Phoenix LIDAR measurements of Mars atmospheric dust

The LIDAR instrument on the Phoenix mission obtained measurements of atmospheric dust and clouds from the surface in the Arctic region of Mars (68.22°N, 234.25°E) during late spring through the middle of summer. The observed vertical distribution of dust indicated that the planetary boundary layer (PBL) was evenly mixed up to heights of 4 km by daytime convection and turbulence. The values of the dust optical extinction coefficient derived from the LIDAR measurements within the PBL reached a maximum of 0.15 km−1 during the period around summer solstice and then decreased to values approaching 0.03 km−1 over the next 60 martian days (sols). The ratio of the LIDAR backscatter coefficient at wavelength 1064 nm to that at 532 nm for dust was obtained in three cases and found to have values in the range 1.18–1.35, relative to an assumed value of unity for the near surface water ice clouds. Mie scattering calculations were performed to determine that the measured dust 1064/532 backscatter color ratios were consistent with particle size distributions having effective radii in the range of 1.2–1.4 μm.