Development of SHACS: Progress on Channel-1 Prototype Demonstrator

Finding solutions to the continuous concerns over climate change has been of increased interest in recent times with efforts targeted at mitigating its effects. Satellite observations and in situ terrestrial networks play key roles in the understanding and management of the problem. Whilst detecting carbon dioxide (CO₂) optically is relatively straightforward, and has been achieved with small satellites, accurate quantitative mapping of CO₂ requires very high precision (~1 ppm uncertainty or better) measurements of gas concentration. This is usually achieved through identifying CO₂ by its spectral absorption bands at 1.56-1.62 and 1.92-2.06 μm wavelength by using high-resolution spectrometers (e.g., 0.27 cm⁻¹ resolution at a signal-to-noise ratio (SNR) of >300:1). This normally requires high performance, large and complex instruments whose high cost, mass, volume, and power requirements preclude their use on small satellites. In this article, we describe the progress made in the design and development of a compact precision spatial heterodyne atmospheric carbon dioxide spectrometer (SHACS), which utilizes the spatial heterodyne spectroscopy (SHS) technique to form a robust, compact, no-moving-part Fourier transform spectroscopy (FTS). We also present the developmental stage and terrestrial atmospheric CO₂ testing of a single channel (1.6 μm) of SHACS instrument. This instrument achieves a high spectral resolution of 0.22 cm⁻¹ at a high SNR of >900:1 and can fit into a micro-satellite platform. With this performance, high-quality measurements of atmospheric CO₂ concentration with an average measurement precision of 1.27 ppm have been achieved.