11:00 AM - 11:15 AM
[SSS12-02] Current status and Recent issues in GNSS-A observations by the Japan Coast Guard
Keywords:Seafloor geodesy, GNSS-A, Marine acoustics
The Japan Coast Guard (JCG) routinely conducts the GNSS-A observation for monitoring interplate slips along the Japan Trench and the Nankai Trough. The observation results are submitted to the Earthquake Research Committee of the Headquarters of Earthquake Research Promotion Headquarters and the Nankai Trough Earthquake Assessment Committee of the Japan Meteorological Agency, and used for evaluating the current status of earthquakes and crustal activities.
Various slow earthquake phenomena are known to occur at plate boundaries, where large earthquakes occur. Understanding these phenomena in detail is an important issue in understanding the physical mechanisms of earthquakes. The JCG has been developing GNSS-A technique to increase their accuracy and frequency to detect slow slip events. As a result, data fluctuations of the GNSS-A time series that were previously considered as errors can be regarded as statistically significant variations reflecting the true geophysical phenomena, and we succeeded in detecting transient changes which is caused by slow slip events on plate boundary (Yokota and Ishikawa, 2020).
On the other hand, there are some cases where data fluctuations are determined to be statistically significant event even for unrealistic variations that cannot be realized as geophysical phenomena. Such systematic errors may cause misinterpretation of the physical background of the data. Through examination of our data that is collected at many numbers of sites over a long period, it is clear that the appearance pattern of this type of error depends on hardware characteristics of the acoustic instruments used for acoustic ranging.
To properly interpret underlying physical phenomena from the GNSS-A time series, it is necessary to understand the effects of such systematic errors. For example, in the case of terrestrial GNSS observations, antenna phase characteristics are investigated in detail, and correction data such as PCV for various antenna models are published to enable precise positioning. Positioning used in marine acoustics is typically on the order of a few meters to tens of meters, and therefore equipment characteristics on the cm order required by GNSS-A are not well understood. Therefore, we conducted experiments to investigate the characteristics of acoustic equipment at the Ocean Engineering Basin at the Institute of Industrial Science, the University of Tokyo. The results of this experiment are expected to reduce the unrealistic behavior of the GNSS-A time series.
Various slow earthquake phenomena are known to occur at plate boundaries, where large earthquakes occur. Understanding these phenomena in detail is an important issue in understanding the physical mechanisms of earthquakes. The JCG has been developing GNSS-A technique to increase their accuracy and frequency to detect slow slip events. As a result, data fluctuations of the GNSS-A time series that were previously considered as errors can be regarded as statistically significant variations reflecting the true geophysical phenomena, and we succeeded in detecting transient changes which is caused by slow slip events on plate boundary (Yokota and Ishikawa, 2020).
On the other hand, there are some cases where data fluctuations are determined to be statistically significant event even for unrealistic variations that cannot be realized as geophysical phenomena. Such systematic errors may cause misinterpretation of the physical background of the data. Through examination of our data that is collected at many numbers of sites over a long period, it is clear that the appearance pattern of this type of error depends on hardware characteristics of the acoustic instruments used for acoustic ranging.
To properly interpret underlying physical phenomena from the GNSS-A time series, it is necessary to understand the effects of such systematic errors. For example, in the case of terrestrial GNSS observations, antenna phase characteristics are investigated in detail, and correction data such as PCV for various antenna models are published to enable precise positioning. Positioning used in marine acoustics is typically on the order of a few meters to tens of meters, and therefore equipment characteristics on the cm order required by GNSS-A are not well understood. Therefore, we conducted experiments to investigate the characteristics of acoustic equipment at the Ocean Engineering Basin at the Institute of Industrial Science, the University of Tokyo. The results of this experiment are expected to reduce the unrealistic behavior of the GNSS-A time series.