本研究將利用TOPEX與JASON-2測高衛星監測天津市和上海市二座大都市之地表垂直高程變化。天津市方面,本研究之計算結果顯示天津市由於過度使用地下水造成地表垂直高程呈現下降趨勢,位於TOPEX經過天津市的兩條軌跡(Pass 001與062)得到之交叉點分析來指出選用OCOG之波形重定法得到Pass 001與062於交叉點之地表垂直高程變化速率分別為-3.7 mm/year與-3.9 mm/year,兩者之垂直高程變化速率差值最接近(約為 1 cm/year)。除了交叉點之計算結果外,只要Pass 001與Pass 062觀測之反射波形良好下,其沿軌跡得到之地表垂直變化速率皆呈現下降的趨勢。上海市方面,本研究透過Pass 229觀測之良好反射波形,來得到準確的重定地表高程,進而得到上海市之地表垂直變化,但測高結果顯示正和負值位移。未來需要更多的研究來確定測高的結果。
We used waveform data from TOPEX and JASON-2 altimeters to determine vertical displacements over the cities of Tianjin and Shanghai, China. The crossover of passes 001 and 062 was over a spot around Tianjin, where waveforms are reasonably good for retracking. Retracked surface heights by the OCOG method near this crossover yielded vertical displacement rates of -3.7 and -3.9 cm/year from the two passes, suggesting that the surface is undergoing subsidence and the rates from the two passes are consistent to better than 1 cm/year. Other sub-satellite points of passes 001 and 062 with good waveforms also showed negative vertical displacement rates. The subsidence in Tianjin was largely due to groundwater retrieval. Over Shanghai, we used retracked waveforms from pass 229 to detect the vertical displacements, but the altimeter result show negative and positive rates of vertical displacements. More study of is needed to produce a conclusive result from altimetry.