data 
Invey 
shal- 
"non 
permis- 
e than 
s far 
idary 
lade to 
je 
ong the 
iis 
with 
area of 
  
- 1151 - 
For: the best aerial view of the zone, the flights were 
made along the axis of the canal, in a SSW-NNE direction at an 
altitude of 6600 feet, permitting a swath about 3500 meters 
(fie. 2). 
A Daedalus 1230, 2-channel thermal scanner (1-2 and 8-114) 
with the black bodies regulated between 16? and 20? C as a re- 
ference, was used for the survey. 
Harmonic analysis 
As the prime aim of the aerial survey was preferably to 
follow the movement of water, the recorded data was elaborated 
on using the 8-11y channel, as it i's more suitable to our pur- 
pose. 
Over a body of water the use of near infrared reflected 
energy and the thermal infrared emitted one, can fairly de - 
scribe two quite different properties of the liquid surface. 
The former, due to the strong absorption can give just a small 
signal, related to the sea roughness; the latter, the emission 
depending on the water temperature, can offer a panoramic view 
of the gradienvs generated both by the current pattern and by 
the waves. Then we can consider two distinct roughnesses, one 
being of geometrical origin, the second referred to as energy 
seepages at the surface produced by the preferential movement 
of the water. 
The applicable technique for data elaboration is the so 
alled "harmonic analysis" consisting in the selection of com- 
ponents forming the original signal of a scan line in the case 
of thermography, and in particular in the choice of the most 
meaningful among them to describe the texture. In the domain 
of thermal infrared, the extraction of a component can posi- 
tiveiy describe the currents field as seen at the surface of 
the body of water, being the lines which the eye correlates on 
the final result, given by the alignment of points showing an 
appreciable thermal gradient. The presence of currents them- 
selves should always produce a thermal gradient. But, unfortu- 
nately, the value itself pends strongly on the direction tne 
phenomenon is observed and, in the case of a scanner, surveyed. 
To remove the influence »f the direction, the component extracted