Visible Infrared Mapping Spectrometer

Jurgens, D. W., Duval, J. E., Lockhart, R. R, Langevin, Y, Formisano, V., Belucci, G. (1990). Visible and infrared mapping spectrometer for exploration of comets. 

The VIRTIS apparatus (Visible Infrared Thermal Imaging Spectrometer) on board can observe the atmosphere and the cloud layers at various depths (on both the day and the night side of the planet). VIRTIS has also provided data for the first temperature map of the hot Venusian surface. These data have led to the identification of hot spots and thus provided evidence for possible volcanic activity (www.esa.int/specials/venusexpress). 

Measurements of the gaseous sulfur dioxide released were obtained with the Total Ozone Mapping Spectrometer (TOMS Krueger, 1983) and with the Solar Backscatter Ultraviolet Spectrometer (SBUV Heath et d., 1983), both carried on the Nimbus 7 satellite. Three instruments on board the Solar Mesosphere Explorer (SME) also revealed features of the cloud the Infrared Radiometer measured the thermal emission from the aerosols, while the Visible and Near Infrared Spectrometers measured the backscat-tered solar radiation. The three instruments are limbscanning and view the atmosphere along the track of the sunsynchronous polar orbit (Barth et d., 1983 Thomas et d., 1983). Ground based and airborne spectro-photometric measurements of sulfur dioxide have also been carried out (Evans and Kerr, 1983). 

The optical requirements for an IR microscope include (i) exact positioning of the sample (ii) spatial isolation of the sample from a larger matrix in the IR beam and (Hi) capability to function in both the visible and the infrared spectral regions. For infrared microspectrometry, a thermal emission source is generally used. Fourier transform spectrometers use interferometers as an effective means to resolve photon energies. Mercury cadmium telluride (MCT) detectors have the sensitivity and speed needed for FTIR spectrometers. The use of synchrotron radiation dramatically improves infrared microspectroscopy and has the power to analyse and map samples at high resolution. SR sources have transformed the IR microspectrometer into a true IR microprobe, providing IR spectra at the diffraction limit. Optics and performance of a /uF llR interfaced with SR were described [423]. Some 15 synchrotron beam lines are equipped with IR microscopes. 

For Raman microscopy, the most common spectrometer system consists of a visible laser coupled to a polychromator and a CCD detector, although near-infrared Fourier transform spectrometers cffe also used. The CCD detector can be used in a variation of Raman microscopy known as Raman imaging a special optical filter allows only one Stokes fine to reach the two-dimensional detector, which then contains a map of the distribution of the intensity of that line in the illuminated area. 

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