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Laser range finder and reflectivity meter for the Mars-96 international space project

A laser altimeter based on the time of flight principle has been developed to be put on board a gondola of a balloon drifting in the atmosphere of Mars. The light source is a PGT:Nd solid state laser ((lambda) equals 1.067 micrometers ) which emits pulses about 10 ns wide at a repetition rate of 0.2 Hz, the energy of each pulse being about 7.5 mJ. Special attention was paid in the development work to minimizing the size, weight and power consumption of the altimeter. Thus its weight is 450 g and the average power consumptions of the electronics and laser have been reduced to about 30 mW and 0.6 - 0.8 W, respectively, by switching on the power supply to the measurement and interface part only during the 50 ms measurement period. The time interval between the transmitted and received signal is measured digitally by counting clock pulses obtained from a 100 MHz oscillator. The measurement range and single shot resolution are about 6 km and +/- 1.5 m, respectively. The laser altimeter contains two peak detectors to measure the amplitudes of the transmitted and received pulses for recording of the albedo on the surface of Mars. Test results show that the altimeter is capable of operating in a temperature range of -80 degree(s)C - +60 degree(s)C and at an air pressure of few torr. The minimum average reflection coefficient of the Martian surface is about 0.1 which enables the measurement range of 13 km if the minimum signal to noise ratio of the measurement is about 10.