GPS/Acoustic測地法是監測海洋板塊位移常用的方法，由於全球板塊每年平均位移約1~10公分，GPS/Acoustic測地法必需達到公分等級定位精度，才能滿足監測如此緩慢之板塊位移速度要求。然而水層聲速隨時間與空間變化，即使頻繁的CTD量測也無法即時反應聲速變化，況且CTD也有可能存在量測偏差，這些因素都會影響海床應答器定位的準確度。為了解決聲速變動與量測誤差對海床應答器定位之影響，本研究透過數值模擬探討GPS/Acoustic測地法在不同收發器詢答分佈測量下，CTD溫度量測、聲速變動及聲訊走時量測誤差對海床應答器定位的影響。模擬結果顯示只要收發器詢答位置分佈對稱於應答器位置，水層聲速量測誤差就不會影響應答器水平定位，只會影響應答器垂直定位精度。因此，本實驗提出線性模型與雙線性模型來近似水層聲速剖面，將兩種方法運用於GPS/Acoustic測地法以提升海床應答器定位精度。最後，本研究利用高雄外海水深300公尺的實驗資料運用雙線性聲速剖面法進行海床應答器定位估算。由實驗結果顯示，雙線性聲速剖面法配合GPS/Acoustic測地法進行海床應答器定位，確實可以降低量測誤差對定位之影響，有效提升GPS/Acoustic測地法的量測精度。

Plate motions over the past few million years have averaged 110 centimeters per year. To monitor such slight deformations in the crust by the GPS/Acoustic geodesy, the accuracy on the order of a few centimeters in positioning seafloor transponders is required. Temporal and spatial variability of sound speed in the water column, however, as well as the measurement error of sound speed, is a main limiting factor in the production of accurate acoustic ranging even though frequent conductivity-temperature-depth (CTD) casts are made. Therefore, in this study, various geometrical options for acoustic ranging are designed in the numerical simulation of GPS/Acoustic geodesy and the effects of various sound-speed measurement errors on the accuracy of transponder positioning are evaluated. The simulation results show that observing slant-range measurements symmetrically around the transponder can nullify sound-speed errors in the horizontal but not vertical positioning of a seafloor transponder. Sound-speed errors produce the vertical positioning error although the slant-range observations are well geometrically balanced. For reducing the effect of sound-speed variation on the precision of GPS/Acoustic seafloor geodesy, this study proposes two synthetic sound-speed profiles of the water column, one linear and the other bilinear, to approximate acoustic travel-time measurements. The approximating sound-speed profile is used in combination with the tomographic estimation in GPS/Acoustic geodesy to estimate the sound speed variation, such that the effect of sound speed variation on the accuracy of transponder positioning is reduced. The performance of the two synthetic models is evaluated for different types of CTD-derived sound-speed profiles and for the acoustic ranging observations collected from a field GPS/Acoustic survey. The evaluation results demonstrate that both the linear and bilinear models can effectively reduce the effect of sound-speed variation on the precision of GPS/Acoustic positioning.

第一章緒論 1
1.1研究動機與目的……….……………….……....……..……………1
1.2文獻回顧………………………………….………………....….…..3
1.3本文架構……………………………………….…………....….…..5
第二章GPS/Acoustic測地法6
2.1收發器定位…………………………………….….……...…….......8
2.2應答器定位估算…………..…………………..…………....….…...12
2.3聲速剖面近似……………………..……………….………....…….15
2.3.1走時比例法…………………………………….……….......….15
2.3.2走時殘差法…………………………….………………...…….16
2.3.3線性聲速剖面法………………………………….……......…..17
2.3.4雙線性聲速剖面法…………………………………........…….18
第三章量測誤差對定位之影響21
3.1溫度偏差……………….…………….......………………...…....…..23
3.2聲速變動……………………………………..…………….........…..27
3.3聲訊走時量測偏差………………………………………….......…..32
3.3.1不同的收發器詢答分佈存在量測偏差….….....................…32
3.3.2對稱的收發器詢答分佈存在量測偏差..................................35
第四章聲速剖面近似性能評估38
4.1數值模擬....................………………………......….…..……………39
4.1.1利用近似法近似300公尺水層聲速剖面……...........................39
4.1.2利用近似法近似1000公尺水層聲速剖面…….........................40
4.2實海域定位資料分析………………………….…………………….43
第五章結論48
附錄A聲速分佈方程式53

邱楫文，「長基線定位系統與載具動態模式之整合研究」，中山大學海下科技暨應用海洋物理研究所，民100年。

張家溥，「利用GPS與聲學量測進行海床應答器之定位」，中山大學海下科技暨應用海洋物理研究所，民98年。

張旭光，「超短基線定位系統之感測器對準校正」，中山大學海下科技暨應用海洋物理研究所，民98年。

杜廣文，「超短基線定位之感測器對準偏差校正」，中山大學海下科技研究所，民95年。

Chen, H., H., Wang, C., C., 2011, “Accuracy assessment of GPS/Acoustic positioning using a Seafloor Acoustic Transponder System,” Ocean Engineering, Vol. 30, No. 13, PP. 1472-1479.

Kido, M., Osada, Y., Fujimoto, H., 2008, “Temporal variation of sound speed in ocean: a comparison between GPS/acoustic and in situ measurements,” Earth Planets Space, Vol. 58, PP. 229–234.

Ikuta, R., Tadokoro, K., Ando, M., Okuda, T., Sugimoto, S., Takatani, K., Yada, K., Besana, G., M., 2008, “A new GPS-acoustic method for measuring ocean floor crustal deformation: Application to the Nankai Trough,” Journal of Geophysical Research, Vol. 113, B02401.

Fujita, M., Ishikawa, T., Mochizuki, M., Sato, M., Toyama, S., I., Katayama, M., Kawai, K., Matsumoto, Y., Yabuki, T., Asada, A., Colombo, O., L., 2006, “GPS/Acoustic seafloor geodetic observation: method of data analysis and its application,” Earth Planets Space, Vol. 58, PP. 265–275.

Kido, M., Fujimoto, H., Miura, S., Osada, Y., Tsuka, K., Tsuka, T., 2006, “Seafloor displacement at Kumano-nada caused by the 2004 off Kii Peninsula earthquakes, detected through repeated GPS/Acoustic surveys,” Earth Planets Space, Vol. 58, PP. 911–915.

Tadokoro, K., Ando, M., Ikuta, R., Okudo, T., Besana, G. M., Sugimoto, S., Kuno, M., 2006, “Observation of coseismic seafloor crustal deformation due to M7 class offshore earthquakes,” Geophysical Research Letters, Vol. 33, L23306.

Xu, P., Ando, M., Tadokoro, K., 2005, “Precise, three-dimensional seafloorgeodetic deformation measurements using difference techniques,” Earth Planets Space, Vol. 57, PP. 795–808.

Osada, Y., Fujimoto, H., Miura, S., Sweeney, A., Kanazawa, T., Nakao, S., Sakai, S., Hildebrand, J., A., Chadwell, C., D., 2003, “Estimation and correction for the effect of sound velocity variation on GPS/Acoustic seafloor positioning:An experiment off Hawaii Island,” Earth Planets Space, Vol. 55, PP. e17–e20.

Spiess, F., N., Chadwell, C., D., Hildebrand, J., A., Young, L., E., Purcell Jr., G., H., Dragert, H., 1998, “Precise GPS/acoustic positioning of seafloor reference points for tectonic studies,” Physics of the Earth and Planetary Interiors, Vol. 108, PP. 101–112.

Vincent II, H., T., Hu, S., L., J., 1997, “Geodetic position estimation of underwater acoustic sensors,” Journal of Acoustical Society of America, Vol. 102, No. 5, PP. 3099–3100.

Spiess, F., N., 1998, “Acoustic techniques for marine geodesy,” Mar. Geod., Vol. 4, PP. 13–27.

Chen, C., T., Millero, F., J., 1977, “Sound speed of seawater at high pressures,” J. Acoust. Soc., Vol. 62, PP. 1129–1135.