低成本农用GPS接收系统的研制及在面积测量中的应用

针对目前我国应用于精细农业的GPS接收系统成本高,不能接收虚拟参考站(VRS)差分信息的问题,采用低成本亚米级精度GPS接收模块,并结合ARM7微处理器、基于GPRS(general packet radio service)方式的无线通信模块、U盘存储模块、键盘和LCD设计研制了低成本GPS接收系统。该GPS接收系统可以通过GPRS方式接收北京VRS控制中心发送的差分改正信息,实现实时差分定位及长时间稳定的通信链路。定位信息通过串口输出(输出频率为1 Hz)和U盘存储2种方式实现数据的输出和保存,用户可利用本接收机进行定位和面积测量。面积测量实验结果表明,该接收机在不同大小、不同形状的面积测量中,其相对测量误差小于3%,满足精细农业中面积测量的要求。     

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.     

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.     

利用地形、土壤和作物信息辅助提高东北漫岗地数字高程模型精度的新方法

【目的】SRTM DEM是可免费访问公开可用的数字高程模型,但是当前SRTM DEM的垂直精度不能满足精细农业对地形数据的需求,提高其垂直精度,为精准农业等领域提供数据基础。【方法】以黑龙江省海伦东兴农机合作社为研究区,采集实际地面高程数据,获取SPOT-6、Sentinel-2A遥感影像和SRTM DEM。提取归一化湿度指数（NDMI）、归一化植被指数（NDVI）、土壤亮度（TCB）、潜在太阳辐射（PSR）等变量分析地形对其影响关系。利用极限学习机（ELM）和反向传播神经网络（BPNN）提高SRTM DEM水平空间分辨率和垂直精度。使用实际地面高程点进行精度验证,与基于无人机和光学立体像对（ZY-3）生成的DEM进行对比。【结果】SRTM、NDVI、NDMI、TCB与改进后高程的灰色关联度在90%以上,是改进SRTM DEM的重要辅助信息。在整个研究区,BPNN方法的RMSE_P为0.98,R²_P为0.98,ELM的RMSE_P为1.00,R²_P为0.90。在平坦区,BPNN方法的RMSE_P为0.84,ELM的RMSE_P为1.00;在起伏区,BPNN方法的RMSE_P为0.99,ELM的RMSE_P为0.94。该方法获得的DEM的垂直精度高于ZY-3光学立体像对生成的 DEM的垂直精度,为提高SRTM的水平空间分辨率和垂直精度提供了新思路。【结论】引入SRTM、NDVI、NDMI、TCB辅助信息有利于提高SRTM DEM的空间分辨率和垂直精度,获得高精度的DEM。BPNN方法获得的数字高程模型的精度整体上高于ELM方法, BPNN方法更加适用于平坦区高精度DEM的获取,ELM方法更加适用于起伏区。     

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。     

Seed Mapping of Sugar Beet

Individual plant care may well become embodied in precision farming in the future and will lead to new opportunities in agricultural crop management. The objective of this project was to develop and evaluate a data logging system attached to a precision seeder to enable high accuracy seed position mapping of a field of sugar beet. A Real Time Kinematic Global Positioning System (RTK GPS), optical seed detectors and a data logging system were retrofitted on to a precision seeder to map the seeds as they were planted. The average error between the seed map and the actual plant map was about 16–43 mm depending on vehicle speed and seed spacing. The results showed that the overall accuracy of the estimated plant positions was acceptable for the guidance of vehicles and implements as well as potential individual plant treatments.     

Combine Harvester Control Using Real Time Kinematic GPS

An accurate vehicle guidance system is required for some precision agriculture operations. It can be used for high speed direct seeding on a farm tractor. Such a system also ensures neither overlapping nor missing areas during the harvest, even when visibility is poor. But, automatic path following in the field is a difficult problem. Many vehicle guidance systems have been studied. Some use two dimensional (2D) information, while others are based upon 3D information. Most of the sensors use output information relative to their environment without absolute reference of the path. As the new reference is based on the previous pass, one of the main problems encountered with the edge following systems is an increase in the amplitude of oscillations due to guidance errors in successive passes. Thus, human operators frequently and periodically sacrifice efficiency in one pass to straighten out the edge of the worked area. Another kind of sensor, centimeter accuracy Real-Time Kinematic based Global Positioning System (GPS) receivers, can be used. The advent of accurate systems, with a standard deviation from the mean of about 10 mm, allows the design and implementation of absolute vehicle guidance systems. A few approaches to GPS-based control systems also include attitude measurement sensors such as fiber optic gyroscope. The preliminary work presented in this paper was aimed at validating the use of a GPS receiver in a vehicle guidance system, without any orientation sensor. We have designed a controller to perform a line-following task. Real-time experiments have been carried out on a combine harvester.     

GPS在沿海围垦动态监测中的应用

采用Ｍａｇｅｌｌａｎ ＰｏｒＭＡＲＫ Ｘ－ＣＭ手持ＧＰＳ接收机,以广东省湛江市通明海海为实验区,通过野外实地数据采集、室内数据差分后处理、与ＴＭ影像准等,探索了一套ＧＰＳ与遥感图像分析相结合、快速、准确析沿海围垦动态数据的工作流程。结果表明：ＧＰＳ应用于ＴＭ影像几何纠正,可提高ＴＭ影像几何纠正的精度,ＧＰＳ采集的数据可以辅助目视解译,提高目视解译精度：ＧＰＳ可以补充ＴＭ影像成像后最新的动态信息。     

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.     

一种高质量的数字高程模型（DEM）建立方法 ——ANUDEM法

建立高质量的数字高程模型(DEM)是正确计算坡度、坡向、提取流域地形特征、进行水文分析 的前提,因而在研究土壤侵蚀、植被建设和土地利用规划与评价中都具有重要意义。ANUDEM采用迭 代有限微分内插技术和地形强化算法,自动去除伪下陷点和生成输入数据错误文件,便于查错改善 DEM质量,并减少了去除伪下陷点的编辑或DEM的后处理过程。本文以黄土高原丘陵沟壑区典型 小流域为例,利用大比例尺(1:10000)数字化地形图,利用ANUDEM建立DEM,从DEM光照模拟图、 回放等高线、提取水系、坡度等方面对建立的DEM的质量进行了评价。研究表明,ANUDEM建立的 DEM表面光滑;回放等高线与原等高线符合度高,能更准确地表现地形起伏;由其提取的坡度准确; 水系连续完整与地形图上河流一致,适宜水文分析,是一种建立高质量DEM的优良方法。     

Using 1-Hz GPS data to measure deformations caused by the Denali fault earthquake

The 3 November 2002 moment magnitude 7.9 Denali fault earthquake generated large, permanent surface displacements in Alaska and large-amplitude surface waves throughout western North America. We find good agreement between strong ground-motion records integrated to displacement and 1-hertz Global Positioning System (GPS) position estimates collected approximately 140 kilometers from the earthquake epicenter. One-hertz GPS receivers also detected seismic surface waves 750 to 3800 kilometers from the epicenter, whereas these waves saturated many of the seismic instruments in the same region. High-frequency GPS increases the dynamic range and frequency bandwidth of ground-motion observations, providing another tool for studying earthquake processes.     

基于GPS技术的定位测量精度试验研究

随着“3S”技术逐步在农业生产中的广泛应用,GPS技术在精细农业中的应用也越来越受重视。对测距码伪距GPS定位模型进行了推导和分析;利用AgGPS132接收机进行了单点定位和差分定位试验,对试验数据进行了分析与比较,试验结果表明差分定位精度要明显高于单点定位,定位精度能达到亚米级。     

Error Sources Affecting Variable Rate Application of Nitrogen Fertilizer

The accuracy and interaction among global positioning system (GPS) horizontal accuracy, differential GPS (DGPS) sampling frequencies and machine delay times of a hypothetical variable rate applicator for nitrogen (N) fertilizer application based on an application map in Florida citrus were studied. Parameters studied included: five GPS horizontal accuracy levels, two levels of DGPS horizontal accuracy, two DGPS sampling frequencies and two machine delay times. Two integrated models were developed which documented the effects of the parameters. Machine delay time was the most important factor and GPS horizontal accuracy was the second most important.     

集思宝G330手持全球定位系统接收机在林区单点定位的精度分析

通过三维激光扫描技术得到的树木枝干点云数据,不仅数据量大,而且特征复杂,不适合采用传统的方法提取等值线。对此,首先把点云数据中树木的枝和干分为不同的部分,然后建立点云的分层模型,并分析点云在树高方向上的数据量分布。在高精度采样下,将分层点云作为等值线的采样数据,对每层数据中不同部分的树木枝干点云分别采用凸包算法进行连接,建立树木枝干的等值线模型。结果表明:在没有先验等值线知识和建立点云对象模型的条件下,利用迭代的凸包算法可以有效地对树木枝干离散点云数据进行连接,得到的等值线符合一般等值线的特点。最后通过实例验证了方法的适用性。图8表1参11     

Evaluating corrections for a horizontal offset between sensor and position data for surveys on land

When regarding evolutions in land-based, motorized sensor data collection it can be generalized that the speed of surveying, sampling rates, digital communications speed and survey resolutions have increased over the last years. Possibilities for accurate positioning have been following pace. However, a spatial offset between sensor and position data can be necessary to avoid interference with the instrument or can be the result of using a sensor array. It can also be due to practical considerations such as mounting possibilities. Unfortunately a severe degradation of positional accuracy is possible when performing corrections for a spatial offset and quantification of the induced error is quite difficult. As a consequence, the actual positional accuracy of sensor measurements is therefore often omitted or unknown, and a correction may be neglected during data processing. In this paper, accounting for a horizontal (spatial) offset is researched by examining the use of several correction methods. To evaluate the degree of loss of positional accuracy and validate several correction procedures, global navigation satellite system (GNSS) data (with real-time kinematic correction) have been simultaneously collected, using a GNSS receiver that was mounted on an all-terrain vehicle and two other receivers that were mounted near the front and end of an elongated sensor sled. The sled was connected to the towing vehicle using a flexible connection. Since the positioning systems’ horizontal accuracies were about 20 mm, it was possible to quantify the horizontal error of the predicted positions for the different correction procedures considered. The best approach for high-resolution surveys, which make use of a connection to a cart or sled that can rotate around a pivot on the towing vehicle, was researched. The strengths and weaknesses of the applied corrections were also evaluated, allowing selection of an appropriate correction for a given survey implementation.     

GPS控制网中基准点的几何分布对精度的影响研究

从某工程GPS平面控制网出发,对3组具有代表性的点位组合用TGO软件进行静态数据处理。通过分析比较,得到了基准点的最优几何位置分布,从而使GPS的定位精度得到明显提高。     

Investigation on pistachio distribution in the mountain regions of northeast Iran by ALOS

Iran supports five different vegetation zones. One of those is the Irano-Touranian zone that is located in the northeast of Iran. This vegetation zone includes arid and semi-arid lands, and its area is about 3.5 million hm². It supports growth of pistachio (Pistacia vera), a deciduous-broadleaved species, which is one of the ecologically and economically most important native species. In this study, we analyzed three images acquired by ALOS satellite, including 10m resolution multispectral band (AVNIR-2), 2.5 m resolution “Backward” PRISM image, and 2.5 m resolution “Nadir” PRISM image, based on a provided rational polynomial coefficient (RPC). Using the “Backward” and “Nadir” images, a 2.5 m resolution digital elevation model (DEM) was produced. Four methods with AVNIR-2 and PRISM data were used to produce pan-sharpening images and conduct an object-based feature extraction process. Normalized Difference Vegetation Index (NDVI) was used to determine the maximum distribution of pistachio in related elevation. The accuracy of the DEM was tested on 28 ground control points in the pair image as tie points, with the value of parallax error of 0.9027 m. The created elevation map indicated that pistachio trees grow up at 650m above sea level (a.s.l.). The result from NDVI in the related elevation showed the maximum density of pistachio at 800m a.s.l. In addition, the result of feature extraction in the forest showed the area of each target element calculated. The results of this research will improve decision-making and lead to sustainable management in general.     

Design of a hyperspectral nitrogen sensing system for orange leaves

The orange (Citrus sinensis) is one of the most important agricultural crops in Florida. Heavy reliance on agricultural chemicals and low fertilizer use efficiencies in citrus production have raised environmental and economic concerns. In this study, a nitrogen sensor was developed to predict nitrogen concentrations in orange leaves. Four design criteria were chosen to maximize the sensing efficiency and reliability. They were: (1) coverage of the spectral N sensing range, (2) no moving parts, (3) single leaf detection, and (4) diffuse reflectance measurement. Based on chlorophyll and protein spectral absorption bands, the sensor's wavelength ranges were chosen to be 620–950 nm and 1400–2500 nm. A reflectance housing was designed to block environmental noise and to ensure single leaf measurement. A halogen light source, two detector arrays, two linear variable filters, and data acquisition cards with 16-bit analog-to-digital converters were used to collect data. The designed N sensor had a spectral resolution less than 30 nm. Test results showed that the nitrogen sensor had good linearity (r > 0.99) and stability. With averaged signal-to-noise ratio (SNR) of 299, the system was able to predict N content with a root mean square difference (RMSD) of l.69 g kg⁻¹ for the validation data set. Using the N sensor, unknown leaf samples could be classified into low, medium and high N levels with 70% accuracy.     

Spatial Variability of Irrigated Corn Yield in Relation to Field Topography and Soil Chemical Characteristics

Corn yield, topography and soil characteristics were sampled on a 26 ha area of a centre pivot irrigated cropland. The aim of the study was to determine relationships between corn yield, field topography and soil characteristics. The study was carried out in the Alentejo region of Portugal. Corn yield was measured with a combine harvester fitted with a grain-flow sensor and positioned by means of the Global Positioning System (GPS). A grid-based digital elevation model (DEM) with 1-m resolution was constructed and several topographic attributes were calculated from the DEM: the local slope gradient (S), profile curvature (Curv), specific catchments area (SCa), and a steady-state wetness index (W). Yield and topographical attributes were computed for areas of radius 5, 10, 25 and 50 m, being considered its maximum, minimum, range and average values. The soil was systematically sampled with a mechanical probe for a total of 109 soil profiles used for analysis of the following soil superficial (<0.30 m) characteristics: extractable phosphorous (P₂O₅) and extractable potassium (K₂O), soil pH, cation exchange capacity (CEC) and exchangeable bases. With centre pivot irrigation systems, the Wave₅₀ index was shown to be useful for the identification of field areas in which low corn yields may be due to lack of water. At the same time, SCa was found to be useful for the identification of field areas in which low yields are due to excess water and drainage problems. Higher positive correlation between pH, Ca and Curv were observed; calcium concentration was found on the transition areas between flat surfaces to concave ones, while lower values were detected in convex and concave areas. Topographical indexes, namely Wave₅₀, SCa and Curv, can be especially helpful in site-specific management for delineating areas where crop yields are more sensitive to extreme water conditions.     

基于无人飞行器航测建立数字高程模型研究

为探索利用无人飞行器获取遥感影像并将之用于建立测区数字高程模型(DEM)的可行性,以南水北调山东省境内济平干渠部分区段为试验对象,进行了无人飞行器的遥感数据采集,并利用全数字摄影测量处理软件VirtuoZo对所得数据进行处理,生成测区数字高程模型.结果表明,数据处理过程中相对定向中误差较小,由于部分试验材料不能满足试验标准,绝对定向的中误差偏大,利用现有材料生成的数字高程模型精度不高.