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Wednesday, February 8, 2023

Tiny Satellites Could Help Warn of the Next Big Hurricane

There have been an unprecedented number of newsworthy hurricanes in recent years—from Hurricane Maria, which dealt at least $43 billion in damage to Puerto Rico’s infrastructure, to last year’s Iota, the strongest hurricane ever to hit Nicaragua, which displaced more than 62,000 people and devastated the country’s harvest. Twelve made landfall in the United States in 2020, breaking the previous record of 9 in a single year. And hurricanes, while the most famous, are actually the least frequent of a broader category of storms called tropical cyclones, which are becoming more violent as the climate warms. So it’s more critical than ever that meteorologists accurately forecast them and send out warnings before extreme events catch people off guard.

That’s the thinking behind Tropics, a first-of-its-kind nanosatellite project expected to launch its first qualification unit on Monday from Cape Canaveral aboard a Falcon 9 rocket. The constellation will ultimately consist of 7 small satellites that will monitor Earth’s tropical zone, which spans about 40 degrees of latitude to the north and south of the equator.

Cyclones have long been one of the most difficult weather phenomena to forecast, and only a few centers around the globe focus on them. The main challenges are nailing down the precise track the storm will take, how intense it will be, and—crucially—where and when it will make landfall. Geostationary satellites give meteorologists a 118-million-foot view, but their effectiveness stops at the cloud tops. They only provide visible and infrared satellite images, which can’t pierce the cloud cover. If you want to “see” below it to collect critical data about the interior of the storm and its motion, temperature, and moisture content, you need the added capabilities of a polar orbiting satellite.

Polar orbiters circle Earth from north to south, taking imagery from all longitudes as the planet rotates. They orbit much lower than their geostationary counterparts, at about 512 miles (2.7 million feet) above the surface. This allows them to gather data in the microwave range, providing a picture of what's going on within a storm. But it takes them 12 hours to complete a full trip around the globe, so by the time forecasters get a second look at a particular storm, what started as a tropical depression over the mid-Atlantic may have progressed to a tropical storm as it nears the Caribbean. That creates a slowdown at a crucial time, because every data point a forecaster has could be a critical piece of the puzzle, allowing them to put together a more accurate picture of the approaching storm.

The Tropics satellite constellation will reduce this lag, offering a new, detailed look at each 16- to 24-kilometer region in the lower latitudes every 30 to 40 minutes. “You’re essentially always getting a new satellite flying over your storm and making a new fresh measurement, capturing all the dynamics and seeing what’s changing, and the temperature and the moisture fields and the precipitation and the rain bands,” says Bill Blackwell, the project’s principal investigator.

To achieve this, the nanosatellites must be launched into a very particular orbital configuration. In early 2022, two units at a time will be sent up aboard three separate rocket rideshares facilitated by the startup launch provider Astra. Each pair of satellites will share an orbit at a slight angle to the equator—30 degrees—on the opposite side of the globe from one another but following the same trajectory. When all three pairs are in orbit, they’ll crisscross the equator at different points, like the movements of three wobbly tops. This unique configuration of pairs of satellites tracing staggered paths around the globe will allow for more frequent coverage of any one spot in the tropical zone. (The test unit will also keep orbiting as the seventh member of the team, but will mainly be used for research and experiments, and perhaps extra support over storms as needed.)

Each unit is fitted with a microwave radiometer, so researchers and forecasters will be able to see phenomena not visible to the naked eye, like water vapor and temperature information. Once the data is transmitted back to Earth, it will be linked directly to the National Weather Service and National Hurricane Center and fed into numerical weather prediction models.

For tropical cyclones, forecasters focus on the storm’s minimum pressure and maximum winds, says Tropics project scientist Scott Braun. These key variables help define the intensity of the storm, and having more real-time data could make the predictions of these models more accurate. Continuous data for the storm’s intensity, he says, “will be useful for understanding things like rapid intensification and weakening, and how that connects to the evolution of precipitation.”

A handful of researchers with NOAA have already tested how effective this extra data could be. In a paper to be published in the American Meteorological Society’s Monthly Weather Review (and already online), a team did a virtual pre-test of the new system. “You basically take a computer simulation of a tropical cyclone, and then you sample from that simulation the data that you would expect to get from your new observing system,” says Robert Rogers, a research meteorologist at NOAA’s Hurricane Research Division in Miami and a coauthor on the paper. “Ideally, you see an improvement in your forecast.”

Rogers’ team found that, aided by a new, regular source of data, the forecast of the tropical cyclone’s track improved by 15 percent. He estimates the intensity prediction got an accuracy boost of about 10 percent, as well. They also found a consistent improvement in temperature and wind forecasts up to five days out, and more accurate humidity forecasts up to 36 hours out.

While larger weather satellites, like the polar orbiter JPSS-1, offer a broader range of coverage and some improved resolution at lower wavelengths, they’re costly undertakings, often totaling billions of dollars. Because the nanosatellites are small, with each weighing under 5.4 kilograms, the cost to develop Tropics totaled $30.2 million, plus another $7.95 million to fund the three launches required to put them in orbit.

Blackwell says smaller satellites also have a much shorter development timeline. NASA selected the Tropics proposal for full funding in 2016, and future nanosats building off of this model could be completed in as little as a year. “It takes 10 years to build one of these big huge weather satellites, so what that means is the technology you’re flying is 15 years old. By the time you finally launch it, you’re launching the equivalent of the Betamax of weather forecasting,” Blackwell says.

The qualification unit is expected to start providing radiometer data within a few weeks. If all goes as planned, the Hurricane Research Division will be able to test out the unit over the North Atlantic this summer. To calibrate and verify the satellite data, they may also conduct an experiment aboard a Hurricane Hunter aircraft, which will release a dropsonde—similar to a weather balloon that can take real-time measurements—into the storm.

Rogers says rapidly intensifying hurricanes can spell trouble for coastal towns and mean a long few days at the National Hurricane Center as the staff tries to assess potential threats and put out warnings. “That's kind of the nightmare scenario,” he says. “Any kind of information we can get, as quickly as possible, to know that things are changing rapidly can help us.”

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