Absolute radiometric calibration of Landsat 7 ETM+ using the reflectance-based method

A key to the continuation of quantitative data from the Landsat series of sensors is the radiometric understanding of the sensor. Vicarious calibration methods are one approach that has been used successfully for the absolute radiometric calibration of Thematic Mapper (TM). One of these vicarious methods is the reflectance-based approach that is applied here to the radiometric calibration of the Enhanced Thematic Mapper Plus (ETM+) sensor on the Landsat 7 platform. This method is described for application to ETM+. Results from ground-based measurements of atmospheric conditions and surface reflectance made at Railroad Valley Playa, Nevada, Roach Lake Playa, Nevada, and White Sands Missile Range, New Mexico are presented including descriptions of the test sites. The gains derived from four dates using these sites spanning the period from June 1999 to October 1999 agree to within 5% of each other and to better than 7% with the prelaunch, laboratory-derived gains. This is within the combined 5% uncertainty of the prelaunch values and the estimated 3–5% uncertainty of the reflectance-based method. The gains determined from the reflectance-based method are all lower than the prelaunch values for bands 1–5 and the values for band 7 exceed the prelaunch gains. These biases could be caused by errors in the treatment of atmospheric aerosols at shorter wavelengths and uncertainties in the assumed solar irradiances used to convert the relative radiances to absolute values at longer wavelengths.