Radiometric calibration of the Landsat-7 Enhanced Thematic Mapper Plus

The Landsat-7 satellite will incorporate an Enhanced Thematic Mapper Plus (ETM+). The addition of the “+” to the ETM acronym indicates a number of sensor improvements, most of which are related to improving the radiometric performance to the 5% absolute level in the reflective channels. Two calibration devices, a full aperture solar calibrator (FASC) and a partial aperture solar calibrator (PASC) have been added to the design. The FASC consists of a diffuser plate that will be deployed monthly in front of the ETM+ aperture to provide a full system, full aperture solar-based calibration. The PASC is a passive device that is permanently in the field of view of the sensor and provides a direct attenuated image of the Sun during every orbit over the North pole. The ETM+ continues to include an internal calibrator identical to the ETM internal calibrator and similar to the Landsat-4 and 5 TM´s internal calibrators. This device provides a shutter at the focal plane to measure the instruments dark level and illumination from an internal calibration lamp and black body during every scan line. Plans also include periodic on-orbit calibrations by reference to ground targets