Stand-alone Global Positioning System Receiver Research Articles

Evaluating Two Low-Cost GPS Receivers for Accuracy and Eventual Use in Pastured Cattle Research

HighlightsA stand-alone GPS receiver produced comparably lower location errors than a smartphone GPS.Low-cost GPS receivers are suitable for use in research on large-herd cattle behavioral response to UAVs.Different testing placements can influence the horizontal accuracy of low-cost GPS receivers and smartphones.Abstract. Using animal-borne global positioning system (GPS) collars, cattle behavioral response to anthropogenic disturbances can be accurately quantified at fine scale. However, the use of dedicated commercial GPS collars in large herd studies is cost-prohibitive. Therefore, low-cost GPS receiver alternatives were evaluated in static placements to determine how their accuracy compares to published data for commercial animal-borne GPS collars. The static accuracies of identical low-cost stand-alone GPS receivers and smartphones were evaluated in an open field without obstructions, under trees with and without canopy, and near an electric fence at 5 min and 1 s sample intervals. The mean circular error probable (CEP) value of the stand-alone GPS receiver was =2 m at 5 min and at 1 s in open field placement. The mean CEP value of the stand-alone GPS receiver was =3 m at 5 min and at 1 s when placed near the electric fence. The smartphone produced mean CEP values of =4 m at 5 min and =3 m at 1 s for the fence line and open field placements. Static testing under trees with canopy at the 5 min sample interval produced mean CEP values 100% greater than under trees without canopy at the 1 s sample interval. Low-cost commercial GPS receivers and smartphones with horizontal accuracy of =5 m at high sample resolution may offer accurate means of quantifying the behavioral response of cattle to UAVs in large herd studies. Keywords: Cattle behavior, Global positioning system, Horizontal accuracy, Smartphone GPS, Stand-alone GPS receiver, UAV, Unmanned aerial vehicle.

Determination of the ionospheric foF2 using a stand-alone GPS receiver

The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities.

A Novel Method for Precise Onboard Real-Time Orbit Determination with a Standalone GPS Receiver.

Satellite remote sensing systems require accurate, autonomous and real-time orbit determinations (RTOD) for geo-referencing. Onboard Global Positioning System (GPS) has widely been used to undertake such tasks. In this paper, a novel RTOD method achieving decimeter precision using GPS carrier phases, required by China’s HY2A and ZY3 missions, is presented. A key to the algorithm success is the introduction of a new parameter, termed pseudo-ambiguity. This parameter combines the phase ambiguity, the orbit, and clock offset errors of the GPS broadcast ephemeris together to absorb a large part of the combined error. Based on the analysis of the characteristics of the orbit and clock offset errors, the pseudo-ambiguity can be modeled as a random walk, and estimated in an extended Kalman filter. Experiments of processing real data from HY2A and ZY3, simulating onboard operational scenarios of these two missions, are performed using the developed software SATODS. Results have demonstrated that the position and velocity accuracy (3D RMS) of 0.2–0.4 m and 0.2–0.4 mm/s, respectively, are achieved using dual-frequency carrier phases for HY2A, and slightly worse results for ZY3. These results show it is feasible to obtain orbit accuracy at decimeter level of 3–5 dm for position and 0.3–0.5 mm/s for velocity with this RTOD method.

Retrieving real-time precise co-seismic displacements with a standalone single-frequency GPS receiver

Nowadays, Global Positioning System (GPS) plays an increasingly important role in retrieving real-time precise co-seismic displacements for geo-hazard monitoring and early warning. Several real-time positioning approaches have been demonstrated for such purpose, such as real-time kinematic relative positioning, precise point positioning, etc., where dual-frequency geodetic receivers are applied for the removal of ionosphere delays by inter-frequency combination. At the same time, it would be also useful to develop efficient algorithms for estimating precise displacements with low-cost GPS receivers since they can make a denser network or multi-sensors combination without putting too much financial burden. In this contribution, we present a new method to retrieve precise co-seismic displacements in real-time using a standalone single-frequency receiver. In the new method, observations prior to an earthquake are utilized to establish a precise ionospheric delay prediction model, so that precise co-seismic displacements can be obtained without any convergence process. Our method was validated with an outdoor experiment as well as by re-processing of 1-Hz GPS data collected by the GEONET network during the 2011 Tohoku Mw 9.0 earthquake. For the latter, RMS against dual-frequency receivers constituted 2cm for horizontal components and 3cm for the vertical component.We specially address the observation biases and their impact on the accuracy of single frequency positioning. Our approach makes real-time GPS displacement monitoring with dense network much more affordable in terms of financial costs.

Simplistic approach for water vapour sensing using a standalone global positioning system receiver

Precipitable water vapour (PWV) is an important input for numerical weather prediction model, meteorology and high-precision navigational applications. Conventional methods for the determination of PWV using radiosonde are not sufficient owing to poor temporal resolution, whereas radiometer-derived PWV is reliable only in fair weather conditions. Global positioning system (GPS) is a very useful and cost-effective tool to determine PWV continuously in all weather conditions. The processing of GPS data to extract the PWV information is, however, very complicated due to very small effect of the PWV (~0.5% of total delay) on GPS frequencies than other sources of delay and errors and requires a network of GPS in differential configuration for such purpose. The authors show how the problem can be handled in a standalone dual-frequency GPS receiver in a relatively less complicated manner with reasonable accuracy. The performances of different dry tropospheric delay models are also investigated. The methodology is tested with GPS measurements at Kolkata (22.57°N, 88.37°E) and Bangalore (13.01°N, 77.5°E). The results indicate that the proposed methodology can be implemented for PWV estimation using single GPS receiver with satisfactory performance.

Global Navigation Satellite Systems Seismology for the 2012 Mw 6.1 Emilia Earthquake: Exploiting the VADASE Algorithm

Online Material: Tables of statistical indexes; figures comparing displacement solutions. The Global Positioning System (GPS) has been repeatedly proven to be a powerful tool to estimate coseismic displacements and waveforms, with accuracies ranging from few millimeters to few centimeters. These promising results were achieved following two main strategies: differential positioning (DP) and precise point positioning (PPP; Bock et al. [1993], Kouba [2003], Larson et al. [2007], Larson [2009], Ohta et al. [2012], Xu et al. [2012], and Hung and Rau [2013]). In particular, both the modeling of fault rupture and the seismic moment estimation could benefit from GPS‐derived displacements, because GPS is not affected by the saturation problems experienced by seismometers located near the epicenters of strong earthquakes. Thanks to the robustness of the GPS‐derived displacement waveforms, in the last years some authors (Bock et al. , 2000; Langbein and Bock, 2004; Blewitt et al. , 2006; Bock and Genrich, 2006) addressed the problem to retrieve them in real time, with accuracies of a few centimeters, from GPS high‐rate observations (1 Hz or more). In this context, the Variometric Approach for Displacements Analysis Standalone Engine (VADASE) has been proposed (Colosimo et al. [2011a], Colosimo [2013]). The approach is based on time single differences of carrier phase observations continuously collected using a standalone GPS receiver and on standard GPS broadcast products (orbits and clocks) that are available in real time. Therefore, one receiver works in standalone mode and the epoch‐by‐epoch displacements (equivalent to velocities) are estimated. Then, they are summed over the time interval when the earthquake occurred to retrieve displacements. Because VADASE does not require either additional technological complexity or a centralized data analysis, in principle, it can be embedded into the GPS receiver firmware and therefore can work in real time. Moreover, differently from DP and PPP, …

Portable device to assess dynamic accuracy of global positioning system (GPS) receivers used in agricultural aircraft.

A device was designed to test the dynamic accuracy of Global Positioning System (GPS) receivers used in agricultural aircraft and other aerial vehicles. The system works by directing a sun-reflected light beam from the ground to the aircraft using mirrors. A photo detector points downward from the aircraft to detect the light beam, and photo detection circuitry triggers an event in the guidance system data file at the aircraft’s location corresponding to the precisely georeferenced position on the ground. Construction details are presented on the mirror-based light reflection system and photo-electronic circuitry designed to trigger an event in the guidance system’s log file. An example application evaluated the horizontal accuracy of a stand-alone GPS receiver by matching dynamic data with data from the aircraft’s guidance system. Results indicated a 2.16 s lead in position registered by the stand-alone receiver over that registered by the aircraft’s guidance system GPS receiver, which had been previously evaluated to be within 0.13 s of Real-Time Kinematic (RTK)-referenced time and position. Keywords: GPS receiver accuracy, agricultural aircraft, aerial application, remote sensing, georeferencing, UAV DOI: 10.3965/j.ijabe.20140702.008 Citation: Thomson S J, Huang Y B, Smith L A. Portable device to assess dynamic accuracy of global positioning system (GPS) receivers used in agricultural aircraft. Int J Agric & Biol Eng, 2014; 7(2): 68－74.

GPS Output Signal Processing considering both Correlated/White Measurement Noise for Optimal Navigation Filtering

In this paper, a dynamic modeling for the velocity and position information of a single frequency stand-alone GPS(Global Positioning System) receiver is described. In static condition, the position error dynamic model is identified as a first/second order transfer function, and the velocity error model is identified as a band-limited Gaussian white noise via non-parametric method of a PSD(Power Spectrum Density) estimation in continuous time domain. A Kalman filter is proposed considering both correlated/white measurements noise based on identified GPS error model. The performance of the proposed Kalman filtering method is verified via numerical simulation.

Crop dusting using GPS

Global Positioning System (GPS) receivers and GPS-based swath guidance systems are used on agricultural aircraft for remote sensing, airplane guidance, and to support variable-rate aerial application of crop inputs such as insecticides, cotton growth regulators, and defoliants. Agricultural aircraft travel at much greater speeds than ground equipment (65 m/s, typically), so longitudinal (along-track) error in GPS-derived position is likely to be pronounced. Due to rapid ground speeds, determination of exact GPS-derived aircraft location requires special methodologies. To meet the need for determining ground position accurately, a ground-based spotting system using two strategically placed mirrors was designed to reflect sunlight to the belly of the aircraft when the plane passed over a ground reference point. The light beam was detected by a photocell on the airplane, causing a solid state relay to close through appropriate circuitry. When the relay closed, a record was placed in the data file for the airplane's Satloc GPS receiver, accurate to 0.01 s allowing exact position to be logged. Two stand-alone GPS receivers were evaluated along with the Satloc system, and their readings were compared with readings from the Satloc. For one day of testing used as an example, the Satloc lagged the ground reference point by an average of -4.53 m (S.D. = 0.68) in the east-west directions and led the reference point in the north-south directions by an average of +7.88 m (S.D. = 0.52). Positioning data from one stand-alone GPS receiver showed a distinct ground speed dependency, making it unsuitable for use in aircraft. Output from the other receiver (designed for aircraft use) was insensitive to ground speed changes but exhibited a look-ahead equivalent to 2-s at the ground speeds evaluated.

An Instrumentation Platform and GPS Position Latency Issues for Remote Sensing on Agricultural Aircraft

To help support and enhance research programs at the Delta States Research Center, Stoneville, Mississippi (USDA-ARS and Mississippi State University cooperating), there has been a need to sense field variables from an easily scheduled remote sensing platform. Agricultural aircraft are widely used for aerial spraying in the mid-southern U.S., so they are also convenient platforms for remote sensing. Research programs are being supported with an eye on providing low-cost imaging tools that can be used by aerial applicators for site-specific management and that include optical and thermal methods for detection of weeds, soil variability, crop stresses, deleterious fishpond constituents, and fire ant mounds. Global Positioning System (GPS) receivers, instrumentation, and pilot controls for use of the remote sensing systems are described, and data and thermal imagery from a field application are illustrated. A novel event triggering device was used to determine positioning accuracy of the GPS receiver that is a component of the Satloc Airstar M3 guidance system. Testing this receiver was a prerequisite to testing two stand-alone GPS units (Garmin 76S and Lowrance Airmap 100) used for position-based camera triggering and image georeferencing. Satloc-derived ground position was found to be within 8 m of actual ground position using the event trigger, so stand-alone GPS units were compared with readings from the Satloc. The Garmin receiver showed a distinct influence of ground speed on position, but the Lowrance unit showed little change in position with changing ground speed. Both stand-alone GPS receivers showed a curious lead in position by as much as 2 s (126 m) over the Satloc, which should be taken into account if using stand-alone GPS receivers for camera triggering or image georeferencing.

In-Car Positioning and Navigation Technologies—A Survey

In-car positioning and navigation has been a killer application for Global Positioning System (GPS) receivers, and a variety of electronics for consumers and professionals have been launched on a large scale. Positioning technologies based on stand-alone GPS receivers are vulnerable and, thus, have to be supported by additional information sources to obtain the desired accuracy, integrity, availability, and continuity of service. A survey of the information sources and information fusion technologies used in current in-car navigation systems is presented. The pros and cons of the four commonly used information sources, namely, 1) receivers for radio-based positioning using satellites, 2) vehicle motion sensors, 3) vehicle models, and 4) digital map information, are described. Common filters to combine the information from the various sources are discussed. The expansion of the number of satellites and the number of satellite systems, with their usage of available radio spectrum, is an enabler for further development, in combination with the rapid development of microelectromechanical inertial sensors and refined digital maps.

A New GPS Data Processing Algorithm for the Positioning of Oceanographic Experiments

Abstract In this paper, the authors present a Global Positioning System (GPS) algorithm for medium accuracy (1-m rms) positioning of ocean buoys. The application addressed in this paper is that of the Fast Pegasus experiments that require the positioning of surface buoys used in collecting subsurface acoustic data for ocean current profiling. The current GPS system designed for the Fast Pegasus experiments requires a land-based single-frequency GPS receiver for differential GPS positioning. In contrast, the technique presented here is designed for the point positioning of a stand-alone single-frequency GPS receiver (which is in motion) and does not require the use of a land-based reference receiver. The precise point positioning algorithm developed here uses postprocessed GPS satellite ephemerides and clock corrections to compute the position of a single GPS receiver. A square root information filter/smoother uses the GPS pseudorange and carrier phase measurements to estimate the position and clock offset...