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For future flight experiments continuous registration of all flight para- 
n::ters, and accurate pre-flight measurements of scan geometry are 
desirable. 
A. second difficulty in superposing the scanner data with sea truth mea- 
surements is caused by the dyn^mics of the water observed. Tidal cur- 
rents displace the water in which measurements were done up to one 
nautical mile during the tine lapse between overflight and measurement. 
Assuming that the water fiow due to tidal currents is laminar, this dis- 
placement can be corrected for, once the current direction and speed in 
the neighbourhood of ship tracks are known. Here, the following proce- 
dure has been used: 
Using Ramming s model of tidal currents in the North sea, the measu- 
rements of the current meters moored at various positions in the EURA- 
SEP 1977 test area have been extrapolated to some positions along the 
ship track to be corrected, and a data set has been created which con- 
tains time, current speed and direction for each of the posiions. Cc,n- 
bining that data with the sampling positions and the corresponding times, 
tide-corrected sampling positions have been CCniputzu through linear ic- 
terpolation. 
The radiances measured by the scanning instrument cannot be related 
directly to the spectra of the water surface being observed, since the 
light received by the sensor is composed of a small part which e:nanates 
from below the water surface and is moreover attenuated by the atmos- 
pKere, and a large part of other origin. The water leaving radiance Lo 
can be computed according to: 
(1) Len 4+L HT 
, 
*L)-T 
À p x) 
where L is the radicnce measured by the scanner, Ty is the transmit- 
tance c^ the window at the bottom of the aircraft, L, is the patn radiance, 
i.e. the amount of light scattered into the scanner by aerosols and dust 
in the atmosphere, T 4 is che atmospheric transmittance at the scan- 
view angle and L_ is composed of sun- and sky glint, i.e. light reflected 
on the water surface. 
If T(h,”) is the atmospheric transmittance between water surface and 
an altitude h, Y* being the angle between nadir and view direction, the 
terms Ly and Ly in eq. (1) can be computed approximatively by: 
  
Ty tan “8 
Ty y, costs) - g? S 
2). L.= 3 The, 8) plot) ———ttee= Tg + Pl) 
To? cos 0 cos B