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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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