3 m. an” s 
mn a I E N 
ESTIMATION OF THE ATMOSPHERIC PATH RADIANCE, 
FROM MULTISPECTRAL INFRARED IMAGES 
T.YOKOTA 
The National Institute for Environmental Studies 
16-2, Onogawa, Yatabe, Tsukuba, Ibaraki, JAPAN 305 
H.HANAIZUMI, M.INAMURA, S.FUJIMURA, H.TOYOTA 
The University of Tokyo 
(-3-1, Hongo, Bunkyo, Tokyo, JAPAN 113 
ABSTRACT 
Described is a method for extracting the spatial pattern of the 
atmospheric path radiance, substantially due to water vapor, in IR region from 
remotely sensed data. We use three IR bands 4.3-5.5um, 4.5-4.9um, and 
10.5-12.5um. The atmosphere gives different affects on the data in these 
bands. By computer simulation and experiments using actual data is confirmed 
that the ratio (W(10.5-12.5)-W(4.5-4.9))/(W(10.5-12.5) -W(4.3-5.5)) calculated 
from the data obtained in the three bands is an increasing function of path 
radiance. Sufficient conditions for the band selection is also discussed. 
o o 
1. INTRODUCTION 
The estimation of atmospheric path radiance is necessary for the 
correction in the temperature measurement from remotely sensed IR data. There 
have been many studies on the temperature correction[1],[2],[3]. However, 
most of them used path radiance models or the regression analysis method 
disregarding the distribution of the radiation absorbers. In the actual 
situation, the spatial variation of path radiance must be considered for more 
precise temperature correction. Thus our first step is set up to extract the 
qualitative pattern of path radiance from the IR images. 
We propose a new algorithm to extract the pattern using three infrared 
bands in which the atmosphere gives different effects on the data 
respectively. To get the pattern, there are three unknowns in the data: the 
spatial variation of the terrain surface temperature, that of the atmospheric 
temperature, and that of the amount of absorbers. Hence, three bands are 
necessary to get the solution. 
The validity of the algorithm is confirmed by computer simulationeusing 
the tables of atmospheric transmittance published by Passmann, Larmore, and 
R.D.Hudson Jr.[4]. It is also confirmed by actual data obtained by an 
airborne MSS. 
2. DERIVATION OF SIMPLIFIED RADIATIVE TRANSFER EQUATION 
The infrared signal Iin obtained at wavelength À by remote sensing is 
composed of three terms: Is(radiation from the surface), Ia(radiation from the 
atmosphere), and Iref(radiation reflected by the surface), that is, 
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