How Carbon Mapper “Sees” Methane and CO2

Published on: May 29, 2024

This post is part of Carbon Mapper’s Methane Remote Monitoring Education Series, which intends to help build a base knowledge of important topics in the methane monitoring space and demystify key concepts that are important to Carbon Mapper’s mission. To recommend a future topic, contact us here.

Introduction

Methane and carbon dioxide (CO2) emissions are invisible to the naked eye, but they harm our climate, air quality, and health. Making these emissions visible is an important step to better understand and ultimately stop them.

Although different processes and technologies can be used to detect greenhouse gases, this post focuses on imaging spectrometers. This is the technology we use in our airborne surveys and soon will be used in space via the first two satellites being developed and deployed by the Carbon Mapper Coalition. Imaging spectrometers act as the “eye” of the aircraft or satellite and enable us to see methane and carbon dioxide emissions and gather important data about them.

How imaging spectrometers work

Anyone who played with a prism in school understands that white light is composed of all colors of the rainbow, each color with a different wavelength. Similarly, imaging spectrometers measure the hundreds of wavelengths of light reflected by the Earth’s surface and absorbed by gases in the planet’s atmosphere.

Greenhouse gases like methane and CO2 absorb different wavelengths of light leaving a kind of spectral fingerprint not visible to the human eye. When analyzed, these light signatures can reveal which substances produced the fingerprint.

The following image shows the difference between methane point and area sources. It supplements the adjacent text that explains the purpose of point and area sources.

Imaging spectrometers take visible light and break it into the full spectrum or rainbow – each color with a different wavelength.

How exactly? The process is complicated, but the basic steps are as follows:

  1. Light enters the instrument, which is usually onboard an aircraft or satellite.
  2. That light is filtered through a slit and then focused onto a grating which diffracts the light into all the different wavelengths.
  3. This information is collected on a focal plane array, which is a device inside the instrument that turns the wavelengths of light (photons) into numbers (electrons) that computers can read.
  4. The computer processes an image that allows us to generate meaningful data and insights about the matter we’re measuring for.

The following image shows the difference between methane point and area sources. It supplements the adjacent text that explains the purpose of point and area sources.

This figure helps illustrate the basic principle of remote sensing using imaging spectroscopy

Source: Bedini, Enton. (2017). The use of hyperspectral remote sensing for mineral exploration: a review. Journal of Hyperspectral Remote Sensing. 7. 189. 10.29150/jhrs.v7.4.p189-211.

How we use imaging spectrometers

Imaging spectrometers are, and can be used in different ways to track emissions at a variety of scales. Carbon Mapper uses imaging spectrometers to detect and quantify super-emitters — large methane and CO2 emissions at the point-source level.

For nearly a decade, Carbon Mapper scientists have used imaging spectrometers onboard airplanes to observe large point-source emissions across the fossil fuel, waste, and agriculture sectors. Starting in North America and scaling internationally these airborne surveys have shown how this technology can gather the high quality data needed to detect, pinpoint, and quantify point source emissions of methane and carbon dioxide.

These spectrometers have advantages gathering actionable insights due to their detection limit and spatial resolution. For example, NASA’s Jet Propulsion Laboratory’s AVIRIS-NG, one of the spectrometer instruments that Carbon Mapper has used in past airborne surveys, measures large methane concentrations at high spatial resolution (typically three to five meters). This allows the spectrometers to detect strong methane emissions at the level of a specific facility or piece of equipment — intelligence that can help decision makers act.

Scaling up observations using satellites

Now, advanced spectrometer technology developed by NASA JPL is being readied for space!

The instrument that will go on board the first two Carbon Mapper Coalition satellites being built by Planet Labs PBC has improved spectral efficiency and is unique in terms of its high optical throughput (more photons = higher precision), spatial and spectral uniformity, stability, and low noise (a function of optical design and electronics). This translates to a system with a high signal to noise ratio that is essential for precise measurements of methane and CO2. Think of this like how the new iPhone takes better pictures in low light.

We look forward to keeping you updated as the team advances along the road to satellite launch!

Recommended reading

Potential of next-generation imaging spectrometers to detect and quantify methane point sources from space

Quantifying global power plant carbon dioxide emissions with imaging spectroscopy

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Definitions

Spectroscopy is broadly defined as the study of how electromagnetic energy interacts with matter. There are many different methods that use the principles of spectroscopy to detect, identify, and quantify data about matter including gasses, liquids, and solids.

Spectrometers are instruments that measure this interaction between these different materials and energy.