A plea for radar brightness

The radar reflectivity coefficient of a distributed scatterer, expressed either as /spl sigma//sup 0/ or /spl gamma/, depends on local incidence angle. Prior to incidence angle projection, the reflectivity coefficient may be called "radar brightness", denoted by "beta nought" /spl beta//sup 0/. In most practical situations, the local incidence angle is not known, so the image radiometrics cannot be corrected for it. It follows that /spl beta//sup 0/ is almost always the more appropriate radiometric attribute of radar imagery, whether calibrated or uncalibrated It is recommended that /spl sigma//sup 0/ (or /spl gamma/) be reserved for situations in which both the local terrain slope and the illumination incidence angles are known, and the image file has been adjusted to take both angles into account. Otherwise, radar brightness is correct, which should be adopted as the standard both as concept and as working terminology. This has been endorsed by the CEOS SAR Calibration Working Group.<>