WASHINGTON — The U.S. National Oceanic and Atmospheric Administration (NOAA) must implement several measures related to operations of a new polar-orbiting weather satellite to ensure continuity of a 14-year record of space-based ocean color observations, the National Research Council (NRC) said in a July 7 report.
No single nation or agency can bear the burden of developing the numerous space-based sensors required for ocean color measurements in the future, and thus increased international collaboration is essential, according to the NRC’s report, “Assessing the Requirements for Sustained Ocean Color Research and Operations.”
Scientists view ocean color data as an essential measurement for studying the health of the world’s aquatic ecosystems. The levels of phytoplankton biomass in the oceans is related to a number of key climate variables, including the amount of man-made carbon dioxide that the oceans have absorbed, the NRC report said.
“Monitoring the health of the ocean and its productivity is critical to understanding and managing the ocean’s essential functions and living resources,” the report said. “Phytoplankton are microscopic organisms responsible for most of the primary production in the ocean, are ubiquitous in the surface ocean, and form the base of the marine food chain. Tracking changes in phytoplankton in the vast expanse of ocean requires a perspective that can be gained only from satellite measurements.”
The first measurements of ocean color data from space were collected by NASA’s Coastal Zone Color Scanner that launched in 1978. For its report, the NRC considered NASA’s Sea-viewing Wide Field-of-view Sensor (SeaWiFS) that operated from 1997 to December 2010 as the benchmark for minimum capability that must be retained.
With SeaWiFS no longer operational, NASA’s Aqua climate satellite carries the only active and adequate U.S. ocean color sensor, the Moderate Resolution Imaging Spectroradiometer. Aqua has been on orbit since 2002 and is well beyond its design life. Because its sensor experienced degradation and was relying on SeaWiFS to calibrate its ocean color data, Aqua’s ocean color data will not be reliable for much longer, the report said.
The European Space Agency’s Medium-Resolution Imaging Spectroradiometer currently provides acceptable ocean color data but is also well beyond its design life. That satellite may not last until the follow-on Ocean Land Colour Instrument aboard the Sentinel-3A spacecraft is launched in 2013, the report said. India’s Ocean Color Monitor sensor produces high-quality data but only for the Indian Ocean region.
NOAA’s next ocean color instrument is the Visible Infrared Imaging Radiospectrometer Suite (VIIRS) that will fly on the National Polar-orbiting Operational Environmental Satellite Preparatory Project satellite set for launch in October. The VIIRS instrument, built by Raytheon Space and Airborne Systems of El Segundo, Calif., had a long and troubled development history and is not certain to deliver high-quality ocean color data because of a manufacturing error in one of its optical components, the report said.
The NRC was enthused by recent testing that showed a software fix overcame part of the hardware deficiency, but nonetheless it is “unlikely that this mission will provide data of sufficient quality to continue the ocean color climate data record,” the report said. The NRC outlined six steps that NOAA must take to continue the data record that are not currently planned for. The agency must:
- Implement spacecraft maneuvers that include monthly looks at the Moon to quantify sensor stability.
- Form a calibration team that would collaborate with mission personnel to evaluate sensor performance and anomalies.
- Calibrate the sensor on orbit with a technique that uses artificial or natural sites on the Earth’s surface and atmospheric models.
- Engage experts in the field to revisit algorithms and products to ensure consistency with legacy instruments.
- Form a data product team to oversee validation efforts and reprocessing of data.
- Provide the capability to reprocess mission data multiple times to incorporate improvements in calibration and correct errors.
For the future, the report recommended NOAA resolve the hardware problem on the next VIIRS instrument slated to fly in 2016.
The NRC’s 2007 Earth science decadal survey outlined three NASA missions that could potentially provide scientists with many advanced ocean color measurements. The Pre-Aerosol, Clouds and Ecosystem mission is planned for launch around 2020, while there are no firm plans for the Geostationary Coastal and Air Pollution Events mission or the Hyperspectral Infrared Imagery mission. Even if those three missions are completed, the United States will still not be able to meet the ocean color data needs of all users. As such, NOAA and NASA should increase efforts to establish long-term data exchange policies with foreign space agencies, the report said.