First Outdoor Measurements of a Submillimeter-Wave Differential Absorption Radar

A differential absorption radar tuned near the 557 GHz water vapor absorption resonance is being developed as an instrument concept to measure absolute humidity out to distances of a few km from a lander or rover on the surface of Mars. Full instrument testing is difficult because Earth's atmosphere is too absorptive near 557 GHz to measure radar backscattering at significant ranges. Therefore, alternative methods for testing critical functions of the radar are being evaluated, including outdoor measurements of the radar tuned to a more transmissive band near 360 GHz.