A New Frontier in Ionospheric Observations: GPS Total Electron Content
Measurements from Ocean Buoys
Abstract
Ground-based Global Navigation Satellite System (GNSS) receivers have
become an ubiquitous tool for monitoring the ionosphere. Total Electron
Content (TEC) data from globally distributed networks of ground-based
GNSS receivers are increasingly being used to characterize the
ionosphere and its variability. The deployment of these GNSS receivers
is currently limited to landmasses. This means that 7/10 of Earth’s
surface, which is covered by the oceans, is left unexplored for
persistent ionospheric measurements. In this paper, we describe a new
low-power dual-frequency Global Positioning System (GPS) receiver,
called Remote Ionospheric Observatory (RIO), which is capable of
operating from locations in the air, space, and the oceans as well as on
land. Two RIO receivers were deployed and operated from the Tropical
Atmosphere Ocean buoys in the Pacific Ocean, and the results are
described in this paper. This is the first time that GPS receivers have
been operated in open waters for an extended period of time. Data
collected between September 1, 2018 and December 31, 2019 are shown. The
observed TEC exhibits a clear seasonal dependence characterized by
equinoctial maxima in the data at both locations. Both RIO receivers,
deployed near the geomagnetic equator, show an 18-35% increase in TEC
during moderately disturbed geomagnetic periods. Comparisons with the
International Reference Ionosphere model show good agreement. The new
capability presented in this paper addresses a critical gap in our
ability to monitor the ionosphere from the seventy percent of the
Earth’s surface that is covered by water.