Ray Richard D, Loomis Bryant D, Zlotnicki Victor
NASA Goddard Space Flight Center, Greenbelt, MD USA.
Jet Propulsion Laboratory, Pasadena, CA USA.
J Geod. 2021;95(7):80. doi: 10.1007/s00190-021-01529-1. Epub 2021 Jun 27.
Satellite altimetry and gravimetry are used to determine the mean seasonal cycle in relative sea level, a quantity relevant to coastal flooding and related applications. The main harmonics (annual, semiannual, terannual) are estimated from 25 years of gridded altimetry, while several conventional altimeter "corrections" (gravitational tide, pole tide, and inverted barometer) are restored. To transform from absolute to relative sea levels, a model of vertical land motion is developed from a high-resolution seasonal mass inversion estimated from satellite gravimetry. An adjustment for annual geocenter motion accounts for use of a center-of-mass reference frame in satellite orbit determination. A set of 544 test tide gauges, from which seasonal harmonics have been estimated from hourly measurements, is used to assess how accurately each adjustment to the altimeter data helps converge the results to true relative sea levels. At these gauges, the median annual and semiannual amplitudes are 7.1 cm and 2.2 cm, respectively. The root-mean-square differences with altimetry are 3.24 and 1.17 cm, respectively, which are reduced to 1.93 and 0.86 cm after restoration of corrections and adjustment for land motion. Example outliers highlight some limitations of present-day coastal altimetry owing to inadequate spatial resolution: upwelling and currents off Oregon and wave setup at Minamitori Island.
卫星测高和重力测量被用于确定相对海平面的平均季节周期，这一参数与沿海洪水及相关应用相关。主要谐波（年、半年、三年）是根据25年的网格化测高数据估算得出的，同时恢复了一些传统测高仪的“校正值”（引潮力、极潮和反气压计）。为了从绝对海平面转换为相对海平面，利用卫星重力测量估算的高分辨率季节性质量反演建立了垂直陆地运动模型。对年地心运动的调整考虑了在卫星轨道确定中使用质心参考系的情况。一组544个测试验潮仪用于评估对测高仪数据的每次调整能多准确地使结果收敛到真实相对海平面，这些验潮仪的每小时测量数据已用于估算季节性谐波。在这些验潮仪处，年和半年振幅的中位数分别为7.1厘米和2.2厘米。与测高数据的均方根差分别为3.24厘米和1.17厘米，在校正恢复和陆地运动调整后分别降至1.93厘米和0.86厘米。示例异常值突出了当前沿海测高由于空间分辨率不足而存在的一些局限性：俄勒冈州近海的上升流和海流以及南鸟岛的波浪增水。
