A New GPS Data Revolution
In 1996 a portion of the signals from the US military’s space-based Global Positioning System (GPS) became freely available, revolutionizing civil precision location, navigation and timing. Shortly thereafter scientists began taking advantage of these free and globally-available radio signals to remotely sense water vapor in the lower atmosphere and the ionized content of the upper atmosphere. In turn, these observations gave rise to a new era of weather forecasting, environmental monitoring, and real time assessment of solar activity in Earth’s geospace. Today another GPS data revolution is in the making, but this time in the realm of energetic particles in Earth’s radiation belts.
From system conception in the 1960s, engineers knew that individual GPS spacecraft would operate in the brutal radiation environment beyond Earth’s atmosphere. There, the subatomic particles of the Van Allen radiation belts relentlessly pummel every satellite. For decades, many (and now most) of the spacecraft host particle detectors that provide constellation operators with a direct view of the environment affecting the health and status of the system. Vital for new scientific research, these detectors have also been monitoring the hyperactive Van Allen belt electrons and protons. These data, however, were not available to the broader scientific community.
National Space Weather Strategy and Action Plan
As part of the US National Space Weather Strategy and Action Plan, and following the 2016 Executive Order 13744, the Department of Defense (DoD) is now opening a more than 15-year record of GPS particle data to scientific scrutiny. Accounting for the number of spacecraft with particle detectors onboard, this means a release of over 160 satellite-years of data! These data can be now combined with other available data over these years on solar output and activity, magnetic data in geospace, other particle data, cosmogenic records on Earth, and more to provide important new understanding of geophysical processes related to the solar-earth environment and trends over time.
Energetic Particle Data for New Research
Preliminary studies by Los Alamos National Laboratory researchers (e.g Morley et al., 2016) have cross-calibrated energetic electron measurements against data from NASA’s Van Allen Probes, and documented links between solar activity and disturbances in Earth’s magnetic domain and upper atmosphere. As noted in Knipp and Giles (2016), GPS measurements at altitudes as low as ~3 Earth radii yield a much-needed extension to the particle environment data record from the National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environmental Satellites by providing broader latitudinal and longitudinal coverage inside geosynchronous orbit.
In a feature article published this week Morley et al. (2017) report that “the large number of GPS satellites, distributed over 6 orbital planes, will provide important context for ongoing and historical science missions, as well as enabling new types of research not previously possible.”
The data are publicly available, hosted by NOAA’s National Centers for Environmental Information and can be found by searching the data.gov portal or at https://www.ngdc.noaa.gov/stp/space-weather/satellite-data/satellite-systems/gps/.
The US DoD, the Office of Science Technology Policy, and the broader space weather enterprise deserve our support and thanks for this data release. This cache of data will likely drive fundamental new developments in geospace research. The data release should be emulated by other nations as they invest in space-based global and regional navigation satellite systems.