SPECTROSCOPY & GHG EMISSIONS
Measuring greenhouse gas emissions accurately and frequently is critical if we want to provide actionable insights on how to reduce emissions. GHGSat does such measurements from space using a satellite equipped with a spectrometer. But how can we measure greenhouse gas emissions using a spectrometer?
The Light Spectrum
Visible light, which is part of the electromagnetic spectrum, comes in many wavelengths which humans see as colors. This is made evident when you look at a rainbow. Every wavelength of sunlight is refracted at a slightly different angle inside water droplets and each color will emerge from the droplets in different directions, creating the colorful rainbows you know.
A spectrometer is a class of optical instruments which decomposes light into multiple wavelengths and measures their intensity. Spectrometers also work at frequencies not visible to the human eye, like the Short-Wave Infrared (SWIR) part of the spectrum where GHGSat’s instrument operates.
Imagine a ray of light coming from the sun, going through our atmosphere, being reflected on the ground, going through the atmosphere in the opposite direction and ending its journey inside GHGSat satellite’s spectrometer. During this journey, light will have interacted with the atmosphere, which is made up of many gases. Every one of these gases interacts differently with sunlight by absorbing it at specific frequencies (or wavelengths) and each gas has its unique absorption spectrum. For example, one gas may absorb a shade of cyan and orange, while another might absorb two different shades of yellow.
As light travels through the atmosphere and back to space, it passes through several gases. Depending on the amount of each gas it encounters, more or less of the initial sunlight makes it back to our instrument, as it gets absorbed at different wavelengths by the gases it encounters. By measuring the amount of absorption at each frequency corresponding to a gas, it is possible to determine the exact composition of our atmosphere.
The spectrometer instrument inside GHGSat’s satellites is very precisely tuned to focus on the spectral fingerprint of CO2 and methane. By focusing on the atmosphere above industrial facilities all over the world, GHGSat can accurately measure how much greenhouse gas they each emit.