This paper describes the modeling of system engineering trades for the LWIR hyperspectral imager. First the operational scenario is defined to constrain the system trade space. Then modeling trades for spectral sampling, spectral bandwidth and SNR are presented. Issues unique to operating in the LWIR band are addressed. These trades are presented in the context of current technology for FPA and optical design. Radiometric calibration is addressed in preparation for flight testing of the sensor.
The design of infrared hyperspectral sensors for airborne applications demands components level performance trades to achieve system level performance objectives. Limitations to signal-to-noise ratio performance issues that are not present in the visible spectrum are manifest in the infrared region. This paper discusses the typical trade space that the designer must address to develop a long wave infrared hyperspectral sensor for airborne applications.
Ground resolvable distance (GRD) provides the system designer with an end-to-end system performance measure to allocate electro-optical sensor design budgets to the engineering disciplines. Laboratory performance for sensor design parameters is defined in terms of modulation transfer function and noise equivalent differential radiance. Linking GRD to sensor design parameters provides management and engineering with the tool to assess the influence of a single system component to total system performance. Although ultimately sensor imaging performance for reconnaissance is measured by the National Imagery Interpretability Rating Scale (NIIRS), engineering prefers GRD since it can be predicted by analysis, measured in the field, and traced to laboratory measurements of system components. The general image quality equation can be used to estimate the expected average NIIRS rating from the same system analysis parameters used to calculate GRD.
KEYWORDS: Sensors, Modulation transfer functions, Signal to noise ratio, Performance modeling, Sun, Palladium, Reflectivity, Sensor performance, Process modeling, Signal attenuation
Modeling of visible band line scan EO sensors in the flight test scenario involves the computation of ground resolved distance (GRD) based on the minimum resolvable delta- radiance (MRDR) criteria for visual perception of tribar targets on an output display device. MRDR is driven by the basic sensor parameters of noise equivalent delta-radiance (NEDR) and modulation transfer function (MTF). Therefore, the modeling process can provide a sequence of steps to reveal the linkage from the basic sensor parameters that produce NEDR and MTF, to expected lab measurements, and then finally to expected GRD performance in the flight test scenario. The MRDR vs GRD curves reveal the EO sensor sensitivity to parameters such as sun elevation, target reflectivity, visibility, and aircraft ground velocity. GRD is not a single fixed value but rather exhibits variability based on both observer statistics and flight test scenario factors.
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