FMARS Sponsors	Progress of Reflectance Experiment 13 July, 2002 by Emily MacDonald On July the 12th the experimental equipment designed to measure the spectral reflectance of various sources was unpacked and assembled inside the FMARS lab for the purpose of testing before use during EVA. All the required equipment was present and intact. The spectral reflectance experiment works as follows - An illumination source is set up, a lamp when indoors or the sun when outside, to illuminate the calibration surface. This special surface is called 'spectralon' and has the property that it reflects light equally in all directions, therefore the light from the illuminating source is reflected by the calibration surface and the reflectance spectrum is measured by the field spectrometer. Next, a source, be it a rock, water or whatever, is placed where the calibration surface was. The same light source illuminates the target and this light is subsequently reflected by it. Again the reflectance spectrum is recorded. The target reflectance spectrum is then divided by the calibration reflectance spectrum and the results are graphed, giving the fractional reflectance of the target with respect to the illuminating source versus wavelength. If the target is perfectly reflecting then the measured fractional reflectance will equal 1 and, conversely, if it is a perfect absorber then it will equal 0. Each target has a certain composition and will reflect light differently depending on its makeup. Therefore, each substance will have its own unique 'spectral signature' which can be used to identify it. If the target is a mix of many substances then 'end member analysis' can be performed on the sample whereby the reflectance spectrum is examined and unmixed, resulting in the determination of the targets composition. In order to test the equipment, spectra of several rock samples were taken within the lab using a standard lamp as the illuminating source. The results, on examination, looked sensible as can be seen in Figure 1. Figure 1 - Reflectance Spectra of Rocks Inside (Y=Fractional Reflectance / X=Wavelength in nm) A: Random Rock Inside - B: Limestone Inside - C: Gneiss Inside - D: Rock with Lichen Inside Figure 2 - Reflectance Spectra of Outside Sources (Y=Fractional Reflectance / X=Wavelength in nm) A: Rock Outside - B: Snow Outside - C: Puddle Outside - D: Lichen on Rock Outside Some spectra of rocks, snow and water were then taken outside the FMARS (out of sim) by way of a consistency check. Again the results looked on the whole sensible, as seen in figure 2, however there were some worrying peaks of high reflectance in two regions at infrared wavelengths. These spectral features were not seen in the reflectance spectra taken inside and were present in all of the spectra taken outside, an example of which is seen in figure 3 which shows the reflectance of water in the lab and a puddle outside. The spectra follow the general expected trend as water is known to reflect at visible wavelengths and to absorb everything at infrared wavelengths however, the spectrum taken outside clearly exhibits these infrared spikes. It is highly possible that these features are due to infrared absorption windows in the atmosphere so, in order to confirm this hypothesis, the spectra have been sent to Mark Helmlinger at JPL to examine. Assuming that these test spectra are deemed acceptable then it would appear that the equipment is good to go. Figure 3 - Reflectance Spectra of Water Inside and Outside Hab (Y=Fractional Reflectance / X=Wavelength in nm) A: Puddle Outside - B: Water Outside Terra, a satellite that is part of the Earth Observing System set up by NASA and the JPL, has an instrument on board which measures the spectral reflectance of the Earth's surface. It has measured the reflectance of the Haughton Impact Crater on Devon Island but, compared to the field spectrometer used on the ground, its resolution is poor. The plan during this FMARS simulation is to scout the impact crater and regions around it for large homogeneous areas that can be easily identified on maps that correspond to what Terra sees from space. Ground reflectance spectra will then be taken and can be compared to the results from Terra giving some insight into the accuracy of Terra's observations. Following this, rock samples collected from these homogeneous sights and from other selected sights will be examined inside the lab. The spectra produced from these rock samples will then be sent to the JPL for analysis and the various rock types and their composition determined. Watch this space!!!
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