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Cha p te r

Scene Spectral Radiance T e n Radiometric Error Measured

Actual

Spectral Power at Detector

FIGURE 10.16 Actual and measured object view spectral radiance versus
spectral power at the detector.

Scene Spectral Radiance Biased Actual

x

x

Spectral Power at Detector
FIGURE 10.17 The effect of calibration source errors on radiometric
calibration.

errors is illustrated in Fig. 10.17. The calibration points on the graph
are misplaced and the resulting calibration line is thus skewed.
There are two types of calibration source errors. The first is a
misevaluation of the radiance supplied by the calibration source. This
is known as blackbody error. Calibration source emissivity error and
temperature error are of this type.
Emissivity is a factor contributing to blackbody errors. To ana-
lyze the effect of underestimating or overestimating blackbody
emissivity, it is interesting to examine Eqs. (10.21) and (10.22). When
everything else is constant, the calculated radiometric gain is
inversely proportional to the emissivity used for the blackbody. The
calculated radiometric offset is, for its part, directly proportional to
the emissivity used for the blackbody. These dependencies translate
into a direct proportionality of a calibrated spectrum [Eq. (10.23)] on
the emissivity used for the blackbody. In other words, the use of
1 percent-inflated emissivity values leads to 1 percent-overestimated