Satellite Based Methane Emissions Monitoring

Quantitative monitoring of methane greenhouse gas emissions is becoming increasingly important as the effects of climate change are becoming harder to ignore.[1] In this series of posts, we will dig deeper into the challenges associated with accurately monitoring methane gas emissions. This being a worthwhile endeavor since methane gas emissions account for up to 10% of total greenhouse gas emissions in the US.[2] Methane gas is especially problematic since it has 84 times more warming potential than carbon dioxide gas over a 20 year period. [3] Our perspective will be that of satellite imaging. While there are numerous methods available for quantifying methane emissions, satellite imaging provides an opportunity to monitor greenhouse gas emissions that might otherwise remain unnoticed. Although there are many challenges to accurately quantifying emission rates using satellite data, the market for satellite based methane data is quickly growing and these data are a key tool in the methane detection ecosystem. These tools are needed to create globally impactful corrections  to the current climate change path we all actively contribute to every day.

Methane Data: Publicly Available

Google Earth Engine’s public data catalog provides a wealth of standard Earth science raster datasets. In this series we will focus on the Sentinel Collections. Sentinel satellites make up a growing constellation that began with the launch of Sentinel-1 in 2014. This initiative is headed by the European Commission in partnership with the European Space Agency (ESA) to replace the current older Earth observation missions that have reached or are nearing retirement. The TROPOspheric Monitoring Instrument (TROPOMI) is an instrument onboard the Sentinel-5 Precursor (S-5P) Mission satellite. TROPOMI provides near real time (within 3 hours after sensing) data products. These near real time data products include total columns of ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide, formaldehyde and vertical profiles of ozone, and cloud & aerosol. Methane column density however is available as an offline product. Methane, tropospheric ozone, and corrected total nitrogen dioxide columns are available within about 5 days after sensing.[4]

Although other publicly available methane datasets exist (see Table 1), we will begin our exploration of global methane emissions monitoring by leveraging the Sentinel-5P methane dataset available through Google Earth Engine.

Table 1

Methane Data: Private Sources

Access to space is now more affordable than ever. The cost to send payloads into space has gone from approximately $10,000/kg to $1,000/kg in the last ten years and expected to drop considerably over the next twenty years.[5] Table 2 contains a non-exhaustive list of the companies focused on providing higher resolution surface reflectance and hyperspectral images. Hyperspectral images monitor wavelength regions of sunlight that are reflected off the Earth’s surface. Light in shortwave infrared regions, for example, allows for a measure of the total column density of methane along the image path of the observing satellite.

Efforts by those companies listed in Table 2 are helping to close the gap between the mobile methane detection methods and the coarse resolution satellite based data products (e.g. Sentinel-5P). Of course there are other private industry efforts aimed at providing hyperspectral image datasets. I focus on these three here since their main goal is the detection of methane gas.

Table 2

California Methane Gas Levels

The figure below illustrates methane gas levels over the state of California for the first half of 2020. The offline methane dataset availability for Sentinel-5P on Google Earth Engine is 2019-02-08 to present. California’s Central Valley is clearly a region with elevated levels of methane gas. East of Los Angeles County and the areas surrounding the Salton Sea exhibit relatively increased levels of methane gas as well. For California in particular, we’ll be digging deeper to better understand methane emission sources and attempt to discern those that are naturally occurring versus anthropogenic. Follow our posts as we investigate further.

Mean Methane column density from 01-01-2020 to 06-30-2020