Artifact correction and absolute radiometric calibration techniques employed in the Landsat 7 Image Assessment System

The Landsat-7 Image Assessment System (IAS), part of the Landsat-7 Ground System, will calibrate and evaluate the radiometric and geometric performance of the Enhanced Thematic Mapper Plus (ETM+) instrument. The IAS incorporates new instrument radiometric artifact correction and absolute radiometric calibration techniques which overcome some limitations to calibration accuracy inherent in historical calibration methods. Knowledge of ETM+ instrument characteristics gleaned from analysis of archival Thematic Mapper in-flight data and from ETM+ prelaunch tests allow the determination and quantification of the sources of instrument artifacts. This a priori knowledge will be utilized in IAS algorithms designed to minimize the effects of the noise sources before calibration, in both ETM+ image and calibration data. Gain and bias estimates for each ETM+ detector that are derived from onboard calibrators are tracked with ground based measurements, and with prelaunch measurements of instrument gains and biases as part of a Combined Radiometric Model (CRaM), to yield improved estimates of absolute gain and bias per channel. Trends in these instrument parameters are observed and recorded, allowing for the development of analytic models of detector gain and bias as functions of time and instrument state. IAS radiometric calibration methodology, utilizing precalibration artifact correction in conjunction with CRaM gain and bias determination, provides a more consistent absolute calibration of the ETM+ than that possible with historical TM calibration approaches