基于DEM的黄土高原退耕梯田地形“逆过程”演变研究

After a large number of agricultural terraces are abandoned, the slope surface of the terraces is undergoing the process of reconstructing by natural force in the Loess Plateau. Because its characteristics are contrary to the original artificial terraces in the external performance and formation process, we call it the ‘reverse process’ of the terrain evolution on the slope of the abandoned terraces. Firstly, from integrating morphology with formation mechanism, the base concepts, essential properties, influencing factors, main types, geomorphology connotation of the "inverse process" will be studied, and on this basis, the qualitative, quantitative and positioning indicators system will be put forwarded. Using high resolution DEM and high resolution remote sensing images as data sources, the automatic recognition method of the topography of abandoned agricultural terraces will be studied. A series of innovative digital terrain methods will be presented that combined micro dissect and macro analysis, integrated field investigation with digital simulation, combined the intrinsic mechanism and morphological analysis, and the essential progress and law of slope microtopography development that caused by the evolution of the ‘reverse process’ of abandoned terraces will be revealed. The study is of great significance to revealing the dynamic mechanism of microtopography evolution of abandoned terraces slope, deepening the research on the loess landform, especially on microtopography of loess slope. The study is also of great significance to innovating the theoretical and technical methods of digital terrain analysis and giving scientific advice to ecological restoration projects for soil and water conservation in the Loess Plateau.

黄土高原大量梯田退耕后，正经历由自然力对梯田坡面的再改造过程。由于其在外在表现与形成过程上与原先人造梯田相悖的特征，我们称之为退耕梯田坡面地形演变的“逆过程”。本课题首先从形态及其成因机理相结合的视角，研究该“逆过程”的基本概念、基本属性、影响因素、基本类型、地貌学内涵等概念模型，在此基础上提出定性、定量、定位描述的指标体系；以高精度DEM和高分遥感影像为信息源，研究退耕梯田地形的自动识别方法；通过微观剖析与宏观分析相结合、野外实地调查与数字模拟相结合、形态分析与内在机理相结合等一系列创新的数字地形分析方法，揭示退耕梯田“逆过程”演变所致坡面微地貌发育变化基本进程与规律。该研究对于揭示退耕后梯田坡面微地貌演变的动力机制及地表响应过程，深化对黄土地貌特别是黄土坡面微地貌的研究，创新数字地形分析的理论与技术方法，以及对于黄土高原地区正在进行的水土保持生态修复工程都具有重要意义。

大量梯田退耕后经历由自然力对梯田坡面的再改造过程，由于其外在表现和形成机制上与原先人造梯田相悖的特征，我们称之为梯田地形“逆过程”演变。黄土梯田“逆过程”演变所致的坡面微地貌发育的基本进程与规律，尚未形成系统性认识。本课题在大量野外调查基础上，以无人机摄影测量获得的厘米级影像与数字高程模型为主要数据源，对梯田地形“逆过程”演变的概念模型、微地貌识别、特征量化、空间差异性和演变模拟进行了研究。重要结论如下：①梯田地形“逆过程”是在梯田在缺乏维护情况下受到风力、流水等外力作用和重力作用而发生的坡面地貌演变。根据地形演变的程度、坡面空间分布、微地貌形态，将黄土高原退耕梯田地形“逆过程”演变分为不同的类型。②崩塌、陷穴、侵蚀沟是黄土退耕梯田地形“逆过程”演变中主要的微地貌类型。利用地形、纹理和光谱特征，提出了基于面向对象的梯田“逆过程”微地貌自动识别方法。③从形态、结构、发育位置和发育程度四个方面，构建了退耕梯田地形“逆过程”演变特征指标体系。基于田坎线的提取分析，实现了从线、面、体不同视角对退耕梯田地形“逆过程”演变程度的定量表达。④黄土高原从北向南退耕梯田地形“逆过程”演变，受到气候、土壤、地貌类型的影响，具有明显的区域差异性。坡面尺度的梯田“逆过程”演变差异性与梯田形态、退耕时间、土地利用方式有关。⑤水文模型方法实现了梯田坡面“逆过程”演变的水流、泥沙、侵蚀与沉积模拟，揭示了降雨条件下梯田“逆过程”演变是流水和重力作用下地表和地下泥沙运动引起的、多种侵蚀沉积动态平衡共存的坡面微地貌发育演变过程。课题研究成果为揭示退耕后梯田坡面微地貌演变的动力机制及地表响应过程奠定基础，深化了对黄土人工地貌和黄土坡面微地貌的研究，对黄土梯田的保护与利用以及黄土坡面的水土保持工程建设具有一定的参考意义。