772 
characteristic for the structure of the watercolumn, 
can be recorded at a single chosen channel as well. 
Fig. 1 shows an example of in situ spectral 
measurements by means of the ASIR. A depth profile 
is shown in Fig. 2. 
dot« 23 12 INERSE-AS1R-STAT10N 21 
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Figure 1. Record of in situ underwater irradiance 
measurements by means of ASIR. Variations of the in 
cident solar irradiance during the whole measuring 
period (a), downwelling irradiance spectra (b) and 
upwelling irradiance spectra (c) are displayed at 
several depths, as measured at a station in Java 
Sea. 
logtE/Eol .-Ed t s Eu 
mEKE-ASlR-SIAIia 21 
dote: 23 12 ti.K 15 IR 
downwelling irradiance and of downwelling radiance 
in the sun-detector plane is needed along with the 
measurement of the upwelling radiance. From a set 
of the collected radiance data, corrected for the 
glitter and atmospheric effects and related to the 
sea truth, algorithms and their variability can be 
studied. The instrument can be mounted on a stable 
platform (turret) above water, or preferably 
employed from a survey aircraft flying at low 
altitudes. Spatial resolution (angle of view) must 
be chosen accordingly to the expected horizontal 
inhomogeneity of the surface layer and to the wave 
amplitude and frequency. Fine spectral resolution 
of the measurements allows than final tuning of 
the algorithms. 
Coastal Remote Sensing Airborne Radiometer 
(CORSAIR) was constructed employing a zoom 
objective lens for the radiance measurements, cosine 
collector for the downwelling irradiance measurements, 
liquid light guides, automatic optical switch and 
correction filters assembly, detector, polychromator, 
optical multichannel analyser, console and a micro 
computer system providing rapid data acquisition 
and storage. Field of view and tilt of the objective 
can be adjusted. 125 channels between 400 and 720 nm 
can be scanned within 32 ms. 
An example of the airborne measurements by means 
of the CORSAIR is presented in Fig. 3 
Figure 3. Airborne measurements by means of the 
CORSAIR as performed during a survey flight above 
the Strait Madura with highly variable suspended 
matter load. Downwelling irradiance (a), upwelling 
radiance (b) and their ratio (c) are displayed as 
function of the wavelength. 
2.3 Broadband measurements above water 
■n 
depth (ib) 
-80 
Figure 2. Depth profile of relative upwelling irra 
diance at 685 nm (fytoplankton pigment fluorescence 
maximum), as recorded by means of the ASIR. 
2.2 Spectral measurements above water 
When large spatial diversity of aquatic conditions 
and/or influence of the glitter and of the lower 
part of the atmosphere are investigated, 
measurements are to be performed above water. In 
order to allow the comparison between the under 
water reflectance with the upwelling radiation 
recorded above the seasurface, rapid detection of 
Some environmental processes and features can be 
remotely measured by using sensors with only a few 
broad spectral channels. For instance total suspend 
ed matter distribution or morphology in the coastal 
regions can be monitored by the Landsat MSS or TM 
instruments. In some cases even the AVHRR of the 
NOAA satellites can be applied. The relationships 
between the optical signals and the sea truth 
(algorithms) are generally dependent on the local 
and temporal (seasonal) conditions and should be 
determined prior to the interpretation of the 
relevant satellite imagery. The low altitude 
measurements, whether from a stable platform or 
from a low flying aircraft, should be preferably 
synchronized with the satellite overpasses. The 
algorithms are currently determined by statistical 
analysis of the low altitude (or under water) 
optical data in relation to the sea truth parameters 
sampled simultaneously. 
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