A Conceptual Study of Land-based Tsunami Monitoring System using Code Correlation Measurements of GNSS Signal Reflected by the Sea Surface

T. Yoshihara, S. Saitoh, N. Fujii, T. Sakai

Abstract:	In our previous study concerning detection method of the sea level variation using GPS signal reflected by sea surface, we have demonstrated to estimate the sea level with a precision of several meters by code correlation curve measurements using a GPS Signal Quality Monitoring (SQM) receiver together with a Right Hand Circular polarized (RHCP) antenna at Mt. Rokko. Because the observational site was located near the coastline, the SQM receiver could observe a code correlation curve of L1-C/A code which included a GPS signal reflected by the sea surface at about 10 several km away together with its direct signal with a low elevation angle of about 3 degrees. Through analysis of path difference between a direct and a reflected signal with code correlation curves, an estimated relative height for total number of ten events varied with a RMS of about 4 meters during 8.5 hours and this variation range was too large to detect tidal waves, which varied with a range of about 0.5 meters during the ten events. However, very large tsunamis produced by a large earthquake were observed near coastal region in Tohoku area, Japan on March 11th, 2011. The maximum wave height of about 5 meters was reported. In this paper, we reconsider our method to apply detection for such large tsunamis taking account of the current progress associated with GNSS receiver such as multi-correlator GNSS receivers and software based receivers. Namely, this paper discusses a concept of land-based monitoring system together with main subjects to proceed, which are improvement of the method to estimate path difference with a better accuracy and a time resolution and capability examination of our method under rough surface condition. In this study, we analyzed simpler experimental data than the previous. The experiment was performed at Muroto Cape in February 2006. The observational site was located close to the coast with an altitude of about 220 meters above the sea. These conditions enabled for us to simplify modeling path difference changes. For improvement of path difference in both accuracy and time resolution, we additionally used code correlation result at receiver tracking point with a sampling rate of 1,000 Hz as amplitude phasing information on receiving intensity. We determined a relative path difference from them under a smooth surface condition and its characteristic was consistent with theoretical results except for elevation angles of as low as 1 degree. We also calculated path differences using code correlation curves for both conditions of smooth and rough surface. As results, its standard deviation varied from 4.58 to 6.83 meters and there was a systematical discrepancy of about 10 meters in comparison with theoretical path difference. We think that these errors were produced by inconsistency of an assumed ideal shape of multipath component in code correlation curve in our estimation process.
Published in:	Proceedings of the ION 2013 Pacific PNT Meeting April 23 - 25, 2013 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	1 - 8
Cite this article:	Yoshihara, T., Saitoh, S., Fujii, N., Sakai, T., "A Conceptual Study of Land-based Tsunami Monitoring System using Code Correlation Measurements of GNSS Signal Reflected by the Sea Surface," Proceedings of the ION 2013 Pacific PNT Meeting, Honolulu, Hawaii, April 2013, pp. 1-8.
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