water in two different coastal areas after discussing photo se- 
lection and instrument optimization. it is to be noted that the 
by aircraft gathered sea photographs veren't taken considering 
the study of wave spectra. Hence the interest in obtaining them 
as an aid to other remote sensing studies. The applicability 
of the photochemical equidensity method is also studied. 
Theoretical Background 
A) Wave Visibility 
Following Stilw&ll'sderivations (10) and with reference to 
figure 1, the light intensity at a given point is: 
x) - KL(9) «($ 
(1) 
where @ is the reflectivity at the incident angle € ,calculated 
from the Fresnel formula; K is a constant and L(0) is the luminan- 
ce of the sky in the direction reflected into the camera. 
m 
The variation of illumination with a change of slope is: 
Ap.) _ ALE) — € 20 37(6) 2€ t 
34 = K 30 «(9 31 + K L(0) 3e dd {23 
and if ¢ is small: 
Gé). 265, = À cos Ÿ (3) 
al = K [28 aL(e) , 4 av (€) 
65). = [v ES suo | (4) 
so that 
Nate, | aL(8) [46 
G = KcosV [2 v($) + LO) e (5) 
The incident intensity of the film can then be approximated. by 
Ie) > 16) + (256), der « et) (6) 
The linearity of I in respect with slope angle is assured if 
I. and 31/34 are constant in the photograph. This is true if the 
film is exposed in the linear region of the film characteristic 
curve; the equation for this linear portion of the curve is: 
D(x,y) » Y bs [CT 16,y)] (7)