System Calibration in Precision Farming

Abstract

The use of measuring sensors for tracking and navigating of moving objects has continued to increase over the past few years. Depending on the application requirements there are several measuring systems available (stand alone GPS, DGPS, RTKDGPS, robot tacheometer, gyroscope, INS etc.) each with varying position accuracy, availability, measurement frequency and data transfer. Systems for autonomous navigation or for automatic control of local processes above all require coordinates for moveable objects in real time. Disturbances, delay and dead time create deviations which can systematically distort the measurement results. With the help of a reference measurement system created by a RTKDGPS system and robot tacheometer capable of real time, the path of a moveable object can be precisely measured to within a few centimeters. Given the differing measuring principles contained in both these systems, it is possible to reach a high level of availability. Horizontal and vertical shadowing can be widely minimized. A combination of GPS and robot tacheometers can be achieved without modification of hardware only through a common time basis. For a lower level of accuracy, the DCF77 (Deutscher Langwellensender Frankfurt; carrier frequency = 77,5 kHz) Signal, operated by the “Physikalisch-Technische Bundesanstalt”, (PTB; www.ptb.de) and “Deutsche Telekom” in Mainflingen, can be used in Central Europe for example. If a common time basis within the GPS time accuracy range is to be used, however, this can be achieved using the PPS (Pulse per second) signal with a supplementary function registered in the GPS receiver. By using this, error factors, which occur during kinematic real time measurement systems can be verified and then corrected using calibration parameters and algorithms (eg. Kalman filter techniques). In addition, the process provides comprehensive information on the real time performance ability of GPS and robot tacheometers. In a three-year research project at the Chair of Geodesy (Chairman Univ.-Prof. Dr.-Ing. habil. Th. Wunderlich) and the Institute for Agricultural Engineering (Chairman Prof. Dr. H. Auenhammer) at the “Technischen Universitat Munchen” (TUM), investigations are to be made using this measuring system on various applications for variable rate technology regarding quality, accuracy and disturbances. The goal of the project is to determine the overall parameters of influence and thus to optimize the process procedure. That is, to guarantee land cultivation with regard to the required application accuracy.