Monitoring, 3D modeling and determination of mines extracted reserves using photogrametry by UAV, case study: sand and gravel mine of Ghods, Lanjan, Isfahan

Photogrametry with UAV (unmanned aerial vehicle) is a fast, accurate and cost-effective approach to obtain high-resolution spatial information. Taking overlapped photos of the target, production of 3-D dense point cloud, digital elevation model and orthomosaic from the region surface as well as verifying their accuracy using a definite number of ground control points, are main stages of the process. In the present research, photogrametry through UAV was used for monitoring, modeling and evaluation of exploited and residual ore reserve of Qods sand and gravel mine in Lanjan district of Isfahan. Based on dimensions and form of the region, nine flight lines with approximately 37m interspacing and 114m flight altitude were designed and traversed. The total number of photos taken from the region is 225 with 75% and 65% longitudinal and transverse coverage for the images, respectively. The number of six control points (five control points and one check point) were also scattered at the region so that the error range from -1.5 to 1.5mm with the total error of about 6.8mm is the appropriate precision. Total accuracy of the survey operation using the UAV was validated through comparing with ground check point via accurate three frequency GPS. The survey errors in the three coordinate directions are negligible, less than 5cm. At the end, the volume of exploited part and residual deposit was determined and with multiplying by average density (1.4 gr/cm3), the amount of extracted and residual ore reserve was calculated 3657.43 and 82942.55 tones, respectively.