Vicarious calibration - A reflectance-based experiment with AirMISR

A vicarious reflectance-based calibration experiment for the Multiangle Ima ging SpectroRadiometer (MISR) airborne simulator, AirMISR, is described as one precursor experiment of this type planned for postlaunch application to MISR itself The experiment produces a set of multiangle near-top-of-atmosp here radiances that are compared with the multiangle AirMISR radiances, est ablished using a laboratory calibration. The field and aircraft data were c ollected as part of an engineering test flight at Moffett Field, CA, on Nov ember 5, 1997. A concrete tarmac was used as the field target. Atmospheric optical depth data were collected adjacent to the target throughout the act ual overflight period using a single Reagan solar radiometer. For logistica l reasons, the surface hemispherical directional reflectance factor (HDRF) was determined 7 days later using the Portable Apparatus for Rapid Acquisit ion of Bidirectional Observation of the Land and Atmosphere III (PARABOLA I II), along with the areally averaged spectral HDRF at normal incidence, obt ained with an Analytical Spectral Devices (ASD) FieldSpec moderate resoluti on field spectrometer. AirMISR overflew the target under clear sky conditio ns though the aerosol turbidity was high (similar to 0.3 at 550 nm). Good t o fair agreement has been obtained at all angles and wavelengths between th e top-of-atmosphere (TOA) radiances calculated for the measured atmospheric and surface conditions and the radiances incident at AirMISR as determined from the laboratory calibration. Some systematic disagreements are present . The largest disagreements (similar to 15% in the blue) are found at the h ighest view angles and the smallest at nadir viewing (<5%). Possible explan ations for the differences in radiances at large view angles are discussed. (C) 2001 Elsevier Science Inc. All rights reserved.