Fig 1. Spectral range of the channels of the 
sensors used during the "Adria 84" 
water, this making soffisticated methods a must to 
finish up with an acceptable precision. 
The processing of the CZCS data consists essentially 
of the following phases: 
- Sensor sensitivity and callibration. The CZCS has 
an internal calibration system, which has never 
indicated an appreciable deterioration of the 
sensors (except for CH 6, the thermal channel). 
Nevertheless there were clear indications of a 
deterioration, obviously an optical surface outside 
the calibration circuit. Deterioration was 
negligible for CH 4, but increased substantially 
with decreasing wavelength for the other channels, a 
phenomenon indicating (cosmic) dust deposit as the 
most probable cause. Sensitivity loss coefficients 
have been established for the channels 1,2 and 3 
relative to CH 4, using the upwelling radiation of 
the clear-water pixels of all CZCS scenes ever 
elaborated at the JRC . 
- Atmospheric correction. The fact that the sea 
reflects so few radiation makes the atmospheric 
correction a must. Although the basis of the 
correction is still the one proposed by Gordon, 
quite some refinements have been added eversince. 
Three effects are'of importance : 
- absorption on the illumination source welling 
down into the sea and on the reflected radiation 
welling up to the sensor. 
- Rayleigh scattering or molecular scattering 
- aerosol scattering 
The first 2 effects can be calculated straight 
forward, the 3d effect is an everchanging quantity 
depending on place and time. 
- Chlorophyll and Total Suspended Substance (TSS) 
determination. An emperical relationship has been 
developed, based on in-situ measurements and the RS 
signature, to establish CHL and TSS concentrations. 
The CZCS spectral resolution does not allow to 
distinguish between CHL and Yellow Substance. In 
coastal regions with no fixed relationship between 
CHL and YS, this might lead to substantial errors. 
Part of this work has been done by a visiting 
scientist, M.Viollier. 
- Geometric correction. For comparison of different 
images, they must be brought on a common 
geometrical footing, in our case the Mercator 
projection (projection cylinder going thru the 
equator) . The classical geometrical correction 
method fails when not sufficient well distributed 
reference point are available, as is regularly the 
case over sea area's. NASA provides for each image 
so-callled anchor points, synthetic reference 
points of which the location is given, derived from 
sensor relative data. 
Experience however has learned that the anchor 
points are not sufficiently precise and can give 
rise to errors of some tens of kilometres. 
A procedure has been developed, essentially based 
on sensor relative data, only corrected with a 
minimum of ground control points, which need not to 
be equally distributed over the scene. The program 
has been developed under contract (M.Langemann, 
A.Popella) under the leader ship of prof. Ph. Hartl, 
of the Technical University of Berlin. 
- Final product. The elaborated images are hard 
copied for subsequent visual interpretation, or 
once again geometrically corrected to fit the grid 
used for the hydrodynamic model of the Adriatic Sea. 
-NOAA AVHRR 
The sea has a much more uniform temperature compared 
to land, reason why sea temperature, when to be 
significant, must be established with much greater 
precision. 
The thermal channels of the AVHRR operate with an 
equivalent precision of around .1 K (at 293 K), but 
due to the atmospheric presence, and in particular to 
the water vapor, errors of several degrees are 
possible, the measured value always being lower than 
the real one. 
The water vapor quantity can be established in two 
ways : 
- with the split window technique, e.i. derived from 
the difference between CH 4 and CH 5. Only NOAA 9 
is equipped with a split window, NOAA 6 has only 4 
channels. 
- by means of the HIRS (High resolution IR Sounder), 
installed on both NOAA satellites, but for this 
scope considered less precise. A procedure has been 
developed, based on the split window technique by a 
visiting scientist G.Dalu (Istituto di Fisica dell' 
Atmosfera, CNR, Roma). 
The procedure consists eesentially of the following 
phases: 
- calibration. 
- determination of brightness temperature for CH 4 
and CH 5 
- determination of the quantity of water vapor 
- determination of the SST (Sea Surface Temperature) 
from CH 4 and the water vapor quantity. 
The objective was to arrive at a precision of .3 K. 
Up to now published SST maps refer essentially to 
scenes with relative large temperature differences, 
e.i. the gulf stream eddies, or the strait of 
Messina, but the Adriatic Sea, especially during the 
summer has very small and slow temperature 
differences, which makes high precision necessary. 
The SST derived from surface radiation refers only 
to the utmost top layer of the water body (20 
microns) and may be more than 1 K below the water 
bulk temperature (at 30 cm depth), depending on water 
evaporating conditions and water turbulence. Actually 
no procedure for geometric correction of AVHRR images 
is available. The processing program is implemented 
on the Amdahl mainframe. 
-Landsat TM 
With the probable shutdown of the CZCS in near 
future, the marine community will be deprived from a 
specific Ocean Color Sensor for an unknown stretch of 
time. The TM might constitute at least a partial 
substitute for the CZCS. 
The major problems with the TM are : 
- less spectral resolution, broader channels, thus 
more difficulties to distinguish CHL and TSS. 
- small swath, thus low daily coverage 
- early morning pass, thus low illumination, 
specially in winter, 
- very expensive on a covered surface basis. 
The JRC will participate in the North Sea experiment 
in May 1986 during which the TM capabilities as an 
ocean color sensor will be investigated. 
-New sensors 
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new sensors will be investigated, as substitute for 
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