Determining Near-Surface Aerosol Properties Using Low Powered Lasers

 The planetary boundary layer, the layer of the atmosphere which is adjacent to and directly influenced by the surface, is an important region of study due not only to its interactions with the planetary surface but also on its influence on the atmosphere as a whole.  We aim to create a low-powered, relatively inexpensive instrument to probe aerosol properties in this area. In this work, we examine the utility of low-powered lasers in combination with an all-sky camera to infer properties of near-surface aerosols in planetary atmospheres.

Our preliminary setup consists of three class 3R continuous lasers (wavelengths 450, 520 and 635 nm) with a 180° field of view camera, tested under both laboratory and field conditions. Aerosol properties such as the single scattering phase function can be inferred from imaged laser backscatter.

In the laboratory, we suspend microspheres of three known sizes (3, 20 and 90 μm) and known concentration in a 160 L aquarium. Each laser beam is reflected several times through the aquarium by mounted mirrors, increasing the path length of the laser. We are able to see the extinction of the laser beam as well as the scattering phase function. We also compare the laser behaviour with a mie scattering model to examine how differing microsphere radii impact these properties. From this we see that at the smaller particle sizes, the phase functions at the different wavelengths tend to diverge more, whereas the phase functions are very similar at each wavelength at a larger particle size where geometric optics tend to take over.

We furthermore analyse images taken in Argentia, Newfoundland, Canada on two nights of heavy fog. We derive the spectral radiance along each laser beam and will use this to determine the optical depth and liquid water content of the fog in a method similar to that used with the Phoenix Lander lidar and Stereo Surface Imager (Moores et al., 2011).

Finally, by the time of the meeting we aim to extend this work and estimate the minimum laser power required to derive aerosol properties on various planetary bodies.  The ability to use low-powered lasers to infer near-surface aerosol properties could be of great interest in the design of future low-cost planetary missions.

 

 

E. Moores, L. Komguem, J. A. Whiteway, M. T. Lemmon, C. Dickinson, and F. Daerden. Observations of near-surface fog at the Phoenix Mars landing site. Geophysical Research Letters, 38(4). doi: 10.1029/2010GL046315.