ASD Document 600540 Rev. J 83 FieldSpec® 3 User Manual
www.asdi.com Appendix B Reference Information
D == effective diameter of foreoptic lens
A == foreoptic's angular field-of-view
X == distance to viewed surface
Y == diameter of field-of-view
Near Field (less than 1 meter):
Y = D + 2 * X * Tan(A/2)
Far Field (greater than 1 meter):
Y = 2 * X * Tan(A/2)
B.1.10 What are the units of radiance?
Radiance is the radiant power per unit source area per unit solid angle. This is
measured in Watts per square meter per steradian (W/m
2
/sr).
However, the FieldSpec spectroradiometer measures spectral radiance, which
is the amount of radiance per unit wavelength. Spectral radiance is measured
in Watts per square meter per steradian per nanometer (W/m
2
/sr/nm).
Reflectance and transmission measurements are ratios of the optical energy
from a sample compared to the optical energy from a reference panel. The
units cancel out, so these measurements do not use the calibration files to
calculate radiance.
Figure B-1 Field-of-view
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