ansmit= 
PD (x,y) 
red 
3 and 
is 
)sod 
secund 
nortan 
lis- 
5 
trens- 
3 
1e 
es in 
ical 
lly the 
, (20). 
ront 
. Hou- 
gurat- 
dot 
ed, 
d 
con- 
sition 
of L5 , P, end P5, . This flexibility.is of considerable 
utility in spatiál filtering applications and when con- 
sidering the analysis of the trensform,since the adjust- 
ment of its scele results in an easier analysis possibi- 
litv. 
t x4 y ) can be expressed in function of tfe opticel dene 
sity Db iy4] of the film as 
-in(y) 
t (xy) = 10° (11) 
Following from this equation and combining equations 6 and 7, it 
results: 
ALL 
thoy) = & [1-846] * (12) 
where 
„4171 
2 
A 
i" 
o [CT 1,6) (13) 
and 
Ag Lem (14) 
If a sinuscidal amplitude grating is defined by t4 (x 31) 2 > . 
(1 « eos ux), then t. is anelogous to dc bies ters end 4 ie 
analogcus to nodulation (contrest) w (15). Hence a Film input 
with low bias. level and high modulation is desirable. 
In the following we will briefly consider the relationship 
between the hight spectrum and the slope spectrum. The power 
spectrum E(K) of the surface waves of wave number k is defined 
by 
E(R,t) = ON mm: ear (15) 
where n (X,t) is the elevation of the sea surface at location X 
end time t; r is the distance betusen the tuo reference points 
and the bar indicates the average about X (12). Since optical 
density of vertical wave photographs is proportional to the 
surface slope |Vn|, it may be expressed as: 
F(K,t) = C J EZTGYTEZTEST el ge (16) 
where C is a constant. Here the dependence uith t is dropped.