Abstract
GNSS signals are critically important for a wide range of commercial,
military, and science applications. Recent studies have identified
threats to the performance of GNSS from both intended and unintended
sources of radio frequency interference (RFI). Understanding the
distribution of the sources of RFI and the nature of the signals they
are emitting is critical to determine and mitigate their effects on the
measurements made by GNSS receivers. Terrestrial RFI can be
substantially detrimental to the received GNSS signals, affecting the
interpretation of related science measurements. NASA’s Blackjack/TriG
GNSS receivers are used for precise-orbit determination and radio
occultation measurements, providing a data record spanning most of the
Earth’s surface for nearly 20 years. We have developed a highly
sensitive detection algorithm which uses variations in the measured
signal to noise ratio (SNR), on the order of 10-50 seconds, common to
all satellites to identify times and locations subject to RFI. Initial
work has focused primarily on detection of the presence of RFI and using
the receiver’s orbital solution to record the location of detection
events. Our inter-mission analysis creates a unique record of global RFI
with the potential for a) rigorous detection of the presence of
interfering signals during science measurements, b) geolocation of RFI
sources, and c) characterization of the nature of the transmitted signal
to better identify intent. Preliminary analysis has shown the presence
of RFI is well correlated with regional conflicts and other geopolitical
activity.