A Spectralon BRF data base for MISR calibration applications

The Multi-angle Imaging SpectroRadiometer (MISR) is an Earth-observing sensor, which provides global retrievals of aerosols, clouds, and land surface parameters. Instrument specifications require an accurate absolute calibration, as well as accurate camera-to-camera, band-to-band and pixel-to-pixel relative response determinations. In order to achieve these requirements, MISR makes use of an on-board calibrator (OBC), as well as vicarious calibration (VC) experiments. The OBC makes use of two Spectralon diffuse panels in order to provide a flatfield illumination. Bi-monthly deployments of these panels into the camera fields-of-view will be made. At these times, solar-reflected radiance values are measured by photodiode detector standards. Accurate relative bidirectional reflectance factor (BRF) data are required to transfer these photodiode-measured radiances into camera-incident values. An independent calibration pathway, known as VC, will also be implemented in order to reduce systematic errors and to provide a crosscheck on the OBC findings. Here, the top-of-atmosphere radiances are computed from in situ observations of surface reflectance and atmospheric transmittances. Key to these measurements is knowledge of the hemispheric/directional reflectance factor (HDRF) of the field reflectance standards. This report describes the BRF measurements of the MISR flight panels, and provides an estimation as to the differences between HDRF and BRF for the MISR view angles. This BRF data base is available from the MISR web site, http://www-misr.jpl.nasa.gov.