次足跡全波形空載光達技術於河床粗糙度分析

SUB-FOOTPRINT TECHNIQUE FOR AIRBORNE FULL-WAVEFORM LIDAR DATA IN RIVERBED ROUGHNESS ANALYSIS

林彥廷(Yan-Ting Lin) ； 徐若堯(Jo-Yao Hsu) ； 韓仁毓(Jen-Yu Han)

《中國土木水利工程學刊》 32卷6期 (2020/10) Pp. 543-550

https://doi.org/10.6652/JoCICHE.202010_32(6).0007

摘要

粗糙度為地表起伏變化或侵蝕程度重要指標，用於地物分類與河流沖積特性分析，而現行河床粗糙度調查仍仰賴人工耗時費力實地檢測。遙感探測技術中，全波形空載光達資訊顯示細微地表變化，具發展為一種獲得地表粗糙度方式。本研究利用波形模擬確立一個足跡中地表幾何及驗證其可靠性，以預處理除去地形效應產生雜訊，由波形樣版對實際資料進行波形匹配與分類，其中波形樣板重建根據感測器參數、地表幾何對於河床粗糙度關係特性，於特定航高及粒徑尺寸建立標準波形，同時考量朗柏表面反射及地形散射之光達回波強度改正，最後波形匹配以最小殘差平方合之類別作為該足跡之河床粗糙度值。依研究成果顯示，能以優於5公分平均粒徑差異符合於現地調查量測結果，有效提升實務應用與成果品質，具體結合新式空間資訊技術與環境分析。

關鍵字

全波形空載光達 ； 河床粗糙度 ； 次足跡技術 ； 曼寧係數n

並列摘要

Surface roughness is an important index characterizing terrestrial variations or its degrees of erosion. In other words, it is a numerical measure of topographic geometry. Nowadays, the acquisition of surface roughness is a time-consuming and laborious task because it requires plenty of field work. On the other hand, owing to rapid hardware and software developments, modern remote sensing techniques have been routinely applied in various spatial data collection and analysis tasks. Particularly, airborne full-waveform LiDAR could capture detailed terrestrial variations and is thus a potential alternative to measure surface roughness. In this research, full-wave form an airborne LiDAR signal and its relation to the topographic variation within a footprint are analyzed. Under the specific flight heights and particle sizes, the reference waveform is reconstructed as a standard waveform based on the parameters of the sensor and the geometry of the ground surface. Besides, an intensity correction of observed full-waveform LiDAR data is applied by using Lambertian reflectance model and DEM information to remove the effects of energy loss during transmission. Finally, the waveform matching between the reference waveforms and the observed waveform data takes the category of the smallest residual square sum as the riverbed roughness value of the footprint. The correspondence between the full-waveform of LiDAR data and common surface roughness index are established. The result shows that the average particle size difference can be better than 5cm to approximate the filed survey data. This technique is successfully developed to benefit the applications in various topographic analyses in geospatial, geotechnical and hydrological fields. Not only the cost of field data acquisition could be greatly reduced, but the efficiency and quality of real applications improved. The proposed study integrates the latest spatial techniques and environmental interests. As a consequence, the technical connotation and industrial value of modern remote sensing techniques are extended.

並列關鍵字

airborne full-waveform LiDAR ； riverbed roughness ； Manning's coefficient n ； sub-footprint technique