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SpectRx NIR Technology
10.6 Radiometric and Spectral Theory 495
Efforts are made to illustrate the presented theory with examples per-
taining to the SpectRx system whenever possible.

10.7 Sensitivity
The sensitivity of the SpectRx system is its ability to transform input
radiance into signal form. This sensitivity is a function of many param-
eters such as noise, transmission, modulation, throughput, and detector
responsivity. The important quality of the system is its ability to distin-
guish the signal from the noise. This is expressed in terms of its signal-
to-noise ratio (SNR), Fig. 10.6. In the context of detection, it is often
stated that the signal can be detected when its amplitude is at least three times
the peak noise amplitude. The computational steps are used to predict the
signal-to-noise ratio of an interferometer system. The presented compu-
tations were performed using in-house simulation software. The evalu-
ation of the SNR is described in the following sections.

10.7.1 Object View Spectral Radiation
Figure 10.7 shows the radiation from an ideal blackbody source at
various temperatures between 100°C and 1600°C on a logarithmic

Scene Radiance

Detector
Irradiance

Detector Current

Photon Noise Johnson
ADC Noise
Noise
Jitter Noise Dark Noise
RSS

NESR

Signal-to-Noise Ratio

FIGURE 10.6 Signal-to-noise ratio computation steps.