Calibration of the HP³ Radiometer on InSight

Abstract

The Heatflow and Physical Properties Package (HP 3 ) radiometer is currently operating on Mars, observing two spots approximately 1 and 3 m north-north-west of the InSight lander. The instrument has primary sensors that are sensitive in the range of 8 to 14 μm and two more sensors with more narrow spectral ranges per field of view. The radiometer underwent radiometric and geometric calibration at DLR-Berlin; and on Mars radiometric self-calibration is performed regularly. The self-calibration confirms that one of the two primary sensors has been stable since the ground calibration, but environmental parameters that are likely associated with the thermal contact of sensor and instrument main body may have slightly changed. The other primary sensor has increased in sensitivity for an unknown reason but is still within expectation from the sensor design. The uncertainty of the two primary sensors is approximately 3 K at night, with somewhat larger errors in the late afternoon. This estimate includes the effect of sensitivity changes that would be too small to be reliably detected by the self-calibration.The HP 3 -RAD radiometer is based on the designs of the MASCOT Radiometer (Grott et al., 2017) on Hayabusa 2, of the MERTIS instrument on Bepi-Colombo (Hiesinger & Helbert, 2010;Walter et al., 2006), and of the MUPUS Thermal Mapper on Rosetta (Spohn et al., 2007(Spohn et al., , 2015. The HP 3 -RAD was radiometrically calibrated in a space simulation chamber under conditions simulating the Mars environment over 2 weeks in April 2017. Onboard calibration occurred regularly after landing starting in December 2018.

A Comodulation Analysis of Atmospheric Energy Injection Into the Ground Motion at InSight, Mars

“…The rapid rise of temperature during the Martian morning imposes steep positive gradients on both the atmospheric and surface temperature ( Fig. 2a), while fast cooling in the early Martian afternoon imposes an inverse temperature gradient, with such temperature swings also measured by previous missions (Hess et al, 1977;Sutton et al, 1978;Schofield et al, 1997;Davy et al, 2010;Banfield et al, 2020;Mueller et al, 2020). The transition from the nighttime to intense turbulence daytime regime takes place after sunrise, a period during which these steep atmospheric temperature gradients induce a distinct shortduration regime.…”

A Study of Daytime Convective Vortices and Turbulence in the Martian Planetary Boundary Layer Based on Half‐a‐Year of InSight Atmospheric Measurements and Large‐Eddy Simulations

“…Surface (i.e., ground) brightness temperature measurements are performed by the HP 3 radiometer onboard the InSight lander. The details on this sensor calibration are described in Mueller et al (2020). The HP 3 radiometer sensors measure the surface brightness temperature in three spectral bands (8-14, 8-10, and 15-19 μm) at two different spots relative to the InSight lander, named the close spot and the far spot (Spohn et al, 2018).…”

“…Another key novel characteristic of InSight's in situ meteorological observations is that measurements of pressure, temperature, and wind are made continuously (Spiga et al., 2018), as they are needed to constrain the atmosphere‐induced seismic noise (Garcia et al., 2020; Kenda et al., 2017; Murdoch et al., 2017) at all times in order to assess how much of the seismic signal corresponds to the activity in the interior of Mars. Those direct atmospheric measurements are complemented by surface brightness temperature sensing (Mueller et al., 2020), color imaging (Maki et al., 2018), and, for the first time, at the surface of Mars, seismic measurements (Lognonné et al., 2020). Furthermore, solar array currents can also be used for atmospheric investigations (Lorenz et al., 2020).…”

Effects of a Large Dust Storm in the Near‐Surface Atmosphere as Measured by InSight in Elysium Planitia, Mars. Comparison With Contemporaneous Measurements by Mars Science Laboratory

“…We use here the measurements from the far spot ( Figure 2), because it is less perturbed by lander thermal contamination or by shadowing during the day. Also, given that the last two spectral bands have comparatively large calibration uncertainties (Mueller et al, 2020), ground surface brightness temperature was retrieved based on the 8-14 μm channel only. The reflectance of the observed ground in the spectral bands of the HP 3 -RAD is expected to be small because the emissivity is close to unity.…”