Compact Spatial Heterodyne SWIR Spectometer for Atomospheric CO2 Monitoring.
Compact Spatial Heterodyne SWIR Spectometer for Atomospheric CO2 Monitoring.
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用于大气二氧化碳监测的紧凑型空间外差短波红外光谱仪。
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发表时间：
2013
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通讯作者：
Ikapay O. Ikpaya
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作者：
Ikapay O. Ikpaya
随着近年来全球对气候变化的关注，人们越来越关注通过使用卫星数据来描述温室气体的源、汇和运输的特征。大气痕量气体如二氧化碳（CO2）的有效测绘需要高精度（0.3%至0.5%）的气体浓度测量。这通常是通过在波长为1.56 μm - 1.62 μm和1.92 μm - 2.06 μm的光谱吸收波段（即短波红外- SWIR）识别CO2，并通过使用高分辨率光谱仪（例如，以相对信噪比为300:1的全宽半最大（FWHM）分辨率为0.27 cm-1）将其与其他温室气体（例如水蒸气）区分开来来实现的。这些要求对所需仪器的尺寸、重量、功耗和成本提出了严峻的设计和技术挑战。满足所需规格的现有星载仪器通常太大、太昂贵，无法考虑在微卫星星座上飞行，如果可能的话，微卫星星座将能够实现更大的时间分辨率。本文通过开发一种紧凑的空间外差SWIR （COMSSWIR）傅立叶变换光谱仪（FTS），为最先进的仪器设计做出了贡献，该光谱仪利用空间外差光谱仪（SHS）技术进行大气二氧化碳监测。SHS类似于传统的FTS，但是用固定反射光栅代替了反射镜。这种新型的紧凑型仪器使用一个标准的SHS在一个梯级模式SHS配置记录干涉图的探测器的二维宽带应用。它被设计为覆盖1599 nm至2060 nm的波长范围，具有适当的光谱分辨率。该实现利用了两个光学平台，每个平台都调谐到一个关键的二氧化碳吸收波段。第一个通道覆盖1599 nm至1611 nm波段，而第二个通道覆盖2045 nm至2060 nm。两个工作台共用一个接收器三镜望远镜，借助二向色分束器将输入信号分成两个通道。该仪器结构紧凑，坚固耐用，无移动部件，在1.6 μm通道（channel -1）和2.0 μm通道（channel -2）的FWHM分别实现了0.17 cm-1和0.13 cm-1的高光谱分辨率。它在1.6 μm和2.0 μm通道中提供了21,984的高分辨率。COMSSWIR仪器的空间分辨率为13 km × 13 km。具有两个仪器通道的完整有效载荷系统已成功建模，其总尺寸为0.69 m x 0.74 m x 0.2 m，满足微型卫星所需的规格。COMSSWIR -1通道的原型已经开发，校准和测试。它实现了bbbb220的信噪比和~ 3ppm的CO2测量精度。有了这些系统特性，高质量的CO2浓度精确测量成为可能，微卫星星座提供清晰的天空空间分辨率覆盖，如果在星座中使用，则具有每天重访的能力。
With the global concern over climate change in recent years, there has been an increased interest in characterizing the sources, sinks and transport of greenhouse gases through the use of satellite data. Effective mapping of an atmospheric trace gas such as carbon dioxide (CO2) requires high precision (0.3% to 0.5%) measurements of gas concentration. This is usually achieved through identifying CO2 by its spectral absorption bands at 1.56 μm - 1.62 μm and 1.92 μm - 2.06 μm wavelength (i.e. in the Short-Wave Infrared - SWIR) and distinguishing this from other greenhouse gases e.g. water vapour by using high resolution spectrometers (e.g. 0.27 cm-1 resolution at Full Width at Half Maximum (FWHM) at a relative signal-to-noise ratio (SNR) of 300:1). These requirements impose severe design and technical challenges in terms of size, weight, power consumption and cost of instrument needed. Existing spaceborne instruments that meet required specifications are generally too large and expensive to consider flying on a microsatellite constellation, which if possible, would enable a much greater temporal resolution to be achieved. This thesis contributes to the state-of-the-art instrument design by developing a compact spatial heterodyne SWIR (COMSSWIR) Fourier Transform Spectrometer (FTS) that utilises the Spatial Heterodyne Spectrometer (SHS) technique for atmospheric CO2 monitoring. The SHS is similar to a conventional FTS but has the mirrors replaced with fixed reflection gratings. This novel compact instrument uses a standard SHS in an echelle-mode SHS configuration to record interferogram on 2-dimensions of the detector for broadband applications. It is designed to cover the wavelength range of 1599 nm to 2060 nm at an appropriate spectral resolution. The implementation makes use of two optical benches each tuned to one of the key CO2 absorption bands. The first channel covers the 1599 nm to 1611 nm band, while the second channel covers 2045 nm to 2060 nm. Both benches share a common receiver three-mirror-telescope which splits the incoming signal with the aid of a dichroic beam-splitter for the two channels. With no-moving parts, this compact, solid state and robust instrument is designed to achieve a high spectral resolution of 0.17 cm-1 and 0.13 cm-1 at FWHM in the 1.6 μm channel (Channel-1) and 2.0 μm channel (Channel-2) respectively. It further offers a high resolving power of 21,984 in the 1.6 μm and 2.0 μm channels. The spatial resolution for COMSSWIR instrument is 13 km x 13 km. The complete payload system with both instrument channels has been successfully modelled and has a total size of 0.69 m x 0.74 m x 0.2 m which meets the specification required for microsatellites. A prototype of COMSSWIR Channel-1 has been developed, calibrated and tested. It achieves a SNR of >220 and a CO2 measurement precision of ~3 ppm. With these system characteristics, high quality precision measurements of CO2 concentration becomes possible from a microsatellite constellation that gives clear sky spatial resolution coverage with a daily revisit capability if used in constellation.