Absolute diffuse source as a part of the radiometric calibration equipment for the space imaging spectrometers

A radiometric calibration of the space imaging spectrometers especially with a wide field of view is performed with a help on an integrating sphere as a radiance source. Spectral radiance of the integrating sphere is defined by a comparison with the absolute diffuse source. As a diffuse source for a calibration of the integrating sphere in units of radiance may be used a halon target irradiated by a halogen lamp. The absolute diffuse source based on the halon target/four halogen lamps configuration with a good radiance homogeneity is described. The diffuse screen with a diameter 180 mm, which is made of polytetrafluoroethylene (PTFE), is irradiated by 4 symmetrically located halogen lamps. The type of the lamp is KGM 24-150. The angle of incidence on the diffuse screen is 34°. Viewing is carried out through the output window along the direction, which is normal in relation to the diffuse screen. The diameter of the output window is 140 mm. A facility for relative radiance graduation and calibration of this diffuse source against a standard lamp traceable to All-Russian Research Institute of Optical and Physical Measurements (VNIIOFI) and the results of the absolute diffuse source radiometric calibration in the spectral range from 400 nm till 2500 nm are described. A spatial inhomogeneity not more than 2.5% along the whole output aperture. A level of radiance at 900 rim is 1.6.108W/m3sr. Described absolute diffuse source was created in according to a contract with the Space Research Institute of the Russian Academy of Sciences for the radiometric calibration of imaging cameras and spectrometer in stereo-spectralimaging system ARGUS for Mars 94/96 missions.