Radar altimeter calibration

The operating principles and design of a radar altimeter representative of those proposed of ERS-1 are described and geophysical influences on the measurements are discussed. General aspects of calibration are examined, and the critical areas of time and frequency resolution pointed out. A method of internal calibration of delay and backscatter coefficient, by rerouting the tramsitter signal, is described. External prelaunch calibration can be carried out by airborne trials, or using a return signal simulator. It is established that airborne calibration requires high altitudes and high speeds, and is likely to be difficult and expensive. The design of a return signal simulator is shown to be very difficult. No feasible design is identified.