Guest essay by Ric Werme
It’s been a long wait, but OCO-2 speaks!
Let’s start with a timeline:
- Feb 2009: NASA’s $273 million Orbiting Carbon Observatory satellite crashed into the ocean near Antarctica shortly after launch today from Vandenberg Air Force Base. Bummer.
- Jul 2014: Try 2 was successful. The instruments checked out, we all look forward to results.
21042014: NASA’s Goddard Spaceflight Center releases an animation of a model of CO2 flow across the Earth. Visually, it’s very attractive and feels right, but it doesn’t look at all like the OCO-2 imagery. It may be the scaling, it may be OCO-2’s poor temporal resolution, it may be partly including a carbon monoxide display. I’m sure the modelers will have lots to do for the next few years!
- Dec 2014: Well, it took a while, but the first image from OCO-2 is release and it’s really not what we expected. There’s a lot of CO2 over China, and a lot that appears related to slash and burn agriculture, but Europe and the US look pretty good.
- July 2015: The New Horizons mission finally reaches Pluto. This team did things right. They posted images as soon as they had them. We could watch it get closer to Pluto, we could see Pluto up close right after the flyby, and they’re still releasing images as fast as the slow, weak downlink delivers them.
- Aug 2015: I get tired of waiting on OCO-2 and send Email to the OCO-2 PR contact asking what’s up. A month later I get a reply that includes:
Over the next couple of months, we will be releasing a number of new OCO-2 visual products to the public. Stay tuned! And thanks for your interest in the mission.
- Oct 2015: I’m not the only impatient person at WUWT, I see. However, Erik Swenson did something about and produced his own imagery. He did a great job.
- Oct 2015: The OCO-2 team releases a YouTube video showing the same sort of images that Erik released. I haven’t compared them yet, I wanted to get this up quick.
Check out first full year of OCO-2 science operations.
The video is interesting, but is missing mid-April to mid-May. I’m impressed at how quickly plants pull down CO2 in the northern spring, though I noticed that before I noticed the missing month. I’m impressed at how much CO2 is released in the tropics. I’m intrigued that there seems to be a bit of a surge in CO2 before spring triggers plant growth. Perhaps thawing ground releases CO2 produced by tree roots and rotting vegetation during the winter.
[Update – on the sampled area.]
A number of early comments refer to how much surface area doesn’t have imagery. I suggest reviewing Erik Swenson’s post and comments, a lot of that dialog applies here.
There’s also a link to NASA’s Data Product User’s Guide which goes into a lot of detail.
First, the CO2 measurements are done with a spectroscope. Light from the Earth’s surface enters a telescope, a small sample is selected from a slit. That line of light is bounced off a diffraction grating onto an imaging chip that provides 1016 pixels of the spectrum. There are three spectrometers tuned to areas of interest for O2 (I assume this is used to measure intensity), and two bands of CO2’s spectra.
Light has to go from the surface of the Earth to the satellite, and to measure the tiny differences due to changes of CO2 concentration, they want a bright source on the ground. They measure from two different paths (on different orbits). First is the “nadir” reading where the satellite looks straight down. This is not very bright, but it has the best spatial resolution. The other direction is to look at sunlight’s glint reflecting off water. This is much brighter, so it’s easier to measure the brightness of the spectral lines.
The measurements require that from the point being observed, the sun has to be at lest 5° above the horizon in nadir mode and 15° above in glint mode. Clouds, terrain, etc. can make for poor or unusable data. Still, it appears to me that NASA isn’t imaging as much data as Erik did.
Keep in mind that OCO-2 is one of the first satellites doing this sort of work. Astronomical spectral analysis generally doesn’t do the resolution that OCO-2 needs and has the opportunity to take very long exposures. So while climate scientists are looking forward to the data, the designers will be looking at things to do for the next design.