A Technique to Account for the Misalignment of Pyranometers Installed on Aircraft

Abstract

Misalignment of pyranometers used for airborne measurements can lead to serious errors in the determination of downwelling radiation flux. The magnitude of these errors depends strongly on the elevation angle of the sun. This note presents an iterative numerical procedure for determining the angles of misalignment of upward-facing pyranometers. Deviations in pitch and roll of the instrument with respect to the aircraft's inertial navigation system (INS) must be added to the pitch and roll angles measured by the INS before the radiometric data are corrected for the attitude of the aircraft. For successful determination of the two angles of deviation, a calibration flight must be performed in which the aircraft flies in at least three directions at the same altitude under clear skies and above any haze.