slewing of satellite. Nevertheless the diameter of FOV may be 
2,000 km and the angular FOV will be 3 degree. Assuming the 
aperture dimension of CCD element and the required ground 
resolution are 14 Jum and 100 m respectively, then the focal 
length of telescope must be 5.32 m. The aperture will be 1.32 
m for F-number 5. It is very easy to get 3 degree of FOV by 
refractive system, but to do it with the focal length and the 
aperture diameter is not conceivable. On the other hand, this 
3 degree of FOV imposes difficulty on Cassegranian reflective 
scheme. The Makstov type or Schmidt type catadioptoric schemes 
are only solutions for this telescope. The scheme (c) is a 
rather exotic scheme which uses the conical scanning on the 
focal plane. In this scheme the total Japan islands are imaged 
in some circular arc area of the focal plane as shown in Fig. 1 
(c). The optical axis of telescope points to somewhere of 
Chinese continent. To image islands from Hokkaido to Kyusyu, 
about 3.2 degree of FOV is required, and to image total islands 
including Okinawa island about 4 degree of FOV is required. 
According to similar consideration as scheme (b), the pertinent 
telescope is the Makstov or Schmidt type catadioptoric system. 
On the focal plane the image of Japan islands are formed along 
with concentric strips, on which all image points are focused 
best and have same optical performances. 
2. Design of Schmidt telescope to observe the Japan islands 
with conical scan from geosynchronous orbit 
2.1 The principle of Schmidt telescope 
Fig. 2 shows the basic principle of Schmidt telescope. S is a 
primary mirror with spherical surface, and C is an aspheric 
lens which called the correcting plate and positioned on the 
center of curvature of the primary mirror. The central part of 
this correcting plate is forming a convex lens, but the 
peripheral part is forming a concave lens and there is no power 
part between these two parts, which does not refract ray. The 
spherical aberration is removed completely by this correcting 
plate. Oblique light beam is symmetrical about the principal 
ray OA. Due to this symmetry there is no coma and astigmatism. 
The focal plane is spherical surface with 1/2 length radius of 
curvature compared to the primary mirror. That is, on the 
spherical focal plane we can get complete image without any 
aberration. 
2.2 Calculation of optical parameters of the Schmidt telescope 
We adopt the scheme (c) and put the image of Japan islands in 
the concentric strips on the spherical focal plane of Schmidt 
telescope. Then the projection of telescope FOV on the Earth's 
surface is a circle, which comes in contact with parallels of 
latitude 29 degree and 61.5 degree, and the center of FOV is 
projected on the parallel 45 degree and the distance from 
satellite on the geosynchronous orbit to the projected image 
center dis: 38,140 km (cf. Fig. 3).: The focal; length £,: the 
distance between satellite and the center of FOV on the ground 
D, the spatial resolution on the ground Ax and the aperture of 
sensor element d are related in formula: 
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