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models are stored in the radiance file in the 
inter-extrapolation subsystem. To make this file we computed 
the theoretical radiances for many combinations of 
wavelengths, flight altitudes, view angles, solar elevation 
angles, ground albedos and atmospheric models. Although 
considerable amount of computer time is required for such 
computations, it is well worth doing. Once the radiance file 
is made, then the intensity is computed very fast for any 
wavelength, flight altitude , solar elevetion angle and the 
optical thickness value with an aid of inter-extrapolation 
program. 
In the correction subsystem we assume that the 
undelying surface is characterized by an albedo for the 
target A t and a mean background albedo A of the area whose 
horizontal scale is about 300m. From Eqs.(1) and (2), the 
reflected upward normal intensity above a target site is 
given by Eq.(3 ) • 
I t =A t (SÂ+T)+(P-S)Â 2 +(Q-T)Â+R (3). 
From Eqs.(1) and (3) we can find a ground albedo value for a 
pixel in the Landsat images in the following. 
(4), 
At=(I obs -(P " S)A2_(Q_T)A " R)/(SA + T) 
(5), 
where I 0 bs is the observed intensity for a target and I 
is the observed average intensity around a target. TheSe 
two quantities are computed from the observed CCT level with 
known gain and offset values of the Landsat MSS. A ground 
albedo data set is, thus, obtained by applying the above 
procedure to each pixel and every band. Since wavelength, 
flight altitude, and solar elevation angle are known 
quantities, the AECS is a system which converts a observed 
Landsat data set (given in a relative scale) into a ground 
albedo data set in a absolute unit if the optical thickness 
of the haze at the time of obsevation is provided. 
ESTIMATION OF OPTICAL THICKNESS OF HAZE 
In order to use the AECS effectively we need to know the 
value of the optical thickness of the haze at the time of 
observation. The value of the optical thickness x can be 
found by using the relationship between the theoretical CCT 
level and the ground albedo. In Figure 3 we show such 
theoretical mean CCT level curves as a function of mean 
ground albedo for several different values of x. Curves in 
Figure 3 are valid only in the case of solar elevation angle 
58"and band 4 of Landsat II. For given values of solar 
elevation angle, the optical thickness , and the mean ground 
albedo A, the mean theoretical intensity is given by Eq.(1). 
The theoretical mean CCT level X is given by