Orientation Calibration of Wide Field-of-View Airborne Cameras by Natural Angular Features: Glory, Rainbow, Hot Spot, and Sun Glitter

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This article presents the instrument orientation calibration of the Observation System Including Polarisation in the Solar Infrared Spectrum (OSIRIS) instrument using natural angular features. The OSIRIS is an airborne prototype of the upcoming Multiviewing, Multichannel, and Multi polarization Imager (3MI) instrument abord the next-generation European meteorological satellite and inherits the design elements of the POLarization and Directionality of the Earth’s Reflectance (POLDER) sensor. The use of natural angular features alleviates the difficulties of the orientation calibration and provides a complementary approach to classical calibration techniques by ground control points (GCPs). Automatic detection of glory, rainbow, hot spot, and sun glitter during scientific data acquisition enables the characterization of instrument orientation under the condition of actual data collection. Application of the technique to OSIRIS’s two most recent field campaigns demonstrates that the orientation calibration by natural angular features improves the quality of geometric information. The applicability and the error estimation of the presented method are discussed, and it is recommended to fly in at least three different flight directions when the solar zenith angle remains in the optimal range (between 10° and 35°) to collect more than 100 angular feature images for reliable orientation calibration.