Directionality Of The Martian Surface Radiation And Derivation Of The Upward Albedo Radiation

Since 2012 August, the Radiation Assessment Detector (RAD) on the Curiosity rover has been characterizing the Martian surface radiation field which is essential in preparation for future crewed Mars missions. RAD observed radiation dose is influenced by variable topographical features as the rover traverses through the terrain. In particular, while Curiosity was parked near a butte in the Murray Buttes area, we find a decrease of the dose rate by (5 +/- 1)% as 19% of the sky was obstructed, versus 10% in an average reference period. Combining a zenith-angle-dependent radiation model and the rover panoramic visibility map leads to a predicted reduction of the downward dose by similar to 12% due to the obstruction, larger than the observed decrease. With the hypothesis that this difference is attributable to albedo radiation coming from the butte, we estimate the (flat-terrain) albedo radiation to be about 19% of the total surface dose.