Saturday | August 27, 2016
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OCO-2, can you see by the dawn’s early light?

This year, two days before America’s Independence Day fireworks celebrations began, a remarkably different “rocket’s red glare” was seen at Vandenberg Air Force Base in California.

This event, which actually occurred a couple of hours before dawn, marked the successful launch of NASA’s first spacecraft dedicated to the study of carbon dioxide (CO2) in the Earth’s atmosphere.

The centerpiece of the ambitious mission of the Orbiting Carbon Observatory-2, or OCO-2, is essentially the mapping of CO2 distribution in Earth’s atmosphere on a continuing basis, for at least two years. While the “OCO-2” acronym nicely describes the target of the mission, there was also an OCO-1 launch in 2009, but things went awry before the spacecraft reached orbit.

To carry out its mission, OCO-2 will orbit Earth at its poles about every hundred minutes or so as a member of a constellation of half-a-dozen satellites, all of which will move together as the “A-Train.” Each “car” in this satellite train is equipped with sensors that collect data that complement each other. For example, while OCO-2 collects CO2 data, two other satellites, CALIPSO and CloudSat, will collect information about clouds and aerosol in the atmosphere at the same time, helping improve the quality of OCO-2’s findings.

Although measuring CO2 in Earth’s atmosphere from space does require some rocket science to accomplish, it isn’t the simple detection of CO2 that’s so difficult, since there’s lots of it in the atmosphere to measure. What makes OCO-2’s job so challenging is that this mission’s chief goal is to help us better understand Earth’s carbon cycle — a global-scale topic with many variables.

In general, human activity and some processes of nature act as CO2 sources, pumping huge amounts of this greenhouse gas into the atmosphere, while other processes occurring in the oceans and on land act as sinks, removing it. Studies have shown convincingly that before the industrial age, human sources of CO2 were small compared with the carbon-removing influence of vegetation, oceans and other natural processes. Modern carbon inventories indicate the balance has been tipped the other way: we’re putting more CO2 into the air than Earth processes can practically remove.

OCO-2 will attempt to unravel this mystery through its mapping of the amount and location of CO2 in Earth’s atmosphere at an unprecedented level of precision and sensitivity. This feat, if accomplished, will produce a better quantitative understanding of regional CO2 sources and sinks.

To do this, OCO-2 will use a sophisticated infrared spectrometer system that measures sunlight energy passing through the atmosphere. The sunlight is absorbed in proportion to the amount of CO2 in the light’s path as it reaches the surface and is reflected back to the satellite. At the same time, OCO-2 will measure light energy emitted during photosynthetic processes associated with CO2 removal.

The potential to identify CO2 sources and sinks is of great interest to volcanologists, as well.

Volcanoes can release significant amounts of CO2 during large eruptions, even though, averaged through time, they add little CO2 to Earth’s atmosphere on a global scale (less than 0.5 percent of that contributed by human activity on average, including large eruptions). Furthermore, volcanic CO2 is associated with magma supply, so the possibility of measuring CO2 from space everywhere on the planet, twice a month, could be very helpful for detecting volcanic restlessness at remote volcanic settings worldwide.

Even if the OCO-2 mission is wildly successful, challenges will remain for applying these CO2 maps to volcanoes. Although the OCO-2 should, theoretically, be able to see fairly small CO2 concentration differences on the Earth’s surface, the detection footprint (as small as 1 square mile or 3 square kilometers) is of the same order as the central crater of many volcanoes where CO2 is emitted. And once volcanic CO2 is released to the atmosphere, it begins to disperse and dilute, making it harder to detect.

A successful OCO-2 mission, one that helps us better understand the quantitative balance between CO2 sources and sinks on regional and global scales, could help guide efforts to effectively decrease human-made CO2 emissions. The volcano science community also is looking forward to fruits of this mission.

Kilauea activity update

A lava lake within Halema‘uma‘u produced nighttime glow visible via HVO’s webcam during the past week. The lava lake level dropped during the week, and was 40-45 meters (130-150 feet) below the rim of the Overlook Crater on July 10.

On Kilauea’s East Rift Zone, the June 27 breakout continues to build a low shield, topped by a lava pond on the northeast flank of Pu‘u ‘O‘o. Overflows from the pond, and breakouts from the base of the levee around the pond, fed small flows that rarely reached the base of Pu‘u ‘O‘o.

There were no earthquakes reported felt in the past week on the Island of Hawaii.

Visit the HVO website ( for past Volcano Awareness Month articles and current Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call (808) 967-8862 for a Kilauea summary; email questions to

Volcano Watch ( is a weekly article and activity update written by scientists at the U.S. Geological Survey`s Hawaiian Volcano Observatory.


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