A CONCEPTIONAL STUDY OF OPTICAL EARTH OBSERVATION 
FROM GEOSYNCHRONOUS ORBIT 
Hajime Koshiishi, Kohzo Homma 
National Aerospace Laboratory 
7-44-1, Jindaijihigashi-machi, Chofu, Tokyo 182 
Japan 
Commission Number: I 
Summary 
At first we assumed that requisitions of earth observation from 
geosynchronous orbit are 100 m spatial resolution at 1.1 um 
wave length. Then design of telescope system had done with the 
Schmidt type telescope. The optical parameters of resulted 
design are 5 m focal length and 1 m aperture. Then we had 
introduced new scanning scheme: conical scan on image plane. 
Analytical calculation by wave optics had been done and it 
became clear that the 100 m spatial resolution can be get with 
very high OTF with this conical scheme. 
Introduction 
For various fields of earth observation, an observation from 
geosynchronous orbit is desired. For example, observation of 
climate condition and warning, ocean observation and forestry 
need geosynchronous earth observation satellite. Especially, 
the Japan islands are covered by clouds steadily and only for 
80 days a year can be observed from remote sensing satellites. 
Therefore the observation from geosynchronous orbit will be 
particularly useful for the Japanese remote sensing users, 
nevertheless such a system is usually excluded because of the 
long distance and the imagined enormousness required for high 
resolution. If we use some catadioptoric telescope and conical 
scan scheme on the image plane, can get 100 m resolution with a 
comparatively small telescope system, and it is realizable even 
by existing technologies. We have done the conceptual design 
of the earth observing system from geosynchronous orbit 
applying a catadioptoric telescope design. This paper presents 
the outline of the design studies. 
l. To observe the Japan islands from the geosynchronous orbit 
There are three schemes of FOV (Field of View) for observation 
the Japan islands from the geosynchronous orbit. The three 
schemes are shown in Fig. 1, (a), (b) and (c). In the scheme 
of (a), a usual small circular FOV and scan are used to observe 
the total area of the Japan islands. That is, some slewing 
motion of satellite is needed. When the diameter of the FOV 
and mean distance between the geosynchronous orbit and the 
Japan islands are assumed to be 600 km and 38,000 km 
respectively, the angular FOV becomes to 0.9 degree. To 
utilize the Cassegranian telescope with parabolic primary 
mirror for this angular FOV may not be good design scheme 
because of various aberrations at the edge of FOV. This 
angular FOV may require the Ritchey-Chretien scheme. In the 
scheme (b) all of the Japan islands is put into one FOV and 
staring mode observation is possible and there is no need of 
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