Photon counting laser altimeter for planetary exploration—the technology demonstrator

Abstract

The European space agency has nominated the laser altimeter as one of the principal devices for planetary research for the next decade. The device should be capable of ranging over distances of 400 - 1000 km and of acquiring information about the probe altitude above the planet surface and about the surface terrain profile with a precision of the order of 1 m. Recently, the technology demonstrator of the altimeter has been under development at the German Air and Space Agency, Institute of Planetary Research, Germany. The altimeter technology demonstrator is based on a diode pumped frequency doubled Nd: YAG laser delivering 50 mJ at 532 nm in 3 ns long pulses with the repetition rate of 20 kHz. The solid state echo signal detector in photon counting mode will be used. The optical part of the altimeter is scaled down to simulate the real background count rate scenario and to reduce the energy budget link by a factor of 104 at the same time. The demonstrator should be capable of ranging objects at distances of 0 - 5 km in both night and day time. We present the concept, design and construction of the timing system and detector part of the laser altimeter technology demonstrator, which has been developed at the Czech Technical University in Prague, optimized for the photon counting altimeter concept. The timing system has interval resolution 0.25 ns, stability and linearity similar to 0.1 ns, epoch resolution 100 mu s and accuracy 1 mu s, and a programmable range gate.