Surface Albedo, Dust, Methane
Project title: A Bigger Whole than the Sum of Its Parts: Joint Retrievals of Surface Albedo, Dust and Methane over Arid Regions and Coastal Oceans
EMIT observations focus on determining the mineral composition of Earth's arid dust source regions by imaging spectroscopy. EMIT is also in the process of developing products for greenhouse gases, notably CH4. The resulting data products will be used to refine Earth System Models (ESMs) and reduce uncertainty in radiative forcing caused by mineral dust.
Mineral dust is a principal contributor to direct radiative forcing over arid regions, impacting agriculture, precipitation, and desert encroachment around the globe. Dust storms are a substantial contributor to the global aerosol population, particularly in the dust belt region, and known to strongly influence the radiation budget due to their significant scattering and absorption properties. A combination of the vertical distribution of dust and the overall aerosol loading allows the computation of the complex balance among shortwave scattering and absorption and longwave absorption and emission, which determines the net impact of dust on the low-level tropospheric temperature profile. Methane is emitted from a variety of anthropogenic and natural sources. Anthropogenic emission sources include landfills, oil and natural gas systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial processes. Methane, which accounts for 20% of all GHG emissions, is the second largest contributor to the warming of the Earth's atmosphere since the industrial revolution. However, this belies the fact that CH4 is a source of the more long-lived CO2, and has a 25 times stronger warming effect than CO2. In view of its more localized occurrence, shorter lifetime, and potent greenhouse effect, spatially resolved CH4 detections would provide valuable observational constraints to account for heat fluxes in ESMs.
We will use the full EMIT spectral range in a time series approach similar to Sanghavi et al. (2010, 2012) to obtain arid surface albedos and dust aerosol optical thickness, making it possible to distinguish between the spectral characteristics of the surface and the dust emitted from it. We will apply the retrieval method of Sanghavi et al. (2012) over coastal ocean soundings to determine the vertical distribution of lofted dust, providing observational constraints of dust height, which is a valuable initialization parameter for Earth System Models (ESMs). EMIT spectra include the strong 2.3 micron methane absorption band. We demonstrate that the inclusion of aerosols significantly improves the accuracy of methane retrievals from EMIT. Using the aforementioned aerosol retrieval methodology, we will develop a coupled dust-methane retrieval for reduced-bias retrievals from EMIT measurements.
Our work will deliver algorithmic data enhancements to support EMIT science objectives by providing key observational parameters - surface albedo, dust AOT, dust height, and methane concentration, to constrain the sign and magnitude of dust-related radiative forcing at regional and global scales in ESMs. Our time series approach will help detect seasonalities and trends in the activity of dust sources, allowing the validation of forecast model predictions of the increase or decrease of available dust sources under future climate scenarios.
Project Team
Suniti Sanghavi
California Institute of Technology