We assessed the positioning accuracy of GNSS-Acoustic (GNSS-A) measurement using a slackly moored buoy. A key feature of real-time buoy-based GNSS-A measurement is that positioning must be performed via single ranging from an arbitrary observation position and encompassing the drifting range of the buoy. In this study, slack-line mooring was employed to resist strong Kuroshio current of up to 5.5 knots in the Nankai Trough. During a year-long sea trial, the buoy drifted within a circle of ~ 4000 m radius, which is much larger than the dimension of a seafloor transponder array. In the sea trial, more than 500 successful regular and on-demand ranging measurements were obtained at various observation positions. The results show that the horizontal positioning accuracy (2σ) of the array for single ranging was 46 cm when the buoy was inside the array and 97 cm when it was outside the array. These accuracies are comparable to those achieved through single ranging in traditional ship-based surveys at the same site. In addition to the distance dependency, we observed directivity in the accuracy, depending on the geometry between an observation point and seafloor transponders. To interpret the accuracy degradation and directivity as a function of observation position, we calculated error ellipses using a dilution-of-precision (DOP) analysis procedure for GNSS-A positioning. The error ellipses clearly illustrate that the variance in array positions is large in the line-of-sight direction from an observation point to the array center. We translated the error ellipses to positioning accuracies using the standard deviation of travel time residuals when an array position is estimated using all pings. The positioning accuracy resulting from the translation corresponded to that obtained using array positions in a buoy observation. The DOP analysis results and their translation into positioning accuracies enabled a detailed assessment of the directional accuracy of GNSS-A positioning at an arbitrary observation position, which is important for real-time measurement of seafloor movement in the event of a huge earthquake.

中文翻译：

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使用松弛的系泊浮标评估GNSS声学测量的方向精度

我们使用松弛的系泊浮标评估了GNSS-声学（GNSS-A）测量的定位精度。实时基于浮标的GNSS-A测量的一个关键特征是必须通过从任意观察位置到涵盖浮标漂移范围的单个范围进行定位。在这项研究中，松弛线系泊被用来抵抗南海海槽中高达5.5节的强烈黑潮。在为期一年的海上试验中，浮标在〜4000 m半径的圆圈内漂移，该圆圈比海底应答器阵列的尺寸大得多。在海上试验中，在各个观察位置获得了500多次成功的常规和按需测距测量。结果表明，浮标在阵列内部时，单次测距阵列的水平定位精度（2σ）为46 cm，在阵列外部时为97 cm。这些精度可与在同一地点进行的传统船基测量中的一次测距所获得的精度相媲美。除了距离依赖性之外，我们还观察到精度的方向性，具体取决于观察点与海底应答器之间的几何形状。为了将精度下降和方向性解释为观测位置的函数，我们使用精度稀释（DOP）分析程序对GNSS-A定位计算了误差椭圆。误差椭圆清楚地表明，从观察点到阵列中心的视线方向上，阵列位置的变化很大。当使用所有ping估计阵列位置时，我们使用行进时间残差的标准偏差将误差椭圆转换为定位精度。由平移产生的定位精度对应于使用浮标观察中的阵列位置获得的定位精度。DOP分析结果及其转换为定位精度后，可以对GNSS-A在任意观测位置的定位精度进行详细评估，这对于在发生大地震时实时测量海底运动非常重要。由平移产生的定位精度对应于使用浮标观察中的阵列位置获得的定位精度。DOP分析结果及其转换为定位精度后，可以对GNSS-A在任意观测位置的定位精度进行详细评估，这对于在发生大地震时实时测量海底运动非常重要。由平移产生的定位精度对应于使用浮标观察中的阵列位置获得的定位精度。DOP分析结果及其转换为定位精度后，可以对GNSS-A在任意观测位置的定位精度进行详细评估，这对于在发生大地震时实时测量海底运动非常重要。