激光扫描和摄影测量在坡面侵蚀演变过程的适用性

为研究激光扫描和摄影测量技术在监测坡面侵蚀演变过程中的精度及适用性，该研究利用近景摄影测量技术和三维激光扫描技术对长历时条件下坡面侵蚀演变过程进行监测，获取不同时段的坡面微地形数据，基于坡面高精度数字高程模型（Digital Elevation Model，DEM）对坡面侵蚀演变过程进行分析，探究2种非接触式测量方法在坡面侵蚀监测中的适用性和精确度。结果表明：1）按主导侵蚀方式的不同，坡面侵蚀过程可分为片蚀阶段、细沟发育阶段和细沟成熟阶段；2）2种非接触式测量方法均能够精确的对坡面侵蚀产沙过程进行监测，最大相对误差为-16.82 %，2种方法在坡面侵蚀量测量方面有很好的适用性。3）近景摄影测量技术在坡面侵蚀产沙监测、细沟深度测量和坡面微地形模拟方面要优于三维激光扫描技术。该研究可土壤坡面侵蚀监测方法的选择提供参考。

Application of laser scanning and photogrammetry in the evolution process of slope erosion

Soil erosion on a slope is one of the most serious soil degradation that caused by the complex dynamic process of water draining down the slope. Quantitative monitoring of the slope erosion process is of great practical significance to clarify the erosion mechanism for the better models in the recent years. A non-contact measurement has been widely used, such as the laser scanning or photogrammetry, due to the high efficiency and accuracy. However, it is still lacking on the accuracy and applicability evaluation in the process of slope erosion, especially for the rill morphology characteristics. In this study, the laser scanning and photogrammetry were selected to monitor the evolution of soil slope erosion under the indoor artificial rainfall, in order to quantitatively explore their accuracy and applicability. The red soil was collected with the granite parent material from the Changting County, Hubei Province, China. The test material was then selected as the leaching, sedimentary, and parent material layer from the bottom to the top at the sampling point. The soil trough was used with the size of 4.0 m (length) × 2.0 m (width) × 0.60 m (height), particularly with the depth of soil filling of 0.50 m. The soil was then filled with the 0.15 m thick parent material layer, 0.20 m sedimentary layer, and 0.15 cm leaching layer before the test. The soil tank was subjected to the multiple cycles of drying and wetting. The static settlement was set at least two months, in order to make the soil layers and particles as close as possible to natural conditions. The whole duration was 1 h for the single-field simulated rainfall or runoff test after the runoff on the slope surface. The total rainfall was 100 h, where the interval was 24 h between each two intermittent rainfall. The rain intensity was also set to (90±5) mm/ h. The sediment ocean was then collected during the rainfall. After that, the 3D laser scanning and close-range photogrammetry were employed to record the micro-topographic and surface morphology of the slope at each rainfall interval. As such, the digital point cloud was obtained on the slope surface after the rainfall. At the same time, the length, width and depth of each rill on the slope were measured at the intervals of 10 cm, in order to determine the evolution of the morphological characteristics of the slope rill. The characteristic parameters of rill morphology were calculated to collect the runoff sediment and measurement. A comparison was also made on the laser scanning and photogrammetry technology in the erosion monitoring test. The results show that: 1) The slope erosion process was divided into the sheet erosion, rill development and maturity stage, according to the different dominant erosion. 2) Both non-contact measurement methods performed better to accurately measure the slope erosion. Specifically, the maximum relative error was -16.82% for the process of sediment production. The better applicability was also achieved in the measurement of slope erosion quality. 3) The close-range photogrammetry technology was superior to the 3D laser scanning in the monitoring slope erosion and sediment production, rill depth measurement, and slope micro-topography simulation. Therefore, the digital expression was realized for the evolution process of slope erosion, in order to promote the high efficiency and high precision of slope erosion monitoring. The finding can also provide the strong reference in the technology selection for the soil slope erosion.