RedEye-1: A New Short-Wavelength Infrared Hyperspectral Imager for Atmospheric Observation

Abstract

Efficient monitoring of atmospheric constituents, particularly methane (CH4) and carbon dioxide (CO2), is of paramount importance in addressing the challenges posed by global warming and its repercussions for climate change. Presently, the field of hyperspectral imaging for atmospheric measurement/reconnaissance is characterised by two predominant categories: large-scale, high-resolution systems and their miniaturised, lower-resolution counterparts. Additionally, the development of hyperspectral systems, particularly in the short-wavelength infrared (SWIR) and beyond, often entails substantial costs due to the necessity of specialised optics and dedicated detectors. In response to these challenges, this thesis presents a compromise solution, RedEye-1, a compact, cost-effective SWIR hyperspectral imager designed with off-the-shelf optical components to bridge the gap between these existing paradigms. RedEye-1 operates within a spectral range of 1588-1673 nm, offering a relatively high spectral resolution of approximately 0.5 nm. This capability, combined with a Ground Sampling Distance (GSD) of roughly 2.4 metres from an altitude of 3 kilometers, positions RedEye-1 as a suitable tool for the measurement and quantification of CH4 and CO2 within the atmospheric layer of the Earth. The development process of RedEye-1 encompassed several stages, including design, construction, assembly, spectral and radiometric calibration, as well as ground and airborne tests. In particular, RedEye-1 embarked on its initial airborne reconnaissance mission on a light aircraft, providing new data that confirm its successful operation and valuable insights into the challenges encountered during airborne operations. Using an inversion model and a Line-by-Line radiative transfer algorithm, the ground-based single path measurement near 1645 nm estimated the CH4 concentration to be around 1912 ppb, indicating a reduction of approximately 5 ppb compared to the standard atmospheric CH4 level. However, the airborne double-path measurement at the same wavelength yielded a higher concentration of approximately 5229 ppb, implying significant CH4 emissions from the coal mine flown over.