Nep

where A is the detector area, Af is the noise equivalent bandwidth, and NEP is the noise equivalent power of the detector. The factor D* is strongly wavelength dependent showing its peak value at the cut-off frequency. Figure 9-16 shows the specific detectivities and the operating temperatures for infrared detectors, and Table 9-12 gives characteristics of infrared detector arrays with read-out electronics.

The selection of a detector or detector array (usually with a read-out multiplexer) is driven by several factors. The primary design issues center on maximizing detectivity in the spectral band of interest while operating at the highest possible temperature and a sufficiently small time constant In addition, we must consider the geometry of the detector and the array as well as associated calibration issues.

9.4.2 Payload Operations Concept

In addition to the technical trade-offs in spacecraft performance, the operations concept for employing the sensor is an important consideration early in the preliminary design. We need to understand the end-to-end mission problem—not merely the physics of collection. The entire process beginning with the ultimate users or customers of the data needs to provide a feasible and efficient means to meet mission objectives.

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Wavelength fy/m)

10"

Wavelength fy/m)

10"

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