Ground-penetrating radar (GPR) gathers information on subsurface features using radio waves that are transmitted into the subsurface that then reflect off differing layers and structures. A planetary model of a GPR, called STRATA, has been devised and was proposed for the Mars Science Laboratory mission^1-3, but not selected. GPR is a non-invasive instrument that can supplement or substitute for activities like drilling used to determine information about features below the ground. Depending on the frequency applied, different depths up to several 10's of meters can be explored. Lower frequencies result in better penetration, but lower resolution. Higher frequencies produce better resolution and less penetration^1-3. GPR is primarily used for the detection of features, especially those that can assist in understanding a region’s past history, such as buried fluvial channels beneath a contemporary desert as exemplified in Bir Kiseiba, Egypt⁴.

The successful utilization of GPR in Bir Kiseiba, Egypt⁴, and multiple additional terrestrial locations with similarities to Martian terrains, helps to set the context for future planetary application of the instrument. Extreme aridity in Egypt enhances the capability of radar to distinguish geologically distinct layers. In Bir Kiseiba, three different layers were distinguished to the ground surface, wind-blown sediments, soils produced by running water, and bedrock all produced unique reflections detected by the radar. Though the Sahara Desert and dry surfaces on Mars have different climate histories and mineralogical compositions⁴, researchers expect the surfaces may respond similarly to the radar. Buried water systems can be revealed 10 to 15 m deep on Earth⁴ and it is expected that they can likewise be revealed on Mars.

It is this assumption that STRATA, the proposal for GPR on the Mars Science Laboratory (MSL), was grounded in^1-3. Assessing habitability and aqueous history of a region on Mars are main objectives of the MSL mission. The STRATA instrument would use a 400-MHz impulse to define stratigraphy at a spacial resolution of tens of centimeters to 10-15 m depth^1-3. The application of GPR would focus on locating, recording, and assessing the history of aqueous deposition, as well as providing the context for other MSL instruments to assess the biological potential of the areas under investigation¹.

Additional work on characterizing the GPR signature of likely planetary materials is also ongoing. This work is funded as a part of the National Lunar Science Institute and focuses on collection of GPR data in places on the Earth where the surface materials are likely similar to those on the Moon and planets. To date, efforts have emphasized characterization of ejecta deposits from around Meteor Crater and Arizona and volcanic deposits in Arizona, Washington, and Hawaii⁵.

Recent efforts culminated with Dr. Grant’s service on the Science Definition Team (SDT) for the Mars 2020 rover Perseverance⁶. As lead advocate for inclusion of a GPR on the science payload for the rover, Dr. Grant was pleased when the RIMFAX GPR (Dr. Grant is not affiliated with either the Mars 2020 rover or RIMFAX science team) was ultimately selected and is currently operating on Mars. 

1.    Grant, J. A., and C. J. Leuschen C. J. (2011), The STRATA ground penetrating radar as a means for constraining the near surface properties of the Moon and Mars, Proceedings of the 2011 IEEE Radar Conference, May 23-27, 2011, Kansas City, MO, paper 3399, 1132-1134.
2.    2. Grant, J. A., Leuschen, C. J., and Russell, P. S. (2012), The Strata ground penetrating radar: Constraining the near surface properties of solar system bodies: International Workshop on Instrumentation for Planetary Missions, abstract 1003, LPI, Houston, TX.
3.    3. Grant, J. A., Leuschen, C. J., and Russell, P. S. (2012), The Strata Ground Penetrating Radar: Constraining the Near Surface Properties of Mars: Concepts and Approaches for Mars Exploration, abstract 4074, LPI, Houston, TX.
4.    4. Grant, J. A., T. A. Maxwell, A. K. Johnston, A. Kilani, and K. K. Williams (2004), Documenting drainage evolution in Bir Kiseiba, southern Egypt: Constraints from ground-penetrating radar and implications for Mars, J. Geophys. Res., 109, E09002, doi:10.1029/2003JE002232.
5.    5. Russell, P. S., Grant, J. A., Williams, K. K., Carter, L. M., Garry, W. B., Morgan, G., Dauber, I., and Bussey, D. B. J., 2012, Ground penetrating radar field studies of lunar-analog geologic settings and processes: Impact crater ejecta and volcanic materials: LPSC XLIII, abstract 1612, LPI, Houston, TX.
6.    Mustard, J. F., M. Adler, A. Allwood, D. S. Bass, D. W. Beaty, J. F. Bell III, W. B. Brinckerhoff, M. Carr, D. J. Des Marais, B. Drake, K. S. Edgett, J. Eigenbrode, L. T. Elkins-Tanton, J. A. Grant, S. M. Milkovich, D. Ming, C. Moore, S. Murchie, T. C. Onstott, S. W. Ruff, M. A. Sephton, A. Steele, and A. Treiman (2013), Report of the Mars 2020 Science Definition Team, 154 pp., posted July, 2013, by the Mars Exploration Program Analysis Group (MEPAG) at http://mepag.jpl.nasa.gov/reports/MEP/Mars_2020_SDT_Report_Final.pdf.