Improvement of dark signal evaluation and signal-to-noise ratio of multichannel receivers in NIR heterodyne spectroscopy application for simultaneous CO2 and CH4 atmospheric measurements

Abstract

This work presents the design of multichannel heterodyne signal detection. The measuring capabilities of the proposed configuration were tested based on the developed multichannel laser heterodyne spectroradiometer (MLHS). The MLHS can simultaneously detect absorption features of atmospheric CO2 and CH4 in the NIR spectral range with an ultra-high spectral resolution of λ/δλ ∼ 6 × 107. Such a high resolution allows the MLHS to measure fully resolved individual line contours at 1.605 µm and 1.655 µm for CO2 and CH4 respectively. We propose a new method for synchronous measurements of dark and mixed signals and discuss its effect on the recorded data. We demonstrate advantages of the proposed technique by detailed comparison of data measured by MLHS and a single channel laser heterodyne spectroradiometer.