No Quick Replacement for Loss of Wind-monitoring Satellite

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SAN FRANCISCO — One year after the demise of QuikScat, the NASA satellite that provided detailed data on the speed and direction of winds over the world’s oceans, the National Oceanic and Atmospheric Administration (NOAA) is working with the U.S. space agency and international partners to develop a new space-based instrument to take its place.

“There are impacts from the loss of QuikScat,” said Paul Chang, leader of the NOAA satellite ocean winds science team. While many officials lamented the loss of QuikScat because it was useful in hurricane forecasts, the satellite’s loss has had an even greater impact on the Ocean Prediction Center, the counterpart to the National Hurricane Center that is responsible for issuing marine warnings and forecasts, he said.

“Any National Weather Service office that has coastal responsibilities around the continental United States or its territories has felt the loss of QuikScat,” he said. Meteorologists in those offices had come to depend on QuikScat “day in and day out” because it offered high-quality data covering wide swaths of the ocean, he added.

QuikScat, built by Ball Aerospace & Technologies Corp. of Boulder, Colo., provided nearly instantaneous data on wind speed and direction over 90 percent of the Earth’s oceans with its SeaWinds scatterometer, an instrument that sent pulses of microwave energy toward the Earth’s surface and measured reflected energy. The satellite, launched in June 1999 as a quick replacement for a NASA scatterometer that failed in orbit two years earlier, was designed to last three years. However, its instrument worked for more than a decade, ceasing only when the bearings in the motor of its spinning antenna wore out on Nov. 23, 2009.

In its wake, NOAA is relying on data from the Advanced Scatterometer, built by Germany’s Dornier Satellitensysteme GmbH, flying on the Metop-A satellite launched in 2006 by the European Space Agency and the European Organization for the Exploitation of Meteorological Satellites. That instrument provides useful data on wind speed and direction, but does not cover wide areas as well as QuikScat did, nor is it as sensitive to higher winds, Chang said.

NOAA officials hope to enhance weather forecasts by obtaining data from the Scanning Scatterometer launched in October 2009 aboard the Indian Space Research Organisation’s OceanSat-2 satellite. “NOAA and NASA have been working with them for the past year to see whether we can get data to mitigate the loss of QuikScat,” Chang said. “That’s an ongoing process.”

In addition, NOAA is working with NASA’s Jet Propulsion Laboratory in Pasadena, Calif., to develop a new instrument, a Dual Frequency Scatterometer designed to obtain data in both C-band and Ku-band. “QuikScat was Ku-band and Advanced Scatterometer is C-band,” Chang said. “There are strengths to both of those frequencies. By using them together, we are aiming for finer spatial resolution and improved ability to measure the highest winds in the presence of rain.”

Discussions are under way between NASA, NOAA and the Japan Aerospace Exploration Agency to include the Dual Frequency Scatterometer on Japan’s Global Change Observation Mission W2 satellite, which is scheduled for launch around 2016, Chang said. If those talks are successful, international weather and climate forecasts would benefit from the pairing of the Dual Frequency Scatterometer on the same platform as the passive microwave sensor Japan plans to fly on Global Change Observation Mission W2 as a successor to the Advanced Microwave Scanning Radiometer currently operating on NASA’s Aqua Earth observing satellite. Coupling the two will offer more detailed data than either instrument could provide individually, Chang said.

Initially, NOAA officials explored the idea of launching their own satellite with an advanced scatterometer as proposed in 2007 by the National Research Council’s Earth sciences decadal survey. Concept studies for that mission, known as Extended Ocean Vector Wind Mission, were led by the Jet Propulsion Laboratory. Those studies produced improvements in sensor designs. However, NOAA officials concluded the mission would be unaffordable. “It was cost prohibitive for NOAA to go it alone, so we started looking at international partnerships,” Chang said.

The decadal survey also called for two NASA missions to support weather forecasting, climate understanding and hurricane monitoring, Precision and All-Weather Temperature and Humidity, a microwave array spectrometer mission, and Three Dimensional Tropospheric Winds, a space-based doppler lidar. NASA officials continue to pursue research on those missions that were included in the third tier of the decadal survey, a listing of missions expected to launch between 2016 and 2020.

Since the loss of QuikScat, NASA has focused on airborne efforts to study the formation of tropical storms and study which storms become hurricanes. In late September, the space agency completed an intensive, six-week research mission called Genesis and Rapid Intensification Processes (GRIP) that relied on remote sensing instruments carried in piloted aircraft and the space agency’s Global Hawk unmanned airborne system to fly repeatedly over and around hurricanes in the Atlantic Ocean.

NASA and NOAA satellites operating in low Earth orbit obtain brief glimpses of the eyes of hurricanes as they pass over, providing useful information on the temperature at the eye of a hurricane compared with the temperature of surrounding air, said Ramesh Kakar, weather focus area leader for NASA Science Mission Directorate programs. GRIP is providing data that are enhancing scientific understanding of hurricanes because the Global Hawk was able to continuously monitor hurricanes, he added.

During one flight, the Global Hawk made 20 passes over Hurricane Karl as it formed, intensified and fizzled out, Kakar said. “We have that information now for the first time,” he said. Those data will help to improve computer models used to forecast which storms will become hurricanes.

NASA plans to continue airborne exploration of hurricanes with a venture-class mission, the Hurricane and Severe Storm Sentinel, Kakar said. That mission was one of five selected in May as part of the NASA Earth Science Pathfinder program. The Hurricane mission will once again employ NASA’s Global Hawk to fly over storms in the Atlantic Ocean during the 2012 to 2014 hurricane seasons, gathering data designed to improve prediction of the intensity of hurricanes.

Further improvements of those models will come from future instruments being developed to fly on geostationary satellites, Kakar said. “The real advantage will come when we have a microwave instrument operating in geosynchronous orbit.” That is the type of instrument planned for the Precision and All-Weather Temperature and Humidity mission.