GENA for radiometric block adjustment
The Spanish company ALTAIS will use the generic network adjustment software platform GENA for the radiometric calibration and modelling of high resolution airborne digital imaging.
Radiometry is the measurement of radiance. It is a fundamental technique of astronomy, Earth remote sensing and modern photogrammetry. A digital imaging sensor measures incoming radiance (L) and stores the result of the measurement as a digital number (DN). Two central phases in the imaging process are the radiance transfer from object to a system and the transfer of the radiance entering the system (at-sensor radiance) to DNs inside the system. The units of L are W·sr^(-1)·m^(-2) (Watt per steradian per square metre). DN is dimensionless.
Radiometric calibration -of at-sensor input L to sensor output DN- is the determination of the parameters of a mathematical model of the sensor radiometric systematic errors: mainly, the vignette effect, the non-uniform quantum efficiency among various sensitive cells and their dark current offsets.
Radiometric modelling -of object-to-sensor L propagation- is the identification of a mathematical model that transforms incoming solar radiance to an object into incoming radiance to a sensor. Such a radiometric model may include an object related Bidirectional Reflectance Distribution Function (BRDF) and an atmospheric radiative transfer model whose core is a Radiative Transfer Equation (RTE).
A BRDF describes the reflectance properties of an object as a function of illumination and viewing geometry. The BRDF depends on wavelength and is determined by the structural and optical properties of the object. A RTE calculates radiance in a single layer of the Earth's atmosphere.
ALTAIS will develop a GENA radiometric model toolbox with numerical combined BRDF-RTE and sensor radiometric calibration models. The unknown parameters of these models will be estimated from a set of overlapping images, radiometric tie points and radiometric control points in a least-squares adjustment with GeoNumerics' GENA platform and ALTAIS' radiometric model toolbox.
ALTAIS Cartografía y Urbanismo S.L. (Madrid, ES) was founded in 1992. It is a geoinformation service provider specialized in cartographic engineering, photogrammetry, surveying, geodesy, cadastral surveying and mapping, land management, urbanism and civil engineering. (http://www.altais-sl.com)
GENA is GeoNumerics' robust non-linear least-squares generic network adjustment engine. With GENA, measurements of geodetic networks, photogrammetric and remote sensing blocks can be adjusted. Observations of different types can be arbitrarily combined into single large adjustments for model-based parameter determination purposes.