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SPACECRAFT

Visible and Infrared Spectrometer (VIR) Instrument

VIR is a Visual and Infrared Imaging Spectrometer in a single optical head. A Shafer telescope is combined with an Offner spectrometer. Spectral images are formed on two matrix detectors to cover the 0.25-1 µm and 1-5 µm ranges. The design uses a dual arm optical and focal design with mapping ability to 5 µm.

The spectrometer consists of three modules: the optical system, 5.0 kg mass; the proximity electronics, 3.0 kg and 5 W; and the cryocooler including driving electronics, 1.3 kg and 12.6 W. A mechanical and thermal mounting of 5.0 kg mass accommodates the spectrometer subsystems.

The Visible and Infrared (VIR) Mapping Spectrometer "sees" from 0.3-5 microns covering the near ultraviolet (UV), visible and infrared regions of the spectrum. The instrument produces an image of the spectrum and has on board its own calibration lamp, which it imaged as part of the tests performed in the weeks after launch.

When you click "View VIR Data" on the second screen of the above interactive, you will see data of Earth taken by VIRTIS, an equivalent imaging spectrometer aboard the Rosetta spacecraft, an ESA mission to a comet. A data cube is a 3-D array of numbers representing spatial and spectral images of a target in space. In this example, light reflected off of and emitted from Earth is focused on the visible and infrared sensors by the telescope and spectrometer, and is stored as a data cube. A two-dimensional image is captured at each frequency, or wavelength of light. The set of images is then stacked to form the three-dimensional cube. Thus, the multi- spectral imaging spectrometer provides both spectral images and spatially specific spectra.

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