Abstract
The Finnish Meteorological Institute (FMI) provides a relative humidity
measurement sensor (HS) for NASA’s Mars 2020 rover. The sensor is a part
of the Mars Environmental Dynamic Analyzer (MEDA), a suite of
environmental sensors provided by Spain’s Centro de Astrobiología. The
main scientific goal of the humidity sensor is to measure the relative
humidity of the Martian atmosphere near the surface and to complement
previous Mars mission atmospheric measurements for a better
understanding of Martian atmospheric conditions and the hydrological
cycle. Relative humidity has been measured from the surface of Mars
previously by Phoenix and Curiosity. Compared to the relative humidity
sensor on board Curiosity, the MEDA HS is based on a new version of the
polymeric capacitive humidity sensor heads developed by Vaisala.
Calibration of humidity devices for Mars conditions is challenging and
new methods have been developed for MEDA HS. Calibration and test
campaigns have been performed at the FMI, at University of Michigan and
the German Aerospace Center (DLR) in Berlin to achieve the best possible
calibration. The accuracy of HS and uncertainty of the calibration has
been also analysed in detail with VTT Technical Research Centre of
Finland. Assessment of sensor performance after landing on Mars confirms
that the calibration has been successful, and the HS is delivering high
quality data for the science community.