采用不同方法测量切沟的误差分析

Error Analysis of Gullies＇ Measurement with Different Methods

使用卷尺测量切沟的体积和面积是研究土壤侵蚀中最常用也是传统的测量方法,着重分析了使用卷尺测量切沟时,测得切沟体积的误差。其误差主要包括由卷尺精度限制而导致的误差,以及由测量原理所造成的系统误差。运用误差传递公式计算由卷尺精度限制导致的误差,这种误差与测量相邻横截面的间隔长度无关,只与测量仪器即卷尺有关;对于不同的切沟,卷尺精度导致的误差占所测切沟体积的百分比也是基本相同的,不到2%。由测量原理造成的系统误差又可分为两种：由于横截面不规则造成的系统误差,最多可达到体积的2%;由于相临两个横截面之间形状不规则造成的系统误差。在野外测量的时候,每次测量距离保持在10 m左右比较合适。卷尺测量与差分GPS测量的切沟体积的比较表明,单次测量误差较大,在10%左右,而两次测量的体积差,即两种方法所得的切沟体积的年际变化量相差不大。也就是说明,用卷尺测量切沟体积的年际变化是有效的。

The authors mainly study the error of the gullies＇ volume when they are measured with tapes, since it＇s a very traditional method to measure gullies＇ volume and area with tapes in the research of gully erosion. The error is mainly caused by limited precision of tapes and mechanism of measurement. The error caused by limited prccision of tapes can be calculated with error transfer formula, and it was found that this kind of error do not depend on the distance between two neighbouring cross sections, but only relate to the tapes we used. The ratio of the error to gullies＇ volume is less than 2%, which is the same for different gullies. The system error caused by mechanism of measurement is comprised of two parts. One is due to the nonidentity of cross sections, which has maximum value of 2% the other one is caused by irregularity of cross sections. In order to minimize the system error caused by the nonidentity of cross sections, it＇s important to decrease the distance betwcen two neighbouring cross sections, which was about 10 meters in our outdoor measurement. Additionally, we also compare the gullies＇ volume measured with tapes with that measured with GPS. It＇s found that the error of single measurement is about 10%, and that the annual variations of gullies＇ volume measured with tapes and GPS are almost the same. Therefore, it＇s an effective method to measure annual variation of gullies＇ volume with tapes.