水深測量為海洋科學與海岸(洋)工程領域中不可或缺的一部分，無論是傳統的船隻航行、能源探勘、近海作戰或救災，又或是近年興起的海域遊憩、離岸風電等，皆需要最新的的水深地形資料。本研究乃針對X-Band雷達應用於水深探測技術的精進進行探討，以提昇並掌握此監測技術的適用性與量測精度，並增加此探測技術的附加應用價值。
本研究選用台南七股北堤安檢所頂樓的X-band雷達於2019年9月20日的回波影像序列資料作為觀測樣本，並以水利署第六河川局於2019年9月在同一海域進行的現場水深測量結果作為比對基礎。首先以Wu et al. (2017)提出之水深演算方法將X-band雷達之回波影像資訊轉換為量測範圍內各空間點位處的水深，並與實際量測水深比較，了解誤差來源。後續進一步選用中值濾波與卡爾曼濾波修正空間域及時間域的誤差，誤差主要來源為量測與分析過程產生的歧異值與系統誤差。藉由上述兩種濾波方法的不同搭配方式，對雷達量測水深資料進行優化與比較，並探討不同濾波方式的優缺點，最後發現最佳的濾波方式是：先對單筆水深資料進行中值濾波，再進行多筆資料的卡爾曼濾波，能夠最有效濾除空間與時間上的歧異值；原始未進行濾波的雷達量測水深與實測水深之相關性(相關係數平方值)是0.93，若以最佳濾波方式得到的水深與實測水深之相關性可提升至0.97；其優點是每輸入一筆雷達觀測資料，就能透過中值濾波提供品質不錯的即時水深資料，再利用後續觀測獲取的水深資料可進行卡爾曼濾波，來修正水深觀測的系統誤差影響，且可有效改善觀測期間因環境惡化造成觀測品質不佳的問題。
本研究除了使用卡爾曼濾波來對改善雷達量測水深的品質，更證明卡爾曼濾波可以有效地預測受潮汐影響的水深，並可從連續時段的雷達量測水深資料中推算及預測當地潮位變化。經與中央氣象局潮位資料比較，兩個最高潮時預測潮位誤差值分別為18公分與21公分，兩個最低潮時預測潮位誤差值分別為9公分與15公分。
以X-band雷達進行水深探測的優勢在於其可進行即時或連續的大範圍觀測，且觀測時間相對較不受天氣與晝夜的影響，在結合本文提出的資料優化技術後，可相當有效地提昇雷達觀測近岸水深的精度；且在進行連續的雷達觀測水深作業期間，如果未能即時取得當地潮位資料的情況下，能夠藉由卡爾曼濾波預測出不同潮時的潮位及水深變化。此外，雷達探測在海況不平靜期間，仍可正常作業，這是其他傳統海洋探測技術不及之處，因此可有效降低水深地形觀測的風險，提升水深量測之效率，並協助權責單位在極端海氣象事件過後得以及時進行海岸保護與防治工作之評估。

The real-time bathymetry mapping is important for maritime management. The X-band radar can operate quickly and continuously over a wide area under all weather conditions. The purpose of this study is to explore the improvement of bathymetry measurement obtained by X-band radar. The proposed technique integrates the median filter with the Kalman filter. The median filter acts spatially to remove the outliers. The Kalman filter acts temporally to reduce system errors. The filtered results were compared with a baseline target bathymetry. The proposed technique is demonstrated by case studies using the X-band radar at Cigu, Taiwan.

[1] Ashphaq, M., Srivastava, P. K., & Mitra, D. (2021). Review of near-shore satellite derived bathymetry: classification and account of five decades of coastal bathymetry research. Journal of Ocean Engineering and Science.
[2] Bass, F., et al. (1968). Very high frequency radiowave scattering by a disturbed sea surface Part I: Scattering from a slightly disturbed boundary. IEEE Transactions on Antennas and Propagation, 16(5), pp.554-559.
[3] Bell, P.S. (1999) Shallow water bathymetry derived from an analysis of X-band marine radar images of waves. Coastal Engineering, Vol. 37, pp.513-527.
[4] Bell, P. S., & Osler, J. C. (2011). Mapping bathymetry using X-band marine radar data recorded from a moving vessel. Ocean Dynamics, 61(12), pp.2141-2156.
[5] Billard, Brian, Ralph H. Abbot and Michael F. Penny, (1986). Modeling Depth Bias in an Airborne Laser Hydrographic System, Applied Optics, 25(13), pp.2089-2098.
[6] Birkemeier, W. A., & Mason, C. (1984). The Crab: A Unique Nearshore Surveying Vehicle. Journal of Surveying Engineering, 110(1), pp.1–7.
[7] Borge, J. N., & Soares, C. G. (2000). Analysis of directional wave fields using X-band navigation radar. Coastal Engineering, 40(4), pp.375-391.
[8] Camp, L., (1970). Underwater Acoustics. John Wiley & Sons, pp.308.
[9] Cohen, P.M., (1980). Bathymetric Navigation and Charting, Ayer Publishing.
[10] Desk, E. C. (1997). Electronic warfare and radar systems engineering handbook. Published in association with MTTS & IEEE.
[11] Emmanouil, G., et al. (2012). Combination of statistical Kalman filters and data assimilation for improving ocean waves analysis and forecasting. Ocean Modelling, 59-60, pp.11-23.
[12] Fabian C. Polcyn, R.A. Rollin (1969). Remote sensing techniques for the location and measurement of shallow-water features, Spacecraft Oceanography Project, pp.1-80.
[13] Flampouris, S., Seemann, J., Senet, C., Ziemer, F. (2011) The Influence of the Inverted Sea Wave Theories on the Derivation of Coastal Bathymetry. IEEE Geoscience and Remote Sensing Letters, Vol. 8, pp.436-440.
[14] Gonzalez, R.C., & Wood, R.E. (2006). Digital Image Processing(3rd Edition), Prentice-Hall, Inc.
[15] Guenther, G. C. (2007). Airborne LiDAR Bathymetry, Digital Elevation Model Technologies and Applications: The DEM Users Manual, 2nd edition, pp. 253-320.
[16] Hell, B. (2009). Towards the Compilation of a New Digital Bathymetric Model of the North Atlantic Ocean, Stockholm University Licentiate thesis.
[17] Holman, R., et al. (2013). cBathy: A robust algorithm for estimating nearshore bathymetry. Journal of Geophysical Research: Oceans, 118(5), pp.2595-2609.
[18] Holman, R., Plant, N., & Holland, T. (2013). cBathy: A robust algorithm for estimating nearshore bathymetry. Journal of Geophysical Research: Oceans, 118(5), pp.2595–2609.
[19] Honegger, D. A., Haller, M. C., & Holman, R. A. (2019,12). High-resolution bathymetry estimates via X-band marine radar: 2. Effects of currents at tidal inlets. Coastal Engineering, pp.103626.
[20] Honegger, D. A., Haller, M. C., & Holman, R. A. (2019,3). High-resolution bathymetry estimates via X-band marine radar: 1. beaches. Coastal Engineering, 149, pp.39–48.
[21] Huff, Lloyd C. and Guy T. Noll (2007). Sonar, Digital Elevation Model Technologies and Applications: The DEM Users Manual, 2nd edition, pp.321-349.
[22] Jawak, S., Vadlamani, S. and Luis, A. (2015) A Synoptic Review on Deriving Bathymetry Information Using Remote Sensing Technologies: Models, Methods and Comparisons. Advances in Remote Sensing, 4, pp.147-162.
[23] Jégat, V., Pe'eri, S., Freire, R., Klemm, A., & Nyberg, J. (2016). Satellite-Derived Bathymetry: Performance and Production.
[24] Jong, C.D. de, G. Lachapelle, S. Skone, and I.A. Elema (2002). Sounding Methods, Hydrography, 1st Edition, Delft University Press, pp.363.
[25] Kearns, Timothy and Lindsay MacDonald (2008). LiDAR Bathymetry, Laser Applications in Environmental Monitoring, Nova Publishers, pp.95-130.
[26] LaRocque, P. E., West, G. R. (1990), Airborne Laser Hydrography: An Introduction.
[27] Mattie, M. G., & Harris, D. L. (1978). The Use of Imaging Radar in Studying Ocean Waves. In Coastal Engineering.
[28] Mattie, M.G., Harris, D.L. (1978). The use of imaging radar in studying ocean waves, Proc.16th Coasal Eng., ASCE, pp.174-189.
[29] Morang, A., R. Larson, and L. Gorman (1997). Monitoring the Coastal Environment; Part III:Geophysical and Research Methods. Journal of Coastal Research, 13(4), pp.1064-1085.
[30] Nieto Borge JC, Reichert K, Jurgen D (1999) Use of nautical radar as a wave monitoring instrument. Coast Engineering, 37, pp.331–342
[31] O'Neill, S. (2013). Electronic Warfare and Radar Systems Engineering Handbook.
[32] Penny, M. F., R. H. Abbot, D. M. Phillips, B. Billard, D. Rees, D. W. Faulkner, D. G. Cartwright, B. Woodcock, G. J. Perry, P. J. Wilsen, T. R. Adams and J. Richards (1986). Airborne Laser Hydrography in Australia, Applied Optics, 25(7), pp.2046-2058.
[33] Pope, R. M., & Fry, E. S. (1997). Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements. Applied Optics, 36(33), pp.8710-8723.
[34] Senet, C.M., Seemann, J., Flampouris, S., Ziemer, F. (2008) Determination of bathymetric and current maps by the method DiSC based on the analysis of nautical X-band radar image sequences of the sea surface. IEEE Transactions on Geoscience and Remote Sensing, Vol. 46, pp.2267-2279.
[35] Simarro, G., Calvete, D., Luque, P., Orfila, A., & Ribas, F. (2019). UBathy: A New Approach for Bathymetric Inversion from Video Imagery. Remote Sensing, 11(23), pp.2722.
[36] Skolnik, M. I. (1990). Radar handbook(2nd Edition). Boston: McGraw-Hill Professional.
[37] Sun, S.-H., Chuang, W.-L., Chang, K.-A., Kim, J. Y., Kaihatu, J., Huff, T., & Feagin, R. (2019). Imaging-Based Nearshore Bathymetry Measurement Using an Unmanned Aircraft System. Journal of Waterway, Port, Coastal, and Ocean Engineering, 145(2).
[38] Tulldahl, M. (2006). Depth Sounding LiDAR Model with Multipixel Receiver. Systems Technology, FOI-Swedish Defense Research Agency Technical Report, pp. 1-24.
[39] USACE (2002). Engineering and Design Hydrographic Surveying.
[40] Welch, G. & Bishop, G. (2006). An Introduction to the Kalman Filter.
[41] Wu, L.C., Chuang, L.Z.H, Doong, D.J., Kao, C.C. (2011). Ocean Remote Sensed Image Analysis by the Two-dimensional Continuous Wavelet Transform, International Journal of Remote Sensing, 32(23), pp.8779-8798.
[42] Wu, L.-C., et al. (2017). Bathymetry Determination From Marine Radar Image Sequences Using the Hilbert Transform. IEEE Geoscience and Remote Sensing Letters, 14(5), pp.644-648.
[43] Wu, L.C., Kao, C.C., Yang, W.H. (2010). Sea State Monitoring from a Mobile X-Band Radar System, Sea Technology, 51(7), pp.40-42.
[44] Wu, L.C., Lee, B.C., Doong, D.J., Kao, C.C., Chuang, L.Z.H. (2008). Nonlinear Influences on Ocean Waves Observed by X-band Radar, Marine Geophysical Researches, 29, pp.43-50.
[45] Young I.R., Rosenthal, W., Ziemer, F. (1985) A Three Dimensional Analysis of Marine Radar Images for the Determination of Ocean Waves Directionality and Surface Currents, Journal of Geophysical Research, 90, pp.1049-1059.
[46] 吳立中、莊士賢、許朝敏、王仲豪、高家俊，2011。「時空合域影像於求取海面波流資訊之應用」，海洋及水下科技季刊，21(1)，第29-33頁。
[47] 吳立中、莊士賢、董東璟、高家俊，2010。連續小波轉換應用於遙測影像之分析—海底地形之解析，第32屆海洋工程研討會論文集。
[48] 吳泓毅，2013。以單一測線進行水下多音束測深系統之疊合測試，國立中山大學海洋環境及工程學系研究所碩士論文。
[49] 邱永芳、薛憲文、蔡金吉，2006。淺水域多音束量測水深技術研究，交通部運輸研究所。
[50] 高家俊、吳立中、董東璟、楊曜存，2004。應用航海雷達於空間波場觀測之研究(1/3)-降雨對雷達回波之影響。行政院國家科學委員會專題研究成果報告（編號：NSC92-2611-E-006-032）。
[51] 莊士賢、吳立中、孫永大、黃瓊珠、鍾育仁、蔡昀展、鄭仁杰，2019。X-band雷達於近岸水深量測精度之改良，第四十一屆海洋工程研討會論文集。
[52] 黃子庭，2018。應用X-band航海雷達於海岸灘線測量之可行性研究，國立成功大學海洋科技與事務研究所碩士論文。
[53] 經濟部水利署第六河川局，2019。台南海岸防護(急水溪口至曾文溪口)基本資料監測調查分析，第一次期中報告。
[54] 薛憲文、史天元、徐佳筠，2012。水域測深方法暨原理探討，航測及遙測學刊，16(3)，第203-217頁。
[55] 謝金原，1997。太空微波遙感與探測原理及其運用。科學知識，46，第17-24頁。
[56] 魏世聰，2012。微波雷達與CCD 影像分析於潮間帶地形測量之應用，國立中央大學水文與海洋科學研究所碩士論文。

網路參考資料
[1] NOAA Ocean Explorer: Deep Scope Background. (2010). Retrieved April 22, 2021, http://oceanexplorer.noaa.gov/explorations/04deepscope/background/deeplight/media/diagram3.html
[2] ESA's Earth Online website. Retrieved April 22, 2021,
https://earth.esa.int/web/guest/missions/
[3] 波浪運動. (2017). Retrieved April 26, 2021,
from http://w3.oc.ntu.edu.tw/chap7/chap7s2.htm