LAUSR

This article intends to establish a reasonable determination criterion for nadir detection of lunar lava tube by Kaguya Lunar Radar Sounder observation. We applied radar cross section analysis to a simple lava tube model that comprises vacuum/basalt media with flat media boundaries, which illustrated that radar echoes from a lava tube are continuously detected through a number of consecutive observations along orbit if the lava tube returns radar echoes strong enough. “Consecutive detection” makes the minimal determination criterion for the detection of a lava tube. We further investigated influence of curved ceiling of a lava tube on its detection using 2-D finite difference time domain (2-D FD-TD) simulation and radar cross section analysis with Geometrical Optics. The work revealed that basalt roof of a lava tube plays a role of a concave lens in the propagation process of a radar pulse hence contributes to reduce lava tube echo intensity in comparison to that of the simple lava tube model. The curved ceiling, however, does not affect the above derived determination criterion. Ambiguity test plays the crucial role in the detection of a lava tube by distinguishing surface clutter. We demonstrated three types of ambiguity tests, i.e., 1) multiorbit data analysis test, 2) surface scattering simulation test, and 3) surface slope echo analysis test. The last two tests were demonstrated on those data which had been documented as radar echoes from large scale lava tubes in Marius Hills in a recent literature. The test results indicated that they are nothing more than a collection of surface clutter.