Space-based Measurements of Carbon Dioxide

Space-based measurements of carbon dioxide (CO₂) are used to help answer questions about Earth's carbon cycle. There are a variety of active and planned instruments for measuring carbon dioxide in Earth's atmosphere from space. The first satellite mission designed to measure CO₂ was the Interferometric Monitor for Greenhouse Gases (IMG) on board the ADEOS I satellite in 1996. This mission lasted less than a year. Since then, additional space-based measurements have begun, including those from two high-precision (better than 0.3% or 1 ppm) satellites (GOSAT and OCO-2). Different instrument designs may reflect different primary missions.

There are outstanding questions in carbon cycle science that satellite observations can help answer. The Earth system absorbs about half of all anthropogenic CO₂ emissions. However, it is unclear exactly how this uptake is partitioned to different regions across the globe. It is also uncertain how different regions will behave in terms of CO₂ flux under a different climate. For example, a forest may increase CO₂ uptake due to the fertilization or β-effect, or it could release CO₂ due to increased metabolism by microbes at higher temperatures. These questions are difficult to answer with historically spatially and temporally limited data sets.

Even though satellite observations of CO₂ are somewhat recent, they have been used for a number of different purposes, some of which are highlighted here.

Remote sensing of trace gases has several challenges. Most techniques rely on observing infrared light reflected off Earth's surface. Because these instruments use spectroscopy, at each sounding footprint a spectrum is recorded—this means there is a significantly (about 1000×) more data to transfer than what would be required of just an RGB pixel. Changes in surface albedo and viewing angles may affect measurements, and satellites may employ different viewing modes over different locations; these may be accounted for in the algorithms used to convert raw into final measurements. As with other space-based instruments, space debris must be avoided to prevent damage.

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