Accuracy of the relative humidity sensor MEDA HS onboard Perseverance rover

<p><span>MEDA HS is the relative humidity sensor </span><span>on the</span><span> Mars 2020 Perseverance rover provided by the Finnish Meteorological Institute (FMI). The sensor is a part of Mars Environmental Dynamic Analyzer (MEDA), a suite of environmental sensors provided by Centro de Astrobiolog&#237;a in Madrid, Spain.</span></p><p><span>The accuracy requirement for MEDA HS relative humidity was </span><span>&#177;</span><span>10% RH for temperatures above -70 &#186;C, and </span><span>&#177;2</span><span>0% RH for temperatures between -83...-73 &#186;C. Dynamic range from 0 to 100% RH </span><span>shall cover</span><span> the whole Martian temperature range from -83 &#186;C to -3 &#186;C. However it must be noted that during the daytime when the relative humidity drops close to zero, the readings are not scientifically </span><span>meaningful</span><span> due to the large relative uncertainty.</span></p><p><span>MEDA HS flight model was tested and calibrated in Mars-like dry environment at FMI together with flight spare and ground reference models from +22 &#186;C to -70 &#186;C and in saturation conditions from -40 &#186;C down to -70 &#186;C. Further, the MEDA HS flight model final calibration is complemented by calibration data transferred from an identical ground reference model which has gone through extensive </span><span>humidity calibration test campaign at DLR PASLAB</span><span>. </span><span>The</span><span> MEDA HS has </span><span>been calibrated to full relative humidity range</span><span> between -70 to -40 &#186;C in CO</span>_{<span>2</span>}<span> in the pressure ranges from 5.5 to 9.5 hPa, representative of Martian surface atmospheric pressure, and partial range up to </span><span>+22 </span><span>&#186;C. For lower temperatures the results are extrapolated.</span></p><p><span>The complex analysis of the MEDA HS </span><span>measurement</span><span> uncertainty has now been finalized and the results are presented in the conference. It has been found that the sensor exceeds the design requirements and </span><span>will</span><span> provide high accuracy relative humidity measurements from the Martian surface to provide important meteorological observations and to support MEDA and other M2020 investigations.</span></p>