26 August 2010 The Specular Array Radiometric Calibration (SPARC) method: a new approach for absolute vicarious calibration in the solar reflective spectrum
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Physics-based exploitation of image data from Earth observing sensors requires knowledge of the accuracy, stability and repeatability of a sensor's radiometric response within its in-flight environment. Vicarious radiometric calibration techniques, using terrestrial targets, provide an effective approach to obtaining this knowledge by measuring system performance under actual operational conditions. This paper introduces a new capability for performing the vicarious radiometric calibration of high spatial resolution sensors. The SPecular Array Radiometric Calibration (SPARC) method employs convex mirrors to create two arrays of calibration targets for deriving absolute calibration coefficients of Earth remote sensing systems in the solar reflective spectrum. The first is an array of single mirrors used to oversample the sensor's point spread function (PSF) providing necessary spatial quality information needed to perform the radiometric calibration of a sensor when viewing small targets. The second is a set of panels consisting of multiple mirrors designed to stimulate detector response with known at-sensor irradiance traceable to the exo-atmospheric solar spectral constant. The outcome is improved radiometric performance knowledge compared to other in-flight vicarious techniques through reduced uncertainties in target reflectance, atmospheric effects, and temporal variability. The only ground truth needed is the measurement of atmospheric transmittance. In addition, the simplification of calibration targets and ground truth collection in the SPARC method makes the deployment more cost effective and portable, thus creating the opportunity to imbed spectral, spatial and radiometric targets at a study site providing references that improve a sensor's interactivity as a phenomenological tool. A demonstration of the SPARC method is presented based on data collected with the IKONOS satellite operated by GeoEye. A SPARC measurement of absolute calibration coefficients for the IKONOS multispectral bands is compared to coefficients derived from the established reflectance-based vicarious calibration method.
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Stephen J. Schiller, John Silny, "The Specular Array Radiometric Calibration (SPARC) method: a new approach for absolute vicarious calibration in the solar reflective spectrum", Proc. SPIE 7813, Remote Sensing System Engineering III, 78130E (26 August 2010); doi: 10.1117/12.864071; https://doi.org/10.1117/12.864071

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