Hyperspectral Imaging from Unmanned Aerial Vehicles for the Calibration and Validation of Earth Observation Satellites

• Main Author: Potts, DR
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2014
• Subjects: Antarc*; Antarctica
• Online Access: https://discovery.ucl.ac.uk/id/eprint/1451799/

The development and testing of two novel hyperspectral cameras intended to fly on a small Unmanned Aerial Vehicle (UAV) and give simultaneous views of the sky and ground over a spherical field of view in the visible and near-infrared is described. These measurements are intended to be gathered concurrent with satellite and ground observations and used in the vicarious calibration of Earth Observation satellite sensors. Hence, stringent accuracy demands guided the project. These were researched as part of a collaborative study into satellite inter-comparison over Dome C, Antarctica, which found typical agreement in Top-of-Atmosphere reflectance between different sensors and other comparison studies of < 3%. A literature review revealed that vicarious calibration, normally performed over bright desert targets, should be carried out over vegetation. The first hyperspectral camera developed employs a bespoke conical mirror coupled with an AOTF. This proof-of-concept system was found to be an innovative step towards a device to continuously capture downwelling and upwelling spectral radiance in the Solar Principal Plane for long periods without reorientation. This makes it extremely useful in studies of the backscattering peak of vegetation angular reflectance. The second camera uses a LCTF and a fisheye lens that trades spectral resolution for improved Out-Of-Band Stray Light and spatial/angular resolution to overcome the limitations of the first camera. Testing revealed the LCTF-based camera meets almost all requirements for vicarious calibration when deployed from either the ground or a low altitude UAV platform. Novel use of the fisheye lens was performed by imaging horizontally to capture both upward and downward hemispheres to allow simultaneous viewing of ground and sky. Less than 4% absolute radiometric accuracy was achieved, but the inter-pixel flat-field calibration of a 190 degree FoV imager presents an original problem that this project reveals is not adequately addressed in the literature.