WFIS: A Wide Field-of-View Imaging Spectrometer

This paper presents the design and initial test results of the laboratory Wide Field-of-View Imaging Spectrometer (WFIS). The WFIS is a patented optical design intended for use in remote sensing of the Earth and the Earth's atmosphere in the hyperspectral imaging mode. It is meant to operate as a pushbroom imager to provide coverage of the Earth from low Earth orbit without scanning mechanisms. The optical system occupies a volume measuring less than 20 cm x 18 cm x 13 cm. The laboratory unit covers the 500 nm to 1000 mm wavelength range over a cross-track field of view of 70 degrees. The image is focused onto a CCD area array such that the spatial component falls along the horizontal direction and the spectral information is dispersed along the vertical direction. The system's focal length is 7.5 mm with an effective focal ratio of 3.7. A holographic grating produced on a unique convex substrate is the dispersing element A key feature of the WFIS is an all-reflective optical path, allowing the basic design to be adapted to wavelength regions from the UV to the IR. Presented are the initial test results of the laboratory spectrometer that characterize its spatial and spectral performance over a 70 degrees x 0.08 degrees field of view.