عنوان مقاله [English]
Investigating and measuring the amount of rill erosion at ground level is one of the sensitive and time consuming tasks in erosion management. The aim was to measure erosion using image analysis in the southwest of Kermanshah. Images of 12 erosion events were taken on different days. Photos were taken in ten-meter increments, magnified and scaled through software. The width and depth of the rills on the ground were measured with a caliper and on the image with the help of software. In this study, a new method was introduced to calculate the depth of erosion. Erosion events were recorded using a full-frame camera with a 100mm and 125mm macro lens. In addition to the two-dimensional data, the wall shadow of the rills was used to measure the depth of erosion. The dimensions of the rills were calculated by direct and indirect measurements, and the obtained data were analyzed. The results showed that the error between the direct and indirect values of the dimensions of the rills is in the range of 5%. The measured data from the recorded erosive images showed that this method has good accuracy in determining the volume. The accuracy and speed of the rill dimensions were measured. In the process of measuring the dimensions of rills erosion, it is generally assumed that there is a real or accurate value, although this exact value may never be revealed; But based on the least time and resources available, we tried to find this ideal value within the ability of the method and tools. The method used during the measurements may have slightly different results. No real or exact value, how do you now report your findings for the best estimate? The most common way is to provide a range of near-realistic data. The closer the measured data on the image (rills erosion dimensions) to the actual data or the accepted value, the more measurement error it provides. This provides the relative accuracy of the measurement. The degree of consistency among independent measurements is the same quantity (here width, rills depth) that results in reliability and reproducibility; Shows measurement accuracy. An ideal or real value is needed to accurately measure the dimensions of the rills on the images. To do this, the field dimensions of the rills were measured three times simultaneously with imaging (February 6, 2017 and May 2, 2016) with calipers and rulers (direct and real data); The same rills erosion was then imaged. Using the image analysis algorithm in the software, measurements were made on the same rills (indirect data). It was assumed that the ideal or real data is the same as the field data; From it for the correctness of the results obtained; used. Because there is no theoretical data for furrow erosion facies, it is assumed that even if the true value is not revealed, the same available field values can be trusted. In this regard, reference data is not available for either the actual value or the measured value to be compared, with both measured values being equally accurate. Therefore, there is no reason for the former to be superior to the latter and vice versa. Uncertainty is an estimate that was considered for the accuracy and precision of measurements.
The accuracy of the data is measured by the proximity of the data extracted from the rills erosion event image to a real value. The distance between the calculated error value and the measured value showed that the method used in this study is reliable.
Accordingly, the data of other images of erosive events were analyzed with reference to the small amount of measurement error between the actual data values and the measured data.
According to the characteristics of the rills in the other images, the results showed that the width of the rills was between 23.7 to 141.26 mm and their depth was between 19.39 to 58.99 mm and their length varied from 6236 to 91755 mm. The width and depth of the rills are suitable indicators to evaluate the development of the rills. In fact, it was used to evaluate the use of field images to measure the properties of rills, auxiliary data, and the position of the sun and amplitude at the time of shooting. With the arrival of these auxiliary factors in the extraction of rills depth data; The distance between the actual data and the data measured on the image minimized their sharpness. Among the rills erosion characteristics, measuring the width and length of the rills was easier than the depth of the rills. Because two-dimensional sizes can be easily measured on image pixels. More than 2450 transects in the width and length of the rills were drawn to calculate the width, shadow length of the rills wall and the length of the rills, from data that were taken three times at the same time as imaging (February 4, 2017 and May 2, 2016) with calipers and rulers. Were measured (direct and real data) used to control indirect data. By comparing the results of this type of measurement with direct measurement of the same data, the amount of measurement error was determined; The results of direct and indirect measurements show that the extracted data of two-dimensional images are suitable for measuring object erosion.
To measure the characteristics of furrow erosion in traditional methods, rulers, chains, filling furrows with soil and other artificial materials are still used, but they do not have the ability to study changes and spatial distribution of furrows, but in this method, which is used in the erosion range It was possible to determine the morphometric parameters of the furrow, which in traditional methods only allows the calculation of the volume of lost soil. In this study, it was found that measuring through ground photographs and analyzing them not only increases the speed and accuracy but also Provides spatial distribution, in addition to estimating the extent of spatial damage of soil erosion.