REMS-H Revisited: Updated Calibration and Results of the Humidity Sensor of the MSL Curiosity

Abstract

The Mars Science Laboratory (MSL) Curiosity rover landed on 6 August 2012 in Gale crater carrying the Rover Environmental Monitoring Station (REMS). REMS measures various atmospheric and surface parameters, and among its instruments is a relative humidity sensor, REMS-H, provided by the Finnish Meteorological Institute. REMS-H has been operating successfully for more than 12 years since the landing, providing the longest dataset on near-surface humidity conditions on Mars. New calibration measurements performed under a Martian analogue environment at the Planetary Analogue Simulation Laboratory of the German Aerospace Center have been used to evaluate the current calibration of REMS-H, and based on the findings a revised calibration has been developed for REMS-H. This paper describes the revised calibration, presents the corresponding updated results up to sol 3965 of the MSL mission, and analyzes the revised interannual, seasonal, and diurnal variations in relative humidity and derived water vapor mixing ratio. Comparisons with results from the previous calibration, modeling, and the Mars 2020 mission are also discussed. In general, the new calibration resulted in lower relative humidity values, although the difference varies without a clear diurnal or seasonal pattern. The water vapor volume mixing ratio derived from the new relative humidity values shows larger changes between the old and the revised data, especially during early night. The recalibration effort has improved the accuracy and reliability of REMS-H data, aligning the results with orbital observations and simulation runs. Results from this recalibration will be uploaded to NASA’s Planetary Data System, replacing the values available to date.