In the course of space camera observation, the ground target and observing condition are changing all the time, so the
light radiance in space camera entrance is different. In order to get appropriate exposure even though ground target is
different, we need to analyze the relationship between observing condition and exposure value of space camera. The
purpose of this paper is to propose a method to calculate exposure value of space camera according to type of ground
target and observing condition. Atmosphere radiative transfer soft PcModWin is developed by Ontar Corporation, USA.
Using PcModWin, we can calculate atmospheric transmittance, solar and atmospheric radiance when solar zenith angles,
atmosphere models, atmospheric aerosols and atmospheric visibility are different according to variation of observing
condition. The target radiance in space camera entrance can be calculated by multiplying ground target radiance by
atmospheric transmittance. Adding atmospheric backscattering radiance and target radiance in camera entrance together,
we can get total irradiation in camera entrance. Then according to camera aperture value and lens transmittance, we can
calculate irradiance of image plane. Finally, by multiplying with exposure time of camera (integral time for TDI-CCD),
the exposure value of space camera can be acquired. We established the relationship between ground target, observing
condition and exposure of space camera. When the ground target, observing time or weather condition is different, we
must set appropriate camera parameters if we want to take qualified photos. This relationship is useful for radiometric
calibration in laboratory.