfactorily at temperatures from _350 C to+350 C and an air humidity up to 98 per.cent; the puncher at temperatures

fr~m 0 to 300 t and an air humidity up ~o 70 per cent.The dimensions and the weight of the automation unit are 850 x 500 x 400 mmand 95 kg, respectively.The AHRS automation unit is installed in a shelter for protection against_9t~ospher~c influences (rain, wind, etc.).

3.4 Example IV (U.S.S.R.). Mudflow radio warner (MRW)

Introduction

Sudden temporary torrents appear in mountainous regions as a result ofheavy rain storms i snow melt and flushins from glacial, moraine-dammed lakes, causingmudflows which are a dangerous phenomenon inflicting heavy damage and casualties.

Protection against mudflows has been a matter of great concern. Variousprecautions are taken for this purpose in the areas where mudflows are likely tooccur: mud dams and chutes are erected, special mud flow watch and warning servicesare established, etc.

The mudflow radio warner is intended to w

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