RTOP number: 291-07-53-00

Research Staff: Beat Schmid, John Livingston, James Eilers, Ric Kolyer, Stephanie Ramirez, Phil. Russell

Collaborators: Univ. of Washington; University of Sao Paulo; NASA Goddard; NASA Langley;, JPL; Univ. of Maryland, Baltimore County.

Write-up Information:

SGG. Title above.

Knowledge of the concentration of atmospheric water vapor and aerosols (solid or liquid particles suspended in air) is crucial for assessing the impact effect of these constituents on climate. Such information can be determined using sunphotometers, which measure the transmission of the direct solar beam through the Earth’s atmosphere in discrete, narrow wavelength bands from the ultraviolet to the near-IR part of the solar spectrum. Frequently, suborbital (ground- and aircraft-based) sunphotometer measurements are used to validate aerosol and water vapor data obtained using space-borne sensors.

One field experiment specifically designed to validate space-borne measurements was the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) field campaign, July 10 - August 2, 2001. The CLAMS campaign targeted mostly clear sky conditions and entailed measurements from the Chesapeake Lighthouse research platform, several land sites, 6 six research aircraft and the Terra satellite of NASA’s Earth Observing System (EOS). CLAMS research goals included validation of satellite-based retrievals of aerosol properties, vertical profiles of radiative fluxes, temperature and water vapor. As part of the CLAMS experiment, the 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) was operated successfully aboard the University of Washington CV-580 research aircraft during 10 research flights (~45 flight hours total). Suborbital measurements of aerosol optical depth (AOD) and columnar water vapor (CWV) were also carried out at several ground sites and aboard five of the six airborne platforms using a variety of techniques. Figure 1 shows AATS-14 installed on the University of Washington research aircraft.

The AATS-14 measures the direct solar beam transmission at 14 discrete wavelengths in the range of (354-1558 nm), yielding aerosol optical depth spectra and columnar water vapor. Differentiation of AOD (CWV) with respect to altitude in favorable flight patterns allows the derivation of aerosol extinction (water vapor density). During coordinated flights of the UW CV-580, AATS-14 measured full column aerosol optical depth spectra at exact Terra overpass time on at least 7 occasions. For five of these opportunities, AOD in the mid-visible part of the solar spectrum was at or below 0.1. During Terra overpass time on July 17, 2001, AATS-14 measured the largest AOD encountered during the entire experiment (~0.48), including a horizontal gradient in AOD of more than 0.1 over a distance of ~80 kilometers. Preliminary data can be viewed at http://snowdog.larc.nasa.gov/ftp/incoming/clams/AATS/index.html. .

Collaborators: Univ. of Washington; University of Sao Paulo; NASA Goddard Space Flight Center; NASA Langley Research Center; Jet Propulsion Laboratory; University of Maryland, Baltimore County