ASD A100800, Руководство пользователя

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ASD Document 600541 Rev. G 36 TerraSpec® User Manual
www.asdi.com Chapter 6 Field Measurements
6.1 Illumination
In order to determine the reflectance or transmittance of a material, two
measurements are required:
• The spectral response of a reference sample.
• The spectral response of the target material.
The reflectance or transmittance spectrum is then computed by dividing the
spectral response of the target material by that of a reference sample.
Using this method, all parameters which are multiplicative in nature and
present in both the spectral response of a reference sample and the target
material, are ratio-ed out, such as:
• The spectral irradiance of the illumination source.
• The optical throughput of the field spectrometer.
Note: An inherent assumption when determining the reflectance or transmittance of
a material in the field is that the characteristics of the illumination are the
same for the reference and target materials.
Variability of the illumination
characteristics between the time the reference and target materials are
measured will result in errors in the resultant spectra .
6.2 Rocks, Soils, and Man-Made Materials
The shape of the spectral signature of rocks and soil tends to be invariant with
respect to the viewing geometry. The overall brightness of the observed
spectrum does change with illumination and viewing geometry due to
changes in the amount of shadow in the field-of-view of the spectrometer.
Absorption features in the spectra of rocks and minerals are due to the
presence of specific molecular groups and are often diagnostic of the minerals
present in the sample.
6.3 Suggested Set-up
6.3.1 RS3 Application
Step 1 Follow the instructions for plugging in the instrument and starting the RS
3
software.
Step 2 Attach an appropriate accessory. Remember that the TerraSpec spectrometer
requires an external (artificial) light source.