For nearly 20 years, Jim Acker, a contract support scientist at the NASA Goddard Earth Science Data and Information Services Center (GES DISC), has helped oceanographers compile and study data collected by satellites. A chemical oceanographer by training, he has been involved in the study of ocean color as viewed from space. He recently wrote a book for NASA about the history of the subject. He is also scheduled to deliver the NASA Goddard Science Colloquium on September 30 at 3:30 p.m. His talk is entitled: “Rise of the Machines: Computational Power and the History of NASA’s Ocean Color Missions.” He gave us a preview of the book and the talk this week.
NASA Earth Observatory: Most of us think of the ocean as blue; in some places, it looks green. So what do scientists mean when they refer to “ocean color?”
Jim Acker: Well, it’s blue and green and brown, and occasionally a few other related hues. Ocean color refers to the science of using satellite sensors to measure the light emanating from the ocean and determining what is in the water based on those light measurements. The main things that change the color of the ocean are phytoplankton—the floating plants at the base of the ocean food chain—dissolved colored substances, and different kinds of sediments.
EO: What are some of the things we have learned by looking at the ocean from satellites?
Acker: One of the main things done with global observations has been estimating how much carbon is produced by the growth of phytoplankton. Ocean color observations have shown how much this can vary, particularly with events like El Niño or La Niña in the Pacific Ocean.
The satellite view also can show how much variation there is over relatively short distances. A ship could be sitting in nice clear water, and just a few tens of kilometers away there could be a strong phytoplankton bloom that they would never know about without observations from space.
The observations also have helped understand phytoplankton patterns in hard-to-reach places like the polar seas and the Red Sea or Arabian Sea. The interaction of the land and ocean, with weather patterns and river inflows, has also been better observed.
EO: Have there been any big surprises?
Acker: Definitely. One of the biggest surprises from the Coastal Zone Color Scanner, the first NASA ocean color mission, was truly how much the ocean varied over small distances. Where oceanographers used to draw simple lines, they realized there were swirls and spirals and curlicues and loops and jets and rings. It was much more complicated.
Another surprise when SeaWiFS and MODIS started making global observations was how cloudy it is over the oceans. It takes really impressive data processing to get accurate values because of that.
And because the satellites make continuous observations, they have observed many different features that weren’t where we expected them to be or they happened more often than we thought.
EO: What provoked you to write a book?
Acker: NASA wanted to have some histories of NASA science, and I wanted to tell the history of ocean color because it’s been so successful. It’s like a well-trained, elite athlete: they make what they do look easy, though a lot of hard effort and training makes that possible.
Ocean color measurements are very difficult to make, but because the missions have been so successful, the public and even most scientists have just seen the beautiful results and have not realized the dedicated, behind-the-scenes work that made them possible. It isn’t just about seeing images from space on a computer monitor. To be sure the data is accurate, there have been some true high-seas adventures. I was able to get a lot of real-life experiences from the scientists and engineers into the book.
EO: What is your favorite book about science? And your favorite writer?
Acker: My favorite book that was sort of about science was The Map that Changed the World by Simon Winchester; I also enjoyed his book about the eruption of Krakatoa. My favorite writers are Pat Conroy and J.R.R. Tolkien. The late Stephen Jay Gould wrote a lot of things about science I liked. And I have to mention that I just read Andy Weir’s The Martian and was quite impressed. I’m looking forward to seeing the movie.