Abstract
Lava tubes can offer protection for human crews and their equipment on
other solar system bodies, in particular from radiation threats and
extreme surface temperatures. Developing strategies to survey regions of
other terrestrial bodies (such as the Moon or Mars) for tubes suitable
for potential habitation will likely become an important part in
planning future space exploration projects. A variety of surface
geophysical techniques, such as ground penetrating radar (GPR) have the
potential to help recognize and map tubes. GPR shows promise for
providing high resolution information on tube geometries. To investigate
GPR’s capacity and limitations, we use GPR, as well as comparative
methods of seismic and magnetic surveys, in conjunction with LiDAR
mapping of tube interiors at the Lava Beds National Monument (LBNM) in
California, USA. LBNM offers a wide variety of tube geometries and
textures. We have collected 2D GPR profiles and small 3D GPR grids (of
parallel 2D lines) with antenna frequencies of 100 and 200 MHz on four
lava tubes with different geometries, textures and at different depths.
Challenges in recovering tube geometries include wave scattering in
fractured rock covering tubes, irregular and “drippy” ceilings and
walls, and blocky floors. Our primary results show that the top of the
LBNM tubes can generally be resolved in the GPR data, while resolving
the bottom is more challenging. The utility of various GPR processing
techniques can be directly assessed by comparing resolved GPR images
against the LiDAR-measured tube geometries.