Optimization of GNSS-controlled land leveling system and related experiments

Abstract: Precise land leveling of farmlands is an important foundation of modern ground irrigation system. It can improve the uniformity of irrigation as well as soil water and salt distribution, thus controlling weeds, saving water and increasing yield. The application of GNSS (global navigation satellite system) -controlled land leveling technology is protected from weather. Besides, it has high speed and working efficiency, which earns broad application prospects. Combined with the actual situation of land leveling in China as well as the early research work, based on GNSS-controlled land leveling technology, the paper developed a leveling system which is suitable for China. The system reduces the cost of equipment and optimizes its leveling function. To reduce the number of discrete devices and improve system integration, the paper designed an integrated control terminal, including an integrated GNSS receiver module, a differential radio module, a core processing platform and a valve control module. The paper also designed the outer covering of integrated control terminal. It can be rotated to adjust the bracket through the tractor cab, and it is protected from dust, making it convenient to operate. To optimize topographic survey, the paper acquired more terrain information, for instance, the area of farmlands, which guides the later leveling operations. It also adds function of real-time display of measurement tracks. What's more, it optimizes the reference design to achieve any grade slope leveling by building a mathematic model and solve it. The optimized system consists of integrated intelligent control terminals, independent differential GNSS receiver module, hydraulic system and flat shovel equipment. Meanwhile, based on Visual Studio 2008 as the development environment, the integrated software helps a lot to land leveling. The software has accomplished the function of topographic survey, reference design and leveling operation. The intelligent precise leveling system has been applied for long experiment on Shang Zhuang experimental station of China Agricultural University. The accuracy of the system is encouraging: the maximum elevation difference after the plane leveling goes down from 20.9cm to 10cm and height standard deviation of elevation drops from 10.6 cm to 5.5 cm; the cumulative percentage, of which the accuracy errors are less than 5 cm, is increased from 77% to 90% after the land leveling. Besides, flat slope gradient goes down from 0.239% to 0.120%, which is in line with the design requirements. The results showed that the system is stable and reliable for operation and it perfectly meets the requirements of precise land leveling. The system developed in this paper is suitable for our farmland and farm equipment with abundant function and is easy to operate while the cost is reduced by more than a half compared with the similar foreign advanced products. It will help as fine irrigation and water-saving equipment in China and it will earn large-scale application in our country.