Radiometric Processing and Calibration of Eo-1 Advanced Land Imager Data

A radiometric and geometric processing system has been developed as part of the Advanced Land Image(r) Assessment System (ALIAS). A derivative of the ALIAS processing system has also been implemented operationally at EROS to generate Advanced Land Imager (ALI) Level 1 radiometrically and geometrically corrected data products. This system replaces the “calibration pipeline” previously used to generate Level 1R radiometrically corrected ALI data products at EROS. The revised calibration systems initially use the same radiometric calibration coefficients as previous systems, i.e., a fixed set of detector-by-detector gains established shortly after launch and biases measured shortly after each scene acquisition by closing the ALI’s shutter. The data are scaled differently in the final products, however. The original calibration pipeline scaled the Level 1R data output by a fixed factor of 300, i.e., to obtain the radiance in mW/cm sr m for a given pixel in any band, you divided the quantized calibrated data value by 300. To scale to W/m sr m, a factor of 30 is used. The revised system uses a band specific multiplicative scaling factor of between 22 and 1100 as well as a band specific additive scaling factor for units of W/m sr m. The band specific multiplicative scaling factor results in better preservation of the ALI’s precision and dynamic range in going from raw to calibrated data, especially in the SWIR bands. This reduces the amount of high signal data being clipped by the rescaling process and reported as saturated in the calibrated data products. Setting the minimum valid data value to “1” DN in the output products combined with the additive factor results in all the valid data being positive values with negligible, if any, loss of valid data. Additional Pecora 16 “Global Priorities in Land Remote Sensing” October 23-27, 2005 * Sioux Falls, South Dakota work is underway to replace the current fixed set of detector gains with time-dependent functions that represent the gradual change in gain of the ALI detectors.