GPD+ Wet Tropospheric Corrections for CryoSat-2 and GFO Altimetry Missions
GPD+ Wet Tropospheric Corrections for CryoSat-2 and GFO Altimetry Missions
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DOI：
10.3390/rs8100851
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发表时间：
2016-10
期刊：
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通讯作者：
M. Fernandes;C. Lázaro
中科院分区：
文献类型：
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作者：
M. Fernandes;C. Lázaro
由于湿对流层改正量具有较大的时空变异性，在卫星测高中仍然被认为是一个重要的误差源。本文介绍了GNSS（全球导航卫星系统）衍生路径延迟加（GPD+），这是波尔图大学为雷达高度计任务检索改进WTC而开发的最新算法。GPD+是通过时空客观分析估算的WTC，结合了点附近所有可用的观测数据：来自机载微波辐射计（MWR）的有效测量，来自GNSS沿海和岛屿站以及机载各种遥感任务的扫描成像MWR。GPD+修正既适用于没有机载微波辐射计（如CryoSat-2 (CS-2)）的任务，也适用于携带该传感器的所有任务，通过解决mwr衍生WTC固有的各种误差源。为了确保校正的长期稳定性，本研究中使用的大量辐射计已经根据特殊传感器微波成像仪（SSM/I）和SSM/I测深仪（SSM/IS）进行了校准。介绍了该算法在CS-2和geo - sat followon （GFO）两种具有代表性的高度计任务中的应用。结果表明，对于两个任务，相对于基于模式的校正，新的WTC显著降低了海平面异常（SLA）方差。对于GFO而言，与MWR衍生的WTC相比，新的WTC也导致了SLA方差的大幅减少，恢复了沿海和极地地区的大量观测数据以及MWR测量缺失或无效时的全套轨道和几个周期。总的来说，该算法可以恢复大量的测量数据，确保了公海/沿海过渡区和高纬度地区校正的连续性和一致性。
Due to its large space-time variability, the wet tropospheric correction (WTC) is still considered a significant error source in satellite altimetry. This paper presents the GNSS (Global Navigation Satellite Systems) derived Path Delay Plus (GPD+), the most recent algorithm developed at the University of Porto to retrieve improved WTC for radar altimeter missions. The GPD+ are WTC estimated by space-time objective analysis, by combining all available observations in the vicinity of the point: valid measurements from the on-board microwave radiometer (MWR), from GNSS coastal and island stations and from scanning imaging MWR on board various remote sensing missions. The GPD+ corrections are available both for missions which do not possess an on-board microwave radiometer such as CryoSat-2 (CS-2) and for all missions which carry this sensor, by addressing the various error sources inherent to the MWR-derived WTC. To ensure long-term stability of the corrections, the large set of radiometers used in this study have been calibrated with respect to the Special Sensor Microwave Imager (SSM/I) and the SSM/I Sounder (SSM/IS). The application of the algorithm to CS-2 and Geosat Follow-on (GFO), as representative altimetric missions without and with a MWR aboard the respective spacecraft, is described. Results show that, for both missions, the new WTC significantly reduces the sea level anomaly (SLA) variance with respect to the model-based corrections. For GFO, the new WTC also leads to a large reduction in SLA variance with respect to the MWR-derived WTC, recovering a large number of observations in the coastal and polar regions and full sets of tracks and several cycles when MWR measurements are missing or invalid. Overall, the algorithm allows the recovery of a significant number of measurements, ensuring the continuity and consistency of the correction in the open-ocean/coastal transition zone and at high latitudes.