High spectral resolution solid state infrared spectrometer for atmospheric air quality measurement

摘要

Spectrometers, in which a grating is coupled with a two dimensional detector array to provide high resolution spectra without the need for spectral scan mechanisms can be designed in compact, rugged, configurations, making them well suited for spaceborne spectral mapping applications. We are pursuing the use of this technology for spaceborne tropospheric air quality monitoring, targeting high spectral resolution solar reflective and thermal emission spectroscopy in the wavelength range 2 to 5 μm. In this region key tropospheric pollutant and greenhouse gases such as O_3, CO, CO_2, CH_4, HCHO, and H_2O, have strong spectral features. The relatively short wavelengths allow for the use of well-developed detector technology and passive cooling. With sufficient resolving power, sensitivity, and judicious combination of spectra, good information on tropospheric vertical distributions, including boundary layer data, can be obtained. This paper describes the performance characteristics of a laboratory prototype of such a spectrometer, focused on the measurement of CO spectra in the range 4.56 to 4.73 μm. The design uses a cooled grating and optical train, coupled with a cooled 1024 × 1024 pixel HgCdTe array. It achieves a spectral resolution of ～0.32 cm~(-1) and NESR of 5.8 × 10~(-9) w/cm2/sr/cm~(-1). Both laboratory absorption spectra and zenith-looking air emission spectra of CO are presented. The spectrometer is the pre-cursor to a combined 4.6/2.33 μm instrument being developed under NASA funding and designed to demonstrate the unique vertical information capability of such a combination for tropospheric CO measurement. We give a brief discussion of a spaceborne concept focused on this technique.