Abstract
Terraces are the major land-use type of agriculture and support the main agricultural production in southeast and southwest China. However, due to smallholder farming, complex terrains, natural disasters and illegal land occupations, a light-weight and low cost dynamic monitoring of agricultural terraces has become a serious concern for smallholder production systems in the above area. In this work, we propose a small unmanned aerial vehicle (UAV) based multi-temporal image registration method that plays an important role in transforming multi-temporal images into one coordinate system and determines the effectiveness of the subsequent change detection for dynamic agricultural terrace monitoring. The proposed method consists of four steps: (i) guided image filtering based agricultural terrace image preprocessing, (ii) texture and geometric structure features extraction and combination, (iii) multi-feature guided point set registration, and (iv) feature points based image registration. We evaluated the performance of the proposed method by 20 pairs of aerial images captured from Longji and Yunhe terraces, China using a small UAV (the DJI Phantom 4 Pro), and also compared against four state-of-the-art methods where our method shows the best alignments in most cases.
Highlights
China has more than 70% of its land made up of mountains and hills, while the main agricultural terraces are located in southwest and southeast China
We design two series of experiments: (i) due to the employment of the same feature point sets, the quantitative comparison on feature point matching is carried out on CPD, GLMDTPS and our method using the precision ratio (PR) [40]; (ii) quantitative comparison and qualitative demonstration on image registration are carried out on all the methods using the root of mean square error (RMSE), mean absolute error (MAE) and standard deviation (SD)
Multi-temporal images of the same planting area captured by small unmanned aerial vehicle (UAV) have only visible image information and are always accompanied by viewpoint changes, image geometric distortions, low image overlapping, brightness changes and color changes such that the images may not be directly used for dynamic agricultural terrace monitoring
Summary
China has more than 70% of its land made up of mountains and hills, while the main agricultural terraces are located in southwest and southeast China. Agricultural terraces have become the most important agricultural land-use type and support the main agricultural production in these areas. It plays an important role in reducing flood runoff, changing terrain slope and maintaining water, soil and conservation fertilizer. Due to Chinese agricultural policy and regional characteristics, most agricultural terraces in southwest and southeast China are farmed by smallholders, and have small sizes, scattered distributions, complex terrains and other characteristics. Such issues have increased difficulty in land use management and planting management of local governments, as well as regular cropping and planting area monitoring of smallholder farmers.
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