In Situ UV Measurements by MSL/REMS: Dust Deposition and Angular Response Corrections
Á. Vicente‐Retortillo, Germán Martínez, N. O. Rennó, M. T. Lemmon, M. de la Torre-Juárez, Javier Gómez‐Elvira
Abstract
Abstract Measurements by the REMS/UV sensor onboard the MSL Curiosity rover constitute the first in situ dataset of UV radiation flux at the surface of Mars. Due to its position on the Curiosity deck, the UV sensor has been directly exposed to dust deposition. Inaccuracies in the original angular response calibration functions have led to discrepancies between measured and physically-expected UV fluxes when the solar zenith angle ( $\theta $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> </mml:math> ) relative to the rover frame is between $20^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>20</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> and $55^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>55</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> . Here we present a methodology to correct UV fluxes when $\theta < 55^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> <mml:mo><</mml:mo> <mml:msup> <mml:mn>55</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> for both effects, and show results of the corrected data set for the first 2003 sols (∼3 Martian Years, MY) of the MSL mission, from L $_{\mathrm{s}} \sim 151^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mo>∼</mml:mo> <mml:mprescripts/> <mml:mi>s</mml:mi> <mml:none/> </mml:mmultiscripts> <mml:msup> <mml:mn>151</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> in MY 31 to L $_{\mathrm{s}} \sim 149^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mo>∼</mml:mo> <mml:mprescripts/> <mml:mi>s</mml:mi> <mml:none/> </mml:mmultiscripts> <mml:msup> <mml:mn>149</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> in MY 34. Close to noon, when $\theta $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> </mml:math> values are typically < $30^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>30</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> , relative differences between corrected and original UV fluxes are ∼35 – 40% on average. Outside hours close to noon, when $\theta $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> </mml:math> is typically > $30^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>30</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> , relative differences are greater than 100%. Measurements acquired when $20^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>20</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> < $\theta < 55^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> <mml:mo><</mml:mo> <mml:msup> <mml:mn>55</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> represent ∼45% of the whole dataset with $\theta < 90^{\circ}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>θ</mml:mi> <mml:mo><</mml:mo> <mml:msup> <mml:mn>90</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> . UV fluxes generated in this study are available in the NASA Planetary Data System ( https://atmos.nmsu.edu/PDS/data/mslrem_1001/DATA_UV_CORRECTED/ ), and are important to study the effect of UV radiation on the variability of atmospheric constituents, to recreate accurate UV doses for biological laboratory experiments, to perform combined analyses of satellite and ground-based measurements, and to allow comparisons of the UV radiation environment at different locations with the upcoming ExoMars 2020 and Mars 2020 missions.