Water Quality Mapping Using Remote Sensing Imagery –Application to Fei-Tsui Reservoir

翡翠水庫為大台北地區的主要自來水源，近年來水質隨集水區人為活動增加等環境因素正逐漸出現優養化情形；目前國內水質優養問題多利用Carlson(1977)所定義之營養狀態指標(TSI)進行，並將各項單一指標平均後得綜合指標加以評估，且由於庫區水域廣大，對於管理者而言僅能以點採樣方式進行水質監測，可能造成水質評估之偏頗。本研究之目的包括討論並修正國內目前經常使用之TSI值，使其符合翡翠水庫水環境生態狀況；其次考慮使用衛星遙測資料改善傳統水質採樣檢測問題，並得到庫區水體之水質空間分布情況再加以評估水質營養狀況。翡翠水庫資料建立透明度、葉綠素-a及總磷三水質參數之間關係，並針對Carlson所提出模式中兩個主要因子，即最大透明度與SDD倍率因子予以修正，重新建構適合翡翠水庫水質環境之營養狀況指標(FeiTsui Trophic State Index, FTSI)，得到三項單一營養狀況指標(FTSI(SDD)，FTSI(Chla)，FTSI(TP))，再利用葉綠素-a濃度(FTSI(Chla))作為營養程度之主要判斷依據，小於61為貧養，大於68為優養，介於61至68間為普養。水質採樣日期接近之SPOT衛星影像資訊，求出不同影像波段水體反射率與三項水質指標之關係，並反推出庫區全水域之水質指標空間分布，而影像推估之水質指標數值與實際採樣結果相比，相關係數達到0.88，而影像運算結果發現，翡翠水庫僅有在上游部分河段及支流匯流口有優養之現象，下游蓄水區水質較佳，整體而言，近年來翡翠水庫水質情形良好，維持在貧養或普養狀態。此方式可大幅提升評估水庫整體優養化之能力，且節省現地採樣所耗費人力、成本和時間，提供管理單位對於水庫未來全面性的水質監控。Fei-Tsui Reservoir is the main source of water supply for the Taipei Metropolis. However, reservoir eutrophication has become a critical concern of the reservoir administration agency due to increasing anthropogenic activities in recent years. The Carlson trophic state index (CTSI) is widely used in Taiwan for monitoring of reservoir water quality. Unfortunately, misuse of CTSI, including averaging individual indices and without calibration for local conditions, has led to serious debates and confusions about the current state of the reservoir water quality. Thus, the objectives of this study are to modify the CTSI model considering the water quality characteristics of Fei-Tsui Reservoir, and to develop a remote sensing technique for reservoir trophic state evaluation. set of modified trophic state indices was developed for the Fei-Tsui Reservoir by considering empirical relationships among Chlorophyll-a concentration, total phosphorous concentration, and Secchi disk depth. Criteria for determining reservoir trophic state using these indices were also proposed. ultispectral images from the SPOT satellite were collected and used to develop algorithms for water quality estimation from radiances recorded by the SPOT satellite. Estimates of water quality based on remote sensing techniques are in good agreement with water quality measurements with correlation coefficients higher than 0.88. Images of water quality distribution derived from remote sensing techniques reveal that eutrophication only occurs in the upstream area and confluence of tributaries and the main channel, while water quality condition generally improves towards downstream. Generally speaking, trophic states of the Fei-Tsui Reservoir are oligotrophic or mesotrophic in recent years.口試委員會審定書 I謝 II要 Ⅲbstract Ⅳ錄 Ⅴ目錄 Ⅶ目錄 XI一章 前言 1-1.1研究緣起 1-1.2研究目的及流程 1-1二章 文獻回顧 2-1.1湖泊、水庫優養化評估方法 2-1.2使用衛星影像監測湖泊水庫水質 2-6三章 翡翠水庫水質參數分析與卡爾森營養狀態指標 3-1.1研究區域介紹 3-1.2水質參數分析 3-2.3 卡爾森營養狀態指標 3-18四章 應用衛星遙測影像推估水質狀況 4-1.1研究區域衛星影像 4-1.2衛星遙測影像資料前處理 4-6.3水體反射率之計算 4-10.4水質參數與衛星影像各光譜波段數值關係建立 4-12五章 結果與討論 5-1.1 翡翠水庫營養狀態指標驗證 5-1.2使用衛星影像評估水質空間變異特性 5-10 六章 結論與建議 6-1.1 結論 6-1.2建議 6-2考文獻 參-