Science and Applications

CO₂

OCO provides global column-integrated CO₂ measurements with an accuracy better than 1 part per million (ppm) at a footprint size of approximately 1.3 km x 2.3 km allowing the geographic distribution of CO₂ sources and sinks and their variability to be determined. With its Snapshot Area Mapping (SAM) mode, OCO-3 can scan large contiguous areas of emission hot spots such as cities and power plants over multiple years providing insight into CO₂ source changes at regional spatial scales.

OCO measures atmospheric carbon dioxide (CO₂) and solar-induced chlorophyll fluorescence (SIF) from space, helping scientists study carbon sources and sinks, plant photosynthesis, vegetation growth and stress, and changes in the global carbon cycle.

CO₂ in the Earth system: CO₂ is important for life on Earth. CO₂ keeps the planet warm enough to support life and is the fuel for plant growth. However, the rapid increase in CO₂ over the past decades has led to global increase in surface temperatures with significant impacts on the terrestrial biosphere and oceans. Although the overall influence of human activities on CO₂ concentrations is well established, critical questions about where, when and how much CO₂ is released and removed from the atmosphere, and how these processes will evolve in future, remain to be answered.

Sources, sinks and the carbon cycle: Carbon is constantly cycling between the land, ocean and atmosphere. Sources to the atmosphere include plant, animal, and microbial metabolism, deforestation, and the combustion of fossil fuels such as coal or gas. Sinks from the atmosphere occur when plants take up CO₂ by photosynthesis. The oceans remove CO₂ both through biological and physical processes.

Mitigating the rate of CO₂ increase: In any given year, approximately half of the CO₂ produced by human activities is absorbed by the terrestrial biosphere and the oceans. However, the annual fraction varies from year to year. The nature and the locations of the sinks that absorb CO₂ are currently not well known and present important, yet unanswered questions: will the efficiency of these sinks change in the future? If so, by how much? Are there ways to increase the uptake and thereby reduce the rate of CO₂ buildup in the atmosphere? OCO measurements are being used to understand the nature, locations, and processes that create these natural sinks. 

Solar-Induced chlorophyll Fluorescence

Plants glow as they absorb light for photosynthesis. This glow, referred to as solar-induced chlorophyll fluorescence (SIF), can dim or brighten as temperature, water, and sunlight become more or less favorable for growth, offering an important signal of vegetation health and stress. 

SIF for carbon cycle science: SIF provides information on where, when and how much plants, such as forests or grasslands, are absorbing atmospheric CO₂. 

SIF for drought forecasting, land and water management: SIF changes as water becomes scarce. These signals can help with forecasting and water management.

SIF for agriculture: SIF can be used to monitor photosynthesis in the context of crop health and productivity, to help optimize irrigation strategies for crops and to get "more crop per drop." SIF measurements can also help with timely and accurate estimation of crop yields, offering the promise of aiding in effective responses to food crises, informing agricultural policies and efficient commodity pricing. 

OCO-2 SIF measurements: Photosynthesis changes at different time scales, from weeks and months to years. The OCO-2 mission provides repeated observations at a fixed time of day (1:30 pm local) for consistent monitoring of global vegetation health over time. OCO-2's continuous decadal scale record of 12+ years has chronicled global change in photosynthesis in response to local, seasonal, and global scale weather patterns.

OCO-3 SIF measurements: Diurnal variations in photosynthesis provide key information on the responses of ecosystems to external drivers. The OCO-3 mission samples around the globe at different times of day, providing a unique perspective on the time-of-day variations of SIF that can inform projections of changes in the global carbon cycle in response to long-term changes in factors such as temperature and water availability in the Earth system.