ASD FieldSpec 3, Руководство пользователя

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ASD Document 600540 Rev. J 65 FieldSpec® 3 User Manual
www.asdi.com Chapter 7 Field Measurements
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.
The dependence of the optical properties of man-made objects on the viewing
and illumination geometry will fall somewhere between that for vegetation
and rocks/soils. This will depend on the amount of light transmission through
elements of the target and on the surface texture of the object.
7.9 Experimental Design
7.9.1 Time of Day / Year
The timing of the field data collection is important if field spectra are to be
used to calibrate or interpret a hyperspectral image. Reflectance spectra used
to interpret a hyperspectral image should be collected under illumination
conditions similar to those when the image was acquired.
Time of day and date are the major controlling factors of direct illumination
geometry, while atmospheric conditions relating to scattering and clouds are
the major factors controlling the geometry and relative intensity of indirect
illumination.
If field spectra are to be used to convert a hyperspectral sensor image to
reflectance, spectra should be acquired simultaneously with image
acquisition. If this is not possible, a water vapor correction should be made to
the image prior to its conversion to reflectance.
7.9.2 Sampling Strategy
The selection of a particular sampling strategy should be based upon the
objectives of the study. If the objective is to determine the detectability of
either a target material or of a process effecting the spectral signature of a
target material, the sampling strategy must encompass examples of the target
material under all expected conditions as well as all other background
materials.
Consideration must be given to all the processes modifying target and
background spectral signatures; these include illumination, slope and aspect,
and target surface architecture. Adequate collection of vegetation is even
more problematic due to the wide range of processes that effect their spectral
signature. These include soil chemical properties, soil reflectance, water
availability, time of day, time of year, cloud cover, temperature, and relative
humidity.
If the purpose of a study is to understand how a process effects the spectral
signature of a target without consideration of how background materials and
other sources of variability affect the spectral signature, variance from sources