Observation and Analysis of Ionospheric Scintillation on GPS signals in Japan

Abstract

This paper shows the impact of ionospheric scintillation on GPS and MSAS (MTSAT Satellite-Based Augmentation System). Ionospheric scintillation is rapid amplitude and phase fluctuation of trans-ionosphere radio waves due to local irregularity of ionosphere. It sometimes causes cycle slips or signal loss of lock on GPS and SBAS (Satellite-Based Augmentation System) receivers. The effect of ionospheric scintillation is most intense in equatorial anomaly region (near geomagnetic equator; ±15 deg. in geomagnetic latitude) after sunset, moderate around polar and aurora region, and slight in mid-latitude region. Around Japan, the geomagnetic equator rises up northward compared with geographic latitude, and the service range of MSAS includes the area about magnetic latitude 15 deg.

We have conducted observation of ionospheric scintillation with GPS Ionospheric Scintillation Monitors (ISM's) since March 1999 at Chofu (N36E140) and Naha (N26E128). The ISM can track up to 11 GPS L1 (C/A) signals and measure amplitude and phase at 50 Hz rate for each satellite. We have collected ISM data log (ISMR) at each 60 sec., which contains C/N₀, standard deviation and spectrum parameters of amplitude and phase, receiver lock time, and other information for each satellite. Chofu is located about 28 deg. in geomagnetic latitude (mid-latitude) and Naha is about 15 deg. (near geomagnetic equator).

Seasonal difference of ionospheric scintillation behavior has been observed. Some severe scintillation effects caused a signal loss of lock for about 1 hour and more. At Naha, the number of GPS satellites whose signals are not influenced by scintillation decreased less than 5 with an elevation mask angle of 5 deg. This result means that ionospheric scintillation is a potential threat to MSAS in terms of availability and continuity.