Fore Optic Discussion - ASD FieldSpec 3 User Manual

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4.3

Fore Optic Discussion

Field of View
ASD.Document 600540 Rev. C
The fiber optic cable provides the flexibility to adapt the instrument to a wide
range of applications. Field measurements can be performed:
• holding the pistol grip by hand, or
• mounting the pistol grip and other foreoptic accessories to a tripod.
Reflected radiance and surface reflectance measurements are typically made
using the hand-held configuration. The pistol grip is available with both a
sighting scope and leveling device when required for more precise
orientation.
These accessories allow viewing the exact spot where the foreoptic is pointed
and orienting the foreoptic in precise, nadir-viewing, geometry. The majority
of irradiance measurements are performed with the irradiance receptor
mounted level on a tripod because of the need for precise geometric
orientation.
ASD's line of spectroradiometers is available with a wide selection of
foreoptics. These interchangeable foreoptics allow the flexibility to adapt the
FieldSpec spectroradiometer to a wide range of applications.
The small size of the FieldSpec's foreoptics allows positioning the foreoptics
at a greater distance from the surface under observation.
A field spectroradiometer with a larger field of view means that fewer
measurements are needed to approximate the spatial resolution of the imaging
sensor, because the pixel size of most imaging sensor systems is several
meters or more.
The small size of the pistol grip and foreoptics greatly reduce errors
associated with instrument self-shadowing. Even when the area viewed by the
foreoptic is outside the direct shadow of the spectrometer, the instrument still
blocks some of the illumination that would normally be striking the surface
under observation, either diffuse skylight or light scattered off surrounding
objects. Thus, the instrument as well as other objects — including the user —
should be placed as far as possible from the surface under observation. This
orientation requirement also applies to white reference measurements.
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Chapter 4 Fiber Optic Interface
FieldSpec® 3 User Manual