Superstorms Drive Home Need for Sea-monitoring Satellites
SAN FRANCISCO — June 11, New York Mayor Michael Bloomberg called for a $20 billion initiative to erect flood barriers to bolster the city’s defenses against the type of flooding that occurred in October 2012 when Hurricane Sandy produced 2-meter storm surges.
“Hurricane Sandy was a tremendous thunderclap,” said Laury Miller, satellite altimetry chief for the U.S. National Oceanic and Atmospheric Administration (NOAA) in Washington. “It opened everyone’s eyes to the possibility of massive dislocation and emphasized the critical need to plan for future storms.”
Initiatives like the one proposed for New York to mitigate the impact of storms rely heavily on space-based altimeters to aid in forecasting severe weather and monitoring the rising sea levels that can heighten the impact of hurricanes and tropical storms.
In 2015, NOAA, Europe’s Eumetsat meteorological satellite organization, NASA and the French space agency, CNES, plan to launch Jason-3, the fourth satellite in a series of altimetry missions dating back to the 1992 launch of the TOPEX/Poseidon satellite. Like its predecessors, Jason-3 will provide fundamental information to help people understand the conditions they will need to adapt to, Miller said.
For more than 20 years, researchers have used data provided by space-based altimeters to observe sea surface winds, wave conditions and circulation patterns. In the past, those data were used primarily to assist in weather forecasting and ocean navigation. Increasingly, researchers and policymakers are recognizing the important role these satellites play in monitoring sea surface heights.
TOPEX/Poseidon and its successors, Jason-1, launched in 2001, and Jason-2, launched in 2008, have given scientists a continuous record of rising sea levels caused by melting glaciers and ice sheets as well as thermal swelling occurring as the oceans absorb heat trapped in Earth’s atmosphere by the increasing concentration of greenhouse gases.
The Jason-3 mission, slated to launch in March 2015 on a Space Exploration Technologies Falcon 9 rocket from Vandenberg Air Force Base, Calif., is designed to continue that data record.
“By watching this steady rise, these missions are charting the influence humans are having on the planet’s climate,” said Joshua Willis, Jason-3 project scientist at the NASA Jet Propulsion Laboratory in Pasadena, Calif. “This is our most sensitive measurement to show how human beings are changing the climate.”
In May, the Jet Propulsion Laboratory shipped to CNES an advanced microwave radiometer, satellite laser ranging reflector, GPS receiver and associated ground equipment. In June, CNES prime contractorbegan integrating the NASA instruments with its own Poseidon-3B radar altimeter and Proteus spacecraft bus.
Jason-3 is designed to measure variations in sea levels with an accuracy of at least 3.3 centimeters. In addition, the mission is designed to offer researchers and policymakers a global mean sea-level measurement with an accuracy of 0.4 millimeters, Miller said.
To achieve that level of precision, the spacecraft relies on the Poseidon-3 altimeter and three systems designed to pinpoint its own position: the satellite laser ranging reflector, a GPS receiver and a CNES microwave tracking system, called Doppler Orbitography and Radiopositioning Integrated by Satellite. Poseidon-3 measures the amount of time it takes C- and Ku-band radar waves to bounce off the water’s surface and return to the spacecraft antenna.
The agencies cooperating on the Jason-3 program also joined forces on Jason-2, the Ocean Surface Topography Mission. The two satellites and their instruments are nearly identical because researchers are seeking a seamless data record. After launch, the Jason-3 spacecraft is expected to move into an orbit 60 seconds behind Jason-2, which resides in low Earth orbit at an altitude of 1,336 kilometers inclined at 66 degrees relative to the equator.
That plan requires the two missions to overlap for at least six months, a prospect that appears likely if the Jason-3 mission launches on schedule because Jason-2 and its instruments remain “in excellent health,” Miller said. In addition, Jason-2’s predecessors have shown remarkable durability. Although the missions were designed to operate for three to five years, TOPEX/Poseidon gathered data for 13 years and Jason-1 continues to function after more than 11 years in space.
Initially, Jason-3 was scheduled to launch in 2013, but the program slowed down due to funding issues. The U.S. Commerce Department, which oversees NOAA, asked Congress to provide $33 million for the Jason-3 program in 2011, $53 million for the program in 2012 and $30 million in 2013. Congress appropriated slightly less than $20 million for Jason-3 in each of those years. The Commerce Department is seeking $37 million for Jason-3 in 2014.