An accurate radiance calibration of an imaging sensor is critical to many remote sensing applications. ASD's line of FieldSpec 4 spectroradiometers play a key role in both pre- and post-launch imaging sensor calibration. Pre-launch calibration typically involve the sensor viewing a uniform radiance source. Large diameter integrating spheres are most commonly used for this purpose since they can be fabricated with apertures that match the imaging sensor. They are often designed with multiple lamps that enable them to be opperated at several different radiance levels. Because of drift in the output of the sphere's individual lamps, they require frequent radiometric calibration. The most accurate image sensor radiometric calibrations are achieved by calibrating the integrating sphere radiance immediately prior to use. This is often achieved by using one of ASD's FieldSpec 4 spectroradiometers as a transfer radiometer to alternately view the integrating sphere source and a known radiance source such as a calibrated Spectralon plaque illuminated by a NIST-traceable 1000W FEL lamp.
Post-launch imaging sensor calibrations typically involve ground targets with known reflectance and the measurement of the atmospheric parameters necessary to compute top of atmosphere radiance values for each of the imaging sensor's bands. Using ASD's FieldSpec 4 spectroradiometers, reflectance of ground calibration targets are measured coincident with the overflight of the imaging sensor. Coupled with ASD's solar tracking stage, the FieldSpec 4 spectroradiometer serves as a hyperspectral sun photometer to accurately measure the key atmospheric parameters needed to convert measured calibration target reflectance to the top of atmosphere radiance values that are used for image sensor calibration.
Users of ASD's FieldSpec 4 line of spectroradiometers rely on the accuracy of ASD's wavelength and radiometric calibrations. ASD's worldwide calibration facilities in the U.S., the Netherlands, China, and Brazil all include NIST traceable wavelength and radiometric calibration equipment. Certificates are provided for all wavelength, radiance and irradiance calibrations.
Learn more about sensor calibration with ASD instruments.