多時影像與DEM資料應用於頭前溪口變遷分析

Change Analysis of the Estuary of Tou-Chien River Using Multi-temporal Images and DEM Data

本研究利用多時期光學影像、航測數值高程模型（DEM）及空載光達資料，經疊合分析後探討頭前溪口附近的地形變遷。其中光學影像均經過幾何校正，藉由影像判釋及疊合分析，以推估河口區的地形變化；航測DEM與光達資料均以TWD97坐標為基準，網格化後直接比對高程差異，而每隔50公尺亦藉由垂直河川剖面，比對分析河道細微的高程變化。初步結果顯示，2000年以前頭前溪口河道寬度變化不大，但新竹漁港南防波堤以南的地形，於港口興建初期有明顯侵蝕現象，2000年以後則有緩慢堆積情形，而漁港北防波堤北側河口處則一直處於堆積狀況；另由2003年與2005年兩個時期的DEM資料疊合比對，顯示漁港北防波堤北側的頭前溪河口附近地形，因堤防的興建而有堆積情形發生，且緊鄰河口北側地形有往外海及往北逐漸堆積趨勢；而比對靠近河口段每間隔50公尺之剖面高程，顯示頭前溪河口處的沙洲北端平均堆積高程在0～2公尺之間，沙洲東南端則有侵蝕現象，且沙洲南端西側的河道有堆積情形，使得河道有變窄的趨勢。 The morphological change within estuary of Tou-Chien River in northern Taiwan for the last25 years is analyzed by using multi-temporal SPOT and Landsat TM images, photogrammetricDEM and LiDAR DEM. Multi-temporal SPOT images are rectified, registered, and classified forobtaining the land-cover changes in a time series. DEMs obtained by both photogrammetry andairborne LiDAR are used for observing topographical changes. DEMs at different times can becompared to estimate the elevation change. In addition, cross-sections are made every 50 metersfor observing detailed change of river profiles. Results show that before 2000, the width of theestuary of Tou-Chien River is relatively stable whereas after the construction of Nan-Liao FisheryHarbor, the southern part of the southern breakwater was subjected to obvious erosion. After 2000, slow depositional process took place. The north side of the estuary of northern breakwater was obvious in deposition. The comparison of the 2003 DEM and 2005 DEM shows that thetopography of the north side of the north breakwater became depositional after the construction ofNan-Liao Fishery Harbor. And, the topography expanded outwards. The 50 meters interval profilesof the estuary show that the north side of the estuary sand-bars has deposits of 0~2m whereassoutheast side of the sand-bar was subjected to erosion and the western channel to the south side ofthe sand-bar was depositional and the width of the channel became narrower.

The morphological change within estuary of Tou-Chien River in northern Taiwan for the last25 years is analyzed by using multi-temporal SPOT and Landsat TM images, photogrammetricDEM and LiDAR DEM. Multi-temporal SPOT images are rectified, registered, and classified forobtaining the land-cover changes in a time series. DEMs obtained by both photogrammetry andairborne LiDAR are used for observing topographical changes. DEMs at different times can becompared to estimate the elevation change. In addition, cross-sections are made every 50 metersfor observing detailed change of river profiles. Results show that before 2000, the width of theestuary of Tou-Chien River is relatively stable whereas after the construction of Nan-Liao FisheryHarbor, the southern part of the southern breakwater was subjected to obvious erosion. After 2000,slow depositional process took place. The north side of the estuary of northern breakwater was obvious in deposition. The comparison of the 2003 DEM and 2005 DEM shows that thetopography of the north side of the north breakwater became depositional after the construction ofNan-Liao Fishery Harbor. And, the topography expanded outwards. The 50 meters interval profilesof the estuary show that the north side of the estuary sand-bars has deposits of 0~2m whereassoutheast side of the sand-bar was subjected to erosion and the western channel to the south side ofthe sand-bar was depositional and the width of the channel became narrower.