Calibration of the videospectral system for the space experiment "Uragan" onboard the ISS

The videospectral system (VSS) intended for ecological space experiment on board of the International Space Station (ISS) has been developed by the Aerospace Researches Department of the Institute of Applied Physical Problems of the Belarusian State University. The VSS is intended for registration of color images and spectra of underlying surface. The system comprises an imaging channel and three CCD-array spectrometers based on diffraction gratings. A CCD-array photodetector of each spectrometer measures the spectral radiation distribution in rows, and the spatial distribution in columns. Astigmatism is a typical aberration of polychromators based on concave spherical gratings rays in tangential and sagittal planes are focused at different points. This degrades the spectral or spatial resolution along the entrance slit. The proposed method of obtaining high spatial resolution without spectral resolution loss consists in a displacement of the output end of the imaging fiber along the optical axis at a specified distance from the entrance slit. The entrance slit operates as a one-dimensional aperture to obtain high spectral resolution. The image and spectral channel of the VSS were calibrated by wavelengths and spectral sensitivity. A method of the second diffraction order correction has been proposed for spectrometers based on diffraction gratings. Some results of laboratory calibration and the first application are presented.