Recent results of the vicarious calibration of the Landsat-7 ETM+ sensor are presented based on the reflectance-based vicarious method using results from a smaller test site in close proximity to the University of Arizona. The typical, larger test site is brighter and more spatially uniform then the smaller site. However, the location of the small test site allows for more frequent data collections and a more complete understanding of the calibration coefficients of the sensor as a function of time. The Remote Sensing Group previously reported results based on data collected from the smaller test site on seven dates. Here we report calibration values for additional dates as well as a comparison of the calibration values for the large and smaller test sites over recent years. The most recent data shows the calibration values using the smaller sites continue to agree within 3% of the large test sites in all bands.
A key aspect to the recently-launched GLAS instrument is understanding its radiometric performance using onorbit verification approaches. One of these approaches compares the reported backscattered signal from a surface to a predicted signal from that same surface. This returned signal depends on both the atmospheric transmittance and the surface reflectance in the backscatter direction. This work describes three methods that have been used to derive the backscatter surface reflectance for the prediction of the hard-target signal at the GLAS sensor. The first relies on a portable field spectrometer carried over a representative area of the surface and the reflected solar irradiance is measured with reference to a known field standard of reflectance. The difficulty with this approach is that it does not measure the backscatter reflectance. Thus, a second method using a laser-based system operating on the ground has been used to determine the surface reflectance. Both of these cases require that ground personnel be present near in time to the GLAS overpass. A third method, relying on reflectances derived from the MODIS sensor increases the available number of data sets for comparison to GLAS. Early results from all three approaches indicate agreement at better than 10% with the GLAS sensor.
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