Objective To explore the applicability of using unmanned aerial vehicle (UAV) and image processing technique for large scale research of gravels on Gobi surface.

Method Taking the pluvial fan at south slope of Tianshan Mountains in Hami of Xinjiang Uygur Autonomous Region as study area, the orthographic images and digital terrain models (DTM) covering a large range of Gobi were obtained by UAV platform and the structure from motion (SfM) technology, and the gravel coverage and diameter were measured and analyzed. From the center to near the edge of the pluvial fan, three typical sample zones were selected, and high resolution images of Gobi surface were shot by camera on UAV. High resolution mosaic image and terrain data of Gobi surface were produced, and the coverage of gravels (diameter ≥ 7 mm) and diameter of gravels (diameter ≥ 32 mm) were calculated.

Result From center to near the edge of the fan, the gravel coverage of the three sample zones was 34.22%, 26.85% and 21.88%, and the mean gravel diameter was 130, 95 and 78 mm. As elevation decreased, the gravel coverage and diameter dropped. The gravel coverage and diameter dropped more slowly from the middle to near the edge of the fan than from the center to the middle of the fan. However, within each sample zone, the relationship between gravel characteristics (coverage and diameter) and elevation was not obvious.

Conclusion On the scale of pluvial fan, the changes of gravel coverage and diameter are mainly affected by elevation. On the scale of sample zone, the change of gravel coverage and diameter may be affected mainly by the vegetation distribution and local topography. Using UAV and image processing technology can efficiently and accurately estimate a wide range of the gravel characteristics and their spatial distribution, which provides basic data and methodological support for the research on Gobi evolution.