Assuming no changes in the mission’s schedule, SpaceX’s cargo-carrying capsule known as “Dragon” will port the instrument to the ISS by Monday, when a robotic arm will reach out and grab it.
The instrument promises to deliver ocean wind data unavailable to scientists through other means.
“Scatterometers provide a measure of near-surface wind speed and direction, via pulses of microwave energy, which can “see” through thick cloud layers,” says Jeff Halverson, Capital Weather Gang’s severe weather expert, who has participated in many hurricane missions for NASA. “That’s important, because these remote sensors can detect low-level, vertical circulations beneath developing tropical storms. The only other way to do this is to fly aircraft into these disturbances – many of which are out of reach from air bases, and there are not enough planes and crews to do this around the clock.”
There are currently two other scatterometers in space that take these measurements, but they cross the equator at the same times each day. “The space station’s orbit will take ISS-RapidScat across almost the entire globe between the Arctic and Antarctic circles at different times of the day,” NASA says. “This will give scientists data they need to study how ocean winds grow and change throughout the day.”
Brian McNoldy, Capital Weather Gang’s tropical weather expert, adds that the existing scatterometers sense winds across narrow swaths, limiting their coverage. “The design of the ISS-RapidScat instrument provides much wider swaths of data, reducing the chance than an overpass will ‘miss’ a hurricane,” McNoldy says.
The ISS-RapidScat data may prove extremely helpful in identifying where tropical weather systems are developing.
“Scatterometers can provide early clues that a tropical cloud disturbance is organizing a larger wind field, and even precisely locate the center of circulation,” Halverson says. “This helps improve the accuracy of track and intensity forecasts, which rely on an accurate assessment of the initial vortex size, intensity and center location.”
The ISS-RapidScat is a replacement for QuikScat, a similar instrument which failed in November, 2009. “The loss of QuikScat after 10 years of operation was a big loss to the hurricane community,” McNoldy says. “Wind vectors were collected over most of the global oceans twice daily, benefiting computer models as well as humans who analyze storms over the ocean.”
QuikScat was at the center of a controversy in 2007 at the National Hurricane Center, when then-director Bill Proenza lobbied for replacing the aging instrument. “[Proenza] unfortunately made claims about the usefulness of QuikScat for improving hurricane track forecasts that were not supported by scientific research,” writes Wunderground meteorologist Jeff Masters. Nearly half of Proenza’s staff revolted, signing a statement urging his dismissal. He was removed from his position and re-assigned within the National Weather Service. (Proenza was fired from the National Weather Service in 2013, for unrelated matters.)
“[Scatterometers] are not perfect; snapshots are not always readily available, and wind intensity estimate tends to suffer in areas of heavy rain,” says Halverson. “But the benefits of scatterometer wind measurements far outweigh these technical issues.”
When QuikScat stopped operating in 2009, NASA was challenged to “quickly and cost-effectively” develop a replacement. “NASA’s Jet Propulsion Laboratory and the agency’s station program came up with a solution that uses the framework of the International Space Station and reuses hardware originally built to test parts of QuikScat to create an instrument for a fraction of the cost and time it would take to build and launch a new satellite,” NASA says.