Climatology of GPS signal loss observed by Swarm satellites

Jaeheung Park,Chao Xiong,Claudia Stolle

doi:10.5194/angeo-36-679-2018

Abstract

Abstract. By using 3-year global positioning system (GPS) measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between ±5 and ±20∘ magnetic latitude (MLAT) and high latitudes above 60∘ MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20∘, and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL) widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver. Keywords. Ionosphere (equatorial ionosphere; ionospheric irregularities) – radio science (radio wave propagation)

Highlights

With steadily increasing usage of the global navigation satellite system (GNSS), e.g., the global positioning system (GPS), reliable navigation becomes more and more important in our modern life
Three latitude bands are highlighted for these events from a global view: one is at low latitudes between ±5 and ±20◦ magnetic latitude (MLAT), forming two bands along the magnetic equator and most prominent at longitudes between −135 and 45◦ E; the other two regions are at high latitudes above 50◦ |MLAT| in both hemispheres, following the magnetic latitude lines and most prominent at longitudes close to the magnetic poles
By using 3-year observations from December 2013 to November 2016 of Swarm GPS observations, we have provided a statistical survey on the GPS signal loss at all latitudes

Summary

Introduction

With steadily increasing usage of the global navigation satellite system (GNSS), e.g., the global positioning system (GPS), reliable navigation becomes more and more important in our modern life. Previous studies found that ionospheric structures, such as the sporadic E (Es), equatorial plasma irregularities (EPIs), equatorial ionization anomaly (EIA), polar patches, and auroral blobs, can cause additional influence on the GNSS signal (e.g., Basu et al, 1980, 2002; Crowley et al, 2000; Kintner et al, 2004, 2007; Yue et al, 2016). These ionospheric structures with spatial scales from hundreds of kilometers down to meters produce rapid fluctuations of the received signal phase and amplitude termed as scintillations.

Swarm mission and onboard GPS receivers

GPS signal loss event detection

Results and discussion

Seasonal dependence of GPS signal loss

Orientation dependence of GPS signal loss

Performance of GPS receiver before and after PLL bandwidth increase

Summary