Viewing Geometry; Suggested Set-Up - ASD FieldSpec 3 User Manual

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7.9.3

Viewing Geometry

7.10

Suggested Set-up

Step 1
Step 2
ASD.Document 600540 Rev. C
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 effect the spectral signature, variance from sources
other than the one of interest should be minimized in the selected targets. This
is achieved by carefully controlling viewing and illumination geometry, often
in a laboratory. This type of study is often performed as a feasibility study
prior to a full study evolving collection of spectra of background material.
The selection of an appropriate viewing geometry depends upon whether the
spectra are used for image analysis or for a feasibility study.
Image analysis: a viewing geometry similar to the airborne sensor is
required.
Feasibility study: it is possible to eliminate much of the confounding
variance typically present in an image data set by fixing the viewing and
illumination geometry.
For vegetation, spectra can be acquired at the spatial scale of the leaf/needle,
branch, or canopy. Canopy level spectra are most suitable for image analysis
and interpretation. Rarely can leaf/needle or branch level spectra be used
directly to interpret an image. Leaf/needle and branch level spectra are useful
to understand how the canopy level spectra are influenced by changes in
leaf/needle and branch spectral changes as opposed to changes in the canopy
structure.
Open the control configuration in the application.
Set the sample, white reference, and dark current averages to 10 scans.
For example, White Spectralon (Labsphere, Inc., Shaker St., PO Box 70,
North Sutton, NH 03260-0070, PH: 603-927-4266, FX: 603-927-4694,
E-mail: sales@labsphere.com, Website: www.labsphere.com). Spectralon is
also available from ASD.
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Chapter 7 Field Measurements
FieldSpec® 3 User Manual