11:00 AM - 1:00 PM
[PPS04-P06] Development for a radiative transfer tool for remote sensing of surface pressure on Mars by CO2 2μm absorption band observed by Mars Express/OMEGA and MMX/MIRS
Keywords:Mars, Radiation Transfer, Meteorological , surface pressure, MMX, Mars Express/OMEGA
On Mars, the received solar radiation varies more than 30% in a year due to its large orbital eccentricity. As a result, global and mesoscale variations of the atmosphere are caused by the condensation and sublimation of CO2 and H2O and the local and seasonal variations of dust. To understand these aspects, knowledge of the horizontal distribution of the surface pressure distribution is important.
On the Earth, the distribution of surface pressure can be obtained by many observation points on the ground. However, on Mars, only a few numbers of landers at specific locations are available and thus the horizontal distribution of the surface pressure has been poorly understood Remote sensing observations of the surface pressure distribution is a powerful tool to investigate it.
Forget et al. (2007) and Spiga et al. (2007) performed the retrieval of mesoscale surface pressure distribution from the orbiter data. They derived the surface pressure using the near-infrared CO2 absorption feature at 2 μm taken by OMEGA onboard Mars Express (MEx) during its initial observation (2004-2005). The CO2 mixing ratio in the Martian atmosphere (well known as 0.9532 in early summer obtained by the Viking Lander mass spectrometer) can be assumed as uniform in the lower atmosphere in altitude, and we can assume that the surface pressure is in proportion to the CO2 column density when the atmosphere is hydrostatic. However, since their results were derived only from the ideal cases (e.g., dust-free, etc.), 0.007% of the total data (29 of ~4000 nadir observations) were utilized. Nevertheless, from those limited data sets, the pressure distribution over 95 x 150 km (2.5 deg in longitude, 4 deg in latitude) could be evaluated and succeeded to show the pressure gradients and atmospheric waves.
We have tried to apply a similar method to the planned Martian Moons eXploration (MMX) mission, which is scheduled to be launched in 2024. As a test case, we are first studying to retrieve the mesoscale surface pressure from the entire period of MEx/OMEGA near-infrared observations (2004-2010). MMX will not only execute the sample return from Phobos but also do the continuous and global observation of the Martian atmosphere in the low-mid latitudes from the equatorial orbit. Following the Forget et al. (2007) and Spiga et al. (2007), the column density derived from the CO2 absorption is used for the estimation of the surface pressure with altitude corrections. We are developing a program to derive the surface pressure by applying a similar method to Forget et al. (2007), from the 2 µm CO2 absorption band data taken by the MEx/OMEGA SWIR (near-infrared) channel 1.8-2.2 µm (25 points, wavelength resolution ~20 nm). First, we prepare about 450,000 synthetic spectra calculated by a radiative transfer equation using a set of physical parameters (atmospheric pressure, temperature, surface albedo, dust opacity, solar zenith angle, solar viewing angle, and phase azimuth angle) that may affect the shape of the observed spectra. In January 2022, we are in the process to make this spectral table and its validation.
In this paper, we will show the retrieval status of the surface pressure from MEx/OMEGA, including the applicability to the Mars mesoscale pressure phenomena. We also discuss the application to the global pressure derivation aiming at MMX.
On the Earth, the distribution of surface pressure can be obtained by many observation points on the ground. However, on Mars, only a few numbers of landers at specific locations are available and thus the horizontal distribution of the surface pressure has been poorly understood Remote sensing observations of the surface pressure distribution is a powerful tool to investigate it.
Forget et al. (2007) and Spiga et al. (2007) performed the retrieval of mesoscale surface pressure distribution from the orbiter data. They derived the surface pressure using the near-infrared CO2 absorption feature at 2 μm taken by OMEGA onboard Mars Express (MEx) during its initial observation (2004-2005). The CO2 mixing ratio in the Martian atmosphere (well known as 0.9532 in early summer obtained by the Viking Lander mass spectrometer) can be assumed as uniform in the lower atmosphere in altitude, and we can assume that the surface pressure is in proportion to the CO2 column density when the atmosphere is hydrostatic. However, since their results were derived only from the ideal cases (e.g., dust-free, etc.), 0.007% of the total data (29 of ~4000 nadir observations) were utilized. Nevertheless, from those limited data sets, the pressure distribution over 95 x 150 km (2.5 deg in longitude, 4 deg in latitude) could be evaluated and succeeded to show the pressure gradients and atmospheric waves.
We have tried to apply a similar method to the planned Martian Moons eXploration (MMX) mission, which is scheduled to be launched in 2024. As a test case, we are first studying to retrieve the mesoscale surface pressure from the entire period of MEx/OMEGA near-infrared observations (2004-2010). MMX will not only execute the sample return from Phobos but also do the continuous and global observation of the Martian atmosphere in the low-mid latitudes from the equatorial orbit. Following the Forget et al. (2007) and Spiga et al. (2007), the column density derived from the CO2 absorption is used for the estimation of the surface pressure with altitude corrections. We are developing a program to derive the surface pressure by applying a similar method to Forget et al. (2007), from the 2 µm CO2 absorption band data taken by the MEx/OMEGA SWIR (near-infrared) channel 1.8-2.2 µm (25 points, wavelength resolution ~20 nm). First, we prepare about 450,000 synthetic spectra calculated by a radiative transfer equation using a set of physical parameters (atmospheric pressure, temperature, surface albedo, dust opacity, solar zenith angle, solar viewing angle, and phase azimuth angle) that may affect the shape of the observed spectra. In January 2022, we are in the process to make this spectral table and its validation.
In this paper, we will show the retrieval status of the surface pressure from MEx/OMEGA, including the applicability to the Mars mesoscale pressure phenomena. We also discuss the application to the global pressure derivation aiming at MMX.