Jason-3 satellite to track rising sea levels, global weather
After several delays throughout 2015, the Jason-3 satellite is now ready to take its place as the latest instrument deployed to track the changing surface height of Earth’s oceans.
A joint effort between NASA, the National Oceanic and Atmospheric Administration (NOAA), the European EUMETSAT and the French CNES organizations, Jason-3 will use the high-precision Poseidon-3B radar altimeter to observe the topography and the height of our planet’s ice-free oceans over time.
The topography of the ocean surface—that is, its own hills and valleys—affects the way the waters transfer heat around the planet. According to Dr. Joshua Willis, project scientist for Jason-3, the seas capture more than 90 percent of the heat that gets trapped by greenhouse gases. By monitoring ocean topography, scientists can gain necessary information about circulation patterns in the ocean and their effect on global climate.
Sea surface height is also an important data point in the study of global climate change. Since missions of this type began with Topex/Poseidon-Jason in 1992, the global sea level has risen about 3 millimeters per year, for a total of 70 millimeters (2.8 inches) over 23 years, according to a news release posted on the NOAA website.
“The rate of sea-level rise is an important indicator of climate change happening around the world,” said Laury Miller, NOAA’s Jason-3 program scientist and chief of NOAA’s Laboratory for Satellite Altimetry, in the release. “We are already seeing significant impacts on coastal regions globally, including more frequent flooding events along the coastal United States.”
Besides long-term observations, these satellite missions have short-term applications in forecasting weather patterns—most notably hurricanes. NOAA uses the altimeter data to look for the kinds of ocean conditions that affect tropical cyclone strength. Specifically, it’s helpful to look for heat along the likely track for the storm, as ocean heat contributes to storm intensity.
“The ocean heat content from satellite altimeters can reduce the error of NOAA’s hurricane intensity forecast models by as much as 20 percent in some instances,” Miller said in the same news release.
Additionally, the data from Jason-3 is useful for forecasting surface waves, tides, currents and El Niño events.
Besides the radar altimeter, the satellite is equipped with the Advanced Microwave Radiometer (AMR), which NASA developed. The AMR is used to measure and, therefore, correct for radar travel time delay. The instrument measures radiation from Earth’s surface, which is then used to determine water vapor and liquid water content in the atmosphere, and from that data, time corrections can be applied to the altimeter.
Jason-3 also carries a GPS receiver, a Laser Retroreflector Array (LRA), and the French system DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). These three instruments will be used to precisely determine the orbit of the spacecraft. To ensure the sea level change data is accurate, the satellite’s orbit height must be known to within 0.4 inches (one centimeter), according to NOAA.
The satellite, built around a CNES/Thales Alenia Space Proteus bus, will take the same orbit as its predecessors. At about 830 miles high (1,336 kilometers), Jason-3 will have to endure fewer interactions with Earth’s atmosphere and gravity field, and with an orbit inclination of 66 degrees north and south, the spacecraft will be able to scout the vast majority of the planet’s oceans.
This orbit “is optimized to study large-scale ocean variability and to provide coverage of 90 percent of the world’s oceans over a ten-day cycle,” according to the Aviso-CNES website. To be precise, the orbit repeats every 9.9156 days. It’s a prograde orbit rather than a Sun-synchronous one, which “avoids aliasing of different tide components at the same frequency,” according to Aviso-CNES.
With launches postponed from March, July and December 2015, Jason-3 is currently scheduled to launch aboard a SpaceX Falcon 9 v1.1 rocket on Jan. 17 at 10:42 a.m. PST (18:42 GMT). Its launch site is Space Launch Complex (SLC) 4 at Vandenberg Air Force Base in California.
The first in this satellite series, Topex/Poseidon, was launched on Aug. 10, 1992, as a joint effort between NASA and CNES. Though it was built for a five-year mission, it operated until January 2006, when the satellite lost its ability to maneuver. At that point, according to NASA, data from the satellite had been used as the subject of “more than 2,100 research publications”.
Its successor was Jason-1, named for the Jason of Greek mythology. Jason-1 was launched on Dec. 7, 2001, and was a joint effort between NASA and CNES. Jason-1 was deactivated and decommissioned in July of 2013.
The follow-on satellite Jason-2, perhaps better known as the Ocean Surface Topography Mission (OSTM), was launched on June 20, 2008. Like Jason-3, OSTM was a joint project between NASA, NOAA, EUMETSAT, and CNES. The spacecraft is still operational and has provided images of the significant El Niño that is currently in progress.
Furthermore, according to a report on the Pasadena Star-News, Jason-2 will operate in tandem with Jason-3 for some time—six months, says NOAA—for calibration purposes, to ensure Jason-3’s data is accurate and reliable. This same step was taken when Jason-2 was launched; it operated closely with Jason-1 to show that the data gathered was the same with both. Once the six months are over, OSTM/Jason-2 will be moved to a different orbit in order to cover more ground.
What’s next after Jason-3? According to NOAA, the partners who contributed to the mission are considering developing new, better radar altimeter satellites, called Jason-CS, with a projected launch date sometime in the 2020s.
“The new satellites, also known as Sentinel-6/Jason-CS missions in Europe, would be capable of measuring sea level more precisely than previous Jason missions and would have a longer design life of seven years,” says NOAA’s website.
For SpaceX, this mission will be notable for several reasons, the first of which is that it will be the last, planned flight of the v1.1 version of the Falcon 9 rocket. Also of interest is that the Jason-3 mission marks only the second time that SpaceX has launched from its Vandenberg launch site. However, all of that is trumped by the fact that SpaceX is planning on attempting to landing the rocket’s first stage on one of the company’s Autonomous Spaceport Drone Ships positioned out in the Pacific.
At present, weather conditions at the launch site are predicted to be perfect to support tomorrow’s flight, with the U.S. Air Force providing a 100 percent chance of favorable conditions for launch. Whether that extends to the landing attempt is not clear.
Rae Botsford End is a freelance writer and editor whose primary work currently is writing technical white papers, contributing to SFI, and working on a speculative fiction novel that she hopes to have published soon. Rae wanted an opportunity to report on the various space-related events in and around Florida's Space Coast and approached SFI's founder about the possibility. Rae now covers an array of subjects for our growing website.