thened when results were discussed with SA experts. They 
confirmed to KISR the propagation of certain errors in their 
results. A new value was given as 63.9 for surface sample 
and 64.1 for bottom sample in the conventional techniques, 
mean values and standard deviations are reduced to (62.3, 
1.47) and (62.7, 1.21) for surface and bottom samples res 
pectively. Residuals are improved but results are still 
not reliable. Decisive answer in favour of physical sen 
sors is taken as we observed some parameters during another 
mission (Ozone and Szucs, 1977) which was dedicated for 
the determination of water currents from helicopter the 
discussion of which is outside the scope of this paper. 
Thus, as far as accuracy concerned, it makes no difference 
if we acquire in situ water parameter values from airborne 
or seaborne platform. 
As an output of this result, it is obvious also that our 
fears that the existance of the boat may disturb the tact 
of the water environment at the locality of the sample are 
out of question relative to measured parameters provided 
certain precautions are taken on board the boat. 
The time needed for either method is the parameter that 
would play a role in taking a decision of which a procedure 
to adopt. The real helicopter time (airport and back to 
airport) is one hour in our case (1030 - 1130). The time 
of the experiment (on shore landing ground-site-measurement- 
back to landing ground) took only 20 minutes including 
search and follow-up of astrayed boat, versus six hours 
boat time. 
CONCLUSION 
This tripple experiment, namely the measurements of water 
quality parameters using airborne physical sensors, sea 
borne physical sensors and conventional analysis of samples 
on board the boat, shows the following: 
o The use of calibrated physical sensors is reliable and 
accurate enough for the determination of water para 
meters needed for correlation with remotely sensed 
data. 
o The use of calibrated physical sensors is far less 
cumbersome than conventional techniques. No systema 
tic or computational errors are liable to occur with 
such sensors once properly calibrated (mainly for 
zero errors). 
o The use of a helicopter for lowering the sensors in 
the water speeds up the operation of in situ data 
acquisition; which match with the requirements of 
monitoring water pollution by remote sensing. It is 
to be quoted, however, that if the body of water to 
be monitored is only few square kilometers (as for 
SA) gain of time is not very essential because boat 
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