A image-motion compensation system of high precision space camera
The leading-in of the velocity/altitude (w/h)
There are many ways to lead in the velocity/altitude ratio (W/H) many velocity/altitude meters are made according to various principles. Now we introduce a leading - in method, which is used in the remoting sensing satellite camera in our country.
In the satellite, there is always a set of satellite attitude control system of high precision. The system measures the important orbit parameters, which include the speed and height of the satellite. So long as the ratio of speed to height of the satellite is computed in real-time, the speed of the image-motion will be calculated by formula (1). This is done by the computer in the satellite.
A high accuracy of the speed of the satellite measured by the satellite attitude control system is required, however, under the influence of the earth topography fluctuation, the measuring accuracy of the flying height is relatively low. Thus it limits the given precision of the velocity/altitude (W/H.) Furthermore the component of the earth rotation speed in the direction of the satellite flying will also reduce the leading -in precision of the velocity/altitude (W/H)
Therefore the height and the speed need to be adjusted as follows:
- To adjust the satellite height by the elevation of the ground objects.
- To adjust the satellite speed by the component of the earth rotation speed in the direction of the satellite flying.
However, to achieve item (a), it is necessary to raise the precision of the given elevation precision of the ground objects, which is very difficult. Thus we introduce the concept of average elevation. We divided the photographic region into several smaller blocks and computed every average elevation, which is used to adjust the satellite flying height. Obviously, the smaller the block is, the higher the leading -in precision of the velocity/altitude (W/H).
The lading -in method of the velocity/altitude (W/H) was implemented by using the satellite orbit parameters (i.e.) the flying speed W and the flying height H) for real time calculation, and by using the average elevation of the photographic block to adjust the flying speed, and by using the component of the earth rotation in the direction of the flight to adjust the flying speed. Such a scheme was applied in the Chinese high-resolution space camera. Its precision is 1.5% which can match with the high quality photo-lens with static resolution 100 pl/mm. Unlike other leading -in and measured instruments such as the velocity/altitude meter, it uses the orbit parameters t calculate the velocity/altitude with high precision, high reliability, and low cost.
