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The case for a new QuikSCAT satellite

By: Dr. Jeff Masters, 2:56 PM GMT on March 26, 2009

The QuikSCAT satellite, launched in 1999, provides crucial measurements of surface wind speed and direction over Earth's oceans twice per day. Forecasters world-wide have come to rely on data from QuikSCAT to issue timely warnings and make accurate forecasts of tropical and extratropical storms, wave heights, sea ice, aviation weather, iceberg movement, coral bleaching events, and El Niño. But QuikSCAT is ailing. Originally expected to last just 2-3 years, QuikSCAT is now entering its tenth year, and is definitely showing its age. The spacecraft's primary transmitter, power control unit, and battery have all failed over the years. The loss of the spares for any of these components will mean the end of QuikSCAT--a satellite that likely provides hundreds of millions of dollars of benefit each year to the public. Just one example of QuikSCAT's value, taken from a recent study (H. Kite-Powell, 2008) wind data from QuikSCAT and the resulting improvements to warning and forecast services save the container and bulk shipping industry $135 million annually by reducing their exposure to hurricane force wind conditions in non-tropical storms by 44% over the North Pacific and North Atlantic. Loss of QuikSCAT would result in a 80 - 90% loss in detection capability for hurricane-force conditions in extratropical cyclones.

Figure 1. NASA's QuikSCAT satellite, launched in 1999. Image credit: NASA.

Alternatives to QuikSCAT
Two valuable alternatives to QuikSCAT are available, but neither can come close to making up for the loss of QuikSCAT. The Windsat instrument aboard the Coriolis satellite (launched in 2003) measures wind speed and wind direction using a different technique. Evaluation of these data at NHC and NOAA's Ocean Prediction Center (OPC) shown the winds to be unreliable in and around the storm environment. There's also the European ASCAT satellite, launched in 2007. Like QuikSCAT, ASCAT can measure global wind speed and direction twice per day. However, the data is available at 25 km resolution (two times coarser than the 12.5 km QuikSCAT), and ASCAT covers only 60% of the area covered by QuikSCAT in the same time period. QuikSCAT sees a swath of ocean 1800 km wide, while ASCAT sees two parallel swaths 550 km wide, separated by a 720 km gap. I find it frustrating to use ASCAT to monitor tropical storms, since the passes miss the center of circulation of a storm of interest more than half the time. On the plus side, ASCAT has the advantage that the data is not adversely affected by rain, unlike QuikSCAT.

The need for a new QuikSCAT
Since the loss of QuikSCAT would be such a significant blow, and the alternative sources of ocean surface wind data are of significantly lower quality, NOAA has been pushing for a QuikSCAT replacement for years. Former National Hurricane Center director Bill Proenza laudably made a big push in 2007 for a new QuikSCAT satellite. Unfortunately, he made claims about the usefulness of QuikSCAT for improving hurricane track forecasts that were not supported by scientific research, an error that may have ultimately led to his downfall. While there is evidence that QuikSCAT data may improve hurricane track forecasts of some computer models, NHC uses many models to make hurricane track forecasts, and some of these models are not helped by QuikSCAT data. For example, a 2009 model study by Dr. Jim Goerss of the Naval Research Lab found that QuikSCAT winds made no improvement to hurricane track forecasts of the NOGAPS model, one of the key models used by NHC to predict hurricane tracks. QuikSCAT is extremely valuable for many other aspects of hurricane forecasting, though. It provides early detection of surface circulations in developing tropical depressions, and for defining gale (34 kts) and storm-force (50 kts) wind radii. The information on wind radii from QuikSCAT is especially important for tropical storms and hurricanes outside the range of aircraft reconnaissance flights conducted in the Atlantic and Eastern Pacific basins, and for the regions where there are no reconnaissance flights (Central Pacific, Western Pacific, and Indian Ocean). Accurate wind radii are critical to the National Hurricane Center (NHC), Central Pacific Hurricane Center (CPHC), and Guam Weather Forecast Office (WFO) watch and warning process, since they affect the size of tropical storm and hurricane watch and warning areas. Between 2003 and 2006, QuikSCAT data were used at NHC 17% of the time to determine the wind radii, 21% of the time for center fixing, and 62% of the time for storm intensity estimates.

Figure 2. Comparison of simulated wind measurements for the Alaska coast, including Juneau and Sitka. Left: the next-generation QuikSCAT XOVWM satellite accurately retrieves winds in the Inside Passage, including a jet of tropical-storm force winds (yellow colors) along one channel. Right: the current QuikSCAT instrument cannot cover the coast or Inside Passage due to its limited resolution, and underestimates the area covered by winds of 42+ knots by a factor of 2 - 3 (orange colors). There is heavy shipping traffic in the areas missed by QuikSCAT coverage. Image credit: NASA QuikSCAT Follow-on Study.

The best solution: a next-generation QuikSCAT
QuikSCAT is 15-year old technology, and has significant limitations in what it can do. The needs of the weather forecasting community would best be served by launching a next-generation QuikSCAT satellite, called the Extended Ocean Vector Winds Mission (XOVWM). This is the solution recommended by the National Research Council in their decadal survey, 2007: Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, page 456.

Some of the limitations of the current QuikSCAT that would be solved by a next-generation QuikSCAT:

1) QuikSCAT has limited spatial resolution, and cannot "see" winds within 20-30 km of the coast. This is where the bulk of ship traffic and fishing occurs. The proposed next-generation QuikSCAT XOVWM satellite would be able to "see" winds within 5 km of the coast.

2) QuikSCAT cannot measure winds greater than approximately 65 mph (a Category 1 hurricane has winds of 74 mph or greater). A next-generation QuikSCAT XOVWM satellite would be able to measure winds up to Category 5 hurricane strength (>155 mph).

3) QuikSCAT cannot "see" through heavy rain. A next-generation QuikSCAT XOVWM satellite would.

Obviously, all of these capabilities would be a huge boost for determining the size and strength of a hurricane, and reduce the amount of uncertainty in hurricane forecasts. The cost of a next-generation QuikSCAT XOVWM satellite was estimated by NASA in a 2008 study to be about $500 million. Ideally, a constellation of two satellites would be launched, to prevent the gaps in coverage that occur with the current single satellite. A two-satellite system was estimated to cost $723 million, as estimated in the 2008 Jet Propulsion Laboratory study, QuikSCAT Follow-on Mission Concept Study (JPL Publication 08-18, April 2008)

The second best solution: a QuikSCAT replacement
A second, cheaper solution that is being considered is to launch a replacement QuikSCAT satellite that has similar capabilities to the current one. NOAA and NASA are exploring a partnership with the Japanese Space Agency (JAXA) to fly a QuikSCAT instrument on their GCOM-Water Cycle satellite, scheduled to launch in 2016. Funding must begin in 2010 in order to meet this launch deadline. The proposed QuikSCAT replacement would be able to measure winds as high as 100 mph (Category 2 hurricane strength), and have improved ability to measure winds in heavy rain. The new satellite would have a 20% improvement in spatial resolution. The cost would be less than that of a next-generation QuikSCAT, since the rocket and and satellite are already paid for. However, there are additional costs involved in adapting QuikSCAT to the Japanese engineering requirements. The final costs of such a replacement QuikSCAT have not been determined yet, but would probably be several hundred million dollars.

This is the type of cause that it is important for we as citizens to lobby Congress for. Write your Senators and Representatives! The earliest a new QuikSCAT could get launched is 2015, and the current satellite is probably going to die well before then. Feel free to use the information above, or come up with your own. Thanks!

Contact info for your House Representative
Contact your Senator

2007 NOAA QuikSCAT user impact study:

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.