CZCS Atlas of Water Optical Properties in the Alboran Seaspatial and temporal variability (Arnone, 1983, 1984). This illustrate that visible satellite data can be successfully data

Naval Ocean Research and Development ActivityAugust 1985- Report 117

CZCS Atlas of Water Optical Propertiesin the Alboran Sea

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DTICDEC 18 1985 .

>4 B

Robert ArnoneRemote Sensing BranchOcean Sensing and Prediction DivisionOcean Science Directorate

Ramon OriolComputer Sciences CorporationNSTL, Mississippi

Approved for public release, distribution Is unlimited. Naval Ocean Research and Duvelopment ,Ativity, NSTL, Misissippi ,396 &-UU4.

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Foreword

Applications of satellite remote sensing for monitoring the oceanographicenvironment are providing. naval operations and planning an increasedawareness of the dynamic spatial and temporal variability of ocean proper-ties. The utility ot visible remote sensing for quantitative bio-optical parameters

J provides global measurements where only limited ship measurements arepresently available. Not only do remote sensing techniques provide increasedsavings for ships and manpower, they also provide a better understandingof the ocean environment.

This rc-port demonstrates the technique of using the Coastal Zone ColorScanner satellite to be used to generate a water optical properties atlas. Potentialremote sensing applications for naval operations and charting are shown, inaddition to awaieness of potential future ocean color satellite systems.

R. P. Onorati, Captain, USNCommanding Officer, NORDA

I$, 4

i ..-.

Executive summary

Optical water properties of the world oceans can be rapidly obtained fromdata from the Coastal Zone Color Scanner (CZCS) aboard Nimbus-7. Satelliteprocessing techniques have been developed to eliminate the atmospheric con-tamination that contributes 90% of the total visible channel signal. The re-maining signal, which constituted the ocean color, is directly related to thediffuse attenuation coefficient (k) at 490 nanometers for the upper surfacewaters. Calculation and geographic registration of k can be done for eachof the 800-square-meter pixel resoluton of CZCS, and results show that theaccuracy is within 25% of ship measurements.

Present ship measurements of water optical data are very limited. Shipoptical instrumentation is difficult to deploy and calibrate, and does not pro-vide synoptic coverage of the optical climate. Obtaining optical propertiesfrom visible satellites enables improved understanding of the temporal and

spatial variability.A series of CZCS images from the Alboran Sea have been processed for

the diffuse attenuation coefficient. The monthly summary of k valuesdemonstrates a technique for generating a k atlas using CZCS data. TheAlboran Sea region illustrates a large majority of water masses: upwelling,strong fronts, river discharge, and clear central gyre. This spatial variabilityis coupled with the complex circulation resulting from the tidal pulsing ofthe inflowing Atlantic water at the Strait of Gibraltar. Results of the CZCSk atlas indicate that the water masses are changing more rapidly than ex-pected. Also indicated is that ship measurements of optical properties in aregion as complex as the Alboran Sea would be extremely difficult to interpret.

This report indicates the processing procedures used to calculate k fromradiance data from the CZCS. Additionally, problems, assumptions, and recom-mendations for future processing are discussed.

4. VI, I ,1 1985

B

Acknowledgments

This research was funded by the Defense Mapping Agency HydrographicTopographic Center, Program Element 63701B/3201. Programming andtechnical assistance is acknowledged to members of the Remote Sensing Branchof NORDA, namely G. Stevenson and S. Peckinpaugh. Appreciation is also

* extended to the National Environmental Satellite Service for making thesatellite available in a timely manner.

LI

Contents

I. Introduction 1

II. Methods 1

A. Coastal Zone Color Scanner processing 1B. Site selection 2C. Processing procedures 3

III. Results 4

IV. Problems 5

V. Recommendations 5

VI. References 21

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iii.

List of figures

Figure 1. Relationship of the upwelling ratio of 443/550 to the 7diffuse attenuation coefficient.

Figure 2. Alboran sea map. 7

Figure 3. Comparison of k. 8

Figure 4. January image. 9

Figure 5. February image. 10

Figure 6. March image. 11

Figure 7. April image. 12

Figure 8. May image. 13

Figure 9. June image. 14

Figure 10. July image. 15

Figure 11. August image. 16

Figure 12. September image. 17

Figure 13. October image. 18

Figure 14. November image. 19

Figure 15. December image. 20

iv

CZCS atlas of water optical properties in the Alboran Sea

I. Introduction the Alboran Sea in the Western Mediterranean. All CZCS

Historically, the oceanographic data base of optical prop- data were screened for cloud-free imagery to obtain at least

erties is severely limited by both the number of observa- two images of the optical properties per month. By com-tions and the type of measurement. It has been shown piling monthly imagery from 1978 to 1982, a statisticalthat for large ocean and coastal regions the existing op- approach to accessing the variability of the optical prop-tical property data base is inadequate for determining the erties should be illustrated by the imagery. This atlas willspatial and temporal variability (Arnone, 1983, 1984). This illustrate that visible satellite data can be successfully

data base, which exists at the National Oceanographic Data utilized to generate temporal atlases of ocean optical prop-Center (NODC), assimilates optics data as Secchi depth erties. The study will indicate the procedures used inmeasurements and contains approximately 96,000 readings generating the optical properties, as well as the problemsdating back to the early 1900s. Problems with the quali- and limitations of the technique. The oceanographic im-ty and the frequency of measurement have demonstrated plications of the result will be discussed in relation to thethat improved techniques for measuring and monitoring processes. Furthermore, recomendations will be discussedthe optical properties were warranted. for improving the methodology to address an operational

The necessity for an improved data base for monitor- system capable of handling large regional coverage.ing the ocean optical properties is based on the require-ment for electro-optical systems to operate within the oceanenvironment. These systems, which operate based on the I Methodspropagation of visible radiation through sea water, arecritically influenced by the spectral optical characteristics. A. Coastal Zone ColorMore specifically, development of laser and multispectral SC a p oesingscanning remote sensing systems by the Defense Map- Scanner processingping Agency to determine bathymetry requires knowledge The use of CZCS data to generate an optical atlas re-of the water optical properties in coastal areas to assess quires that a large amount of cloud-free data be availablesystem performance. Since coastal waters have extremely for a region and that it be collected thoughout a periodhigh spatial and temporal variability, methods to improve of several years. Large amounts of CZCS data are presentlyon data collection and analyses are required. archived at the National Environmental Satellite Data In-

Recently, ocean color imagery from the Coastal Zone formation Service (NESDIS), with additional imagery ar-Color Scanner (CZCS) aboard the Nimbus-7 satellite has riving daily. These data sources are still limited for world-been used to determine the optical property of the diffuse wide atlas development because of cloud-cover restraints.attenuation coefficient in the surface layer (first attenua- CZCS was launched in November 1978 and has been col-tion coefficient). The absolute water-leaving spectral ra- lecting world-wide data based primarily on user requests.diance in two of CZCS channels has been empirically Some key locations that border the U.S. routinely haverelated to the attenuation coefficient. The application of data collected. The world coverage from CZCS is difficultCZCS imagery in providing the optical data base allows to access, since many locations are not cloud-free; however,a unique capability in determining the spatial and tern- extensive world coverage provides data for a large percen-poral variability. The synoptic coveiage of the 1500 tage of the oceans. NESDIS has computer searches availablenautical-mile swath of the satellite, ,oupled with the near for rapid assessment of CZCS data. Presently, CZCS hasdaily coverage, permits absolute optical values to be corn- limited operation, since it has well surpassed its designputed for each of the 800-meter pixels within the scene. life of two years. it now acquires about 30% of the oiginalSatellite retrieval of oceanographic data is far more cost data rate. User requests are still permitted on a no-chargeeffective and is not limited by political boundaries, basis.

The objective of this study is to demonstrate the ap- CZCS is a six-channel multispectral scanner in sun-plication of CZCS data for generating an optical atlas for synchronous orbit with a ground resolution of 800 m at

nadir (Hovis et al., 1978). the narrow spectral channels aerosol scattering can be used in summation to determineare listed below: the atmospheric contribution. Rayleigh scattering can beChannel Center Bandwidth Sensitive Parameter computed based on the angular position of the ground

(nm) (nm) position with respect to the solar and spacecraft position.Aerosol scattering is more difficult to determine, since

1 443 20 chlorophyll it responds to the various types of aerosols (size distribu-2 520 20 "yellow substance" tions, compositions, spatial variabilities, etc.). However,3 550 20 suspended sediments if it is assumed that channel 4 (670 nanometers) is only4 670 20 atmospheric aerosols a measure of the aerosol contribution, then by subtract-5 750 100 land/water boundary ing the water-leaving radiance, the three visible channels6 11500 1000 surface temperature can be computed. The subtraction is not straightforward,

The selection of these spectral channels was based on the however, since the aerosol contribution at 670 nanometers

scattering and spectral absorption of the ocean water con- is different then at 443, 520, or 550 nanometers. Thestituents. For example. in open ocean waters the method used to address the spectral relationship between

phytoplankton pigment concentration of chlorophyll has atmospheric aerosols isstrong absorption at 443 nanometers (Arnone, 1982). LaX 70 1CZCS has a four-gain setting that permits the the scan- /U)ner to measure subtle changes in the ocean color in three 670 Avisible channels. (Channel 4, which is in the red portionof the spectrum, is not assumed to contribute to the ocean where LaX = aerosol contribution,color and therefore represents atmospheric contamination i? = Angstrom coefficient.only (Gordon and Clark, 1980)). CZCS has a repeat timesuch that coverage for three consecutive days is followed Several approaches to applying this technique in estimatingby two absent days. The scanner is also able to tilt 200 the Angstrom coefficient and performing the atmosphericahead of or behind the satellite's nadir track, wlich per- correction have resulted in encouraging results (Gordonmits data collection to avoid seasonal sungli-., areas and et al., 1983). The procedure used in processing the CZCSenhance ocean color quality, imagery for this atlas is documented by Arnone and La

The technique by which CZCS data can be utilized to Violette (1984).generate an optics atlas is based on a relationship established Following the subtraction of the atmospheric contribu-by Austin and Petzold (1980). Figure 1 illustrates that tion for each pixel in the visible channels, the resultingthe diffuse attenuation coefficient, (k) (at 490 nanometers), water-leaving radiance is ratioed and a diffuse attenuationis related to the ratio of the upwelling/water-leaving ra- coefficient computed from the algorithm shown by Austindiance at two wavelengths. Water-leaving radiance is that and Petzold (1980; Fi,. 1). Good agreement with shipflux measured just below the sea surface. This suggests measurements will be shown in the following section.that if it were possible to descend the satellite to just belowthe sea surface and measure the upwelling radiance at 443 B. Site selectionand 550 nanometers, then the diffuse attenuation coeffi The selection of the ocean area in which an optics atlascient at 490 nanometers can be computed from their ratio. could be generated was 5ased on several criteria. The firstThe problem arises with eliminating the influence of the was that adequate cloud-free CZCS coverage be availableatmosphere. This problem is compounded, since approx- for the area. Second, thc area should contain various op-imately 90% of the signal sensed by CZCS (channel 1 tical types of waters, ranging from relatively open oceanis greater) arises from the atmosphere. The remaining 10% to coastal. Third, the area should be restrictive in sizeof the signal, which is the water-leaving radiance, can be (512 by 512 pixels) to imit the amount of processing.used to compute the diffuse attenuation coefficient. Finally, the areas should contain ship measurements coin

The method by which the atmospheric contamination cident with the CZCS data to pet mit an evaluation of theis removed was originated by Gordon (1978). P-moving atlas results. The area selected was the Alboran Sea.atmospheric contamination does not include cloud areas, The West Alboran Basin is the first Mediterranean basinsince the sensor cannot see through them. The removal east of the Strait of Gibraltar (Fig. 2). The general cir-process applies to CZCS pixels, which "so," the sea sur- culation of the Alboran Sea has been characterized as anface. Single-scattering models of photon interaction with inflow of Atlantic water through the strait that is conthe atmosphere indicate that Rayleigh scattering and fined to the upper 200 m. This water flows eastward along

2

the Spanish coast for 100 kin, then turns southward toward diance has been subtracted from the total radiance for eachCap Tres Forcas on the North African coast, where it pixel.splits ino an east-west flow. This circulation creates a large PHASE 2. A second output that results from enteringanticyclonic gyre (Alboran Gyre) that occupies most of the CCT subsection into IDSIPS is the generation of athe West Alboran Basin. The coastal water along the control points file. The geometric registration of subsec-southern Spanish coast is cold, highly saline, and nutrient- tion to a standard projection is necessary for developingrich. The complex interaction with the inflowing Atlan- an atlas, since it allows comparison from one scene totic water is associated with the local meteorology, another. The control points file is r ecessary for thebathymetry, and tidal response at the inflow (Arnone and transform by which the subsection can be remapped intoLa Violette, 1984; La Violette, 1984; La Violette and Ker- a Mercitor projection. This file is generated from the 50ling, 1983). The large sea surface temperature variability latitude and longitude points inbedded within each line(La Violette, 1984) indicates strong mixing or upwelling of CZCS data. Geometric registration is critical, sincethat should produce rapid changes in the amount of CZCS imagery is highly distorted, especially toward thenutrients available for bio-optical activity. Additionally, ends of the swath. Control points are obtained only fromthe volume biological character of the waters are constantly positions within the subsection area. For this atlas the upperchanging in response to the advection or depletion of left corner was selected as 37048 N, 6042 E. The subsec-nutrients. Consequently, the optical properties that are tion area extends 512 to the east and south of this point,directly related to the phytoplankton pigment concentra with each pixel reprsenting 0.6 nautical miles. All CZCStion should show similar variability. Strong changes in imagery used in this atlas will be registered to thisthe optical character are expected at the frontal positions. configuration.

PHASE 3. In certain instances the subsection contain-C. Processing procedures ing the Alboran Sea was contained on two separate scenes.

The CZCS data contained in the atlas were processed When this occurred, the scenes and control points hadover an 18-month period. Initially, the CZCS archives were to be mosaicked into continuous format.searched for cloud-free scenes of the Alboran Sea. All PHASE 4. To perform accurate geometric registration,CZCS data collected from November 1978 through the subsectioned image must be resamplcd across the swathNovember 1982 were considered. A final selection of ap- such that each pixel represents an equal ground area. Atproximately 80 images was determined based on "quick nadir the ground and pixel resolution is 800 m, and aslook" photographs available through NESDIS. Computer the pixel approaches the limits of the swath, the groundcompatible tapes (CCT), level 1, were received for proc- resolution increases in response to earth curvature andessing on the Interactive Digital Satellite Image Process- scanner angle. The procedure is then to linearize the scaning System (IDSIPS) located in the NORDA's Remote line by resampling or increasing the number of pixels suchSensing Branch. that each is an equal area. Linearization was performed

The entire scene (channel 4) for each CCT was initial- on the subsectioned image for all thiee channels in addi-ly entered into IDSIPS, and a subsection of the scene con- tion to modifications to the control points output file.taining the Alboran Sea was determined. This subsection PHASE 5. The spatial remapping (warp) of the linearizedwas typically one-quarter of the swath width of the entire subsection to a Mercator projection is applied by fittingtwo minute scene. The subsection scene containing three a polynomial function to the control points to define thechannels (1,3,4) was reentered into IDSIPS for 10 phases transformation. During this phase the error that theof processing. polynomial calculates for the control points is checked.

Pt'ASE 1. As the CCT subsection is read into IDSIPS, This error establishes how closely the registered imagetwo unctions are performed on the pixels as each line conforms to the Mercator projection. Values are betteris entered. The first is that the data is calibrated into total then 2 pixels (1-2 nautical miles). This rubber map 77..absolute radiance received (/W/cm2). Second, the transform is resampled by nearest-neighbor reassignment.Rayleigh contribution of the atmosphere is computed for In generating this image, the output file nu contains threeeach pixel, based on the angular position of the ground channels, all registered to a Mcrcator projection with theposition with respect to the satellite and solar location, configuration shown in Phase 2. This registration permitsThis calculation is performed for each channel based on each pixel in the image to ha'e a corresponding latitudethe LOWTRAN IV model (Kneizys et al., 1980). The and longitude.resulting image from this phase is a three channel (1,3,4) PHASE 6. The atmospheric aerosol t orrection is percalibrated output in which the atmospheric Rayleigh ra- formed using the three-channel (1,3,4) registered image.

3

The selection of the Angstrom coefficients is obta:ned by the diffuse attenuation coefficient was measured from shipan interactive procedure (Arnone and La Violette, 1984), at several locations across the Alboran Front (Arnone,by first using channels 1 and 4, then channels 3 and 4. 1983; Arnone and La Violette, 1984). Figure 3 illustratesFor each pixel in the registered image (512 by 512), the that good agreement was found with the CZCS calculated670-nanometer value is weighted by the appropriate values of the diffuse attenuation coefficient. Additionally,Angstrom coefficient and sub~racted from the 443- or the it was shown that temporal changes in the diffuse attenua-550-nanometer value. The procedure results in two im- tion coefficient (0.05 to 0.1 m) occur within 24 hoursages, one the water-leaving radiance at 443 nanometers in the Alboran front region. These changes are knownand a second at 550 nanometers. to be frequent and are presently being investigated as to

PHASE 7. The ratio of the 443- to the 550-nanometer possible sources of origin.image is computed for each of the registered pixels. This Figures 4-16 contain 21 CZCS images processed by theratio, as discussed earlier, is directly related to the diffuse previously mentioned procedure and illustrate the monthattenuation coefficient at 490 nanometers (Fig. 1). The ly (January-December) optical data base for the Alboranresulting ratioed image represents a digital optical data Sea. As noted by the dates on the figures, cloud-free im-base with addressable latitude-longitude gridding. agery was processed from 1978 through 1982. Although

PHASE 8. The land in the ratio image is edited to zero it was attempted to obtain at least two images per month,values and inlays a land mask of the same area to which only one imqge was avaitable for March, April, andthe image was registered. The land mask is generated by November that was consiered acceptable for inclusionusing the Central IntelliLence Agency Data Base (1977) in the data base. Many images contain some cloud cover,for land-water boundary. This program requires similar which limits the usefulness for obtaining the diffuse at-upper left latitude-longitude coordinates, pixel-to-degree tenuation coefficient in these regions. For many monthsratio, and 512 by 512 pixel coverage that was used in additional images were processed, although only the twoPhase 2. By replacing the land with zeros, the data base best images have been included in this atlas.enhances the display of the optical variability. Figure 4 illustrates significant spatial variability of the

PHASE 9. To compensate for any problems caused by diffuse attenuation coefficient for January. As illustratedinaccuracies in the atmospheric correction or calibration by comparison with the other monthly images, similarprocedures, the ratioed images are normalized to clear circulation features are characteristic of this region. Thewater values in the central Alboran Gyre. These waters circular blue region with k values of 0.04 represents theare relatively phytoplankton poor, and the diffuse attenua- Alboran gyre. The frontal boundary surrounding the gyretion coefficient ranges from 0.04 to 0.05 m -. Since this represents the Alboran front and is typically charactercentral gyre water can be easily defined, the ratioed values ized by elevated k values (yellow to red) 0.08 0.15. Thiswere normalized to coincide with these values. This pro- frontal boundary is well formed on 21 January 1982.cedure did not dramatically influence the data base and whereas on 1 January 1981, it is not. In response to theprovided more accurate optical values. upwelling that occurs along the southern Spanish coast

PHASE 10. The subtle changes in the optical values (36010N, 50W), the k values are quite high (0.08-0.2)are enhanced by using a color table when displaying the and extend southward from the coast for 30 km. Borderratioed 'values. The color table also enables the display ing the Spanish coast, waters that have k 'alues greaterto readily classify dominant water masses. The color table than 0. 1 occasionally ocLur, as illustrated by the figuresused in this atlas enhances the diffuse attenuation coeffi- for the other months.cient values for all water types ranging from clear to tur In the %aters associated with the Strait of Gibraltar,bid. By selecting other color tables, the variability of spedfic significa..t optical variability is obser ed. These change3water types can be better represLnted. At this stage the can be expected, since the hydrology is extremely comratioed image is displayed on IDSIPS and the color table plex as a result of the Atlantic inflow mixing with theapplied. Following the graphic overlay of a latitude- Mediterranean outflow in response to tidal andlongitude grid, the display CRT is photographed. Note meteorological forcc3. Note that along the x'est Spanishthat the data base still resides in digital form on computer coast north of the Strait of Gibraltar (36'30 N, 6'15 W)disc. the k values are 0.5 and greater. Waters along this coast

are greatly influenced by the discharge of the RioGuadalauivir located north of Cadiz. Turbid water is

III. Results observed during all months.In October 1982 an international experiment was con Along the northern African coast, turbid plumes of

ducted in the Alboran Sea (e.Donde Va?, 1984) in which coastal waters are observed to extend 35 km north'vard

4

into the Alboran Sea on 1 January 1981. The coastal posi- The atmospheric removal techniques have several limita-tion of these offshore extensions can be observed to oc- tions that ultimately result in the accuracy from whichcur in other images in the atlas, which suggests that cer- the attenuation coefficient can be computed. Thetain coastal areas are frequently influenced b, the offshore radiometric decay of the sensors from prelaunch calibra-circulation. These areas will exhibit greater spatial and don is an initial problem. Various investigators have showntemporal optical variability. The atlas therefore provides encouraging results on modeling the decay coefficientsa method to determine which coastal areas have a high (Gordon, 1983, Sun, 1983). The assumption that thereprobability of variability, is zero water-leaving radiance at 670 nanometers is not

Figures 5-16 illustrate somewhat similar results to the valid in very turbid coastal water with high suspendedgeneral features as for January, except that the spatial vari- sediment concentration. At k values starting at approx-ability can be significantly'different. The clouds have been imately 0.7, a small underestimate of the value is expectw.identified in most of the images. At this time it is difficult As the k value increases, the CZCS value will be furtherto speculate on the causes of both the spatial and temporal underestimated. Improvements to this method byvariability. Present research is directed at understanding the estimating the water-leaving radiance at 670 nanumetersprocesses that produce the variability observed. In general (Smith and Wilson, 1980) are presently under investiga-this region appears to display a high %ariability in response tion. The selection of the Angstrom coefficient is basedto the complex circulation patterns associated with the on the characteristics of the aerosol. Although the op-region. The temporal changes appear to occur on a much timum coefficient is selected fur the entire region, fineshorter time scale than monthly. For example, the changes spatial Nariations in the aerosol type are nut accountedin the sptial variability of k are observed in Figure 13 for (Arnone and La Violette, 1984). Improvements arefor October 6-13, 1982. The position of the Alboran front presently being researched.changes, and the k values at this position change from The time required to process the 512 by 512 pixel CZCS0.04 to 0.15 within 6 days. Comparisons of the monthly data to the format of this atlas is approximately eight hours.k values do not appear to indicate any type of seasonal The processog procedures implemented have not beentrend, but are dominated by the spatial xariability resulting streamlined for operational processing. Impruo ements tofrom the circulation. This atlas represents an extremely both software and hardware are required if larger formatdynamic region atypical of most ocean regions. atlases are to be constructed.

Present estimates are for CZCS to fail within 1986.CZCS has well outlasted its design life by five years.

IV. Problems Presently, the Ocean Color Scanner (OCS) is being testedas the replacement. An OCS system is being consideredU sing the C Z C S data for atlas developm ent presents on a N A p l r o bi e 6 th N vy R m e O c n

several problems. on a NOAA polar orbiter ani the Navy Remote Ocean* Lack of seasonal data coverage Sensing System (N-ROSS) II in the mid 1990s.* Accuracy of computing absolute k values

- decay of onboard sensors and resulting calibration V Recommendations- assumption of channel 4 (670 nanometers) having

zero water-leaving radiance This atlas illustrates that extremely strong spatial and- assumption of uniform aerosol "type" temporal variability occurs in optical properties. This

* Computer processing time variability should be tested in other ocean regions to deter-• CZCS has exceeded life expectancy and replacement mine if the Western Mediterranean region is atypical. Ad-

satellite not expected until mid 1990s ditionally, long-term ground measurements would great-The lack of world-wide seasonal coverage is mostly the ly aid in interpreting the ',alidity of measurements from

result of cloud contamination. Aboit 80% of the CZCS CZCS, which suggests that long term (yearly) Uptical moordata is expected to be cloud co'ered. This problem re ings should be placed in coastal and shelf waters. Coinquires repeated coverage of certain regions, especially those paring these data with CZCS calulations should prokefor which limited quality is a'ailable. Requests for coxerage highly beneficial to determine how the 800 pixel resuluto increase data availability are currently accepted. tion of CZCS relates to smallscale -ariability.Although CZCS is not an operational system and should Research should also addi css how the diffuse attenuanot be expected to provide operational coverage, a large tion coefficient 'alues .omputed from CZCS are relateddata in'ventory is a'ailable from which initial world coastal to thc total coefficient of the Water Lulumn. SinLe the signaloptical properties can be established, that the satellite receies represents the first attenuation

5

length of the water mass (Gordon and McCluney, 1975), this sensor have provided the framework for an improvedany changes that occur below this depth will not be in- operational sensor. Multispectral sensor technology hascluded in the CZCS catculation. Since the majority of the improved significantly in the past decade, and many ofoptical signal is generated in the euphotic zone, little op- the problems that we. shown to exist with CZCS willtical changes are expected to occur below the first attenua- be eliminated with the launch of a new satellite. It is strong-tion length in open ocean waters. In coastal and frontal ly recommended that the follow-up visible satellite to CZCS,waters, however, where stratification of water mass types be considered for launch in the near future.is strong, the character below the first attenuation length This CZCS atlas has demonstrated the presentmay be sigrificantly changing. Research is required to bet- capabilities of existing algorithms for assessing ocean op-ter understand these processes and -o validate interpreta- tical variability. Although the atlas exists in both digitaltion of the CZCS calculations. and pictorial format, the compilation of a world-wide data

Continued research is required in the area of atnospheric base has not been adequately defined. The present datacorrection. Coastal regions that contain high sediment con- base exists as a series of eighty 512 by 512 files, eachcentrations (river discharge) present problems to the exist- of the same location but each of a different time. Theseing CZCS processing algorithms. Recent progress has am- data can be stored on either a 200-megabyte disc or a nine-plified this problem and encouraging results are apparent. track computer tape. For a world-wide digital data base

The utility for CZCS-type sensors is only beginning to to be constructed, the methodology of the data base hasbe demonstrated, especially in ocean optical monitoring, yet to bc a.,dressed. Data redvction techniques for averageUnfortunately, this experimental satellite is outdated and monthly/yearly and statistical relationships for areas hasno similar new visible satellite is planned for the near- not been considered. This development should be basedterm launch. CZCS has provided the experimental plat- on the user needs. Once these have been established, thenform to demonstrate ocean color monitoring. Results from a follow-up digital base can begin to be constructed.

6

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VI. References Gordon, H. R. and D. K. Clark (1980). Atmospheric

Arnone, R. A. (1983). Evaluation of CZCS and Land- Effects in Remote Sensing of Phytoplankton Pigments.

sat for Coastal Optics and Water Properties. Seventeenth Boundary Layer Meteorology, v. 18, p. 299-313.Symposium on Remote Sensing of the Environment, Ann Gordon, H. R. and D. K. Clark (1981). Clear WaterArbor Michigan, May 9-13. Radiances for Atmospheric Correction of CZCS Imagery.

Arnone, R. A. (1983). Water Optics of the Mis- Applied Optics, v. 20, n. 24, p. 4175-4180.sissippi Sound. Naval. Ocean Research and Develop- Gordon, H. R., D. K. Clark, J. W. Brown, R. H. Brown,ment Activity, NSTL, Mississippi, NORDA Technical R. H. Evans, and W. W. Broenkow (1983). Phytoplankton

Note 63. Pigment Concentration in the Middle Atlantic Bight; Com-

Arnone, R. A. (1984). Optical Variability in the Alboran parison of Ship Determination and CZCS Estimates. Ap-

Front Monitored by CZCS. Preliminary Results of the plied Optics, v. 22, p. 20.Donde Va Experiment, G. Parrilla (ed.), Spanish Gordon, H. R. and W. R. McCluney (1975). Estima-

Oceanographic Institute Report No. 24, p. 185. tion of the Depth of Sunlight Penetration in the Sea in

Arnone, R. A. and P. E. La Violette (1984). A Method Remote Sensing. Applied Optics, v. 22, p. 20.Hovis, W. A., D. K. Clark, F. Anderson, R. W. Austin,IE.I. Butler, D. Ball, H. R. Gordon, J. L. Mueller, S. F.Quantitative Ocean Color Data from Nimbus-7 CZCS. EI-Sayed, B. Sturm, R. C. Wrigley, and C. Yentsch (1981).

Proceedings of Ocean Optics VII, Vol. 489, Society of Nimbus-7 Coastal Zone Color Scanner: System DescriptionPhoto-Optical Instrumentation Engineers, Monterey, and Initial Imagery. Science, v. 210, n. 4465, p. 60-63.California, pp. 25-28, June. Kneizys, F. X., E. P. Shettle, W. 0. Gallery, J. H. Chet-

Amone, R. A. and P. E. La Violette (1984). Bio.Optical wynd, Jr., L. W. Abren, J. E. A. Selby, R. W. Fern, andVariability in the Alboran Sea as Assessed by Nimbus- 7 R. A. McClatchey (1980). Atmospheric Transmit-Coastal Zone Color Scanner. Naval Ocean Research and tance/Radiance: Computer Code Lowtran-5.Development Activity, NSTL, Mississippi, NORDA AFGL-TR-80-0067, Air Force Geophysics Laboratory.Technical Note 283. Also submitted to Journal of La Violette, P. E. (1984). The Advection of SubmesoscaleGeophysical Research. Thermal Features in the Alboran Sea Gyre. Journal of

Amone, R. A. (1984). Secchi Depth Atlas of the World Physical Oceanography, v. 13, n. 2.Coastline. Naval Ocean Research and Development Ac- La Violette, P. E. and J. L. Kerling (1983). An Analysistivity, NSTL, Mississippi, NORDA Report 83. of Aircraft Data Collected in the Alboran Sea During

Austin, R. W and L. J. Petzold (1980). The Determina- Donde Va? 6 October through 18 October 1982. Navaltion of the Diffuse Attenuation Coefficient of Sea Water Ocean Research and Development Activity, NSTL,

Using the Coastal Zone Color Scanner. In: Oceanography Mississippi, NORDA Technical Note 222.

from Space, J. F. R. Gower (ed.), Plenum Publishing Cor- Smith, R. C. and W. H. Wilson (1981). Ship and Satellite

poration, p. 239. Bio-optical Research in the California Bight. In:Oceanography from Space, J.F.R. Gower (ed.), Plenum

Central Intelligence Agency, Office of Geographic and Publishing Corporation, p. 281.Cartographic Research (1977). Cam-Cartographic Sun, Y. Y. (1983). Corrections for In-flight CalibrationAutomatic Mapping Program Documentation-5th Edi- of the CZCS. International Journal of Remote Sensing,tion. June, NTIS Pb-270304. v. 4, p. 829-834.

Gordon, H. R. (1978). Removal of Atmospheric Effects The i Donde Va? Group (1984). Donde Va-Anfrom Satellite Imagery of the Oceans. Applied Optics, Oceanographic Experiment in he Alboran Sea. EOS,v. 17, p. 1631-1636. v. 65, n. 36, pp. 682-683, September.

21 77

UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE A JYF1 563

REPORT DOCUMENTATION PAGE

Ia, REPORT SECURITY CLASSIFICATION 1b. RESTRICTIVE MARKINGS

Unclassified None2a, SECURITY CLASSIFICATION AUTHORITY DISTRIBUTIONAVAILABILITY OF REPORT

2b SCHEDUApproved for public release; distribution is2b DECLASSIFICATIONDOOWNGRADING SCHEDULE unlimited.

4, PERFORMING ORGANIZATION REPORT NUMBER(S) S MONITORING ORGANIZATION REPORT NUMBER(S)

NORDA Report 117 NORDA Report 117

6, NAME OF PERFORMING ORGANIZATION 7a, NAME OF MONITORING ORGANIZATION

Naval Ocean Research and Development Activity Naval Ocean Research and Development Activity

6c, ADDRESS (City, State, and ZIP Code) 7b, ADDRESS (City, State, and ZIP Code)

Ocean Science Directorate Ocean Science DirectorateNSTL, Mississippi 39529-5004 NSTL, Mississippi 39529-5004

8a NAME OF FUNDING/SPONSORING ORGANIZATION 8b OFFICE SYMBOL 9, PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER(I1 applicable)

Defense Mapping Agency

8c. ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NOS.

PROGRAM PROJECT TASK WORK UNITHydrographic Topographic Center ELEMENT NO, NO. NO. NO.

Washington, DC 20380 63701 B

11. TITLE (include Security Classlllcation)

CZCS Atlas of Water Optical Properties in the Alboran Sea12, PERSONAL AUTHOR(S)

R. A. Arnone and R. Oriol*13a. TYPE OF REPORT 13b, TIME COVERED 14, DATE OF REPORT (Yr., Mo., Day) 15. PAGE COUNT

Final From - To August 1 985 2416. SUPPLEMENTARY NOTATION

* with Computer Sciences Corporation17, COSATI CODES 18, SUBJECT TERMS (Continue on reverese it necessary and Identify by block number)

FIELD GROUP . satellite, Alboran Sea, optical water propertes

19 ABSTRACT (Continue on reverse il neissi;y and Identify by block number)")Optical water properties of the world oceans can be rapidly obtained from data from the Coastal Zone ColorScanner (CZCS) aboardtltimbus-70. Satellite processing techniques have been developed to eliminate the at-

mospheric contamination that contributes 90% of the total visible channel signal. rhe remaining signal, whichconstituted the ocean color, is directly related to the diffuse attenuation coefficient (k) at 490 nanometersfor the upper surface waters. Calculation and geographic registration of k can be done for each of the800-square-meter pixel resolution of CZCS, and results show that the accuracy is within 25% of shipmesurements.

This report indicates the processing procedures used to calculate k from radiance data from the CZCS, Ad-ditionally, problems, assumptions, and recommendations for future processing are discussed.

20 DISTRBUTIONIAVAILABILITY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION

UNCLASSIFIEDIUNLIMITED 0 SAME AS RPT N DTIC USERS 0 Unclassified22a. NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE NUMBER (Include Area Code) 22c OFFICE SYMBOL

R. A. Arnone (601) 688-5268 Code 321

DD FORM 1473, 83 APR EDITION OF I JAN 73 IS OBSOLETE UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE

op