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The need for the development of a low-cost, low-energy, portable remote sensor of hazardous chemicals for first responders and facility protection has been recognized. Differential absorption radiometry (DAR) based on uncooled detectors has been identified as a possible solution. However, uncooled detectors have lower detectivity than cooled detectors and thus require efficient light management. Two prototype DARs, one consisting of two cryogenically cooled HgCdTe detectors and the other consisting of two LiTaO3 pyroelectric detectors, designed to detect methanol vapor, were built and tested in the laboratory to compare their relative performance by measuring detectivity limits under controlled conditions. With ΔT = 8.3 K between the methanol vapor and a radiation source having an emissivity of εs = 0.92, methanol detection limits of 3.14x10-4 atm-cm and 3.5x10-3 atm-cm were projected for the HgCdTe and pyroelectric based DARs with similar optics, respectively, assuming that a minimum SNR less than or equal to 5 is required for positive detection and identification. Evaluation of the individual detectors in each DAR demonstrated that the detector limited noise equivalent temperature difference (NETD) for the HgCdTe detector was 381 μK whereas the detector limited NETD for the pyroelectric detector was 110 mK. With a 1 s exposure to the source, temperature fluctuations in the environment increased the NETD of the HgCdTe detector to 31.0 mK whereas the NETD of the pyroelectric detector was 115 mK. These results indicated that the advantage of the HgCdTe based DAR relative to the pyroelectric based DAR is much smaller than the advantage projected by their detector limited characteristics such as D*. Thus for remote sensing applications where cost is critical, the use of pyroelectric detectors can provide acceptable performance characteristics when the signal incident on the detector is increased only by x10 relative to the signal required for similar sensitivity using HgCdTe detectors.
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