Performance of two measurement methods of pin meter and laser disto meter in the measurement of microtopography Created by desert pavement

Extended abstract
Introduction:
Wind erosion is one of the main factors of soil degradation and air pollution. Roughness by creating an obstacle to wind flow, decreases wind speed and consequently reduces the amount of wind erosion, hence its measurement in wind erosion is important. Roughness is one of the most effective factors. In soil erosion by water and wind by accuracy measurement of soil surface roughness, can be used by them as indicators of ecosystem healthMethods for measuring of soil surface roughness using Roughness meter can be classified into two large classes. Contact methods which mechanical devices are directly in contact with the soil. Non-contact methods that the measuring instruments are far away from the soil surface and do not touch with surface of the soil.
Pin meter includes a row of pins with equal distances which is placed in a frame that can be placed according to high and low levels of roughness.
Materials and methods
Yazd - Ardakan Plain with a total area of 7,15950 square kilometers Is located in the northern part of Yazd province.and Is located in   Longitude 748337 to 296893 East and in latitude 3559572 to 3566743 North




After determining the studied area, 10 randomly selected samples were selected in the Yazd-Ardakan Plain and the sampling was carried out in both methods. Roughness data of soil surface were taken randomly by using laser distance measuring and pin meter in 10 transects. In each transect, roughness height was measured of length 50 cm. The distance between the pins in pin meter method is 2 cm and measuring distance in Laser Distance Meter is 2 cm. Thus, the height of the points was recorded separately by both methods, in each transect,
 


Methods for measurement of roughness index
Pin meter
In this way, with the help of pins on the soil surface, Height of pebbles, is measured at several points to the base level. That way, Roughness altitude information was recorded. According to the definition, this index (roughness) is the standard deviation of the height of the points, which is obtained using the following equation:

That in, SD, , , and n are respectively, standard deviation of points Height, the height of each of the points (mm), Average height and the number of sample points in the transect


Laser method:
This method, measures roughness using the laser meter model (X310) from the Leica Company. The laser meter is A small and handy device, that calculates the exact distance, by using laser technology and by calculating round-trip time of laser lightworking method is as follows: The laser beam is emitted to the target and the calculation is performed with an error of less than 3 mm. Thus, the height of the points is measured at 50 cm up to the base level


(Result)
The maximum amount of the calculated average by the method of the pin meter and laser distance meter is 2 and 1, respectively. The minimum amount of calculated average for both methods is in the point 10. The highest and lowest amount of standard deviation derived from laser distance meter and pin meter methods are for points 2 and 10 respectively.


In Table 1, are presented the results of the comparison of the two methods of pin- meter and Laser rangefinder. As can be seen:
 
 
Table (1): Statistical comparison of roughness index of two methods at 2 cm distance






t


Degrees of freedom













Mean ± Invalid Criterion













Groups

 2cm



characteristics













438/1
24
70/1±83/21
pin meter
Point 1
The roughness index


28/2±66/23
Laser


120/1-
24
37/2±50/23
pin meter
Point 2


53/2±50/22
Laser


646/0-
24
99/1±58/17
pin meter
Point 3


30/2±87/16
Laser


040/1-
24
1±50/10
pin meter
Point4


08/1±08/11
Laser


924/0
24
91/1±62/19
pin meter
Point5


69/1±50/18
Laser


793/0-
24
30/1±66/9
pin meter
Point 6


54/1±37/10
Laser


221/1-
24
10/1±29/14
pin meter
Point 7


95/0±12/15
Laser


175/0-
24
11/1±79/11
pin meter
Point 8


16/1±12
Laser


135/0
24
10/1±9
pin meter
Point 9


23/1±12/9
Laser


809/0
24
59/0±04/7
pin meter
Point 10


09/1±83/7
Laser




 



Figure (1): shows the Matching charts, two methods of laser distance meter and pin meter.
These two methods are Good match to all points, But this match, have more matches at points 2, 3, 5, and 6 Compared to other points.


 
























Figure (1): Charts for the matching of the two methods at the sampling points.




 
Discussion and Conclusion
The Calculated Statistical indicators by the two methods, are almost the same at all harvested points. The results of the t- student test also showed that, the mentioned two methods, in all sampled points, there is no significant difference at 95% level. Which indicates the ability of two devices For measuring roughness Which, depending on the conditions, can replace each other.the results of this study, with the results of the studies of Zhang et al. (2012), that investigated the methods of measuring the roughness of the soil to provide a Universal and comprehensive method, and concluded that the best method for determining the roughness is laser scanning method and followed by it is pin meter method. labideh (2015), measuring the aerodynamic roughness length of the harvested soil using اa pin meter. It was concluded that a pin meter could be used to estimate aerodynamic roughness. Which is accommodation with the results of our studies.so it may be concluded that so it may be concluded that using the pin meter method as a traditional tool in pavement roughness measurement, similar results will be obtained using laser method. Therefore, according to the cost of laser distances, pin meter method can be used with similar results.