Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is quickly maturing toward the objective of becoming a viable alternative for operational coastal sea-level (SL) altimetry in a geocentric reference frame. SL has immense societal implications related to climate change. Of particular interest is the exploitation of existing coastal GNSS sites for reflectometry by means of signal-to-noise ratio (SNR) observables. We report results from the first inter-comparison campaign on SNR-based GNSS-R. The goal was to cross-validate retrieval solutions from independent research groups under comparable conditions. This action was an initiative of the International Association of Geodesy working group 4.3.9 (2015–2019 term). Data collected at the Onsala Space Observatory for a 1-year period (2015–2016) were compared to a co-located tide gauge (TG). SNR data for the GPS L1-C/A signal were processed by four groups, in Sweden, Luxembourg/Brazil, Germany, and the UK. Semidiurnal tidal constituents showed good agreement between TG and all GNSS-R groups. SL variations at diurnal and longer periods were also well captured by all series. Most GNSS-R solutions exhibited spurious tones at integer fractions of one sidereal day, the satellite revisit time of the particular GNSS constellation employed (GPS). Band-pass filtering between 3 h and 30 h confirmed that the dominant tidal components were well captured by most GNSS-R solutions. Higher-frequency SL variations (periods < 3 h) are poorly represented by GNSS-R as a consequence of its low temporal resolution. The solution with the worst agreement neglects a correction associated with the rate of change in sea level and uses narrower satellite elevation ranges per retrieval. Overall, there was excellent agreement, with correlation coefficients exceeding 0.9 and RMSE smaller than 5 cm.

中文翻译：

---

用于沿海海平面高度测量的基于 SNR 的 GNSS 反射计：来自第一次 IAG 比对活动的结果

地面全球导航卫星系统反射计 (GNSS-R) 正朝着成为地心参考系中沿海海平面 (SL) 高度测量的可行替代方案的目标迅速成熟。SL 具有与气候变化相关的巨大社会影响。特别令人感兴趣的是利用信噪比 (SNR) 可观测数据利用现有的沿海 GNSS 站点进行反射测量。我们报告了基于 SNR 的 GNSS-R 的第一次比对活动的结果。目标是在可比条件下交叉验证来自独立研究小组的检索解决方案。该行动是国际大地测量协会工作组 4.3.9（2015-2019 年任期）的一项倡议。将 Onsala 太空天文台收集的为期 1 年（2015-2016 年）的数据与同位潮汐计 (TG) 进行了比较。GPS L1-C/A 信号的 SNR 数据由瑞典、卢森堡/巴西、德国和英国的四个小组处理。半昼夜潮汐成分在 TG 和所有 GNSS-R 组之间显示出良好的一致性。所有系列也很好地捕获了昼夜和更长时期的 SL 变化。大多数 GNSS-R 解决方案在一个恒星日的整数部分表现出虚假音调，即所采用的特定 GNSS 星座 (GPS) 的卫星重访时间。3 小时到 30 小时之间的带通滤波证实，大多数 GNSS-R 解决方案都能很好地捕获主要潮汐分量。由于其时间分辨率低，GNSS-R 不能很好地代表高频 SL 变化（周期 < 3 小时）。一致性最差的解决方案忽略了与海平面变化率相关的校正，并在每次检索时使用更窄的卫星高度范围。总体而言，具有极好的一致性，相关系数超过 0.9，RMSE 小于 5 cm。