油菜机械直播作业厢面地表粗糙度测量与分析

Measurement and analysis of surface roughness of rapeseed mechanized direct seeding operation

油菜机械直播后种床整理质量是影响油菜成苗率的关键要素。针对目前油菜机械直播种床厢面粗糙度测量和数据处理方法不能完全反映地表真实情况的现实问题,该文提出一种基于激光雷达扫描技术的区域地表粗糙度现场测量和量化方法,通过测量装置可快速获取油菜直播厢面幅宽内的地表高程三维数据。基于油菜机械直播作业特性,对采集的作业厢面高程数据进行去倾斜趋势和去边坡趋势处理,降低了厢面倾斜和边坡特征对粗糙度计算的影响。对不同空间采样间隔和不同采样角度截面数据的粗糙度统计结果表明:170mm采样间隔下的平均均方根高度和均方根高度平均误差均高于5mm采样间隔下的计算结果;在垂直机组前进方向0°、45°和90°三个方向上地表截面高程数据的均方根高度最大差值和相关长度最大差值分别为7.69mm和25.14mm,且带有种沟等结构化特征的油菜种床厢面存在明显的各向异性。以不同大小区域的滑动取样窗口进行局部粗糙度量化的统计结果表明:当窗口宽度为厢面幅宽和0.5倍时,窗口长度大小不低于1.2m可使均方根高度的标准差稳定在0.27mm以内,而通过对每个取样窗口进行单独去倾斜趋势处理可消除地表局部倾斜对粗糙度计算的影响。研究结果可为油菜机械直播作业厢面粗糙度测量和量化方法提供参考依据。

The quality of seedbed after seeding such as soil surface leveling,soil-breaking rate and seed furrow preparing and so on,are the main factors affecting the seedling rate of rapeseed.A good seedbed is a necessary condition for uniform seedling emergence,increasing the rate of subsequent seedlings and promoting the homogeneity of plants after sowing.In view of the fact that the measurement and data processing methods of rapeseed seedbed surface roughness under mechanized direct seeding cannot fully reflect the real soil surface condition,a method of measuring and quantifying roughness surface area by using laser radar scanning technology is proposed in this paper.The main components of the measuring device are the lidar,linear guide,stepper motor,portable computer and other components.The device can quickly acquire soil surface data in three dimensions through the whole working width of direct seeding machine.The surface roughness data of rapeseed combined direct seeder and no-tillage direct seeder after operation were used to detect the effect of two kinds of seedbed operation on seedbed surface.The characteristics of rapeseed direct seeding process were analyzed,three-dimensional digital modeling and detrend processing of ground data after two kinds of direct seeders were carried out by using MATLAB.The least square method was utilized to eliminate the inclined tendency of seedbed surface,the fourth order polynomial was applied to remove the slope trend in the width direction of the soil surface of rapeseed combined direct seeder.The root mean square(RMS)height and the correlation length were involved as evaluating parameters to analyze the data.Statistical results of roughness parameters for different spatial sampling intervals and different angles cross-section data showed that the average RMS height and RMS height mean error of 170 mm sampling interval were all higher than that of 5 mm sampling interval,the average RMS height of the 170 mm sampling interval was 2.2 mm higher than that of the 5 mm sampling interval,the corresponding correlation length was around 1.8 times the latter;and the RMS height and the correlation length error of the 170 mm sampling interval were higher than that of the 5 mm sampling interval.The maximum difference of RMS height and correlation length of surface elevation data were 7.69 and 25.14 mm respectively in the three directions of 0,45 and 90 degrees in the forward direction of vertical unit,and there was obvious anisotropy on the surface of seedbed with structural characteristics such as seed trench.Statistical results of local roughness quantification using sliding sampling windows in different size regions showed that when the window width is 0.5 times the compartment width,the standard deviation of RMS height can be stabilized within 0.27 mm if the length of the window is not less than 1.2 m,and the influence of local surface tilt on the roughness calculation can be eliminated by the trend treatment of the tilt of each sampling window.The results can provide reference for the measurement and quantitative analysis of surface roughness in rape direct seeding operation.