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Analysis of NOAA-AVHRR data 
  
Since the obtained raw AVHRR data contain geometric distortion, the 
geometric correction must be made in order to superpose the AVHRR data on the 
processed Landsat-MSS images. The correction procedure consists of tangent 
correction and affine transformation. 
The geometric scheme of the tangent correction is shown in Fig. 5, and the 
actual correction for each pixel digital count of AVHRR data is carried out by 
following equation(Ref.8), 
1 Rsin (mrA 91/R) * 
n = arctan } (2) 
A61 R+ r - Rcos (mrA 01/R) 
  
  
Where, 
r ;height of satellite (883Km), R ;radius of the earth (6370Km) 
n ;pixel digital count before correction 
m ;pixel digital count after correction 
A01 ;instantaneous field of view of AVHRR (0.9443mrd) 
After the tangent correction, the corrected AVHRR images are superposed on 
the Landsat images using the affine transformation which is decided in reference 
with several GCP's on the Landsat and NOAA images. 
The temperature calibration of thermal infrared data is carried out using 
the internal calibration data recorded in a raw AVHRR-CCT and the digital count 
of the thermal infrared band is converted into brightness temperature by 
following equation(Ref.8), 
N= GX +O (3) 
Where, 
N ;observed radiance of the object, X ;CCT count of the object 
G ;gain, 0 ;offset 
G and O are specified as follows, 
G = (Nsp - Nt) / (Xsp - Xt) 
0 = Nsp - G Xsp (4) 
Where, 
Nsp ;average radiance of space 
Nt ;average radiance of internal calibration target (ICT) 
Xsp ;average count corresponding to space radiance 
Xt ;average count of ICT 
The temperature T (°K) and the radiance Nt of the black body at T (°K) 
observed with AVHRR are related by the following equation {Plank's formula 
B (9,71 
, 
ve = { g (9017 viz 9 v4 4 (5) 
Where, 
x V ;wave number of infrared light 
$( V ) ;responce function of the sensor (Ref.9) 
V1, v2 ;lower and upper bound wave number of filter 
The final step of the analysis of NOAA-AVHRR data is the generation of sea 
surface temperature map (SST) from the caribrated thermal infrared image. The 
isotherms are generated automatically by the computer software. The interval 
for isotherms is 0.5-1.0 degree in centigrade and the final SST map is obtained