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Analysis Procedure 
The analysis of the photographs (or transparencies) con- 
sisted of an optical analysis as described above and of a photo- 
chamical equidensity analysis. The last was performed using 
Agfacontour Professional film, which showed tc be an easy medium 
cost method for operetionel interpretation. The equidensity 
analysis (also reforred to as density slicing in other papers) 
causes a loss of information, the determination of uhich is 
deduced mathematically. It results that it is pessible to mini- 
mize this information loss by the choice of suitable width and 
position of the equidensities. 
The equidensity analysis requires a prior densitometric 
analysis of the photographs from which the density levels to 
be used are mathematically determined. Theresulting contours 
after the photochemical process shoued to be useful uhen study- 
ing the directional spectrum ; though the limit for color analy 
sis uas found to be of eight diffarent density levels. A com- 
plete description of the Agfacontour method may be found in (21) 
Data Collection 
The photographs used in this study were taken by Hasselblad 
Camsras on board of a CASA 212 aircraft operating either at 3000 
or at 400 meters altitude during the oceanographic missions 
NAUCA 77 and DELTA 77, In both the use of aerial imagery was 
intended as support to other experiments. Thus that the selec- 
tion of transparencies has been limited by the quality and suit- 
ability of the existing imagery which in many cases presented 
the disadvantage of showing in part a strong sun-glint. This, 
es mentioned above, may overemphasize a determined slope direc- 
tion, but this error can be compensated if enough. data of the 
area are provided by other sources. 
The CASA 212 fleu at a speed of 150 knots under cicar sky 
conditions, being the scale of the photographs 1: 120,000 and 
1:16,0C0 for each altitude of flight. The starting and ending 
times of each series of photographs is indicated and the rate is 
one each 26 seconds; this rate is variable to allou overlapping 
for stereo analysis. 
The selection of the transparencies was made ttending to: 
i) influence of sun-glint, ii) uniformity pattern of the scene, 
iii) contrast, iv) interaction with coastal and/or islands 
accidents and v) interest of the area. In total 25 photographs 
were selected from which only seven resulted acceptable when 
densitometric analysis was performed. In this paper we give the 
results of three analysis as an example of the suitability of 
the method,