WASHINGTON — The U.S. National-Geospatial Intelligence Agency (NGA) on Nov. 19 announced plans to continue buying ocean color data collected by GeoEye’s aging OrbView-2 imaging satellite, which is expected to remain in service perhaps another three years following  a successful orbit raising in July.

OrbView-2 is a commercial remote sensing satellite that carries a payload called the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), which detects slight changes to land vegetation and the amount and types of plankton in the oceans. Under a first-of-its-kind partnership, the satellite was built and launched by Dulles, Va.-based GeoEye — then a division of Orbital Sciences Corp. — in exchange for a contract to sell the data to NASA for five years.

The NGA for four years has been buying SeaWiFS data to incorporate into mapping products distributed to many military and civil government agencies. Maps provided to the U.S. Navy, for example, rely on SeaWiFS data to show the amount of sediment in coastal waters. The NGA plans to contract on a sole-source basis with GeoEye to continue providing these data for one year, with options that could extend the contract two additional years, according to a Nov. 19 posting on the Federal Business Opportunities website. The annual value of the contract is expected to be about $250,000 to $300,000, NGA spokesman Timothy Taylor said in a Nov. 26 e-mail.

OrbView-2 was launched in 1997 and is the oldest of GeoEye’s three active imaging satellites. Some 300 government, academic and commercial customers around the world use the satellite’s low-resolution, wide-swath imagery. GeoEye in recent years has considered ending OrbView-2 operations because it contributes  little to the company’s earnings and glitches have forced the spacecraft to go into a safe-hold mode numerous times, according to filings with the U.S. Securities and Exchange Commission.

Earlier this year GeoEye decided to extend operations of OrbView-2 and crafted a plan to modify its orbit. Originally placed into a 705-kilometer near-polar orbit, OrbView-2 had drifted down to an altitude of 699 kilometers, said Greg Hammann, director of OrbView-2 operations and engineering. The time of day that the satellite was crossing the equator had also been getting progressively later over the years and was in danger of falling outside the acceptable limits for data collection, Hammann said in a Nov. 23 interview.

Through a series of thruster firings the satellite was successfully boosted to an altitude of 781.5 kilometers and its inclination was modified to cross the equator at the proper time, Hammann said. OrbView-2 is expected to drift down slightly from that altitude and settle into a stable orbit.

OrbView-2 is healthy, but the 13-year-old satellite has been relying on backup systems since around 2005.

“We’re on a couple of redundant systems now, but it took us eight years to get into those redundant systems,” Hammann said. “We fully expect another three years of operations and maybe more. Given that it was a five-year operation, every day is a gift to the science community.”

Since OrbView-2 was launched, several operational ocean color instruments have been put on orbit. NASA’s Terra and Aqua satellites, launched in 1999 and 2002, respectively, each produce ocean color data with their Moderate Resolution Imaging Spectroradiometer instruments, which relied on SeaWiFS data for calibration. The satellites are currently expected to last until at least 2017, NASA spokesman Steve Cole said Nov. 23. The European Space Agency’s Envisat spacecraft launched in 2002 also has an ocean color capability with its Medium Resolution Imaging Spectrometer.

The next U.S. instrument capable of collecting ocean color data is the first Visible Infrared Imaging Radiometer Suite (VIIRS) that will fly on a civilian polar-orbiting weather satellite planned for launch in late 2011. The Raytheon-built VIIRS instrument had a long and troubled development history, and the first flight unit will not be able to produce the quality of ocean color data that was originally sought. Scientists are hoping OrbView-2 lasts long enough to be able to calibrate VIIRS as it did for the Terra and Aqua sensors, Hammann said.

“NASA and [the Naval Research Laboratory], the people that actually use the data, consider SeaWiFS the gold standard in ocean color information,” he said.

“The [VIIRS] specifications to determine chlorophyll concentration and the geophysical parameters for ocean color are less [precise] than SeaWiFS, and they are planning to use SeaWiFS to calibrate VIIRS similar to how it is used to calibrate the [Moderate Resolution Imaging Spectroradiometers].”