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Visible / Near Infrared 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.
|Wavelength range||350-2500 nm|
|Spectral resolution||3-30 nm|
|Time required for one spectrum||1-2 seconds in sunlight|
|Dimensions||33 x 11 x 41 cm|