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1.3 Since 15 March 2011, the AUTO METAR system has been
operational 24/7 at Rotterdam-The Hague Airport (EHRD). This was
the final step of the introduction of the AUTO METAR system at
civil airports, military airbases and off-shore structures in the
Netherlands, although further improvements to the AUTO METAR system
itself are planned for the near future. Professional meteorological
observers are currently employed by KNMI only for carrying out
aeronautical observations at Amsterdam Airport Schiphol (EHAM). The
added value of the observer with respect to the capacity of the
Mainport Schiphol makes their presence undisputable for the
moment.
1.4 The rationale for introducing the AUTO METAR system is cost
savings as local MET offices and local observing staff at airports
are no longer required. The current state-of-the-art of observation
techniques and technology is such that it is possible to provide an
automated observation of good quality if specific measures are
taken into account. At the same time, the AUTO METAR system
facilitates the possibility to acquire meteorological information
from airbases that are closed and unmanned during weekends and from
off-shore structures on the North Sea so that a denser, both
temporal and spatial, network of aeronautical meteorological
observations becomes available to users.
2. DESCRIPTION OF THE AUTO METAR SYSTEM
2.1 The term “AUTO METAR system” is used to denote the entire
system used for the automated production of all meteorological
aeronautical reports, of which the AUTO METAR is one. The system
does not only designate the sensors, the associated technical
infrastructure for data acquisition, data processing and data
dissemination in suitable formats, but also includes: back-up
sensors, systems and procedures; remote monitoring by
meteorologists and service staff; communication with users covering
daily briefings, intermediate updates and handling of sensor or
system maintenance or malfunction; and provisions for local points
of contact for the verification of the local meteorological
situation. The AUTO METAR system also includes the documentation,
the procedures and the service level agreement with ATC.
2.2 It is important to note that the content of the observation
reports itself can differ between airports or between states, e. g.
an AUTO METAR that contains pressure, wind direction and wind
speed, air temperature and dew point only versus an AUTO METAR that
contains visibility, clouds, weather and TREND as well. The AUTO
METAR system used at civil airports in the Netherlands always
contains the full set of parameters although not all weather
phenomena and descriptors are included due to limitations of
automated observations.
2.3 There are different “flavours” of the AUTO METAR system used
in the Netherlands. At off-shore structures, the system has no
redundancy and generates only the AUTO METAR every half-hour which
is disseminated without human interaction. At civil airports, the
AUTO METAR system includes back-up sensors, system redundancy and
back-up procedures; AUTO METAR reports (as well as auto local
routine and auto special reports which are generated); and all
reports are disseminated after verification and complementation
remotely by a meteorologist.
2.4 Although the individual components of the AUTO METAR system
have proven reliable, redundancy has been taken into account in the
set-up used at civil airports and airbases. This includes measures
ranging from back-up sensors using independent components of the
observation infrastructure to redundant server systems. The set-up
used at Rotterdam-The Hague Airport only has single points of
failure for visibility and runway visible range, which needs to be
assessed in the touchdown zone of the runway in use, and clouds due
to the availability of a single sensor for these parameters. In
case visibility information at touchdown is not available, it may
be possible to approach the runway from the other side which has
its own visibility sensor for instrument precision approach and
landing operations.
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Alternatively, the remote aviation meteorologist, using
available information including images of video cameras and or
consulting of ATC staff, can advise whether visual flight rules
conditions are applicable or not.
2.5 The AUTO METAR system produces meteorological observation
reports that meet ICAO requirements and includes coding issues such
as: UP (unknown precipitation); TS (lightning); NCD (no clouds
detected); and CB/TCU (convective clouds). During the evaluation of
the AUTO METAR system various complaints of users were related to
the lack of representativeness of automated visibility and cloud
observations. The situation experienced by local users conflicted
with the observations reported by the AUTO METAR system or the
latter showed a large delay. It should be noted that these user
complaints were partly related to the unfamiliarity of ATC staff
with the details of the measurement systems and internationally
agreed observation principles. The measurements principles and data
processing algorithms have been documented and the characteristics
of the automated results have been provided to users. In some
cases, the situation could be improved; for example, by using a
so-called marked discontinuity criteria in the averaging of
visibility and also the criteria for issuing an auto local special
report, such as the delay after reporting an improvement of the
situation, have been redefined by mutual agreement.
2.6 The handling and reporting of missing, incomplete or
incorrect sensor information has been facilitated and agreed with
the users. Missing or incomplete information is indicated in the
meteorological reports either by an invalid entry in the
corresponding group or by adding a suitable remark. Incorrect or
missing sensor information can be overruled orally by the aviation
meteorologist, which is logged in the shift reports and voice
recorded by ATC and KNMI.
3. EXPERIENCE WITH THE AUTO METAR SYSTEM
3.1 The time between the introduction of the AUTO METAR system
and the acceptance by ATC has been used to acquire experience with
the AUTO METAR system, its performance and characteristics. In this
period changes have been made to the AUTO METAR system, including
the documentation, communication and procedures used. Several
assessments have been performed, both by KNMI and ATC, which
provided useful information on pending issues. Sometimes it turned
out that the technical items identified by KNMI were not essential
issues for users; instead, users had a need for additional
information or service from KNMI. The assessments also gave
recommendations that have either been solved or are under
investigation with the parties involved.
3.2 Several technical improvements are currently under
investigation. However, the usage and usefulness of all the
elements contained in the (auto) local routine and (auto) special
reports are also being investigated. Issues are, for example: which
elements are actually used; whether parameters other than wind and
visibility should be runway dependent; which elements should differ
for the separate arrival and departure reports that are issued at
Amsterdam Airport Schiphol; and whether it is necessary to include
a TREND in the auto local routine and auto local special
reports.
3.3 The introduction and acceptance of the AUTO METAR system in
the Netherlands was a difficult process. Several factors influenced
this process, such as the emotions of staff involved; the
perception that the system is operated without technical
supervision and without monitoring by a meteorologist at a remote
location with the possibility to provide additional information;
unfamiliarity with the added value of a local observer and
characteristics of automated weather observation products; and lack
of experience with similar systems and the impact on operations and
safety. The auto local routine and auto local special reports
turned out to be the most crucial parts of the acceptance process.
Open discussions between the parties involved clarified the key
issues of the (AUTO) METAR system
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and were beneficial to the acceptance of the AUTO METAR system
and its quality. One key issue was that ATC and KNMI agreed on a
pro-active role of the aviation meteorologist in case of
significant deviations from the expected or perceived
meteorological situations or for specific events.
4. ACTION BY THE AMOFSG
4.1 The AMOFSG is invited to note the contents of this
information paper.
— — — — — — — —
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AMOGSG/9/IP-8 Appendix
APPENDIX
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
i
Table of contents Table of contents
.......................................................................................................................................
i 1. The AUTO METAR system
...................................................................................................................
1 1.1 Introduction
.........................................................................................................................................
1 1.2 AUTO METAR – a container concept
.................................................................................................
1 1.3 Description of automated aeronautical meteorological reports
at civil airports .................................... 2 1.3.1
Definitions
........................................................................................................................................
2 1.3.2 Characteristics
.................................................................................................................................
3 1.3.3 Coding practices
..............................................................................................................................
4 1.3.4 Availability and distribution channels
...............................................................................................
5 1.4 Description of automated aeronautical meteorological reports
at military airbases ............................. 6 1.5
Description of automated aeronautical meteorological reports at
North Sea off-shore structures ........ 6 2. Observation
infrastructure of the AUTO METAR system
......................................................................
7 2.1 Components of the observation infrastructure
....................................................................................
7 2.1.1 Meteorological sensors
....................................................................................................................
7 2.1.2 Sensor layout at EHRD
....................................................................................................................
7 2.1.3 Sensor layout at other locations
.......................................................................................................
8 2.1.4 Video camera system at EHRD
.......................................................................................................
9 2.1.5 Video camera system at other locations
........................................................................................
10 2.1.6 SIAM sensor interface and
multiplexer...........................................................................................
10 2.1.7 Server systems
..............................................................................................................................
11 2.2 System redundancy and backup measures
......................................................................................
11 2.2.1 Backup sensors
.............................................................................................................................
11 2.2.2 Infrastructure redundancy
..............................................................................................................
11 2.2.3 Backup procedures for visibility and clouds
...................................................................................
12 2.2.4 Server redundancy
........................................................................................................................
12 2.3 Optimization of the observation infrastructure
...................................................................................
13 2.3.1 Backup measures
..........................................................................................................................
13 2.3.2 Sensor issues
................................................................................................................................
13 2.3.2.1 Insects reduced visibility
.............................................................................................................
13 2.3.2.2 Representativeness of visibility and cloud observations
.............................................................. 14
2.3.2.3 CB/TCU information
....................................................................................................................
15 2.3.2.4 Video cameras
............................................................................................................................
15 2.3.3 Reporting rules
..............................................................................................................................
15 2.3.4 Documentation issues
...................................................................................................................
15 3. Supervision of the AUTO METAR
system...........................................................................................
16 3.1 Monitoring of the AUTO METAR system status
................................................................................
16 3.1.1 Sensor
status.................................................................................................................................
16 3.1.2 Monitoring by service staff
.............................................................................................................
16 3.1.3 Monitoring by operator
...................................................................................................................
16 3.2 Remote verification and complementation
........................................................................................
17 3.2.1 Video camera images
....................................................................................................................
18 3.2.2 Local sensor information
................................................................................................................
18 3.2.3 Regional sensor information
..........................................................................................................
19 3.2.4 Other sources of information
..........................................................................................................
20 3.2.5 Communication
..............................................................................................................................
20 3.2.6 Complementation
..........................................................................................................................
21
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
ii
4. Introduction process of and experiences with the AUTO METAR
system ........................................... 22 4.1 Task
Force Update Criteria (AUTO) SPECIAL
..................................................................................
22 4.2 Assessments of the AUTO METAR system
......................................................................................
23 4.2.1 Technical assessment by KNMI
.....................................................................................................
23 4.2.2 Safety assessment by KNMI
..........................................................................................................
24 4.2.3 Safety assessment by ATC (LVNL)
...............................................................................................
25 4.2.4 Assessment of system performance
..............................................................................................
25 4.2.4.1 Phase 1 availability of sensor information
...................................................................................
25 4.2.4.2 Phase 2 availability of (AUTO) METAR and elements
................................................................ 26
4.2.4.3 Phase 3 availability of (AUTO) ACTUAL and (AUTO) SPECIAL
and elements ........................... 26 4.2.4.4 Phase 4
analysis of situations with non-representative values
.................................................... 27 4.3
Stakeholder Consultation and User Satisfaction
...............................................................................
28 4.4 Handling of user
complaints..............................................................................................................
30 4.5 Future improvements
........................................................................................................................
31 4.5.1 Video Cameras
..............................................................................................................................
31 4.5.2 Representativeness of cloud observations
.....................................................................................
31 4.5.3 CB/TCU cloud types
......................................................................................................................
32 4.5.4 Representativeness of visibility observations
.................................................................................
32 4.5.5 Visibility observations corrected for insects
....................................................................................
32 4.5.6 Representativeness of weather observations
................................................................................
32 4.5.7 Improved precipitation type discrimination
.....................................................................................
32 4.5.8 Content of reports
..........................................................................................................................
33 4.5.9 Documentation
..............................................................................................................................
33 5. Conclusions and lessons learned
.......................................................................................................
34 6. References
.........................................................................................................................................
37 Appendix A: Fact sheet update criteria (AUTO) SPECIAL
......................................................................
38
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
1
1. The AUTO METAR system
1.1 Introduction Since March 15, 2011 the so-called AUTO METAR
system is operational at Rotterdam The Hague Airport (EHRD). As a
result the weather observations are performed fully automated, but
supervised by a meteorologist in the central weather room at the
main premises of the Royal Netherlands Meteorological Institute
(KNMI) at De Bilt. The automation of meteorological observations
started at KNMI in November 2002 when all synoptic meteorological
observations were fully automated. Using the same instruments and
related equipment, but with algorithms tailored to suit
aeronautical requirements, automated aeronautical meteorological
observations were introduced at Groningen Airport Eelde (EHGG) and
Maastricht Aachen Airport (EHBK) in May 2004. First this so-called
AUTO METAR system was used only during closing hours of the
airports, but since August 2007, after an evaluation by Air Traffic
Control The Netherlands (ATC/LVNL), the AUTO METAR system became
operational 24/7. From 2005 onwards the AUTO METAR system was
introduced on production platforms at the North Sea. Currently 13
off shore platforms are fully equipped. In 2008 the AUTO METAR
system was introduced on nine military airbases. The AUTO METAR
system was introduced at Rotterdam The Hague Airport beyond opening
hours in December 2010 and has been operational 24/7 since March
2011. The introduction of the AUTO METAR system at Rotterdam The
Hague Airport was for the present the final step. Professional
meteorological observers are currently employed by KNMI only for
carrying out observations at Amsterdam Airport Schiphol (EHAM). The
added value of the observer with respect to the capacity of
Mainport Schiphol makes their presence undisputable for the moment.
The rationale to introduce the AUTO METAR system is twofold.
Developments in observation techniques and technology lead to the
belief that it is possible to provide an automated observation of
good quality. At the same time the introduction of the AUTO METAR
system leads to significant cost savings as local MET offices and
local observing staff at an airport are no longer required. As a
by-product the AUTO METAR system facilitates the possibility to get
meteorological information from airbases that were closed and
unmanned during weekends and from productions platforms on the
North Sea so that a denser, both temporal and spatial, network of
aeronautical meteorological observations became available to the
users. In this document the AUTO METAR system operational at
Rotterdam The Hague Airport and the process of how it was achieved
and approved are presented.
1.2 AUTO METAR – a container concept It is important to
recognize the distinction between the product “AUTO METAR” and the
“AUTO METAR system” and to bear this in mind when reading this
document. The product “AUTO METAR” is a routine observation at an
aerodrome and is issued as meteorological report for dissemination
beyond the aerodrome. The prefix AUTO in the report is to indicate
that the report is generated without intervention of a human
observer at the aerodrome concerned. The term “AUTO METAR system”
is used to denote the entire system used for the automated
production of the meteorological aeronautical reports, and includes
all automated observation reports, of which AUTO METAR is one.
These reports are:
• AUTO METAR; • AUTO SPECI; • AUTO Local Routine Report, in this
report referred to as AUTO ACTUAL; and, • AUTO Local Special
Report, in this report referred to as AUTO SPECIAL.
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
2
The term “AUTO METAR system” does not only designate the
sensors, the associated technical infrastructure for
data-acquisition, -processing, and the generation and dissemination
of the meteorological aeronautical reports in suitable formats. The
AUTO METAR system also includes the information of remote sensing
systems for the detection of lightning and CB/TCU, the usage of
backup sensors and systems, and the remote monitoring by
meteorologists and service staff using suitable tools including
e.g. real-time sensor data displays and video camera images. The
meteorologist also adds the TREND to the reports. The system also
includes the communication with the users covering regular daily
briefings; intermediate updates for sudden changes in
meteorological conditions; handling of sensor or system maintenance
or malfunction; and provisions for local points of contact at air
traffic control and the airport itself that can be used for the
verification of the local meteorological situation. Finally, the
AUTO METAR system also includes documentation, procedures and the
service level agreement with ATC. It is also important to note that
the content of the observation reports itself can differ between
airports or between states. E.g. an AUTO METAR that contains
pressure, wind direction and wind speed, air temperature and dew
point only versus an AUTO METAR that contains visibility, clouds,
weather and TREND as well.
1.3 Description of automated aeronautical meteorological reports
at civil airports A more detailed description of the automated
meteorological aeronautical reports at civil airports at The
Netherlands is provided underneath.
1.3.1 Definitions The “AUTO METAR” is an aviation routine
meteorological report for dissemination beyond the aerodrome. The
meteorological information contained in the AUTO METAR is generally
representative for the aerodrome and its immediate vicinity. The
AUTO METAR is generated at H+20 and H+50 using corresponding sensor
information and is disseminated after validation and addition of
the TREND by a meteorologist at a remote location. The time label
of the AUTO METAR is H+25 or H+55. The “AUTO SPECI” is a similar
meteorological report as the AUTO METAR. The only difference is
that the AUTO SPECI is issued in between the fixed time intervals
of the AUTO METAR when certain criteria are met, e.g. a change of
the visibility exceeding specified thresholds. As the METAR and
AUTO METAR are produced half-hourly in The Netherlands the SPECI
and AUTO SPECI reports are not produced at civil airports in
accordance with ICAO Annex 3 (paragraph 4.4.2 b) standards. The
“AUTO ACTUAL” is an aviation local routine meteorological report
for landing air traffic disseminated at the aerodrome. The
meteorological information contained in the AUTO ACTUAL is
generally representative for the touchdown (take-off) zone or the
situation along the runway. The AUTO ACTUAL is generated at H+20
and H+50 using corresponding sensor information and is disseminated
after validation and complementation by a remote meteorologist. The
meteorologist adds the TREND to the AUTO ACTUAL and can set
indicators for specific weather phenomena (cf. section 1.2.1.2).
The time label of the AUTO ACTUAL is H+25 or H+55. The “AUTO
SPECIAL” is a similar meteorological report as the AUTO ACTUAL. The
only difference is that the AUTO SPECIAL is issued in between the
fixed time intervals of the AUTO ACTUAL when certain criteria are
met, e.g. a change of the visibility exceeding specified
thresholds. Note that there is a difference in representativeness
between AUTO METAR and AUTO SPECI at one side and AUTO ACTUAL and
AUTO SPECIAL at the other side. The same applies for several
elements in the reports itself. E.g. the 10 minute averaged wind
speed and direction is reported in the AUTO METAR whereas in the
AUTO ACTUAL the 2 minute averaged wind is reported. Furthermore the
wind of a designated wind sensor is used in the AUTO METAR whereas
the wind corresponding to the runway in use is reported in the AUTO
ACTUAL. Finally it should be noted that the criteria used for
issuing a SPECIAL, determined by national agreement, can differ
from the international SPECI criteria.
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
3
1.3.2 Characteristics The coding and contents of the automated
meteorological reports are basically equal to the manual reports
although there are some differences. Apart from the inclusion of
the term AUTO itself and specific codes related to sensor
limitations like NCD (No Clouds Detected) or UP (Unknown
Precipitation) some weather phenomena or descriptors are not
reported in the automated reports since there are no suitable
sensors to detect them - e.g. patches of fog (BC) or smoke (FU).
Also note that the AUTO METAR, AUTO ACTUAL and AUTO SPECIAL are not
fully automated since all reports are monitored and complemented by
a meteorologist at a remote location, nor are the METAR, ACTUAL and
SPECIAL completely manually generated. The so-called visual
parameters related to visibility, cloud and weather information are
generally entered manually, but most fields in the METAR, ACTUAL
and SPECIAL are filled in automatically using processed sensor
information. The meteorologist (or observer in case of a METAR,
ACTUAL or SPECIAL) can discard the sensor value. In such an event
the backup sensor is used automatically for most parameters, but
for some, like RVR at touchdown, no alternative can be given.
Identical information in manual and automated meteorological
observation reports The following parameters are measured
automatically and reported identically in reports compiled by a
human observer and in automated reports:
• Wind • RVR • Air temperature • Dew point • QNH and QFE
In addition the runway in use is indicated by ATC and reported
automatically in the (AUTO) ACTUAL and (AUTO) SPECIAL.
Meteorologists at the central forecast office at De Bilt monitor
the observation and shall, when appropriate, add the following
items to the automated reports:
• RSM: runway state message (AUTO METAR only) • LLTI: low level
temperature inversion ((AUTO) ACTUAL and (AUTO) SPECIAL only) •
Windshear report • Windshear forecast ((AUTO) ACTUAL and (AUTO)
SPECIAL only) • TREND: a two hour forecast at the end of the
observation report
Note that at Amsterdam Airport Schiphol (EHAM) the local
observer adds the above items to the reports, but the Windshear
forecast and TREND are added after consultation with the aviation
meteorologist at De Bilt. Differences between manual and automated
meteorological observation reports Visibility
• The visibility reported in AUTO METAR, AUTO ACTUAL and AUTO
SPECIAL may occasionally vary compared to a manual observation in
situations where visibility is rather inhomogeneous. This is due to
the point measurement principle in automated reports. For example,
when fog is reported in automated reports and no fog is present
above the runway, visibility at the runway may be higher. The
differences can be most pronounced between METAR and AUTO METAR
since an observer reports the prevailing visibility, i.e. the
greatest visibility which is reached within at least half of the
horizon circle or within half of the surface of the aerodrome,
whereas the AUTO METAR reports the 10-minute averaged, or 2 to 10
minute averaged in case of a marked discontinuity, visibility
assessed by a designated visibility sensor.
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
4
RVR • RVR and visibility for usage in local MET reports are
determined automatically for ACTUAL and
SPECIAL as well as for AUTO ACTUAL and AUTO SPECIAL. However,
the RVR is not included directly in the local MET reports. A RVR
indicator is included instead, which informs ATC whether one or
more of visibility sensors at the aerodrome reports an RVR or
visibility below 1500 m. In that case ATC starts requesting the RVR
of all visibility sensors. The RVR indicator is set automatically
in the AUTO ACTUAL and AUTO SPECIAL, whereas it is set manually in
ACTUAL and SPECIAL.
Clouds • Cloud base height reports in automated reports are
based on observations by laser ceilometers.
Cloud cover (cloud amount) is derived by using a specific
algorithm to account for the fact that a ceilometer provides point
measurements. The cloud algorithm converts a 10-minute time series
of individual cloud bases reported by the ceilometer into cloud
layers each with a corresponding cloud base height and cloud
amount.
• The information of a ceilometer and a nearby visibility sensor
are used to distinguish between a cloud base and sky obscured. In
the latter case the vertical visibility is reported instead of the
cloud base and amount.
• Cloud type in the form of cumulonimbus (CB) or towering
cumulus (TCU) will be included in automated reports based on an
algorithm which uses lightning, weather radar reflectivity and
satellite information.
• Additional information about the convective characteristics of
the clouds through (near) real time weather radar observations is
available via the Meteorological Watch Office (MWO) at De Bilt,
Meteorological Self Briefing units, ATC centres and via the
aviation weather website of KNMI.
Present Weather Automated meteorological reports contain a
subset of present weather codes, not the complete set as used in
METAR, ACTUAL and SPECIAL reports.
• Present weather in the vicinity of the aerodrome cannot be
observed and therefore the code VC is not used in automated
reports.
• If precipitation type cannot be determined by the sensor, the
code UP (unknown precipitation) is reported.
• The following weather phenomena or descriptors are not
reported: FC, SS, DS, PO, SA, DU, FU, VA, MI, BC, PR, DR and BL
(see ICAO Annex 3, Appendix 3 paragraph 4.4.2 for explanation of
codes).
• Observations of present weather are carried out by a present
weather sensor located on a fixed location. Only weather occurring
at that specific location will be reported.
• Thunderstorms (TS) are reported when lightning is detected
within a distance of 15 km from the aerodrome reference point (ARP)
based on information gathered by the national lightning detection
network.
1.3.3 Coding practices Codes not provided in automated
meteorological observation reports
• FC, SS, DS, PO, SA, DU, FU, VA, MI, BC, PR, DR and BL (see
ICAO Annex 3, Appendix 3 paragraph 4.4.2 for explanation of
codes).
• VC: vicinity. • CAVOK: clouds and visibility OK. • SKC: the
term "sky clear" is no longer used in manual and automated MET
observations.
Codes used in automated meteorological observation reports
only
• AUTO: indicator of an automated report. • NCD: no clouds
detected. When the sensor does not detect clouds and no CB/TCU are
detected,
the code NCD is reported due to the point measurement principle.
• UP: unknown precipitation. When the type of precipitation cannot
be determined by the present
weather sensor.
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AUTO METAR system at civil airports in The Netherlands:
Description and experiences August 5th, 2011
5
Codes used in manual and automated meteorological observation
reports
• NSC: no significant clouds. When no clouds of operational
significance (cloud base 5000 ft or more and no CB/TCU) are
observed, the abbreviation "NSC" is used.
Additional remarks in the REMARK section AUTO METAR can contain
up to three remarks in the REMARK section. The REMARK section is
disseminated in the Netherlands only, in line with international
data exchange rules.
• RMK TS INFO NOT AVBL: in situations where lightning data is
not available. • RMK CB INFO NOT AVBL: in situations where weather
radar information is not available. • RMK WX INFO NOT AVBL: in
situations where the local present weather sensor data is not
available. These REMARKs are for the moment disabled in AUTO
ACTUAL and AUTO SPECIAL as the broadcast system of ATC is not yet
capable of translating these codes into a voice message. As is the
case with ACTUAL and SPECIAL, the meteorologist can add REMARKs on
visibility, TS, CB, HAIL or Tornado, SEV SQUALL, Clouds and
Turbulence in AUTO ACTUAL and AUTO SPECIAL. Coding of missing
information in automated meteorological observation reports It is
essential that the absence of weather or cloud information in an
automated report is clearly identified as either the result of the
absence of the phenomena itself, or due to failure of the sensor.
In the first case the associated group is sometimes omitted in the
(AUTO) METAR whereas in the latter case the group is indicated by
two or more slashes. When ceilometer information is not available
due to technical reasons, the cloud group will be reported by using
six slashes "//////". In that case it may still be possible to
report “//////CB” or “//////TCU”. The unavailability of weather
information will be indicated by "//" and the unavailability of
visibility information by "////". Similarly, forward slashes are
used to indicate the unavailability of all other parameters. The
AUTO ACTUAL and AUTO SPECIAL are distributed to ATC as a comma
separated file, which is then automatically translated into a
broadcast via the Automatic Terminal Information Service (ATIS).
The available strings have always a distinct content. When an item
is not available due to reporting practices the item is indicated
by a space “ “. When an item is not available due to technical or
other reasons the item is given as “N.A.”.
1.3.4 Availability and distribution channels The AUTO METAR of
Rotterdam The Hague Airport is disseminated internationally in the
AUTO METAR format via the Aeronautical Fixed Telecommunication
Network (AFTN) and available via the regional Operational
Meteorological (OPMET) centres. The AUTO METAR is nationally
available via Teletext and the aviation website of KNMI. The AUTO
METAR is also available via the Amsterdam MET Broadcast (VOLMET)
and available on the Closed Information Circuit System (CCIS) of
ATC. It should be noted that the METAR and AUTO METAR are made
available and disseminated via the main office of KNMI at De Bilt.
The AUTO ACTUAL and AUTO SPECIAL are locally available only via the
Automatic Terminal Information Service (ATIS), the system of ATC
that broadcasts the meteorological information to the pilots. The
reports are also available on the Closed Information Circuit System
(CCIS) of ATC. It should be noted that apart from the
meteorological information contained in the AUTO ACTUAL and AUTO
SPECIAL ATC also receives near real-time sensor information,
specifically wind and RVR. The AUTO ACTUAL and AUTO SPECIAL and
sensor information is generated on the airport server system and is
made available to ATC via a local network connection.
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1.4 Description of automated aeronautical meteorological reports
at military airbases Military airbases provide AUTO METAR, AUTO
SPECI, AUTO ACTUAL and AUTO SPECIAL. Currently there are seven
airbases at The Netherlands: Arnhem/Deelen (EHDL), Eindhoven
(EHEH), Gilze-Rijen (EHGR), Leeuwarden (EHLW), Volkel (EHVK),
Woensdrecht (EHWO) and De Kooy (EHKD). At military airbases the
AUTO ACTUAL and AUTO SPECIAL are called QAM and contain identical
information. The only difference is that a so-called colour state
and a colour state forecast, based on NATO specifications, are
included in the QAM instead of the TREND. An AUTO QAM is generated
on the airport server system and is made available, via a local
network connection, to military users. KNMI is responsible for
operating and the maintenance of the AUTO METAR system at the seven
military airbases. This includes the sensors at the airport and the
hardware and software of the data acquisition, processing and
dissemination modules. It should be noted that the military system
also includes presentation systems that display the meteorological
reports and sensor information to military air traffic controllers
and other local users such as Search and Rescue (SAR) and the fire
brigade. Similar presentation systems are also installed at
centralized approach of the Air Operations Control Station.
Differences exist between the civil and military AUTO METAR system.
The meteorological observation infrastructure differs slightly from
the civil aerodromes. For example the data communication lines and
power supply facilities, which are provided by ATC and the
military, differ and have different redundancy levels. Also the
usage of backup sensors is different and no video cameras are used
at airbases. Furthermore, the military system uses a single
redundant server for data acquisition, processing and
dissemination, whereas at civil airports data dissemination is
handled by a separate redundant server. Finally, a meteorological
technician with observer skills is available at each airbase during
opening hours and can offer assistance to military air traffic
controllers and pilots on request.
1.5 Description of automated aeronautical meteorological reports
at North Sea off-shore structures On the Netherlands continental
shelf are approximately 110 offshore structures with helicopter
decks. Approximately 30 of these are manned structures of which 13
provide a half hourly AUTO METAR. The report is produced fully
automated. The products AUTO SPECI, AUTO ACTUAL and AUTO SPECIAL
are not produced. There are no backup sensors and camera’s
installed at the structures. The meteorological sensors and sensor
interface used at platforms are identical to the ones used at civil
airports and military airbases and are operated and maintained by
KNMI. The data-acquisition systems at the platforms are owned by
third parties. These systems take care of the local presentation of
the meteorological data and make the raw data of the KNMI sensor
interface available to the external FTP server of KNMI every
minute. The central server system at De Bilt acquires the data of
all platforms and generates the AUTO METAR. Note that the AUTO
METAR of a platform is not monitored, validated and complemented
remotely by a meteorologist before dissemination.
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2. Observation infrastructure of the AUTO METAR system
2.1 Components of the observation infrastructure
2.1.1 Meteorological sensors The meteorological sensors used by
KNMI are listed in Table 1. Table 1 reports the sensor, the
associated Sensor Intelligent Adaptation Module (SIAM) sensor
interface and the meteorological units. All sensors meet the
requirements of the World Meteorological Organization (WMO, 2008)
and the International Civil Aviation Organization (ICAO, 2010) and
are maintained and calibrated by KNMI. Identical sensors are used
at civil airports, military airbases, platforms at the North Sea,
and at the automated weather observation stations.
Table 1. A list of meteorological sensors used by KNMI. The
table also gives the associated SIAM sensor interface and the
meteorological units reported by the interface.
Sensor SIAM SIAM Unit Unit description
Vaisala Impulsphysik LD40 ceilometer C4 C1 First cloud base C2
Second cloud base C3 Third cloud base CX Vertical range of
measurement ZV Vertical visibility Paroscientific Digiquartz 1015A
barometer P1 PS Air pressure Kipp & Zonen CM11 pyranometer Q1
QG Global radiation KNMI precipitation gauge R2 NI Precipitation
intensity ND Precipitation duration Pt-500 platinum resistor
element U1 TG Grass temperature 0.10m Pt-500 platinum resistor
element TA Ambient temperature 1.50m Derived by SIAM TD Dew point
temperature 1.50m Vaisala HMP-233 capacitive hygrometer RH Relative
humidity 1.50m KNMI cup anemometer W0 WS Wind speed KNMI wind vane
WR Wind direction Vaisala LM11/21 luminance meter Z4 ZA Background
luminance Vaisala FD12P present weather sensor ZM Visibility (MOR)
NI Precipitation intensity ND Precipitation duration PW
Precipitation type ATC Runway information system B0 BB Runway
usage
The last entry of Table 1 is not a meteorological sensor, but a
system of ATC that indicates the runway in use. This information is
provided to KNMI as a serial string with the format of the SIAM
sensor interface so that it can be processed similarly as the
sensor information.
2.1.2 Sensor layout at EHRD The positions of the meteorological
sensors used at Rotterdam The Hague Airport are shown in Figure 1.
Rotterdam has a CAT I runway for instrument precision approach and
landing operations. The runway can be used from both sides (06 and
24). Hence according to ICAO (2010) recommendations it is equipped
with a wind sensor and a visibility sensor near the touchdown zone
at both ends of the runway. Both of these visibility sensors are
equipped with a background luminance sensor. The background
luminance is used in the derivation of visibility for aeronautical
purposes and the Runway Visual Range (RVR) from the Meteorological
Optical Range (MOR) reported by the visibility sensor. The
pressure
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sensor is located at the wind mast of runway 24 and the
temperature and humidity sensors are situated at the measurement
field near 24 touchdown. The measurement field also contains the
ceilometer, the rain gauge and a global radiation sensor. The
latter two sensors are used for synoptical and climatological
purposes only. Backup sensors for pressure, temperature and
humidity are located at the wind mast and touchdown zone of 06.
Note that the visibility sensor used at Rotterdam The Hague Airport
is in fact a so-called present weather sensor which also reports
the precipitation type. The precipitation type in combination with
other meteorological information is used to derive the weather
information. Lightning, which is also included in the weather
information, is not measured locally, but is provided from the
central processing unit of the lightning detection system at De
Bilt. The lightning information in combination with information
from weather radars and METEOSAT satellite is used to provide
information on the presence of convective cloud types CB and TCU,
which is added to the cloud information. Both the lightning and the
CB/TCU cloud type information are provided through the network
connection between Rotterdam The Hague Airport and the main offices
of KNMI at De Bilt.
KVS1
Techinical Room KNMI
W = windZ = visibility / weatherC = cloudU = temperature /
humidityP = pressureQ = radiationR = precipitationO = video
camera
↓↑WP ZRUQCWPUZKVS2
24↓↑ 06Threshold
Aiming point
Threshold
Aiming point
Figure 1: The position of the meteorological sensors and video
cameras at Rotterdam The Hague Airport. The sensors and cameras
associated to touchdown 06 and 24 and their respective relay
station (KVS) and data communication line to the technical room of
KNMI at the airport are shown in red and blue, respectively. The
measurement field not only contains temperature and humidity
sensors and a ceilometer for cloud observations, but also a rain
gauge and a global radiation sensor for synoptic purposes.
2.1.3 Sensor layout at other locations The layout of the
meteorological sensors at EHRD is typical for a civil airport with
a CAT I runway. A similar layout is used at EHGG. The sensor layout
for the civil airport EHBK is nearly identical, but it contains an
additional visibility sensor at the mid position as is required for
a CAT III runway. A similar instrumentation is used for all CAT III
runways of EHAM with 3 visibility sensors per runway and wind
measurements representative for the touchdown and take-off position
of each runway. Details of the sensor layout of Amsterdam Airport
Schiphol can be found in Wauben and Sondij (2009). The military air
bases generally have a sensor layout similar to EHRD with backup
sensor for pressure, temperature and humidity, two visibility
sensors per runway, but are equipped with 3 wind sensor sets. The
measurement field which is located near the middle of the runway
contains the primary pressure, temperature and humidity sensors and
a wind sensor set on a 10-meter mast. The backup sensors for
pressure, temperature and humidity are located at touchdown of the
runway together with a transmissometer visibility sensor and wind
on a 6-meter mast. The alternate or end position contains the FD12P
present weather sensor and wind on a 6-meter mast.
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The platforms on the North Sea and the military airbase EHKD
contain only a single sensor set. At platforms a dual wind sensor
set is often used. In these cases wind is measured at opposite
sides on the vent stack. The upstream sensor set is automatically
selected for operational use. Also note that the precipitation
gauge and pyrometer are not used at platforms.
2.1.4 Video camera system at EHRD A dual video camera system is
mounted on the wind mast of 24 touchdown (cf. Figure 2). The system
consists of cameras mounted at 2 and about 9 m, and facilitates
monitoring of the representativeness of the visibility measurements
at the touchdown zone during daytime. In addition a video camera is
located about 500 m before the threshold of runway 06 at a height
of 2.5 m and pointed towards 24 touchdown. This camera can be used
by the meteorologist to check the general meteorological
conditions, particularly of cloudiness and visibility at the
airport. Note that no quantitative information on the visibility
can be derived from the video camera images. Only a rough check of
the measured visibility can be estimated from the images. However,
the cameras provide information on the nature of obscuration
(shallow fog, patches). The video signal is made available via the
data communication network to the central weather room and service
staff of KNMI at De Bilt.
Figure 2: The FD12P visibility sensor and the wind mast with
KNMI cup anemometer and wind vane near 24 touchdown at Rotterdam
The Hague Airport. Video cameras are mounted at 2 m and near the
top (9 m) of the frangible wind mast.
camera →
camera ↓
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2.1.5 Video camera system at other locations A dual video camera
system as described above for EHRD is also installed near the main
touchdown of EHGG; at both ends of the runway of EHBK; and at
touchdown of runway 18R of EHAM, which is located about 7 km from
the local observer.
2.1.6 SIAM sensor interface and multiplexer All sensors are
operated in combination with a so-called SIAM sensor interface, a
Sensor Intelligent Adaptation Module. A SIAM communicates with the
sensor and converts the sensor output into meteorological
quantities in a fixed serial format. A SIAM runs asynchronously and
polls the sensor and gets the meteorological as well as the status
information. Generally the SIAM polls the sensor every 12 seconds,
but if necessary the sensor interface samples the sensor with a
higher frequency, e.g. the cup anemometer and wind vane are sampled
with 4 Hz and the sensor interface calculates the 3 seconds running
average in order to calculate the wind gust and take account of
marked discontinuities of the wind. The SIAM performs a format and
a range check on the meteorological quantities and generates an
output string every 12 seconds. The sensors and SIAM sensor
interfaces are installed in the field and are connected via fixed
copper lines to a nearby relay station (KVS) of ATC which also
supplies the no-break power supply. A relay station typically
serves half of the runway, e.g. the sensors associated with 06
touchdown are connected to KVS1 and the sensors associated with 24
touchdown and the measurement field are connected to KVS2 (cf.
Figure 1). The SIAM sensor interfaces are situated in the field
either directly at the sensor, e.g. in the electronic box of the
wind mast or of the visibility sensor or in the central data box at
the measurement field. The latter also contains a MUF (MUltiplexing
Facility) so that all SIAM data can be sent to KVS2 via a single
data line. At the relay station the serial SIAM information is
multiplexed on a single serial line and forwarded to the technical
room via copper lines. In the technical room all incoming MUF
strings are duplicated by splitters, multiplexed on to a single
line and given to the server pair for further processing. An
overview of the technical observation infrastructure at Rotterdam
The Hague Airport is shown in Figure 3. Note that information of
the Runway Information System (RIS) of ATC, which indicates which
runway is in use, is also fed as a SIAM string into the MUF
cascade.
Technical Room
Measurement fieldKVS 2
KVS 1
Data Box
De Bilt
Splitter
Splitter MUF
ADCM 0
ADCM 1
Splitter
Pressure 24
VideoCisco modem
Radiation
Precipitation
Temperature Humidity
DP1
Clouds
MUFXQ1
XR1
XU1
MUF
Splitter
Pressure 06DP1
Temp/Hum 06DU1
MUF
Visibility 06DZ4
Wind 06DW0
VAIS
Wind 24DW0
Splitter
MUF
MOXATest system
Cisco switch
DC4
Visibility 24 Splitter
VideoCisco modem
DZ4
Schiphol
KNMI LAN
MIS 0
MIS 1
ATC
Runway Information System
Figure 3: An overview of the sensors and SIAMs and splitters in
the MUF cascade at Rotterdam The Hague Airport. Black line and
boxes denote connections and components which a single point of
failure. Blue lines and boxes show the secondary server system with
associated sensor data. The video cameras components are denoted in
green and the sensor data that is forwarded to the test server
system at De Bilt is shown in red. The backscatter information of
the ceilometer that is forwarded to De Bilt for monitoring of
volcanic ash is also given in red.
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2.1.7 Server systems The 2 outputs of the MUF cascade, each
containing all sensor and RIS information, are fed into a redundant
server pair. In normal operation one of these ADCM (Aviation
Data-acquisition and Communication Module) servers is hot and
ingests all sensor data. The SIAM data that is transmitted
asynchronously by the SIAM is assigned to a 12 second interval at
the hot ADCM. Generally the last SIAM string of each sensor that
arrived at the server in a 12 second interval is labeled with the
time at the end of the interval. Some processing is involved to
handle reception of either none or two SIAM strings in a 12 second
interval. The ADCM monitors the status of the sensors and it also
takes care of derivations, e.g. RVR and cross wind calculations and
the handling of automated backup of sensors, and the generation of
meteorological reports. A copy of all raw and derived data is
forwarded to the cold server that stores it. The cold server
continuously monitors whether the hot server is available. If
communication is lost the cold becomes hot and starts processing
the data. It is also possible to force a manual failover so that
maintenance of the cold server can occur without interruption of
the data flow. During a start-up the server checks whether a hot
server is present in which case it will go into the cold mode. When
2 servers are hot, e.g. after a failure of the network
communication between the 2 servers, the secondary server will
automatically switch to cold. Both servers are connected to the
KNMI LAN at Rotterdam The Hague Airport. Note that the server
systems have 2 network cards and are connected to 2 separate
network switches. The sensor and derived data is generally updated
every 12 seconds. About 275 out of the total amount of 770
variables available at Rotterdam The Hague Airport update every 12
seconds. The ADCM server performs the crucial tasks of
data-acquisition and processing. In order to avoid any loss of
performance due to data requests by users a copy of all data is put
on the MIS (Meteorological Information Server) server pair which
handles the data requests for local users at the aerodrome.
2.2 System redundancy and backup measures
2.2.1 Backup sensors As indicated in Figure 3 the sensors in the
field are potential single points of failure. As part of the AUTO
METAR system backup sensors for pressure, temperature and humidity
were installed at the wind mast and touchdown zone of 06 at EHRD.
The backup of pressure, temperature, humidity and wind is
automatically taken into account in the processing at the airport
server system. Wind can be backed up by the sensor at the opposite
end of the runway since their distance is relatively small (about 1
km) and the sheltering factors at both sites are similar. The pair
of visibility sensors, however, cannot be used as each others
backup as the visibility obtained with the other sensor at a
distance of about 1100 m can differ significantly. Since the runway
visual range and visibility should be representative for the
touchdown zone a backup by the other sensor is not possible in all
conditions. Rotterdam The Hague Airport is equipped with a single
ceilometer.
2.2.2 Infrastructure redundancy A full redundancy of the system
at Rotterdam Airport is available after the splitters in the
technical room (cf. Figure 3). In case of a failure or malfunction
of a system or communication line after the splitter, the full set
of information is still available or after an automated failover to
the secondary system. The splitters themselves and the components
before the splitters like a sensor are also redundant, but in a
different way. In case e.g. a sensor fails a backup sensor will be
used automatically. There is, however, no backup for visibility
representative for the touchdown position and clouds. A sensor and
its backup sensor are located at different physical locations at
the airport and they use other parts of the observation
infrastructure such as power supply, multiplexers, splitters, data
communication lines and relay stations in order to get the sensor
information to the servers systems in the technical room. Hence,
should a sensor or an associated component of the observation
infrastructure fail then the backup sensor is still available. Even
if a connection to a relay station or a MUF at a relay station or a
splitter in the technical room fails and all the sensor data of
that end of the
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runway is not available, the backup sensors of pressure, wind,
temperature, humidity and weather are still available. There is,
however, no automated backup for visibility and clouds. Note that
at Amsterdam Airport Schiphol the redundancy of the infrastructure
is at a higher level since sensors and other equipment in the field
are connected to a no-break power supply provided by ATC; the
sensor information is split at the relay stations in the field and
is fed twice to a redundant data communication infrastructure of
ATC; the redundant server systems are located at 2 different
locations.
2.2.3 Backup procedures for visibility and clouds In case of a
failure of a visibility sensor or ceilometer or associated
infrastructure the visibility information of the corresponding
touchdown position or the cloud information is not available. In
such a situation the aviation meteorologist in the central weather
room of KNMI at De Bilt can orally provide the missing visibility
or cloud information. For that purpose the meteorologist uses the
images of the video cameras, the information provided by the
meteorological network from nearby stations, information from
remote sensing systems, the expected atmospheric conditions and
verification of the meteorological situation with local staff of
the airport or ATC by means of asking direct questions, e.g.
whether visibility markers are visible or not. Note that in such a
situation the meteorologist does not make an observation, but
indicates whether so-called Visual Flight Rules (VFR) conditions
are applicable or not. During VFR conditions the runway can still
be used although the air traffic capacity is less than for
instrument precision approach and landing operations that apply for
Instrument Flight Rules (IFR). The information that is provided
orally in case of a malfunction of an observation system or
associated infrastructure is logged in the shift reports and voice
recorded by ATC and KNMI. When the information of the visibility
sensor at touchdown is not available the runway can only be used if
a visibility of 3000 meters or more can be determined by using the
cameras or via consulting the ATC staff by telephone. For this
purpose Air Traffic Controllers have been provided with a 360
degree overview map of the airport containing reference objects
with defined visibility distances. If the visibility cannot be
determined or is below 3000 meters the airport cannot be used for
instrument landing approaches. However, in such a situation it may
be possible to approach the runway from the other side and use the
visibility sensor at touchdown. Naturally any failure is handled by
KNMI service staff according to the agreed response time as given
in the service level agreement between KNMI and ATC The
Netherlands.
2.2.4 Server redundancy The server pair for processing the data
(ADCM) and providing the data to the local users (MIS) is
duplicated. In case one server fails the other takes over
automatically. At Amsterdam Airport Schiphol there is even a third
server system with a different operation system, a different
application with only the basic functionality and implemented by
another manufacturer using different software tools that can
provide the most essential data in case the redundant ADCM/MIS
fails. The network components at Rotterdam The Hague Airport are
also redundant and each server has 2 network cards and connects to
both network switches. Since the servers are located at the airport
itself the processing and dissemination of meteorological data to
local users runs autonomously and continues uninterrupted if the
network connection to De Bilt is lost. In such a situation the
airport users still get the local routine and local special reports
(AUTO ACTUAL and AUTO SPECIAL) and have access to the processed
wind and runway visual range data. During a disruption of the
network connection to De Bilt, Rotterdam The Hague Airport receives
no lightning and CB/TCU information. This missing information is
indicated in the meteorological reports. Loss of the network
connection to De Bilt also means that the monitoring of the sensor
information by the meteorologist is hampered. For that purpose a
backup network connection between Rotterdam The Hague Airport and
Amsterdam Airport Schiphol is available. The KNMI observer at
Schiphol can monitor the sensor information and add the TREND
forecast, as well as Runway State Message, Windshear and Low Level
Temperature Information, in close collaboration with the aviation
meteorologist at De Bilt when needed.
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2.3 Optimization of the observation infrastructure The period
between the first introduction of the AUTO METAR system at
Groningen Airport Eelde and Maastricht Aachen Airport in May 2004
and the implementation of the AUTO METAR system at Rotterdam The
Hague Airport in March 2011 was used to improve the system based on
the experiences and feedback from users. Some improvements to the
system are highlighted in the following subsections.
2.3.1 Backup measures The implementation of backup sensors at
Rotterdam The Hague Airport has already been mentioned in section
2.2.1. Note that backup sensors for pressure, temperature and
humidity have also been installed at Groningen Airport Eelde and
Maastricht Aachen Airport. Visibility and runway visual range at
the touchdown position have no backup. The reason for this is that
due to the large spatial differences that can occur for visibility
the sensor at the other end of the runway cannot be used as a
backup. A suitable backup sensor for visibility would require an
additional visibility sensor near the touchdown position. However,
even if such a backup sensor would be available near the touchdown
position it would still use the same infrastructure unless the
complete chain would be duplicated, which would be very expensive.
Visibility at touchdown position is an accepted single point of
failure. Note that in the current situation the same infrastructure
as for the ATC systems is partly used. Hence in case of a
malfunction at e.g. the relay stations or the connections to the
technical room the corresponding ATC systems would also be not
available. The introduction of backup measures only makes sense by
considering the total context. Note that in case the visibility at
a touchdown position is not available, the sensor at the other end
of the runway, which uses a different part of the infrastructure,
will generally still be available so that the runway can be
approached from the other side. When the visibility conditions are
critical the wind conditions are usually such that there are no
restrictions in that respect either. In case of good visibility
conditions the runway can be used under so-called visual flight
rules (VFR). The video cameras have been introduced at the airport
as a tool for assisting the meteorologist to verify whether VFR
conditions apply. The meteorologist can also consult ATC staff by
telephone. For this purpose Air Traffic Controllers have been
provided with a 360 degree overview map of the airport containing
reference objects with defined visibility distances.
2.3.2 Sensor issues
2.3.2.1 Insects reduced visibility During the evaluation of the
AUTO METAR system at Rotterdam The Hague Airport situations
occurred when the MOR reported by the visibility sensor sometimes
reported reduced values around sunset. Investigations showed that
insects in the measurement volume can cause a significant decrease
of the MOR reported by a forward scatter visibility sensor.
Collaboration with manufacturer was established in order to filter
the spikes due to insects in the raw sensor signal before
calculation of the MOR. A field test evaluation of the MOR reported
by an FD12P equipped with firmware that filtered for insects showed
good results (cf. Wauben, 2011). KNMI currently prepares the
introduction of an updated firmware with insect filtering of the
MOR for operational use at civil airports.
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0 3 6 9 12 15 18 21 2440
100
1000
10000
50000
Time (UT)
MO
R (m
)
MOR FD12P raw (m) MOR FD12P corrected (m) MOR Reference (m)
Background Luminance FD12P (cd/m2)
3
10
100
1000
10000
50000
Background luminance (cd/m
2)
Figure 4: The 1-minute averaged MOR and background luminance
observed by a FD12P forward scatter visibility sensor at De Bilt on
August 5, 2010. The background luminance (blue curve with scale on
the right) is 4 cd/m2 at nighttime and show a sharp increase near
sunrise (3:30 UT) and a decrease near sunset (20 UT). The MOR
(black curve with scale on the left) show values exceeding 10 km.
Around sunrise (3 to 5 UT) and at night (22-24 UT) low MOR values
occur during fog. Similar MOR values are reported by a
transmissometer at De Bilt during these periods (not shown).
Reduced MOR values due to insects occur around sunset (19:30 to
20:30 UT) with values below 1 km. The MOR of the transmissometer
shows no reduced MOR values during this period. The insect
filtering of the FD12P mitigates the MOR reduction significantly
(red curve) although the corrected MOR still shows MOR reductions
compared to a constructed reference (green curve) which is in fact
the rescaled MOR of the transmissometer. The corrected MOR is,
however, above aeronautical visibility limits.
2.3.2.2 Representativeness of visibility and cloud observations
During the evaluation of the AUTO METAR system at the regional
airports various complaints of users were related to lacking
representativeness of the visibility and cloud observations by
visibility sensors and ceilometers. The situation experienced by
local users conflicted with the observations reported by the AUTO
METAR system or the latter showed a large delay. Hence users
complained about faulty sensor observations. Analysis of these
situations showed that the sensors and corresponding algorithms
worked correctly, but that measurements at a specific location can
deviate significantly from that of an observer looking around. For
example clouds associated to a front can only be reported by a
ceilometer once they are directly overhead and then it takes
10-minutes before the cloud algorithm changes the cloud cover to
overcast. Similar deviations can occur for visibility. The reported
visibility is generally a 10-minute averaged value. A so-called
marked discontinuity criteria is used which reduced the averaging
period to 2-minutes when the visibility changes significantly. It
should be noted that the user complaints that were related to
lacking representativeness of the visibility and cloud observations
were partly related to the unfamiliarity of ATC staff with the
details of the measurement systems and internationally agreed
observation principles.
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The usage of multiple sensors, e.g. ceilometers, has been
considered to improve the spatial representativeness of the
observations. The cloud algorithm uses a 10-minute time series of
individual cloud base height measurements reported by the
ceilometer. The fraction of the sky evaluated by the cloud
algorithm can be imagined as a narrow strip along the sky, the
width of this strip is determined by the opening angle of the
ceilometer and the length by the movement of the clouds due to the
wind aloft. Several of such strips are considered when multiple
ceilometers are combined in the cloud algorithms. Even by using
several ceilometers only a small portion of the entire sky will be
sampled. Analysis of the use of three instead of one ceilometer at
Schiphol versus the observer in 2002 showed therefore only little
improvement. Another observation technique is required to solve the
spatial representativeness issue. For that purpose a scanning
pyrometer, the so-called NubiScope, has been evaluated (Wauben et
al, 2010). The NubiScope performs a scan of the entire sky every
10-minutes during which the thermal infrared sensor determines the
sky temperature in 1080 orientations. From the sky temperature the
presence of clouds can be determined. The total cloud cover
obtained with the NubiScope showed good results, but accurate
height information, which is crucial for aeronautical purposes, is
unfortunately lacking.
2.3.2.3 CB/TCU information In 2004 CB/TCU information was not
included in the AUTO METAR system. At the end of 2006 CB/TCU
information derived from lightning and precipitation radar
reflectivity data was added to the system. Recently, the CB/TCU
product has been improved by using METEOSAT satellite data in
addition to radar and lightning data.
2.3.2.4 Video cameras Video camera systems have been installed
at civil airports as a tool for the meteorologist to check the
meteorological conditions at the airport remotely. The video images
can be used as a source of information on cloudiness, visibility
and present weather. Although the images give an indication of
cloudiness and visibility, the quality of images is generally
considered too poor for an accurate estimation of cloudiness and
visibility. Options to improve the video camera systems are
currently considered.
2.3.3 Reporting rules During the evaluation period some bugs in
the software and configuration were identified and solved.
Furthermore it was noted that sometimes an undesired delay occurred
as a result of a combination of the integration time for the
derived variable and the criteria for issuing a local special
report, the so-called (AUTO) SPECIAL. The SPECIAL criteria used in
The Netherlands were reviewed by a Task Force consisting of experts
of KNMI and ATC. The recommendations of the Task Force which
consisted of adjustments to thresholds and criteria for issuing a
(AUTO) SPECIAL have been accepted and implemented by both
organizations. For example the delay in reporting the improvement
of the visibility has been specified as 5 minutes, by local
agreement. In addition, a marked discontinuity was introduced in
the calculation of the 10-minute averaged visibility in order to
reduce the response time for sudden changes in visibility
conditions.
2.3.4 Documentation issues Several issues reported during the
evaluation of the AUTO METAR system at the regional airports could
be traced to misunderstanding or misinterpretation of the results
or reporting rules. For that purpose a fact sheet on SPECIAL
criteria, and other documents explaining specific aspects of the
AUTO METAR system, have been created. Special attention was given
to the so-called visual parameters - visibility, clouds and
weather. For these parameters the introduction of the AUTO METAR
system not only led to different reporting rules, but also resulted
in changes to the characteristics of the reported parameters. Hence
the interpretation of these reported parameters needed to be
adjusted in close cooperation with the users. In addition,
so-called introduction sessions with air traffic controllers were
held on location and aviation meteorologists were instructed in ATC
operations.
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3. Supervision of the AUTO METAR system
3.1 Monitoring of the AUTO METAR system status
3.1.1 Sensor status The advanced meteorological sensors perform
a real-time check on the sensor status. For that purpose the signal
of various sensor modules are monitored internally and warning or
errors messages are generated when certain threshold values are
exceeded. Internal check can also include measurement of the
electronic noise, the stability of an emitter and the sensitivity
of a receiver against internal references as well as the
contamination of the lenses of optical sensors. The sensor status
is passed on to the SIAM sensor interface and is available in near
real-time together with the measured values itself. The sensor
interface performs a real-time validation on the format of the
received sensor messages. It also does internal checks on the
quality of the received meteorological data. All parameters are
checked against the climatological range. Depending on the expected
variability of a meteorological unit under consideration additional
checks on a too large variability or sudden jumps or a lack of
variability in the observed unit are performed. When more
meteorological units are available at a SIAM sensor interface, e.g.
wind speed and direction or ambient and dew point temperature, then
a cross validation of the units is performed. At the server system
additional cross checks are performed. All these checks use warning
and error thresholds and provide their results in near real-time to
the airport server system. The warnings and errors are uniquely
translated into a data quality which is available for each
variable. Hence users as well as maintenance staff can see
immediately when a warning or error status is issued.
3.1.2 Monitoring by service staff KNMI service staff monitors
the sensor status of the entire network on a daily basis using the
SIAM status information. Based on this information corrective or
preventive maintenance is planned. Preventive maintenance is based
on operational experience with the sensors. The calibration
interval of the sensors ranges between 8 month for the humidity
sensor and 36 month for the pressure and temperature sensor. A
sensor is returned to KNMI just before the calibration is expired
and replaced by another sensor. At the calibration laboratory it is
first checked whether the returned sensor deviates from the
reference within the allowed limits. The calibration interval is
changed if the allowed limits are exceeded either too often or
hardly at all. Next maintenance is performed on the sensor; it is
calibrated and put into stock. Preventive maintenance in the field
is also based on experience. At civil airports and airbases
maintenance is performed every 2 months. The limiting factor here
is cleaning of the lenses of the visibility sensors. Corrective
maintenance is performed when either the sensor status or users
indicate its necessity. If e.g. contamination of the lenses is
reported then an additional maintenance visit is made to clean the
lenses, or trained local staff is asked to perform the maintenance.
A real-time check of the sensor status and output is made during
and after maintenance has been performed.
3.1.3 Monitoring by operator Apart from the daily monitoring and
planning of maintenance by service staff, an operator (the
so-called “procesbewaker”) monitors the correct functioning of all
crucial KNMI systems continuously. In case of malfunctions service
staff can be alerted or requested. Action is taken according to the
service level agreement. The importance and hence the priority of
the maintenance of the sensor depends on the (expected)
meteorological situation. If applicable corrective maintenance will
be applied on a 24*7 basis. The operator has various tools to his
disposal that facilitate the monitoring of the correct operation of
crucial server systems and the availability of sensors and sensor
information. Figure 5 shows some examples of screen available on a
GDIS (Graphical DISplay) client system showing the status of
sensors and MetNet systems at Rotterdam The Hague Airport.
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Figure 5: Screen shots of MetNet systems giving an overview of
the status of Rotterdam The Hague Airport. Going clockwise from top
left they show: (i) central server at De Bilt (CIBIL) giving an
overview of the entire MetNet including the server and sensor
status at Rotterdam; (ii) ADCM server at Rotterdam showing the
(derived) sensor data on a map (iii) and in the AUTO METAR and AUTO
ACTUAL report generation screen (both use the convention black data
is valid; magenta denotes warning or backup; red ? is faulty or
missing; and italic is manually confirmed/adjusted); (iv) the final
screen shows the incoming sensor data (again color code to indicate
good, warning status and error of corrupt data). The latter also
shows an overview of the status of the server systems at Rotterdam
The Hague Airport.
3.2 Remote verification and complementation A continuous
verification of the validity of the meteorological information is
performed by the aviation meteorologist who has access to the 12
second meteorological data. The validation can be performed by
using the information from other sensors at the airport, by
consulting the video camera images at the airport, by using the
information of nearby meteorological stations, by considering the
general meteorological conditions or by contacting local staff of
the airport or air traffic control. The aviation meteorologist has
access to near real-time data from other airports, off-shore
platforms and automated weather stations that are part of MetNet,
as well as satellite and weather model information. Some sources of
meteorological information are illustrated below.
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3.2.1 Video camera images Figure 6 gives an example of the
images obtained continuously from the video cameras at Rotterdam
The Hague Airport. These images are available to service staff and
the aviation meteorologist at the central weather room at De
Bilt.
Figure 6: Illustration of the images obtained with the video
cameras at 24 touchdown at Rotterdam The Hague Airport (top panels)
and the camera before the threshold of runway 06.The yellow
rectangle indicates the field of view of the video camera at 9 m
equipped with a tele lens in the image obtained with the video
camera at 2 m equipped with a wide-angle lens.
3.2.2 Local sensor information Figure 7 shows graphs of some
meteorological variables centrally available in MetNet with an
update every minute. Note that local information at Rotterdam The
Hague Airport can also be viewed on a GDIS with a 12 second update
by connecting to the ADCM server system. Other screens for
displaying the local sensor information are shown in Figure 5.
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Figure 7: Time series of the sensor data that is centrally
available in MetNet with an update every minute. The screen has
four panels showing information for the civil airports Amsterdam
Airport Schiphol (top left), Groningen Airport Eelde (top right),
Maastricht Aachen Airport (bottom right), and Rotterdam The Hague
Airport (bottom left), respectively.
3.2.3 Regional sensor information Figure 8 presents a
geographical overview of the visibility observations centrally
available in MetNet with an update every 10 minutes. The graph
shows the visibility at the civil airports, military airbases,
platforms on the North Sea and automated weather observing stations
that are all part of Meteorological Network. The information of
other meteorological parameter can also be presented either
geographical or in trend curves.
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Figure 8: Illustration of the MetNet visibility information in
the Netherlands that is centrally available and can be visualized
geographically with an update every 10 minutes.
3.2.4 Other sources of information Apart from the information
mentioned above the meteorologist has also access to satellite and
weather model information. All information sources combined enables
the meteorologist to create a mental image of the meteorological
situation which is continuously checked against available
information and updated.
3.2.5 Communication Contact between the meteorologist and local
staff of the airport or air traffic control can be established in
order to give information or feedback on the current and upcoming
meteorological conditions. Note that the aviation meteorologist can
overrule the sensor derived visibility, clouds and present weather
values reported in the aeronautical reports orally or force sensors
to fault so that the sensor data is disabled or, if applicable, the
backup is used. The meteorologist also adds the TREND, a landing
forecast with a validity of 2 hours, to the meteorological reports
that are issued at least every half hour. Furthermore the
meteorologist adds, if required, the runway state to the AUTO METAR
report and can issue other reports (wind shear report, wind shear
forecast and low level temperature inversion) as part of the AUTO
ACTUAL and AUTO SPECIAL manually. There is regular contact between
the aviation meteorologist and air traffic controllers. Each
morning a briefing is held during which the expected meteorological
situation of the next 24 hours is reported. Furthermore, contact is
established when there is a significant deviation in the expected
meteorological situation, in case there is a need for an update on
behalf of a
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specific event, in case of reasonable doubt concerning the
meteorological information provided, or when there is a malfunction
in the observation infrastructure.
3.2.6 Complementation Figure 9 illustrates the AUTO METAR system
Rotterdam Airport, the redundancy of the system and backup
procedures. The products added by the aviation meteorologist are
indicated as well as the communication between the aviation
meteorologist of KNMI at De Bilt and ATC at Rotterdam Airport. Note
that CB/TCU is only provided by the meteorologist orally in case of
a network failure between De Bilt and Rotterdam The Hague Airport.
In normal situations the CB/TCU information is added automatically
to the observation report based on an algorithm that runs at De
Bilt and uses satellite and weather radar information.
Figure 9: Illustration of the AUTO METAR system at Rotterdam The
Hague Airport in The Netherlands showing the relation between the
aviation meteorologist at De Bilt and the air traffic controller at
Rotterdam Airport. The effect of a failure of the data
communication network is illustrated as well.
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4. Introduction process of and experiences with the AUTO METAR
system Rotterdam The Hague Airport is the alternate for Amsterdam
Airport Schiphol. As such there is a relationship between the
introduction of the AUTO METAR and the Mainport capacity. Hence the
AUTO METAR system was introduced at Rotterdam The Hague Airport in
line with standard ATC The Netherlands quality and performance
analysis procedures. The time period between the first introduction
of the AUTO METAR system at Groningen Airport Eelde and Maastricht
Aachen Airport in May 2004 and the final implementation of the
system at Rotterdam The Hague Airport in March 2011 was used to
gain experience and to improve the system. Before the introduction
safety assessments of the AUTO METAR system at Rotterdam The Hague
Airport were performed and the user requirements with respect to
the local routine and local special reports ((AUTO) ACTUAL and
(AUTO) SPECIAL) were updated and implemented in the system.
4.1 Task Force Update Criteria (AUTO) SPECIAL The introduction
of the AUTO METAR at Maastricht Aachen Airport and Groningen
Airport Eelde resulted in several issues or shortcomings of the
products AUTO ACTUAL and AUTO SPECIAL. An KNMI analysis showed that
part of these shortcomings were not specifically related to the
AUTO METAR system but arose from international coding practices and
additional user requirements. ICAO Annex 3 explicitly states that
the requirements should be established in consultation with the
users: ‘’4.4.1 A list of criteria for special observations shall be
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