双星跟飞测高卫星在轨初步验证

Preliminary verification of dual-satellite tandem altimetry on board

卫星测高反演重力场的常规做法是利用海面高差求解垂线偏差,进一步计算海洋重力异常和海洋大地水准面高等信息。显然,提高海面高差的测量精度可以直接提升海洋重力场的反演精度。本文给出了双星跟飞卫星测高原理,通过轨道设计使双星星下点跨轨间距(即分辨率)在1′左右,双星同时测量沿其轨道的海面高差及跨轨的星间海面高差,此时轨道径向误差表现为星间或单星历元间的相对轨道径向误差,而与大气传播和地球物理效应等有关的改正项,对于地面轨间距只有1′的双星近似相等,其在海面高差中几无体现,因此海面高差的精度相比于传统的单星测量将有显著提高。利用测高A/B双星的实际观测数据,初步验证了相对轨道径向误差和海面高差中的8项改正的差值误差。结果表明,对于定标阶段约25 km的星下点间距,干对流层、湿对流层、电离层、固体潮、极潮和逆大气压等改正项的差值误差均在5 mm量级;海潮改正差值、海况偏差差值中分别有约1 cm和2 cm的残留误差;对于业务轨道约2 km的星下点间距,相对轨道径向误差约为3 mm,除了海况偏差差值有约0.52 cm的残留误差,其他改正项的差值误差均小于0.05 cm,可完全忽略不计。

The classic method to derive gravity field from satellite altimetry is first to calculate the deflection of the vertical using the sea surface height difference(SSHD),and then further to calculate the marine gravity anomaly and the marine geoid height,et al.Obviously,improving the measurement accuracy of SSHD can directly improve the inversion accuracy of ocean gravity field.The dual-satellite tandem altimetry principle is proposed in the paper.By designing the orbit of dual-satellite,the cross orbit distance(i.e.resolution)between the sub-satellite points of the dual-satellite can be reached about 1 arcmin.The dual-satellite simultaneously measure the SSHD along their orbital direction and in the cross orbital direction.At this time,the radial error of the orbit is showed as the relative orbital radial error between dual-satellite or between single satellite observation epochs,and the corrections related to atmospheric propagation and geophysical effects are approximately equal for dual-satellite with a ground orbit spacing of only 1 arcmin,and are rarely reflected in the SSHD.Therefore,the accuracy of SSHD will be significantly improved compared to that of the traditional single satellite condition.Using the actual observation data from our twin altimetry satellites A,B,the difference error between the relative orbit radial error and the eight corrections in the SSHD was preliminarily verified.The results show that for the calibration stage with a distance of about 25 km between sub-satellite points,the difference errors of corrections such as dry troposphere,wet troposphere,ionosphere,solid tide,polar tide,and reverse atmospheric pressure are all on the order of 5 mm.There are residual errors of approximately 1 cm and 2 cm in the difference in tidal correction and sea state deviation,respectively.For the sub-satellite point spacing of about 2 km in the business orbit,the relative orbital radial error is about 3 mm,and except for the residual error of about 0.52 cm in the sea state deviation difference,the difference error of other corrections is less than 0.05 cm and can be completely ignored.