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Visible / Near Infared Spectrometer

The VNS instrument provides spectra that are primarily useful for mineralogy, and can also indicate the presence of chlorophyll (although interpretation is often ambiguous). During the year one expedition, the VNS was an ASD portable field spectrometer, a backpackable unit separate from the rover. Readings were taken using a hand-held optical head / illumination source attached via fiberoptic to the backpack unit. After the rover passed through an area, the VNS operator followed up by taking readings at targets indicated by the science team. Readings could be taken during the day, but were most frequently taken at night due to operational constraints.

The most important feedback from the science team was that they were not able to precisely register the position of the VNS spectra with the SPI high-res images and FM images. This problem was caused by operational procedures that, in retrospect, should have been more carefully considered. Targets for the science instruments were specified by the science team as pixel positions in SPI panorama or high-res images. A member of the rover support team, following the rover, would then use the image to find and mark the target. Typically, this meant putting down a piece of paper next to the target, with a description of what was to be sensed (e.g., this rock, soil in this area). Later, at different times and often at night, the sensor operators would find the marker and take a reading somewhere in the area, using their own judgement to choose the precise position so as to provide a useful reading. These positions were not recorded in any way, making it impossible to precisely register the readings after the fact.

To understand why registration is so important, consider the case of seeing an interesting fluorescence feature in an FM image. A natural question is whether the VNS shows a chlorophyll signature at that location, or perhaps the signature of a known fluorescent mineral. If it is not clear that the VNS sensed the same location, there is no way to do this follow-up. Also, for geological interpretation, it is important to know whether the VNS is sensing a rock, soil next to the rock, or detritus on top of the rock. This requires precise registration in the context of the SPI images. The need for good registration will be an important design driver for the integrated sensor suite in year two.

The VNS deployed in year one was demonstrated to be a mature instrument technology. The instrument performed as expected, and good calibration minimized data interpretation issues. Integration issues, such as registration with other sensors, remain to be addressed.

Specifications
Wavelength range350-2500 nm
Spectral resolution3-30 nm
Time required for one spectrum1-2 seconds in sunlight
Dimensions33 x 11 x 41 cm
Mass8.6 kg

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