CO_2 Phase and Amplitude Spectra Measured over 2 km Outdoor Path With a Dual-Comb Spectrometer

摘要

Optical absorption is a direct, powerful method to probe the concentration of atmospheric gases important to climate change providing inputs for carbon transport models and characterizing carbon sources and sinks. It is used to retrieve total atmospheric column densities through passive satellite-based spectrometers, up-looking solar Fourier Transform Spectrometers (FTS), and future down-looking laser-based systems. These systems provide global coverage but struggle to achieve challenging accuracy standards to characterize sources and sinks near to the ground. At the other extreme, absorption base point sensors can detect concentrations at a single location with high accuracy but suffer from "representation errors" inherent in point sampling spatially varying concentrations and extrapolating to the km-scale grid of regional transport models. Broadband, horizontal-path, kilometer-scale, open-air path measurements provide an ideal combination of broad gas species coverage at an ideal spatial scale with the required sensitivity, accuracy. Open-path FTS has been applied for sensing volatile organic compounds , however, the combination of low spectral resolution and constraints path geometry hinders the accurate and sensitive detection of small molecules.