A field experiment in Saharan Algeria for the calibration of optical satellite sensors

A field experiment took place in February-March 1993 to characterize the reflectance properties of four Saharan desert sites, identified from satellite imagery as having remarkably stable optical properties. The objective of the experiment was to measure reflectances so that they can be used as references for the calibration of optical satellite sensors. Bidirectional measurements of the surfaces in reflectance (and also in polarization) were collected in different planes, in the visible, near infrared, and shortwave infrared. Particular attention was given to instrumental calibration, with independent calibration experiments in the laboratory and in the held. The surface reflectance measurements were then adjusted against an empirical model of bidirectional reflectance, and converted to reflectances at the top of the atmosphere (TOA) using an atmospheric radiative transfer model. The angular dependence of these TOA reflectances, named reference reflectances, was tested against those seen by AVHRR on the four desert sites. This comparison shows that multiangular calibration of optical sensors using reference reflectances can be achieved with an accuracy better than 1 per cent.