High Resolution Optical Remote Sensing Satellites - Challenges and Techniques

High spatial resolution satellite data is essential to identify small objects and extract minute details of the terrain. This data is provided by many satellites and being used in numerous applications. The realization of high resolution satellite is a challenging task. Significant complexity lies in the realization of high spatial resolution camera starting from material selection, high stiffness-low mass opto-mechanical system design, detector selection to high speed camera electronics design. The mass and size of camera increase with the improvement in spatial resolution. Alternate methods such as Step and Stare, and time delay integration methods can be used to achieve high signal to noise ratio images. The performance of satellite bus subsystems like structure, the data handling, and storage system, the data transmission system, attitude sensors and actuators should also be improved to achieve good quality data. The data handling system has to be designed to handle high data rate and data volume. The capacity of the data storage system has to be increased to cater the high data volume storage requirement. The data transmission system needs to be sufficiently capable to transmit the high volume imaging data to the ground station. As the spatial resolution improves, the spacecraft pointing accuracy and drift rate requirements become stringent. Improved attitude sensors and high capacity actuators are essential to meet these stringent requirements. Generally, high resolution cameras are combined with high speed electronics to handle high data rates which need more power. In this paper, we discuss various techniques being employed to obtain high resolution data with reasonable SNR. The challenges involved and the improvements required in various spacecraft subsystems to support these high resolution cameras are presented. Techniques employed by different space agencies to obtain high spatial resolution images are also discussed. The characteristics of high resolution satellites are also tabulated and compared