OCO Satellites: Measuring CO2, Plant Fluorescence, and Global Agriculture from Space

Overview

PBS Space Time explains NASA's Orbiting Carbon Observatory missions and how they monitor CO2 from space to reveal sources and sinks on a planetary scale. The episode also highlights a surprising capability, solar induced fluorescence, that allows us to see plants breathing in real time. The data has implications for climate science, agriculture, and global security, and the video discusses budgetary risks that could threaten the continuity of this critical time series.

Introduction

In this episode, PBS Space Time examines the Orbiting Carbon Observatory (OCO) program, a cornerstone of Earth observation that tracks atmospheric CO2 with high sensitivity and resolution. OCO-1 faced a launch failure in 2009 when its launch vehicle fairing did not separate as planned. The resulting setback became a catalyst for later success: OCO-2 launched in 2014, and with spare parts from both OCO-1 and OCO-2, NASA developed OCO-3 which now resides on the International Space Station. The program demonstrates how a targeted instrument suite can transform our understanding of the carbon cycle and its impacts on climate and society.

What OCO Measures and How It Works

OCO operates as part of the A-Train, a close-fitting constellation of Earth observing satellites in near polar, sun-synchronous orbit around 700 kilometers above the planet. OCO-2 largely shares this orbit, while OCO-3 on the ISS has a lower, faster orbit. The core measurement involves capturing light that passes through Earth's atmosphere, reflects off the surface, and returns through the atmosphere. Different molecules imprint unique absorption lines in the spectrum, creating a barcode-like signature. The instrument focuses on the infrared CO2 and oxygen lines, with line depths revealing molecule counts and line widths giving pressure and temperature information. An advanced radiative transfer model is used to solve an inverse problem: which CO2 profile best explains the observed spectra given the viewing geometry? The result is a precise column-averaged CO2 density along the observation path, enabling the creation of high-resolution CO2 maps across the globe with a few kilometer scale and sensitivities of about one part per million.

Surprising Capability: Solar Induced Fluorescence

A remarkable outcome of OCO is the ability to detect chlorophyll fluorescence induced by sunlight, a faint infrared glow produced by photosynthesis. This solar induced fluorescence provides a window into plant metabolism, allowing scientists to monitor when and how efficiently plants are photosynthesizing. The data reveal daily and seasonal shifts in vegetation health and activity across forests, savannas, oceanic phytoplankton, and agricultural lands. This capability offers a new dimension to understanding plant responses to heat, drought, and other stressors, improving our ability to forecast agricultural yields and to assess ecosystem resilience.

Applications and Implications

Beyond climate science, OCO data offer economic and humanitarian value. Accurate crop yield predictions at granular scales have already demonstrated value for the US corn belt, where yield forecasts can inform futures markets and farmer revenues. Agriculture and related industries contribute hundreds of billions to trillions of dollars to national economies and employ millions of people. When coupled with other atmospheric data, OCO helps model global CO2 circulation and track the fate of carbon, including the emergence of urban and industrial emission sources. The ability to detect new power plants or factories could provide strategic insight into carbon-intensive activities that might otherwise be hidden from traditional surveillance systems.

Continuity and the Value of a Time Series

The video stresses that maintaining a continuous, cross-calibrated time series is essential. OCO-2 and OCO-3 together form a decade-long baseline that future satellites will rely on for calibration and continuity. While GeoCarb had been proposed to augment OCO data in geostationary orbit over the Americas, it was canceled due to cost overruns, leaving a gap in planned capability. The transfer of OCO data into policy and planning contexts underscores the importance of investment in Earth observation for climate resilience, agriculture, and geopolitical stability. The episode concludes by highlighting the existential and economic value of these instruments and urging continued support to preserve this vital capability.

What Comes Next

The discussion ends with a warning: any decision to deorbit OCO-2 or shut down OCO-3 could sever a critical, long-running data stream that informs climate science, food security, and global governance. The piece emphasizes the need to consider the broader value of OCO beyond climate mitigation, including economic returns through agricultural prediction and the strategic advantage of monitoring carbon activity worldwide.