Assessing GNSS correction signals for assisted guidance systems in agricultural vehicles

Accuracy levels achieved with differential global positioning system (DGPS) receivers in agricultural operations depend upon the quality of the correction signal. This study has assessed differential signal error from a Dedicated Base Station, OmniSTAR VBS, European Geostationary Navigation Overlay System, European reference frame-IP for internet protocol (EUREF-IP) and radio navigation satellite aided technique (RASANT). These signals were utilized in guidance assisting systems for agricultural applications, such as tillage, harvesting, planting and spraying, in which GPS receivers were used under dynamic conditions. Simulations of agricultural operations on different days and at different time slots and simultaneously recording the tractor′s geo-position from a DGPS receiver and the tractor′s geo-position from a real-time kinematic (RTK) GPS allowed the comparison of the GPS correction signals. The hardware used for tractor guidance was a lightbar (Trimble model EZ-Guide Plus) system. ANOVA statistics showed a significant difference between the accuracy of the correction signals from different sources. GPS correction signal recommendations to farmers depend upon the accuracy required for the specific operation: (a) Yield monitoring and soil sampling (<1 m) are possible with all the GPS correction signals accessed in any time slot. (b) Broadcast seeding, fertilizer and herbicide application (<0.5 m) are possible for 80% of time with OmniSTAR VBS, 40% of time with RASANT and EUREF-IP and 100% of time with a dedicated base station. (c) Transplanting and drill seeding (<0.04 m) are not possible with the accuracy correction provided by any one of the systems used in this study.     

DGPS数据分析及定位精度研究

本文进行了DGPS数据分析及定位精度研究。通过试验分析表明，Ag132GPS接收机接收到的卫星信号数可以满足使用卫星数量的要求。采用伪距差分纠偏后，Ag132GPS接收机的DGPS单点定位精度可以达到0．232m，满足亚米级的定位精度。     

农机直线行走作业DGPS导航软件开发

对于大中型宽幅农业机组的田间行走作业,利用DGPS进行导航具有很多优点,本研究利用VB6.0编程语言,对农机直线行走作业DGPS导航涉及的GPS定位信息的获取、坐标投影变换、导航AB线的确定等编制了相应的程序,开发了应用软件。农业生产中可利用触摸屏计算机实现对机组田间直线行走作业导航。田间作业记录进行模拟试验表明,此软件可有效地实现导航功能,并同时具有作业行走记录和行走距离、作业面积实时显示的功能。     

基于GIS的玉米数字信息智能管理系统的研究

全球卫星定位系统(DGPS)、地理信息系统(GIS)和专家系统(ES)技术是实现农业数字化的重要技术支撑[1,2].通过探讨应用DGPS、GIS、ES、数据库技术以及本体论技术实现对吉林省玉米信息精确管理.详细阐述了采用MapObjects控件和相关技术研制玉米数字动态信息智能管理系统的过程、系统的主要功能及实现方法.同时把本体论引入到该系统来处理农业空间关系,实现了玉米地块空间数据库与关系数据库的动态连接.     

GPS航向仪的研究

为了降低小型船舶安装导航设备的成本,设计了GPS航向仪,通过GARMIN GPS-12、Ashtech Z—Xtreme GPS两种型号5台GPS进行同时观测,共得到1500组观测数据,并对这些数据进行计算分析,分别得到两种型号GPS的实测航向,以验证航海型GPS用作航向指向系统的可行性。结果表明：航海型差分GPS的航向为141．4114°,航海型GPS航向的最大偏差为3．6227°。表明GPS航向仪完全可以满足航海上的需要。     

Evaluation of Sub-Meter and 2 to 5 Meter Accuracy GPS Receivers to Develop Digital Elevation Models

The digital elevation model (DEM) is considered by many to be an important base map for a precision farming GIS (Geographic Information System). Previous work has shown that dual-frequency survey grade GPS (Global Positioning System) receivers are capable of rapidly producing accurate positional data from a moving vehicle from which DEM's can be developed. However, this type of GPS receiver is expensive and somewhat difficult to use properly. This paper presents the results of a study to evaluate the potential of using single frequency sub-meter and 2–5 meter horizontal accuracy GPS receivers to enable the farmer to collect multiple passes of GPS data during normal field operations from which DEM's can be developed. The results show that when using a single frequency sub-meter GPS receiver: (1) it is possible to develop a DEM with standard deviation of the elevation accuracy on the order of 0.12–0.14 m, (2) in order to collect data with this level of elevation accuracy, data should only be collected when the GDOP (Geometric Dilution Of Precision) is less than 5.0, (3) at least 10 passes of data with appropriate data averaging is required to produce this level of elevation accuracy. The results also indicate that the vertical error associated with a 2–5 meter horizontal accuracy GPS receiver is such that it is not recommended for use in collecting data to develop DEM's in this application.     

A harvest area measurement system based on ultrasonic sensors and DGPS for yield map correction

Unknown crop width entering into the header and the delay time caused by the uncertain start and stop of cutting are the two main error sources in a yield map. A harvest area measurement system (HAMS) is presented in this article. The system has ultrasonic sensors mounted on both sides of the harvest header to detect the presence of crop, which was used to start or stop data recording, as well as measure the cutting width. A high-precision Differential Global Positioning System (DGPS) receiver was used to measure the travelled distance. Field tests were conducted to evaluate the performance of the system. Results showed that: Firstly, the developed HAMS can be used to reduce the area error and the data collected by the HAMS can be used to correct the yield data. In a yield map, the area error reached 6.89% relative to the actual area calculated based on the DGPS tracks. The travelled distance error accounted for about 1.08% and the cutting width error accounted for the other 5.81%. However, the error of the area measured by the HAMS decreased to 0.95%. The position offset of yield points could be calculated and the correction coefficient at each sampling point was determined. Secondly, ultrasonic sensors could replace the header position sensors in most yield monitoring systems, as ultrasonic sensors can detect the presence of the crop, which can be used to start or stop data recording. Finally, the HAMS also provides a potential solution to realize online correction of yield data. The time delay estimated by the HAMS between cutting and sensing was 3–6 s at the start of cutting, and was 1–7 s at the end of cutting. An online correction model of yield data was proposed.     

土壤水分空间变异研究

以天津市静海县良种场内一块长约110 m,宽约40 m的冬小麦田作为试验区,采用规则格网采样,按照10 m×10 m设置格网,共设48个采样点,通过GPS手持机进行定位,分别于小麦越冬前、拔节期、灌浆期,利用便携式土壤湿度数据采集器对试验地各个采样点0～20、20～40 cm2种深度土壤含水量进行了测定,利用ARC/INFO的地统计分析模块绘制了冬小麦3个不同生育期试验区土壤水分空间分布图,并分析了其垂直和水平方向的空间变异特征,以期为确定最佳灌溉时机和灌溉量提供科学依据。     

Performance of two low-cost GPS receivers for ground speed measurement under varying speed conditions

A global positioning system (GPS) receiver is an important sensor used in modern farming, particularly in precision agriculture to determine geographic location and ground speed. The aim of this study was to investigate the effectiveness of two low-cost GPS receivers for measuring ground speed under varying speed conditions on four different dates. A rotary shaft encoder on an auxiliary wheel mounted on an agricultural tractor was used as a reference. A significant time lag between the rotary encoder speed and the GPS speed was found over a range of speeds. It was observed that the GPS speed lagged the encoder speed in both increasing and decreasing speeds. The average time lag was found to be between 3.6 and 5.2 s for Receiver 1 while Receiver 2 had a time lag from 1.7 to 2.5 s. A significant difference was found between the two receivers for increasing and decreasing speeds in terms of time lags (P < 0.05). A post correction by shifting the GPS speed increased the accuracy of the speed measurement capability of both receivers resulting in an average correlation coefficient of 0.30–0.90 for Receiver 1 and 0.65–0.98 for Receiver 2. Effect of USB-to-COM converter was also studied and it did not have a significant effect on time delay. The GPS receivers provided reliable data during constant speed operating conditions; however, caution should be exercised in varying speed conditions when using low-cost GPS receivers. Also, the companies that produce GPS-based speed sensors should supply technical specifications related to velocity estimates during acceleration and deceleration.     

A yield mapping system for hand-harvested fruits based on RFID and GPS location technologies: field testing

It is proposed that radio frequency identification (RFID) technology be used to overcome the limitations of existing yield mapping systems for manual fresh fruit harvesting. Two methods are proposed for matching bins—containing harvested fruits—with corresponding pairs of trees. In the first method, a long-range RFID reader and a DGPS are mounted on an orchard tractor and passive low-cost RFID tags are attached to the bins. In the second method, the DGPS is not used and RFID tags are attached to individual trees as well as bins. An experimental evaluation of the accuracy and reliability of both methods was performed in an orchard. The first method failed in half of the trials because the tree canopies interfered with the GPS signal. The RFID reader miss ratio for the detection of the bins was 0.32% for both methods. However, the attachment of RFID tags on suitable tree branches (to achieve 100% detection), in the second method, is not a well-defined procedure; some trial is demanded to determine the best positions and orientations of the tree tags in order for the RFID reader to successfully detect them. The first method seems more promising if robust tractor location under foliage can be achieved.     

农机直线行走作业DGPS导航算法研究

对于大中型宽幅农业机组在大面积的田间行走作业中利用DGPS进行导航具有很多优点。本文对农机直线行走作业DGPS导航涉及的投影转换、导航AB线、行驶方向角、机组在导航AB线的左右位置、机组当前导航线与导航AB线之间的距离、偏航距离及左右确定等问题进行了分析并给出了算法。通过编程测试表明,本文涉及的算法可行,可用于农机直线行走作业DGPS导航中。     

GPS技术在土地测绘地籍控制测量的应用

介绍了GPS技术在地籍控制测量中的应用,探讨了精度测算、网型布设等应注意的问题和GPS RTK应用于地籍细部测量及在建设用地勘测定界中的应用。     

GPS在南方林区的应用试验

应用Ｍａｇｅｌｌａｎ Ｐｒｏｍａｒｘ Ｘ－ＣＭ ＧＰＳ接收机在广东省新丰县小镇镇林区进行野外样地定位等试验,结果表明,林冠郁闭度、天线类型、天线高度对卫星信号的接收均有一定的影响;ＧＰＳ在杉木林中基本能定位;ＧＰＳ与ＴＭ卫星影象套合误差小于一上象元;差分ＧＰＳ定位技术在南方山区林业调查应用是可行的。     

限水灌溉与施N时期对小麦旗叶光合作用及产量性状的影响（摘要）

[目的]实现小麦优质高产节水省肥提供科学合理的水氮运筹模式。[方法]在大田条件下,研究灌水次数及施N时期对小麦旗叶Pn、叶绿素荧光参数及产量的影响。[结果]灌水次数对旗叶Pn、Fv/Fo、Fv/Fm、qP、qN及产量的影响均达到显著或极显著水平,且不灌水与灌水处理间差异较大;N肥全部基施与返青期追施（40%）处理间旗叶的Pn、Fv/Fo、Fv/Fm、qP和qN差异不大,但2个处理的光合参数与产量均明显低于拔节期或孕穗期追施（40%）处理。[结论]灌水次数与施N方式对Pn、叶绿素荧光参数及产量性状的调控存在显著的互作效应,其中以W2N4处理组合效果最好。     

Centimetre-precision guidance of moving implements in the open field: a simulation based on GPS measurements

High quality and sustainable agricultural production in the open field will be supported by centimetre-precision guidance of agricultural implements. In this paper, a complete guidance system is proposed and simulated using real sensor data obtained from a real time kinematic (RTK) differential global positioning system (DGPS). This type of the satellite navigation system became available commercially in 1997 and is claimed to reach cm accuracy. It uses real time kinematics to improve the accuracy of a position fix by phase comparison of the carrier signal. The simulation primarily aims to investigate the accuracy of the guidance system that can be obtained with RTK DGPS. Using real DGPS measurement errors the simulated system showed a tracking error less than 0.005 m when the PID-controller had settled.     

基于机器学习方法的宁夏南部土壤质地空间分布研究

【目的】基于历史数据,利用机器学习方法分析宁夏南部土壤质地空间变异规律及其与环境因素之间的关系。【方法】基于宁夏回族自治区南部428 个20世纪80年代第二次土壤普查土壤剖面点数据,采用分类回归树（CART）和随机森林（RF）两种机器学习方法,结合地形因子、土壤类型、归一化植被指数,探究与宁夏南部地区土壤质地分布相关性较强的环境因素,并用两种机器学习预测该区土壤质地类型的空间分布,用剖面点验证集数据以及宁夏回族自治区海原县实测样点数据验证模型精度。【结果】（1）RF和CART对剖面点验证集土壤质地类型的预测正确率分别为 62.36%、55.29%,接收者操作特性（receiver operating characteristic,ROC）曲线下面积（area under roc curve,AUC）分别为0.7515、0.6933,对海原县122个实测样点的预测正确率分别为54.10%、48.36%,AUC分别为0.6599、0.5981,RF的预测精度高于CART。（2）该区土壤类型（ST）是与土壤质地空间分布相关性最强的环境因素,其次是高程（Ele）,高程越高,土壤质地越黏重。风力作用指数（WEI）和坡度（Slo）对土壤质地的影响较小。（3）研究区土壤质地类型以轻壤土为主,空间分布格局基本呈现为南部土壤质地黏重,北部土壤质地较轻。【结论】RF更适合预测宁夏南部地区土壤质地的空间分布,且充分利用历史数据,结合新的野外采样,可以达到预测制图的精度要求;土壤类型（ST）和高程（Ele）是与土壤质地空间分布相关性较强的环境因素。     

基于参数优化支持向量机的水稻施氮水平分类研究

[目的]应用参数优化支持向量机对水稻施氮水平进行准确分类预测,为水稻精准施肥和高产管理提供科学依据.[方法]以水稻品种金优458为试验材料,设4个施氮水平(从高至低折合纯氮用量分别为225、150、75和0 kg/ha),通过叶绿素测量仪SPAD-502获取水稻第6~9叶序叶片的SPAD值(即叶尖、叶中和叶枕的SPAD值),并分别应用网格搜索算法和粒子群算法参数优化支持向量机对4个施氮水平下的水稻叶片SPAD值进行训练和预测分类.[结果]对于第7、8叶序、第7~9叶序及第6~8叶序叶片组合,粒子群算法参数优化支持向量机对水稻施氮水平的分类识别效果均优于网格搜索算法,其准确率均高于75.000%,对归一化处理后的第7、8叶序叶片组合识别率最高,达88.889%.[结论]基于粒子群算法参数优化支持向量机适用于水稻施氮水平分类预测,能满足农学研究的需求.     

Crop height variability detection in a single field by multi-temporal terrestrial laser scanning

Information on crop height, crop growth and biomass distribution is important for crop management and environmental modelling. For the determination of these parameters, terrestrial laser scanning in combination with real-time kinematic GPS (RTK–GPS) measurements was conducted in a multi-temporal approach in two consecutive years within a single field. Therefore, a time-of-flight laser scanner was mounted on a tripod. For georeferencing of the point clouds, all eight to nine positions of the laser scanner and several reflective targets were measured by RTK–GPS. The surveys were carried out three to four times during the growing periods of 2008 (sugar-beet) and 2009 (mainly winter barley). Crop surface models were established for every survey date with a horizontal resolution of 1 m, which can be used to derive maps of plant height and plant growth. The detected crop heights were consistent with observations from panoramic images and manual measurements (R² = 0.53, RMSE = 0.1 m). Topographic and soil parameters were used for statistical analysis of the detected variability of crop height and significant correlations were found. Regression analysis (R² < 0.31) emphasized the uncertainty of basic relations between the selected parameters and crop height variability within one field. Likewise, these patterns compared with the normalized difference vegetation index (NDVI) derived from satellite imagery show only minor significant correlations (r < 0.44).     

扎龙湿地恢复初期丹顶鹤孵化期觅食生境选择

2002—2005年3—5月,在扎龙国家级自然保护区通过定点观察法、样方法、因子测定法等对丹顶鹤孵化期的觅食生境选择进行了研究,旨在为积累濒危鸟类繁殖生态学的基础资料。研究结果表明:孵化期丹顶鹤对觅食生境的选择具有特异性和非随机性,警戒因子、食物保障因子和生境类型是其觅食生境选择的主要因子。     

Implement lateral position accuracy under RTK-GPS tractor guidance

The accuracy of global positioning system receivers can be improved by differential correction systems (DGPS), which deliver sub-meter accuracy. Higher-accuracy, of about 1 cm on-the-go, is delivered by units generally referred to as real-time kinematic (RTK) DGPS systems. RTK-DGPS systems are presently used by commercial companies for automatic guidance of tractors in row-crop operations. Since high-end DGPS systems with high-accuracy are generally very expensive, it is necessary that the commercial benefit be maximized and that any related errors will be minimized. In the present study, the deviations from a predetermined route of a three-point hitch implement mounted on a RTK-DGPS based automatically guided tractor were recorded and were used to validate that the implement deviation is strongly dependent on the distance from the tractor rear axle. The recorded deviations were analyzed for paved and rough surfaces; the latter caused substantially greater deviations. Based on the above hypothesis, a possible way to improve the performance by reducing the deviations at a point on the implement is suggested.