Diurnal and Seasonal Variations of Aerosol Optical Depth Observed by MEDA/TIRS at Jezero Crater, Mars

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 in the thermal infrared, 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 cloud, 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.