Spectral radiancemeters for the prelaunch calibration of JERS-1 OPS

The characteristics of the spectral radiancemeters for the prelaunch calibration of the VNIR and SWIR radiometers of the JERS-1 OPS launched in 1992 are described. The radiancemeters are used for a comparison between the radiance sources of black bodies and integrating spheres. They consist of mirror optics, a double grating monochromator and Si photodiode detectors and a liquid nitrogen cooled InAs photodiode. They cover the wavelength range from 500 nm to 3000 nm. The wavelength accuracy and purity are important in the radiance comparison between a blackbody and an integrating sphere which have different spectral distributions. A Si and a Ge crystal were used for wavelengths longer than 1200 nm and 2000 nm, respectively, which show different transmittance in the position. The size of the source effect, the nonsymmetry effect of the source position and the slit width effect are measured. The absolute responsivity is measured by a set of fixed point blackbodies and the agreement is better than ±1%