The GNSS-acoustic technique is a geodetic method for oceanic areas that combines GNSS positioning of a sea-surface platform and acoustic ranging of seafloor stations. Its positioning accuracy is typically a few and several centimeters for the horizontal and vertical positions, respectively. For further accuracy enhancement, we examined the errors in travel time, the most fundamental data in acoustic ranging. The reference signal used in our observations is a series of sinusoidal waves modulated by binary phase-shift keying with a maximal length sequence whose auto-correlation has a clear main peak at zero lag. However, cross-correlation between the actual returned signal and reference signal is often accompanied by many large sidelobes and looks very different from the synthetic auto-correlation. As a practical measure, we have chosen empirically one peak among several comparable peaks in the cross-correlation, though that is likely to lead to systematic errors in travel time. In this study, we revealed that a variety of cross-correlation waveform primarily depends on the incident angle of acoustic paths and that sidelobes were significantly reduced by substituting phase-only correlation (POC) for conventional cross-correlation. We therefore developed a template-matching technique using POC for the peak detection. POC templates were prepared by stacking actual POCs with certain ranges of the incident angle for each campaign. In the application of this method to actual data, we achieved successful results of our numerous campaign data to date. We consider that POC is advantageous in identifying the main peak uniquely and performing template matching more robustly, because POC enhances short-period components and thus highlights the timing of phase changes further than conventional cross-correlation.

GNSS声学技术是一种针对大洋区域的大地测量方法，它结合了海面平台的GNSS定位和海底站的声学测距。对于水平和垂直位置，其定位精度通常分别为几厘米和几厘米。为了进一步提高准确性，我们检查了行程时间中的误差，这是声学测距中最基本的数据。在我们的观测中使用的参考信号是一系列由二进制相移键控调制的正弦波，具有最大长度序列，其自相关在零延迟时具有清晰的主峰。但是，实际返回信号和参考信号之间的互相关常常伴随着许多大的旁瓣，并且看起来与合成自相关非常不同。作为实际措施，我们在经验上选择了互相关的多个可比较峰中的一个峰，尽管这很可能导致行程时间的系统误差。在这项研究中，我们发现各种互相关波形主要取决于声波路径的入射角，并且通过用仅相位相关（POC）代替常规互相关来显着减少旁瓣。因此，我们开发了一种使用POC进行峰检测的模板匹配技术。POC模板是通过将实际POC与每个活动的特定入射角范围堆叠而成的。迄今为止，通过将这种方法应用于实际数据，我们已经获得了众多活动数据的成功结果。我们认为POC在唯一地识别主峰和更稳健地执行模板匹配方面具有优势，