The science and technology case for a global network of compact, low cost ground-based laser heterodyne radiometers for column measurements of CO2 and CH4

Abstract:

The importance of atmospheric carbon dioxide (CO2) and methane (CH4) in determining Earth's climate is well established. Recent technological developments in space-borne instrumentation have enabled us to observe changes in these gases to a precision necessary to infer for the responsible geographical fluxes. The Total Carbon Column Observing Network (TCCON), comprising a network of upward-looking Fourier transform spectrometers, was established to provide an accurate ground truth and minimize regional systematic bias.

NASA Goddard Space Flight Center (GSFC) has developed a compact, low-cost laser heterodyne radiometer (LHR) for global column measurements CO2 and CH4. This Mini-LHR is a passive instrument that uses sunlight as the primary light source to measure absorption of CO2 and CH₄in the shortwave infrared near 1.6 microns. It uses compact telecommunications lasers to offer a low cost (<$30K/unit), suitcase sized, highly sensitive (< 1 ppm for CO2 and <20 ppb for CH4) measurement solution to supplement TCCON measurements.

We will deploy Mini-LHR instruments to accompany the NASA AErosol RObotic NETwork (AERONET) which has more than 500 sites worldwide. In addition, the NASA Micro-Pulse Lidar Network (MPLNET) provides both column and vertically resolved aerosol and cloud data in active remote sensing at nearly 50 sites worldwide. Tandem operation with AERONET/MPLNET provides a clear pathway for the Mini-LHR to be expanded into a global monitoring network for carbon cycle science and satellite data validation, offering coverage in cloudy regions (e.g., Amazon basin) and key regions such as the Arctic where accelerated warming due to the release of CO2 and CH₄from thawing tundra and permafrost is a concern. These vulnerable geographic regions are not well covered by current space-based CO2 and CH4 measurements. We will present an overview of our instrument development and the implementation of a network based on current and future resources.

We will also present preliminary Observing System Simulation Experiments to demonstrate the effectiveness of a network Mini-LHR instruments in quantify regional CO2 fluxes, including an analysis of measurement sensitivity, information content, and the impacts of aerosol and how these could minimized by incorporating information from AERONET/MPLNET.