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The Ocean Chromatic: SeaWiFS Enters Its Second Decade
09.19.07
 
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The Little Observatory that Could

As space-based research goes, SeaWiFS (Sea-viewing Wide Field-of-view Sensor) merges the best parts of cost effective planning with the brightest, most focused scientific goals of understanding and protecting Earth’s living oceans. When launched in 1997, the instrument promised to significantly improve on the historical proof-of-concept successes of its predecessor, the Costal Zone Color Scanner (CZCS), while leveraging the economic benefits of simultaneously providing valuable commercial data to international clients in support of economic and recreational activities.

Manifested as the only instrument on the low cost, low power SeaStar satellite, the instrument proved once again that a tightly defined, rigorously followed set of mission goals can deliver valuable data on spec and on budget.

And valuable it’s been, indeed! This tenth year anniversary of the instrument and the wealth of information it’s gathered about life on Earth provides experts an opportunity to consider the profound implications of its findings while humans face a variable and changing climate.

Still from the North Atlantic animation
+ North Atlantic Streaming Video (Windows Media Viewer)

“SeaWiFS is still the gold standard for all visible radiometers in space,” says NASA’s Dr. Gene Feldman, SeaWiFS project manager. “Without SeaWiFS, any chance of producing data to assess climate change would not be possible. It’s the benchmark of long term, stable observations.”

What Color Means

In terms of oceanography, ocean color by itself means little. But taken as a proxy for other phenomena, ocean color serves as a measurable gauge for a wealth of vital subjects. Most remote sensing uses ocean color as a means of grading and quantifying data from different colors of light into visual depictions of ocean properties that scientists can understand; the idea of “false color” describes a process of applying a color scale to the different amounts of light collected by the satellite sensor in different regions or colors of the light, or radiative, spectrum. The collected data set visually depicts numerical measurements of the ocean properties.

Still from SeaWiFS 6 year animation
+ SeaWiFS Six Year Streaming Video (Windows Media Viewer)

But scientifically speaking, ocean color is not only a translational tool for ocean properties. In some cases, the color of the ocean can be directly observed in its own right, and when it is, color of the ocean becomes a measure of ocean properties. Primary productivity from single-celled ocean plants, called phytoplankton, is just such a property estimated from satellite ocean color measurements. By measuring ocean color, experts can quantify, understand, and monitor the biological productivity of a given ocean, coastal, or lake region, that is, the rate by which plants go through photosynthesis and growth, converting carbon dioxide and water to carbon-based biomass. The conversion process is called photosynthesis, and the phytoplankton, or primary producers as the basis of the marine food chain, are responsible for supporting higher trophic levels, including fish, which support marine mammals. It is only since the onset of space-based observations of ocean color have we been able to understand the global ocean ecology and productivity, as well as the impacts of a variable and changing climate on the fertility and health of our oceans.

Photosynthesis is the process that produces carbon-based plant biomass that supports almost all life on Earth. Accurate measurements of phytoplankton biomass and primary productivity provide powerful tools to study and manage ocean ecology, biogeochemistry, habitats including those in coastal areas, the impact of natural and anthropogenic hazards as they occur and impact our oceans, and the feedbacks to global climate change.

Measurements and Meaning

Still from animation showing temperature changes over the years.
+ Temperature Scale Streaming Video (Windows Media Viewer)

SeaWiFS has revolutionized our understanding of the ocean's response to environmental change. Here's one example: over the last ten years, the instrument has gathered daily global bio-productivity readings. When coupled with daily sea surface temperature readings over the same time span, we immediately see a relationship between temperature and productivity. In this sequence the red line going up it indicates a cooling ocean and when it goes down a warming ocean; the green line shows productivity. Notice how closely the green follows the red, which clearly shows the strong influence of climate variability on ocean biology.

One interesting note: the graph shows a strong change in temperature and productivity during the first year and a half. This signal comes from the La Nina phenomenon, measured in the latter part of the 1990s. The following decrease in productivity is from a prolonged warming period. The relationship between temperature and productivity stays linked, even during dramatic periods of change.

Doing Science the SeaWiFS Way

The SeaWiFS mission is one of NASA’s first attempts at a commercial partnership and “data buy”, and by universal acclaim, it’s been wildly successful. Prior to SeaWiFS, the space agency had experience contracting with outside companies for instrument development and project oversight, but never specifically for raw data. Following the initial RFP, Orbital Sciences (now called GeoEye) won the award as a fixed price contract. The initial scope of the bid promised $42 million over five years. More significantly, the structure of the contract limited the government’s liability for any potential cost overruns and creeping mission goals. Relative to other missions, this data purchasing arrangement promised to be less expensive than other comparable missions. History will show that it lived up to that promise.

Still from the Launch web video
+ Launch Streaming Video (Windows Media Viewer)

The deal said that Orbital would retain all commercial rights to the data, and NASA would own the educational and scientific research rights. Commensurately, NASA believed that a commercial incentive on the shoulders of a corporate partner would provide strong motivation to keep the instrument and the quality of its data in peak condition.

Originally NASA scoped the project to last five years. But here in 2007, SeaWiFS continues to operate well, gathering worldwide data everyday as it now enters its 11th year. It’s true that some spacecraft systems –like batteries and GPS for data transmission -- show the signs of millions of miles of spaceflight. But the scientific benefits keep coming in, and the data today is as useful now as the day it first came on line.

According to Dr. Feldman, SeaWiFS continues to be one of the only and certainly the best calibrated Earth observing platforms ever. “We’re looking at very subtle changes in the Earth’s parameters over time, and precision of the instrument continues to deliver extremely high quality, high resolution data.”

Still from SeaWiFS satellite beauty animation
+ SeaWiFS Satellite Streaming Video (Windows Media Viewer)

Plus, there’s a value-added component to the data in that taken as an aggregated group, they showcase a growing record of planetary change over time. For every extra year of data gathered, that historical record grows.

In addition to its remarkable map of ocean plant productivity, SeaWiFS is also responsible for facilitating the best calibrated land vegetation measurement in history, too. By utilizing an algorithm developed by for the NDVI (Normalized Difference Vegetation Index) program, SeaWiFS continues to gather daily measurements of global land vegetation cover, thus enabling bio-productivity analysis for the whole planet.

SeaWiFS Day to Day

SeaWiFS transformed global measurements of photosynthesis by providing those images for the first time, ever. Its predecessor instrument, called CZCS (Coastal Zone Color Scanner), essentially proved the concept and basic techniques of measuring ocean color from space, but it took the new technical design and program methodologies of SeaWiFS to fully realize the potential of global ocean color measurements.

Still from the Galapagos web video
+ Galapagos Streaming Video (Windows Media Viewer)

Every day, SeaWiFS measures the concentration of phytoplankton chlorophyll—essentially the amount of greenness or primary photosynthetic pigment--at the surface of the ocean. Chlorophyll is the green pigment found in most plants; it’s also the pigment that turns ambient carbon, water, and sunlight into energy—energy that powers plant growth. Generally speaking, the greener the chlorophyll signature, the healthier the plant.

Measurements of phytoplankton pigments essentially determine the health of the planet’s most fundamental and most productive family of plant life, called phytoplankton. Taken en masse, these microscopic plants numbering in the trillions convert more carbon and sunlight into growth and plant biomass than anything else, including the verdant, leafy plants of equatorial jungles. Photosynthetic growth also means a release of oxygen—oxygen is the waste product of photosynthesis—and thus it becomes immediately clear that vibrant photosynthesis means a steady supply of oxygen for a breathing planet.

Still from Yoder animation
+ Phytoplankton Streaming Video (Windows Media Viewer)

Nearly every day for the past 10 years, SeaWiFS has measured the global color of the oceans. That means scientists now have a decade- long, daily record of global bio-productivity, among other ocean biological and ecological properties such as biomass of specific calcium carbonate-based and harmful algae, and global observations of carbon species important for understanding oceanic uptake of greenhouse gases,. And while ocean color’s many measurements have portrayed hundreds of discrete ecological, biological, and chemical oceanographic events, perhaps the most important part of the little instrument’s legacy is its overall continuity of data of key observations that allow international researchers to detail the impact of environmental change, as well as climate variability and change on the ocean. With a running measurement of planetary health via phytoplankton biomass and productivity over the course of a decade, patterns of growth, recession, and change offer unique tools for experts to consider large scale trends in the health of Earth across the global ocean and in the coastal or regional zones.

Of course some things naturally have changed in the course of ten years. Orbital Sciences changed its name; following several corporate acquisitions and transformations now called GeoEye. NASA shares the cost of a data buy for the past two years with NOAA, The National Oceanic and Atmospheric Administration. And the value of a discretely focused, data oriented mission not only has been proved, but also continues to pay for itself everyday in the volume of research, education, and outreach uses worldwide. The demands that SeaWiFS data makes on existing NASA computational pipelines is so minimal that it simply doesn’t make sense for the agency to say no. Says Dr. Feldman, “It’s so stable that it’s an asset to which the agency does not want to lose access.”

Think Small: Phytoplankton and the Carbon Cycle’s Foundation

The ocean is not simply empty space filled with water and the occasional fish. It teems with life of myriad varieties, and pulses like a heartbeat with the changing seasons. That rhythm plays a fundamental role in regulating the health of all life on Earth. But while the familiar forms of stingrays and blue whales and kelp beds and sea urchins are the most easily recognizable, in terms of the biosphere, the action starts in a different population.

Still from the Falkowski animation
+ Phytoplankton Streaming Video (Windows Media Viewer)


At the primary producer level are phytoplankton. They’re tiny, single celled plant organisms that form the root of the oceanic food chain. Little more than bits of greenish implications of life, immense and uncountable clouds of these plants appear like floating carbon signatures around the globe, offering evidence about the planet’s health for those who can read the signs.

The word "phytoplankton" comes from the Greek. Phyto-, meaning "plant", and –plankton meaning "free floating". The most common species of phytoplankton is a tiny specimen called Prochlorococcus. Each individual in a colony of Prochlorococcus measures less than one micron across. In fact, it’s largely due to the extremely small size of this humble life form that its existence wasn’t even known until the middle of the 1980s. The same goes for a sibling species of phytoplankton called Synococcus. Although less common than Prochlorococcus and slightly larger, by itself it composes one of the most populous photosynthetic life forms on the Earth.

For years, researchers have only been able to study phytoplankton in discrete areas and synthesize a variety of suppositions about how it interacts with the natural world. But a global look at these humble plants has not been possible. Until SeaWiFS.

Missing Carbon: Global Biosphere with Carbon Dioxide Growth Overlaid

Carbon defines the backbone of life on Earth. By measuring the seasonal changes in growth of plant life, scientists can measure carbon uptake from the atmosphere, and thus gauge important aspects of the health of the global biosphere.

Still from animation of the Pacific biosphere
+ Biosphere Pacific Streaming Video (Windows Media Viewer)

This animation shows the global biosphere as measured by SeaWiFS with a corresponding graph of measured carbon dioxide in the foreground. The measurements forming the biosphere visualization show phytoplankton concentrations in the ocean and vegetation index readings over land.

As years advance in this sequence, notice how the greening of the land oscillates between north and south. Notice, too, how this corresponds to the carbon dioxide graph. As the northern hemisphere turns green, ambient carbon dioxide decreases due to the fact that plants are absorbing more carbon dioxide. As the northern hemisphere enters autumn and winter and thus looses much of its green, atmospheric carbon dioxide increases. These fluctuations in atmospheric carbon dioxide are seasonal.

What’s important in this sequence, however, is a demonstration of how the overall carbon dioxide trend from1980 to 2005 slopes upward steadily. Increases in total carbon dioxide in the atmosphere has been linked to a warming planet and potentially substantial overall changes to the Earth’s climate.

SeaWiFS Turns Ten

Still from the SeaWiFS web package video Image right: + Click for a closed captioned reporter's package

To say it out loud, it doesn’t sound like much: SeaWiFS just measures Earth’s ocean’s color.

But when you talk to an expert, the ten years of measurements gathered from this spunky space-based observatory are the stuff of drama and poetry…and vitally important science.

Now entering its second decade, SeaWiFS continues to deliver the most consistent, most precisely measured readings of the planet’s overall biological health. Its daily measurements of ocean and land color provide a solid accounting of how well plant life on Earth manages to convert carbon dioxide into growth. This not only provides a snapshot of overall plant health, but also serves as a proxy for bigger questions, like global carbon dioxide trends and large scale climate change.

NASA turned over responsibilities for acquiring SeaWiFS data to NOAA a few years ago. But the space agency continues to be the hub of all SeaWiFS data products, from global biosphere maps to spectacular true color images of major planetary events. What’s more, the computing environment that the SeaWiFS project helped create works so well that it’s now the data backbone of many of NASA’s other important Earth observing assets.

But the little spacecraft that could…keeps chugging along. Now entering its second decade of operation, it continues to deliver important scientific data and vital health information about the Earth.

 
 
Michael Starobin
Goddard Space Flight Center