EOS Validation Program

Institution: University of Idaho
                    375 S. Line Street
                    Moscow, ID 83844-3021
Phone: (208) 885-5058
FAX: (208) 885-5058
E-mail: vonw@uidaho.edu

Robert Stone, NOAA-CMDL
David Tobin, SSEC, University of Wisconsin-Madison

February 2003
April 2004

The Antarctic Plateau is an ideal ground site for calibration and validation of infrared satellite instruments. This large continental ice sheet is one of the most homogeneous land surfaces on earth in terms of surface temperature and emissivity. Ground-based measurements of upwelling infrared radiation from the surface between 8-12 micrometers are very nearly equal to those measured by satellite instruments because of minimal atmospheric absorption. Therefore, accurate measurements of spectral infrared radiation over the Antarctic Plateau can provide valuable information for both radiance and product validation for the Atmospheric Infrared Sounder (AIRS) instrument.

We will conduct a field program at Dome Concordia in Antarctica (74.5 S, 123 E) to measure upwelling (from the surface) and downwelling (from the atmosphere) spectral infrared radiances with the Polar Atmospheric Emitted Radiance Interferometer (PAERI). An infrared thermometer (IRT) will map changes in surface radiation at spatial scales similar to the field of view of AIRS. A GPS/Loran Atmospheric Sounding System (GLASS) from NCAR will be used to obtain temperature and humidity profiles. A ground-based global positioning system (GPS) unit will be used measure the total precipitable water. The viewing angle of the PAERI will be adjustable in both nadir and azimuth to match the AIRS viewing angle of both the surface and through the atmosphere. The IRT will be dragged behind a snow machine similar to one used in the Arctic as part of the SHEBA experiment. The IRT will be calibrated frequently in the field using the PAERI. The PAERI will measure upwelling radiance from a small area on the surface to within 0.05 K. The radiometer will measure variations in surface radiation on scales of kilometers, relative to the PAERI. The GLASS sondes will provide atmospheric profile information for use as input to radiative transfer models; the humidity profiles will be scaled to the TPW measured by the GPS.

Our primary activity for AIRS will be the validation of level-1B radiances. Our measurements will provide more accurate radiances for validation purposes than similar measurements made in the tropics, due to the uncertainties in the absorption coefficients of the water vapor continuum. The AIRS radiances will be compared with top-of-the-atmosphere radiances derived from PAERI and radiosonde measurements. Additional validation of level-2 products will be performed, including land surface temperature and spectral emissivity, cloud emissivity, and cloud-cleared radiances. Of particular importance to AIRS, these measurements over the Antarctic Plateau will represent the driest and coldest atmospheric conditions on earth, similar to those found in the upper troposphere.