ERAST - Measurement of Solar Spectral Irradiance on Unmanned Aerospace Vehicles


Research Staff: Peter Pilewskie, Warren Gore, and Larry Pezzolo

During Spring 1999 the Radiation Group completed a major field program, the joint NASA ERAST/DOE ARM-UAV (Environmental Research Aircraft and Sensor Technology/Department of Energy Atmospheric Radiation Measurement Unmanned Aerospace Vehicle) Hawaii experiment at the Barking Sands Pacific Missile Range Facility (PMRF) in Kauai, Hawaii. The Solar Spectral Flux Radiometer (SSFR) (Figure 1) was integrated on the NASA Altus UAV (Figure 2) and the DOE Sandia Twin Otter (Figure 3) in both zenith and nadir viewing modes. The experiment objectives are the following:

[Image of SSFR, Altus and Twin Otter Spectra]

To measure solar and longwave fluxes at cloud top and cloud base to determine both the radiative properties (such as the spectral and broadband albedos, infrared emittances) and the radiative budget of cirrus.

To provide measurements (such as spectral reflectances, lidar backscatter, diffuse and direct fluxes) that can be used to deduce key optical properties of cirrus (such as profiles of extinction, optical depth and scattering asymmetry information) and to relate these to the radiative energy budget.

To provide measurements that can be used to assist in the development and support of new remote sensing techniques applicable to cirrus either directly from UAV data or from satellite sensors such as from the TRMM (Tropical Rainfall Measuring Mission) CERES (Clouds and the Earth’s Radiant Energy System) and VIRS (Visible and Infrared Imaging Radiometer Suite) instruments.

To demonstrate the utility of a UAV in a science mission.

Over 60 hours of data were collected during seven flights between April 25 and May 17. This was the first flight of the Solar Spectral Flux Radiometer on a UAV. These SSFR data (Figure 4) are being used to assess the radiative characteristics of high sub-tropical cirrus and to assess its effects on the radiative energy budget. Spectral irradiance will be compared to radiative transfer model simulations to assess the effectiveness of our ability to model both the clear and cloudy sky radiative energy budget in the subtropics and to assess the climate effects of high altitude, optically thin cirrus clouds.

This is a collaborative effort with DOE, Sandia National Laboratory, Colorado State University, and the University of California, San Diego.

Collaborators: Maura Rabbette, National Research Council Associate; John Pommier, Symtech

Point of Contact: Peter Pilewskie, (650) 604-0746,