Development of a 1.65 μm pulsed laser DIAL System to map atmospheric CH4 distributions

Abstract

We present the results of a system study conducted to develop and demonstrate a high sensitivity ground-based and airborne DIAL System for measuring atmospheric CH4. This program addresses the 2007 NRC Decadal Survey recommendation that ‘if appropriate and cost-effective methane technology becomes available, methane capability should be added’ to close the carbon budget. A highly efficient absorber of IR radiation, methane is a potent greenhouse gas with a warming potential 72 times greater than CO2 per molecule, over a 20-year horizon. The proposed measurement will enable scientific assessments globally, and in particular of northern latitude CH4 emission impacts on climate and enhance understanding of ecosystem response to climate variability and land cover change. This system will provide simultaneous ranging and high resolution measurements of aerosol and cloud distributions. This will incorporate a pulsed 1.65 mm OPO laser; an existing receiver system redesigned to optimize its performance for this wavelength by incorporating an optical filter; a commercially available InGaAs APD and an existing 3-D scanner. High resolution FTIR laboratory spectroscopic measurements in the R4 transitions of 2ν3 of CH4 will be conducted to maximize accuracy of retrievals. This development demonstrates an azimuthal scanning system for ground-based mapping and monitoring of range-resolved, near-surface CH4 emissions and airborne detection of dry CH4 boundary layer and total vertical column fractions. Due to its relative insensitivity to aerosol and cloud interferences, this system will be ideal for investigating high latitude CH4 releases over polar ice sheets, permafrost regions, wetlands, and over open ocean during night and day as well as commercial applications in of natural gas leaks. The proposed task is applicable to NASA sub-orbital, satellite validation, and venture class programs.