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ABSOLUTE RADIOMETRIC CALIBRATION Maxar products are delivered as relative radiometrically corrected image pixels. Their values are a function of how much spectral radiance enters the telescope aperture and the instrument conversion of that radiation into a digital signal or digital number (DN). That signal depends on the spectral transmission of the telescope and filters, the throughput of the telescope, the spectral quantum efficiency of the detectors and the analog-to-digital conversion. Image pixel data are therefore unique to each sensor and should not be directly used in a radiometric sense. In addition, bands taken at different time delay integration (TDI) levels may give misleading spectral information if le in digital number space. Image pixels should be converted to top-of-atmosphere spectral radiance at a minimum. A pre-flight calibration has been performed and these data are provided in the .IMD metadata file that is delivered with the imagery. Since launch, Maxar has performed an extensive vicarious calibration campaign to provide an adjustment to the pre-launch values. The top-of-atmosphere radiance, L, in units of W μm-1 m-2 sr-1, is then found by converting from DN using the equation. Conversion of imagery Digital Numbers (DN) to Radiance (L) ■ "L" is at-sensor radiance found independently for each band and pixel ■ "dES" is the earth-sun distance in AU for the date (TLCTime goves the data and time of the collection) ■ "Es" is the band-averaged solar exoatmospheric irradiance at 1 AU ■ "θ" is the solar zenith angle (90-meanSunEl from IMD file) The TDI-specific abscalfactor and effective bandwidth are delivered with the imagery in the metadata file. The digital number, DN, is the pixel value found in the imagery. The GAIN and OFFSET are the absolute radiometric calibration band dependent adjustment factors that are given in Table 1 (and Table 3 for WorldView-3 CAVIS). Note that these values are revisited annually and improved upon, although the sensors themselves have been found to be very stable throughout their lifetimes. Note that the calibration uses Thuillier 2003 solar curve. CONVERSION TO REFLECTANCE A smooth transition from WorldView-3 Care is taken to ensure that the WorldView-3 and SWIR instruments display a smooth transition even though they are two completely different. ROBUST VALIDATION METHODS Railroad Valley, NV, USA is used for validation and as a secondary calibration site. info@maxar.com maxar.com