關鍵詞：光達、海岸像片地形圖、高程濱線指標、數值地形模型
4. 對臺灣空載光達資料在海 岸監測的建議
海岸受到海水作用的影響，動態性遠高於陸域 環境，就一年內來看，海水位除了受隨潮汐變化而 漲落，也受到季節性和偶發性天氣影響，所以航照 拍攝或光達施測的時間選擇需要有明確的規範，除 了考慮飛行安全和拍攝品質，還要盡可能降低海岸 的天然變動對海岸監測造成的干擾(Graham et al., 2003; Ruggiero et al., 2003)。
以美國為例，針對海岸經營目的訂定的光達測 量規範，包括拍攝時必需為晴朗天氣，也必須考慮 到海灘季節性的動態變化，並且以植被較少的季節 進行拍攝，以取得較為精確的地面資料，潮汐也是
必須考慮的因素之一，必須選擇平均更低低潮位 (Mean Lower Low Water)時期進行測量(Leigh and Hale, 2005)，以取得較大範圍的海岸地貌，並且避 免風浪的遮蔽。此外，美國官方一向以平均高水位 線(mean high water line)為濱線指標，從早期現場實 地測量到航空照片攝影測量，都以取得平均高水位 線為繪圖、測量的目標(Graham et al., 2003)，所以 最近期的光達資料也可以和過去的濱線製圖成果 結合。例如，美國地質調查所曾於 2004 至 2006 年間進行大範圍的海岸濱線變遷研究計畫(Morton et al., 2004; Morton et al., 2005; Hapke et al., 2006)，
1998 年之後以空載光達為資料來源，在此以前回 溯至1850 年代，則是以地形圖(Topographic sheets, T-sheets)和航空照片為資料來源。
重新取樣大小 體積變化量 （m3） 重新取樣大小 體積變化量 （m3）
5 m -31976.28 25 m -26895.85
10 m -27200.18 30 m -25201.52
15 m -24355.30 50 m -26421.60
20 m -23068.78 100 m 10695.52
臺灣在海岸地區的圖資雖然豐富，但是幾乎沒 確度較高，Ruggiero et al. (2003)在研究中指出，即 便在美國專程飛航規劃下所繪製的高水位線，也與 (Ackermann, 1999)，不但可以快速且精確的擷取濱 線資料，還可以利用多期的高程資料計算海岸地形
在不同風浪、潮汐情形下拍攝，勢必造成一些限制。 ml，上網日期：2008-1-30。
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1Research Assistant, Central Geological Survey, MOEA Received Date: Jun. 22, 2009 2Associate Professor, Dept. of Geography, NTNU Revised Date: Sep. 23, 2009 3Associate Research Fellow, Institute of Earth Sciences, Academia Sinica Accepted Date: Oct. 21, 2009 4Geologist, Central Geological Survey, MOEA
* Corresponding author, Phone: 886-2-77341634, E-mail: [email protected]