Abstract
L-1 Standards and Technology has developed a detector-based calibration system utilizing tunable laser sources for characterizing moderate aperture imagers. Currently, the spectral coverage is set by reference detector standards, calibrated by NIST, that cover the range from 360 nm to 1775 nm. Future expansion is possible as the tunable lasers produce light from below 300 nm to greater than 2500 nm. The sources consist of a large Spectralon integrating sphere with a 180 mm diameter exit port and, for increased radiance, collimators/projectors with a 170 mm diameter aperture that use a smaller integrating sphere. The sources reside on a large translation stage and the collimators have motorized pointing. There are TVAC chambers with a large window for measuring the temperature dependence of radiometric performance. The system has been used for prelaunch calibration of commercial imaging sensors. It enables full-aperture illumination (testing as the sensor is used) and direct measurement of the absolute response as a function of wavelength to uncertainties of less than 1 % (k=2) in the VNIR. Additional characterizations include linearity and flatfielding measurements to the 0.1 % (k=2) level, and stray light rejection, e.g., size-of-source and off-axis response. While the system can be used to map-out with great resolution the imager spectral response, for example, even measurements at relatively few wavelengths can validate and anchor to an absolute scale the imager radiometric model.
A System for Pre-launch Characterization of Imaging Sensors using Tunable Laser Sources
L-1 Standards and Technology has developed a detector-based calibration system utilizing tunable laser sources for characterizing moderate aperture imagers. Currently, the spectral coverage is set by reference detector standards, calibrated by NIST, that cover the range from 360 nm to 1775 nm. Future expansion is possible as the tunable lasers produce light from below 300 nm to greater than 2500 nm. The sources consist of a large Spectralon integrating sphere with a 180 mm diameter exit port and, for increased radiance, collimators/projectors with a 170 mm diameter aperture that use a smaller integrating sphere. The sources reside on a large translation stage and the collimators have motorized pointing. There are TVAC chambers with a large window for measuring the temperature dependence of radiometric performance. The system has been used for prelaunch calibration of commercial imaging sensors. It enables full-aperture illumination (testing as the sensor is used) and direct measurement of the absolute response as a function of wavelength to uncertainties of less than 1 % (k=2) in the VNIR. Additional characterizations include linearity and flatfielding measurements to the 0.1 % (k=2) level, and stray light rejection, e.g., size-of-source and off-axis response. While the system can be used to map-out with great resolution the imager spectral response, for example, even measurements at relatively few wavelengths can validate and anchor to an absolute scale the imager radiometric model.