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The two upward‐looking Thermal InfraRed Sensor (TIRS) channels from the Mars Environmental Dynamics Analyzer (MEDA) instrument suite on board the Perseverance rover enable the retrieval of total aerosol optical depth (dust plus water ice cloud) above the rover for all observations when TIRS is taken. Because TIRS observes at thermal infrared wavelengths, the retrievals are possible during both the day and night and thus, they provide an excellent way to monitor both the diurnal and seasonal variations of aerosols above Jezero Crater. A retrieval algorithm has been developed for this purpose and here, we describe that algorithm along with our results for the first 400 sols of the Perseverance mission covering nearly the entire aphelion season as well as a regional dust storm and the beginning of the perihelion season. We find systematic diurnal variations in aerosol optical depth that can be associated with dust and water ice clouds as well as a clear change from a cloud‐filled aphelion season to a perihelion season where dust is the dominant aerosol. A comparison of retrieved optical depths between TIRS and the SkyCam camera that is also part of MEDA indicates evidence of possible diurnal variations in cloud height or particle size. Plain Language Summary: Observations made by the Thermal InfraRed Sensor (TIRS) instrument on the Perseverance rover enable the amount of airborne dust and clouds above the rover to be determined. The TIRS instrument observes thermal infrared radiation so it can observe the dust and clouds both during the day and night. Here, we present results for the first 13 months of observations by TIRS. These results show that the dust and clouds vary as a function of season on Mars and as a function of the time of day. At the beginning of the period of time studied here, there were more clouds than dust, and the clouds were maximum just before dawn and just after dusk. Later in the season, dust became the dominant aerosol, with the diurnal maximum near midday. Key Points: The Thermal InfraRed Sensor (TIRS) upward‐looking sensors enable the retrieval of total aerosol optical depth during both day and nightAerosol optical depth shows clear diurnal and seasonal trends. Diurnal maximum opacity is near dawn for clouds and near noon for dustTIRS retrievals of aerosol optical depth can detail the complex time history of rapidly changing events such as dust storms [ABSTRACT FROM AUTHOR]

This article describes a comprehensive testing method for the thermal calibration of the Thermal InfraRed Sensor (TIRS) onboard NASA's Perseverance rover. Ground-based IR detectors operating at the surface of Mars are subjected to inaccuracies caused by the inclusion of thermal gradients in their packages. To reduce such uncertainties, it is necessary to compensate for their effects. Here, details of the TIRS thermo-mechanical design and a simplified thermal mathematical model (TMM) that accounts for the presence of thermal gradients in the detector's package are provided. Then, a set of equations for the estimation and compensation of thermal gradients are proposed based on the results of the TMM. Thermal calibration tests to identify the mathematical estimators are analyzed, providing details of the test setups and highlighting their limitations and restrictions. Finally, experimental results of the calibration tests are presented, along with the uncertainty sources and potential systematic errors associated with the estimation of the gradients. The results presented here show a significant improvement in the accuracy of TIRS versus previous work, thus fulfilling of the radiometer scientific requirements set by the Mars 2020 science team. • A new thermal calibration plan for a ground-based Martian IR radiometer. • Detectors package thermal gradients estimation based on thermal modeling and tests. • Simplified test setups and differences with the Martian environment. • Performance analysis accounting for test setup uncertainties and thermal modeling. • Uncertainties meet the scientific requirements stated by the Mars 2020 science team. [ABSTRACT FROM AUTHOR]

The Mars Environmental Dynamics Analyzer (MEDA) is a suite of environmental sensors onboard NASA’s Mars 2020 mission. The Thermal InfraRed Sensor (TIRS), developed at Centro de Astrobiología of Spain, is one of the six sensors comprising MEDA, and it will measure the net thermal infrared radiation and reflected solar radiation at the surface, as well as the atmospheric and surface skin temperatures using five different channels. In combination with MEDA's other sensors, TIRS will allow the quantification of the surface energy budget and the determination of key geophysical properties of the terrain such as the albedo and thermal inertia. Here we present a general description of the TIRS, its channels scientific requirements, and the mechanical and thermal design. Then, a detailed sensor mathematical model and a sensitivity analysis to model uncertainties are described. Some characterization test results to model parameters identification are included. Finally, accuracy and resolution calculus for each channel versus operational temperature is presented. The calculus is performed based on sensitivity equations, the practical tests results and the estimated values for different uncertainty sources. [ABSTRACT FROM AUTHOR]

• A new radiometric and angular calibration plan for a Martian IR radiometer. • Simplified test setups and differences with Martian environmental are described. • Spectral response analysis vs. radiation incidence angle and operational temperature. • Performance analysis accounting for calibration uncertainties and set-up limitations. • Uncertainties meet the scientific requirements stated by the Mars 2020 science team. This article describes a comprehensive testing method for the radiometric and angular calibration of the Thermal InfraRed Sensor (TIRS) onboard NASA's Mars 2020 mission. First, details of the TIRS opto-mechanical design, construction aspects of the IR detectors, and an update of the mathematical model used for the calculation of sensor internal IR fluxes are provided. Then, a set of sequential calibration tests to identify the radiometer model parameters are defined. The test setups are described, highlighting their limitations and restrictions based on differences between simulated and actual Martian environmental conditions. Finally, the uncertainty sources and potential systematic errors associated with the calibration tests are quantified and compared with the radiometer scientific requirements established by the Mars 2020 science team. [ABSTRACT FROM AUTHOR]

The article discusses that Despite the importance of sand and dust to Mars geomorphology, weather, and exploration, the processes that move sand and that raise dust to maintain Mars' ubiquitous dust haze and to produce dust storms have not been quantified as the missions lack either the necessary sensors or a sufficiently active aeolian environment.