Integrated measurement method for field surface topography and tillage depth in rotary tillage operations

Field surface topography and tillage depth are crucial information for guiding crop production. However, the separate measurement of field surface topography and tillage depth increases production costs. To address issues, this study proposes an integrated measurement method for field surface topography and tillage depth in rotary tillage operations. Based on the operational characteristics of the rotary tiller, a simultaneous measurement method for field surface and the tillage bottom-layer topography (FS-TBLSM) was proposed. Building on this, a method was developed to arrange grid points, referred to as the directional adaptive gridding method in plane topography (DAG-PT), and a sample-approximated Gaussian process regression (SA-GPR) algorithm was used to estimate the field surface topography height and tillage depth at a given grid point. The accuracy of these methods was evaluated using verification and field tests. The verification results showed that the FS-TBLSM method achieved a static root mean square error (RMSE) of less than 15.00 mm along all three axes, with dynamic RMSEs below 20.00 mm, confirming the effectiveness of the FS-TBLSM method and its good dynamic tracking capability. Further field test results indicated that the field surface topography measured using the FS-TBLSM method aligned with the true topography. The measured field surface topography height exhibited an average absolute error (AAE) of 18.13 mm and an RMSE of 20.58 mm, validating the accuracy and reliability of this method for field surface topography measurement. Using true surface topographic height and tillage depth at 20 points as references, an AAE and RMSE of 17.13 and 17.95 mm, respectively, were obtained for surface topographic height estimation; estimated tillage depth exhibited an AAE and RMSE of 14.52 and 16.49 mm, respectively. These results demonstrate that the SA-GPR algorithm can accurately estimate the field surface topography height and tillage depth after rotary tillage operations. The integrated measurement method performs the measurement in a single operation, reducing the number of field operations by 50 %, saving an estimated 15.57 kg/ha in fuel consumption. Additionally, this study provides key inputs for leveling operations, including setting the base height, calculating earthwork volume, and planning paths. It also supports active control of seeding depth and provides references for yield assessment.