Small Lidar for Profiling Water Vapor and Winds from Planetary Landers

The planetary boundary layer (PBL) is the lowest layer of the atmosphere that interacts directly with the surface. For Mars and Titan, processes within the PBL are very important scientifically because they control the transfer of heat, momentum, dust, water, and other constituents between surface and atmospheric reservoirs. For Mars understanding these processes is critical for understanding the modern climate, including how the regolith exchanges with the atmosphere, how wind shapes the landscape, how dust is lifted and transported, and for being able to improve general circulation models. The PBL is also critical for operations since it is the environment in which landed missions must operate. The PBL is difficult to observe from orbit, and so detailed observations of it have been mostly limited to those from landers. The lack of PBL observations has led to significant gaps of understanding in several key areas. These include diurnal variations of aerosols, water vapor and direct measurements of winds, the combination of which provides information on the horizontal and vertical transport of water, dust, and other trace species and their exchange with the surface. The Mars atmosphere has complex interactions between its dust, water and CO2 cycles. Because these quantities are interrelated it is important to them simultaneously, ideally with the same instrument. Here we propose to develop and demonstrate a small, highly capable atmospheric lidar to address these needs for a future lander on Mars or Titan. The lidar will measure vertically-resolved profiles of water vapor by using a single frequency laser. The laser will be tuned onto and off strong isolated water vapor lines near 1911 nm. The vertical distribution of water vapor will be determined from the on- and off-line backscatter profiles via the differential absorption lidar (DIAL) technique. The same laser is used for measuring aerosol and wind profiles via the Doppler shift in the backscatter. It emits two beams that are offset 30 deg from zenith and perpendicular to one another in azimuth, allowing directional wind profiles to be resolved. Both lidar measurement channels are otherwise identical and use common lens-type receiver telescopes. These lidar measurements address important science needs that are directly traceable to MEPAG science goals relating to climate, surface-atmosphere interactions, and preparing for human exploration. Our lidar will measure vertical profiles of water vapor, and dust and water ice aerosols and winds with km-scale vertical resolution from the surface to > 15 km altitude. These measurements will directly profile the full planetary boundary layer, which is key for understanding how water, dust, CO2 and trace species exchange between surface and atmosphere. The lidar will uniquely providing observations of all quantities simultaneously. The lidar on the Phoenix Mars lander mission previously measured aerosol backscatter profiles at 1064 nm and 532 nm as a function of altitude and time. Our team’s approach to remotely profiling atmospheric water vapor and winds via lidar at 1911 nm is new. Our team though has directly relevant experience since we previously developed a tunable single-frequency lidar to measure atmospheric column CO2 and backscatter profiles near 1572 nm. Measuring vector wind profiles from a small surface lidar is also new, but our team has previously demonstrated a similar Doppler wind lidar approach at 1064 nm. A key component of the receiver, the highly sensitive avalanche photodiode detector, is already available. Over the project’s 3-year duration we will develop the remaining lidar components from TRL 2 to 4, and develop a breadboard of the lidar. The laser part of the breadboard will be used to measure water vapor in a laboratory cell, and the breadboard lidar will be used to demonstrate measurement profiles of water vapor and wind from the Mauna Kea astronomy site. More »