Statistics – Applications
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.a43d1564b&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #A43D-1564
Statistics
Applications
0300 Atmospheric Composition And Structure, 0305 Aerosols And Particles (0345, 4801, 4906), 0394 Instruments And Techniques
Scientific paper
Aerosols have a profound effect on the radiation balance of the atmosphere. Current estimates of the direct and indirect effects are -0.9 to -0.1 and -1.8 to -0.3 W m-2, respectively, but remain highly uncertain (IPCC, 2007). These uncertainties are tied to our inability to accurately estimate spatial and temporal distributions of aerosol concentrations, size, and composition. Measurements of aerosol optical depth (AOD) are needed from widely distributed locations, both over land and ocean. AOD measurements from the surface are routinely made by sunphotometers. Most notably, NASA's AERONET system makes routine measurements of AOD at many sites throughout the globe. The problem is that very few measurements are made over the ocean because of operational considerations, i.e. ships do not present a stable platform and the salt water spray is damaging to the mechanisms used by the sunphotometers to track the sun. This paper reports on the development of a sunphotometer that can obtain AOD without moving parts. Such an instrument has the potential to be small, lightweight, and rugged. Potential applications are use in extreme environments, on ships and ocean buoys, and perhaps in unmanned aerial systems (UAS). Due to its small size and light weight, the Advanced Sun Photometer can be adapted for use on extraterrestrial bodies with sensible atmospheres, such as Mars or Titan. Concept: Eliminating the need for a tracking mechanism can significantly reduce instrument weight and size while increasing system robustness. The Advanced Sunphotometer uses a compact optical system to provide a hemispherical field of view, removing the need for a sun tracking mechanism. A CCD array is placed at the base of the optical system captures and records the light. Measurements at specific wavelengths are achieved by interposing various interference filters into the light path by means of a filter wheel. The instrument measures the diffuse radiation as well as the direct sun beam. Computer algorithms are used to separate the direct from the diffuse radiation. Current work: Although the CCD array records both the diffuse light entering the cone as well as the direct solar beam, current efforts are have been focused on validating the direct beam measurements of AOD. Efforts have been primarily focused on characterizing the instrument angular response, as well as validating measurements of aerosol optical depth, and water-vapor columnar abundance. Comparisons of the Advanced Sunphotometer AOD measurements will be made with the AOD readings taken with a commercial Microtops II handheld sunphotometer.
Brill Russ
Le Truong
Papdopoulos P.
Strawa Anthony W.
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