Studying the Ocean from Space
Because of its excellence in satellite-based research, the College of Oceanic and Atmospheric Sciences (COAS) at Oregon State University was selected to develop a center of excellence in satellite remote-sensing research and modeling of the ocean. The Cooperative Institute for Oceanographic Satellite Studies (CIOSS) was established by the National Oceanic & Atmospheric Administration in April 2003.
It is difficult to observe the vast ocean that controls much of our climate and other Earth-system processes. Research cruises and moored instruments are expensive. Some areas are difficult to get to or work in, especially the Southern Ocean, where wave heights are often six meters or more.
However, instruments on satellites can make a variety of measurements over much of the global ocean in a period of one to several days.
• Infared (IR) sensors measure surface temperatures that show upwelling areas, where cooler, nutrient-rich waters support productive fisheries.
• Sensors that measure light (ocean color) at several wavelengths in the visible spectrum allow estimates of phytoplankton biomass and growth.
• Microwave instruments use radio waves to see through clouds, allowing all-weather measurements of the ocean surface (IR and visible bands cannot see through clouds).
• Microwave radar scatterometers measure winds, which show their mixing power and driving force for ocean currents, as well as the strength of the transfer of heat and CO2 through the ocean’s surface.
• Microwave radar altimeters measure sea-surface heights, which show currents in the upper ocean, along with significant wave heights.
• Microwave radiometers measure surface temperatures on a coarser grid than the IR sensors, but look through clouds.
Many of the instruments also are used to look at the atmosphere, clouds and the amount of radiation that reaches the ocean’s surface. By collecting measurements over time, oceanographers can see patterns that indicate circulation and variability on time scales ranging from days (storms) to decades (global change).
Satellites fill need for ocean measurements
Sea surface temperature over three days, as seen by the all-weather AMSR sensor on the Aqua satellite. One can find equatorial cold tongues, tropical instability waves, eastern boundary current upwelling, the Gulf Stream and other features.
The QuikSCAT scatterometer satellite measures wind speed and direction at the sea surface and provides coverage of 90% of the globe each day.
According to CIOSS director Ted Strub:
“COAS was chosen by NOAA to form CIOSS because of its strength in satellite remote sensing. Mike Freilich helped design the scatterometer; he and Dudley Chelton are international leaders in analysis of scatterometer ocean surface winds. Chelton has led in designing altimeters and using sea surface height measurements of large-scale ocean circulation and eddies. Mark Abbott, Ricardo Letelier, Peter Strutton and Curt Davis are similarly leaders in the design and use of ocean color sensors to explore phytoplankton and ecosystem dynamics. Ted Strub uses combinations of various types of satellite data to look at mesoscale circulation patterns along the boundaries of the ocean.
“However, remote sensing only sees the surface of the ocean. We need subsurface measurements from ships, moorings, drifters and automated underwater vehicles. CIOSS researchers Jack Barth, Mike Kosro and COAS co-workers provide the skill to collect these data, with an emphasis on the large-scale coastal ocean.
“Computer models of ocean circulation bring together information from satellites and instruments beneath the surface.
Why was COAS chosen to establish CIOSS?
Andrew Bennett literally wrote the book on “data assimilation,” which combines data with numerical models. Jim Richman and Bob Miller apply these models to the basin-scale circulation, while an even larger team models the coastal ocean and atmosphere (John Allen, Gary Egbert, Alexandre Kurapov, Roger Samelson, Eric Skyllingstad). Yvette Spitz extends these physical models to include the plankton ecosytem.
“On the atmospheric side, Steve Esbensen teams with Chelton and Freilich to look at interactions of the lower atmosphere and upper-ocean. Jim Coakley examines cloud structure and the transfer of radiation through the atmosphere to the ocean surface. Eric Maloney works on the largest atmospheric scales, considering connections between the tropical Pacific Ocean and the weather over North America.
“All three types of research (remote sensing, at-sea data collection and modeling) are needed to understand the ocean and the atmosphere-ocean interface. The U.S. “Integrated Ocean Observing System” (IOOS) that is planned for the future will incorporate each of these methods to meet societal needs, especially in coastal regions. Because of its expertise and leadership in all of these areas, CIOSS/COAS and its NOAA partners will help design the IOOS system and advise NOAA on future satellite sensors.”
Tracking Harmful Algal Blooms In a harmful algal bloom (HAB) a bloom of harmful algae (certain species) at the coastline causes toxins to accumulate in filter-feeding shellfish, such as mussels, clams, oysters and scallops. To prevent people from eating toxic shellfish, affected beaches are closed. The incidence and persistence of individual HAB events are increasing.
Monitoring programs, however, only detect an event after it has affected coastal communities. Oceanographers work to identify conditions favorable to blooms of toxic species so they are detected before reaching the beaches. They hope to define the optical signatures of harmful species so they can identify and track blooms using satellite data.
Pete Strutton of COAS works with Michelle Wood, a biologist with the University of Oregon, to study HABs in the highly productive area off the Oregon coast. Strutton and Wood will analyze a decade of sea surface temperature, ocean color and domoic acid concentration data off Oregon, looking for satellite-based physical and optical signals that indicate HABs. They will collect data over Heceta Bank southwest of Newport, a possible “incubator region” of the toxic species, and test the ability to detect HAB water masses from satellites.
The researchers also will work with NOAA CoastWatch to develop satellite products that can be disseminated to the scientific and coastal management community. Ultimately, such products could serve as an early-warning system for coastal managers, health officials and commercial and recreational fishers.
A Climatological Atlas of Ocean WindsFrom its orbit onboard the QuikSCAT satellite, the SeaWinds radar scatterometer measures surface winds over 90 percent of the Earth’s oceans every 24 hours. SeaWinds sends pulses of microwave radiation down to the wind-roughened surface and measures the backscatter of the radiation that returns to the satellite. From this data, wind speed and direction can be estimated.
COAS graduate student Craig Risien worked with advisor Dudley Chelton and Mark Hodges of NOAA to develop a five-year climatology of global ocean winds. The climatology is a web-based interactive atlas from which users can retrieve wind statistics, in tabular and graphic form, for a region of interest. The data have been averaged over 50-km regions to form monthly averages for approximately 150,000 grid cells distributed evenly across the global ocean. This provides wind information on many regions of the world ocean that are almost never sampled by ships and buoys.
One useful application is a product for the NOAA Office of Response and Restoration with responsibilities for oil spill responses. The data will also be used by NOAA and the National Weather Service for training at regional marine workshops.
CIOSS scientists track harmful algal blooms (HAB), which cause toxins to accumulate in filter-feeding shellfish, such as mussels.
Pete Strutton
A QuikSCAT display of wind
speed and direction around
the Hawaiian Islands. Each arrow can be
clicked for more details. Warmer
colors indicate faster wind speed.
Mapping Currents in the Coastal Ocean with Radio Waves
COAS is well known for strengths in remote sensing, at-sea data collection and modeling. Besides making use of the expertise of its faculty, CIOSS supports post-doctoral research scientists in this work. This advances scientific understanding and transfers the expertise of one generation to the next.
• Paul Choboter extended a theoretical model proposed by Joseph Pedlosky to explain the alongshore coastal currents during the process of wind-driven upwelling.
• Coastal circulation is also being examined by Martin Saraceno and Byoung-Ju Choi by using satellite altimeter, scatterometer and coastal radar data alone (Saraceno) or by combining these data with more complete computer models of the coastal ocean circulation (Choi).
• Natalie Perlin couples models of the coastal ocean and atmosphere to explore the atmosphere’s affect on the ocean, while post-doc Qingtao Song traces the effect of sea surface temperature changes in the ocean into the atmospheric boundary layer, using atmospheric models.
• Post-doc Hai-Ying Jiao compares and combines scatterometer winds with winds estimated by a new type of satellite using a passive microwave sensor.
• Post-doc Guang Guo has finished a project using satellite data to estimate the solar and infrared radiation at the ocean’s surface. These post-docs are tomorrow’s leaders in remote sensing and modeling.
Post-Docs: Modeling and Observing Coastal Currents and Winds Some satellite sensors
have difficulty using data from the coastal area because the land signal is very strong and contaminates the signal from the water. An alternate technology is provided by high-frequency (HF) radio techniques, which estimate ocean surface currents with high space and time resolution, many kilometers from the coast. Mike Kosro and other COAS researchers have installed HF radar surface current systems along the entire Oregon coast.
Each coastal site consists of two low-power radio antennas; one transmits and one receives. The equipment measures ocean currents using the echoes of radio waves scattered from ocean waves. The received radio waves are shifted in frequency by the effects of ocean currents, allowing estimates of those currents. The system provides hourly-to-daily maps of surface currents out to 100-150 miles from shore.
The circulation of coastal ocean currents can have profound impacts on fisheries, birds, man-made structures, search and rescue operations, and dispersal of pollutants. CIOSS research projects are combining the coastal radar current measurements and the satellite data to examine coastal circulation patterns, in some cases incorporating the data into models of coastal dynamics and circulation.
Map of surface currents off the
Oregon coast. Arrows indicate current speed—
red are the fastest.
The Next Generation of SatellitesOne focus of CIOSS research is to evaluate present and planned satellite systems and models, in partnership with colleagues at NOAA/NESDIS. This includes providing evaluations of plans for changes in the present (POES and GOES) and future (NPOESS and GOES-R) satellite systems. Other activities include work within the IOOS system to understand the needs of research and non-research users for satellite data and products, considering differences in their accuracy, resolution (in time and space), etc.
As an example related to surface winds, CIOSS sponsors research and workshops (two so far) on Ocean Vector Winds (OVW). The goal is to better understand the properties of remotely sensed ocean vector wind fields from different sensors, compared to the needs of operational ocean wind and
wave forecasters. Results from the OVW workshops help CIOSS provide input for future OVW sensors. Similarly, research and workshops sponsored by CIOSS for members of the Coastal Ocean Applications and Science Team (COAST) help design future ocean color sensors through community workshops, field campaigns to collect new data and participation in NOAA-NASA discussions of changes to the NPOESS VIIRS sensor. CIOSS personnel also participate in the NOAA-NASA deliberations concerning future altimeters and microwave SST sensors. Discussion of future sensors lead to considerations of whether the sensors will allow construction of “Climate Data Records,” maintaining consistent quality for past, present and future sensors in order to construct long-time records for detection of climate-related changes in ocean conditions.
CIOSS Influence on the FutureDirector Ted Strub looks at what lies ahead for CIOSS:
“During CIOSS’ first four years, CIOSS Fellows have established an ever-increasing number of partnerships with their NOAA colleagues, within NESDIS and other Line Offices, which help to accomplish common CIOSS and NOAA goals. CIOSS is conducting research that improves satellite products, uses remote sensing fields to better understand processes in the ocean and atmosphere, and helps to plan improved satellite sensors.
“Within the context of the U.S. system of Integrated Ocean Observing Systems (IOOS), CIOSS projects are improving NOAA’s ability to fulfill its role as the “National Backbone” for remote sensing. CIOSS Fellows are also active in the IOOS components for direct ocean
observations and nowcast/forecast models of the coastal ocean. The improved understanding of satellite sensors, remote sensing techniques, modeling capabilities and ocean processes that CIOSS contributes will impact oceanographic research scientists, resource managers and the public for several decades.”
As an undergraduate, Craig Risien attended the University of Cape Town, South Africa, majoring in environmental and geographical science and ocean and atmospheric science. He wrote his honors thesis on satellite oceanography before coming to OSU to continue in that field. As a COAS Marine Resource Management (MRM) graduate student, Craig Risien used satellite wind data to create a climatological atlas of global ocean winds.
Risien chose to come to COAS because his advisor, Dudley Chelton, was familiar with his master’s thesis work and encouraged him to apply. After finishing his degree, Risien expanded the global surface wind climatology, in order to make it easier for ocean
modelers to use the data. The CoastWatch node at Monterey, Calif. will incorporate Craig’s wind atlas into its system. Craig will continue to work at OSU with CIOSS Fellow Jack Barth, helping to design the Oregon Coastal Ocean Observing System.
Ted Strub
Meet Craig Risien
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A snapshot of surface chlorophyll from the SeaWiFS sensor off Oregon in September 1998. The Columbia River is at the upper right.
College of Oceanic and Atmospheric SciencesOregon State UniversityCOAS
College of Oceanic and Atmospheric Sciences104 COAS Administration BuildingOregon State UniversityCorvallis, Oregon 97331-5503
www.coas.oregonstate.eduPhone: (541) 737-3504Fax: (541) 737-2064
