GPS Calibration Research Articles

A local filtering approach to mitigating the GNSS multipath effects in relative precise positioning considering the multipath spatial correlation

Multipath delay is a significant error in GNSS precise positioning and affected by the station surroundings. This error cannot be effectively eliminated by observation difference techniques and must be carefully calibrated. Although the spatiotemporal correlation feature of multipath plays an important role in static multipath mitigation, this feature lacks research and needs to be thoroughly investigated. Therefore, the local filtering (LF) approach based on least square collocation (LSC) and moving average (MA) methods is proposed and investigated. The space correlation feature is characterized by covariance function or correlation function, and the residuals with small correlations are neglected while only that with relative larger correlations are used in multipath modelling and calibration. The experiments with short baseline MAT1_MATE and KERG_KRGG for both GPS and Galileo multipath calibration show that, the LF approach based on LSC, simple MA and weighted MA methods achieve better performance in multipath mitigation over short and long-time spans compared with conventional grid approach. For example, the GPS double difference (DD) residual variance reduction rates of baseline MAT1_MATE for the calibration of the next day with LF approach based on the three methods reach73.2%, 72.1% and 70.2%, respectively, which are obviously larger than 63.7% of the grid approach. The improvement reaches maximum 16.4% in the case of baseline KERG_KRGG for Galileo and the average value is around 11.5% i.e. the relatively numbers of the two values reach 29.9% and 20.2%, respectively.

Ability of RTK-Based GPS Measurement Method in High Accuracy Work in Geomatics Study

Abstract: Insfrastructure development require significant changes and transformation in Geomatics field for the upcoming decade. The use of new technology in Geomatics and surveying is essential and can be leveraged in many survey application that will help on building the nation towards a sustainable future. In the last 5 years, GNSS technology has been widely used and practiced to replace total station for survey work. Main factors that contributes to this busniness changes are the availability of much cheaper equipment with good technical capability in the market that helps surveyor to perform their work faster and more efficient. Global navigation satellite system services for accurate positioning has also rapidly increased and provide many option and solution for industry player or surveyor to choose. Combination of multiple global navigation satellite system providers such as GPS, GALILEO,GLONASS and BeiDOU has developed good satellite networks and increased numbers of available satellites for observation that improve absolute position accuracy. CHC i70 is among the best selling GNSS model on the market right now. The receiver can receive signal from GPS,GALILEO,GLONASS and BeiDOU simultaneously. This study will outline and focus on the capability of the RTK-Based method ( 30 second to 1 minute observation period) using CHC i70 instrument in high-precision measurement work. The research was done using the GPS calibration test site at Politeknik Sultan Haji Ahmad Shah (POLISAS) and was also practiced in the actual work for establishment of Temporary Bench Mark (TBM) along Jalan Melor to Ketereh, Kelantan. The result of the study found that RTK-Based method can meet the precision work that is permitted under 2cm accuracy. Studies show that the method of using RTK- Based is suitable for high precision work and improve the measurement time and work duration at field.
 
 Keywords : Beidou, Chc and RTK-Based GPS and PDOP

Prototipe Sistem Deteksi Jantung Manusia dan Lokasi Berbasis Internet of Things (IoT)

Based on data from The Institute for Health Metrics and Evaluation (IHME) (2016), it shows that deaths in the world caused by heart and blood vessel diseases reached 17.7 million people or around 32.26 percent of total deaths in the world. The representation of heart health can be seen from the number of heart rate (HR) and oxygen saturation (SpO2). The purpose of this study is to determine the condition of the human body through the number of heartbeats and SpO2 using the MAX30100 sensor and to be able to find out the location of the patient via GPS Adafruit Ultimate Breakout. GPS calibration uses two calculation methods, namely using the Haversine formula and using the distance measurement feature on Google Earth. The method is then compared to get the difference between the coordinates obtained by the smartphone GPS as a reference with the patient's GPS (Adafruit Ultimate Breakout). The HR measurement calibration on the MAX30100 sensor is then compared with the pulse on the left wrist for accuracy. The value of the sensor is calculated every time when it detects a beat/pulse, while the manual count is calculated every 60 seconds. Therefore, the value on the sensor is taken using an average of 10 data to find the accuracy value. The results of this study indicate the level of coordinate accuracy obtained by GPS Adafruit is not more than 5 meters. The average HR accuracy value is 98,23 percent and the SpO2 calibration results get an accuracy of 98,99 percent. The waiting time required for the GPS to receive coordinates from the satellite with the GPS condition uncovered by the casing is about 7 to 13 minutes, while when the casing is closed the GPS cannot get the coordinates. MAX30100 can work optimally and obtain accurate values when the patient is in a relaxed position and does not do too much movement.

Anomaly Detection of Trackside Equipment Based on GPS and Image Matching

The health of trackside equipment often seriously affects the safe driving of the train, while manually checking their status is an indispensably laborious task. In order to automate the task, this paper addresses the problem of automatically and accurately detecting anomalies of equipment located along the track through GPS and image calibration techniques. Considering the unnoticeable changes in equipment, including screws missing and cable corrosion, detection by classification-based machine learning methods is difficult to implement, thus in this paper we propose and conduct a novel detection mechanism by an efficient way of image subtraction. Especially, our method consists of four steps. The first step is to collect images of the trackside equipment and their corresponding mileage in the same route several times through cameras and GPS devices installed in the inspection train. Then, by introducing an improved RANSAC algorithm, the GPS data is further corrected. Secondly, we define one pass of the collected image data along with GPS information as template, and for the rest passes that need to be detected, the first frame alignment operation is operated through GPS and image information. For the third step, the SURF algorithm is implemented for image matching, and then the subtraction operation is conducted between each matched image pairs. Finally, we use empirical filtering mechanism to remove false positives that we have detected. Experimental results demonstrate the efficiency and effectiveness of our proposed method for anomalies detection of trackside equipment.

A Bus Arrival Time Prediction Method Based on Position Calibration and LSTM

Bus arrival time prediction not only provides convenience for passengers, but also helps to improve the efficiency of intelligent transportation system. Unfortunately, the low precision of bus-mounted GPS system, lack of real-time traffic information and poor performance of prediction model lead to low estimation accuracy - greatly influence bus service performance. Hence, in this paper, a GPS calibration method is put forward, while projection rules of specific road shapes are discussed. Moreover, two traffic factors, travel factor and dwelling factor, are defined to express real-time traffic state. Then, considering both historic data and real-time traffic condition, a hybrid dynamic BAT prediction factor, which achieves accuracy enhancement by taking into account traffic flow evaluation results and GPS position calibration, is defined. A LSTM training model is construct to realize BAT prediction. Experiment results demonstrate that our technique can provide a higher level of accuracy compared to methods based on traditional time-of-arrival techniques, especially in the accuracy of multi-stops BAT prediction.

Absolute field calibration for multi-GNSS receiver antennas at ETH Zurich

ETH Zurich developed an absolute GNSS antenna calibration system based on measurements taken in the field. An industrial robot is used to rotate and tilt the antenna to be calibrated. This procedure ensures good coverage of the antenna hemisphere and reduces systematic errors. The calibration system at ETH Zurich is validated by a direct comparison of the obtained calibrations with calibrations from the anechoic chamber method (University of Bonn) and from another absolute field calibration method (Geo++® GmbH). Calibrations by ETH Zurich agree on the sub-millimeter level with both reference calibrations. A second validation was conducted using real measurements on short baselines. Data were acquired on four stations in direct vicinity and processed using different phase center correction models. The experiment shows that individual corrections of ETH Zurich reduce the residuals in the coordinate domain when compared to type-mean calibrations of the International GNSS Service (IGS). However, residual biases between GPS and Galileo coordinates remain. These biases are efficiently reduced when using the new type-mean calibrations from the IGS that include calibration values for all GNSS, including Galileo. The ETH Zurich calibration system is proven to deliver meaningful calibrations that agree with other calibrations on the millimeter level in the azimuth and elevation domain. The field validation shows evidence that the consistency of the Galileo and GPS calibration should be further enhanced by performing a combined GPS and Galileo analysis, which is not yet implemented.

Research of a High Precision Time Synchronization Method Based on GPS Calibration

With the higher requirement for clock accuracy in power system, the accuracy and stability of wild area punctuality in GPS cannot meet the demands of the high–precision measuring instruments in power system. Firstly, this paper establishes the mathematical model of crystal oscillator clock error using polynomial fitting method. Then, it estimates the parameters of polynomial model with generalized least squares method. Thirdly, it updates the error-model of crystal oscillator clock dynamically for modifying its predicted error. The result shows, this method can not only predict accurate time error, but also filter out random errors well in GPS.

A packet-based precise timing and synchronous DAQ network for the LHAASO project

Aiming to high sensitivity and wide spectrum of cosmic ray detection, the Large High Altitude Air Shower Observatory (LHAASO) project consists of over 10,000 detectors of different types, spreading over 1.2km2. To precisely reconstruct the air shower events with high angular resolution, all detector electronics and digitizers should work in synchronous acquisition mode with a global timing error less than <5ns (rms). This large scale and high precision timing requirement exceeds the capability or feasibility of traditional methods such as GPS and echo-delay calibration. Recently an emerging method named White Rabbit (WR) was proposed and demonstrated as a cost-effective solution that combines Gigabit Ethernet data transfer and subnanosecond precision timing transfer over the same fiber media. Furthermore, the White Rabbit network also enables direct digitization and trigger-less data acquisition mode for each detector, which will greatly reduce the complexity and improve the performance of the data acquisition (DAQ) system. In this paper we will demonstrate the design and development status of a WR timing and DAQ network in the LHAASO project.

Construction and uncertainty evaluation of a calibration system for GPS receivers

GPS is already a main method of positioning measurement in geodesy and is applied widely in many fields. In order to maintain and ensure the accuracy of positioning, an accurate and efficient system for calibrating the GPS receivers must be established. A highly accurate GPS calibration network, tied to the ITRF coordinates of IGS stations, can be effectively used to evaluate the performance of GPS receivers. This study addresses the feasibility of establishing a system for calibrating GPS receivers and the system's traceability in metrology. Uncertainties of the GPS calibration networks were established and maintained by NML (National Measurement Laboratory, Taiwan). Furthermore, the networks are evaluated based on the method suggested by the ISO (International Organization for Standardization). The uncertainties of NML network coordinates are obtained and used as a basis for calibration. The results of the slope distances between pillars measured by the GPS processing units and the precise EDM units are discussed. Analytical results indicate that the 3D expanded uncertainty of the main station TNML of the network in the ITRF system is around 33.2 mm at the 95% confidence level. The 3D expanded uncertainties of the calibration points of the ultra-short distance network and the short distance network are evaluated to be about 2.2 mm and 3.4 mm, respectively in relation to the main station TNML at the 95% confidence level. The precision of the NML network coordinates suffices to calibrate the geodetic and navigational GPS receivers of regional users and is available through the Internet.

Canadian surveillance of space concept demonstrator—metric accuracy and limiting magnitude assessment

Defence R&D Canada (DRDC), in partnership with the Canadian Forces’ Surveillance of Space Project, is developing an array of three remotely operated, ground-based optical observatories for space surveillance (the Concept Demonstrator, CD). Manual metric accuracy testing of the CD, performed using a single sensor, began in December 2003, and focused on GPS calibration satellites. Results from this study are promising, with angular residual uncertainties less than 3 ″ with arcsec level biases. This short metric accuracy campaign also permitted a rough sensitivity performance check. This paper summarizes these metric accuracy and sensitivity performance checks of the CD.

Second international airborne remote sensing conference and exhibition

The conference provided four days of displays and scientific presentations on applications, technology, a science of sub-orbital data gathering and analysis. The twelve displayed aircraft equipped with sophisticated instrumentation represented a wide range of environmental and reconnaissance missions,including marine pollution control, fire detection, Open Skies Treaty verification, thermal mapping, hydrographical measurements, military research, ecological and agricultural observations, geophysical research, atmospheric and meterological observations, and aerial photography. The U.S. Air Force and the On-Site Inspection Agency displayed the new Open Skies Treaty verification Boeing OC 135B that promotes international monitoring of military forces and activities. SRl's Jetstream uses foliage and ground penetrating SAR for forest inventories, toxic waste delineation, and concealed target and buried unexploded ordnance detection. Earth Search Sciences's Gulfstream 1 with prototype miniaturized airborne hyperspectral imaging equipment specializes in accurate mineral differentiation, low-cost hydrocarbon exploration, and nonproliferation applications. John E. Chance and the U.S. Army Corps of Engineers displayed the Bell 2 helicopter with SHOALS that performs hydrographic surveying of navigation projects, coastal environment assessment, and nautical charting surveys. Bechtel Nevada and U.S. DOE displayed both the Beech King AIR B-200 platform equipped to provide first response to nuclear accidents and routine environmental surveillance, and the MBB BO-105 helicopter used in spectral analysis for environmental assessment and military appraisal. NASA Ames Research Center's high-altitude Lockheed ER-2 assists in earth resources monitoring research in atmospheric chemistry, oceanography, and electronic sensors; ozone and greenhouse studies and satellite calibration and data validation. Ames also showcased the Learjet 24 Airborne Observatory that completed missions in Venus cloud cover analysis, Quadantid meteor shower studies, extra-solar far infrared ionic structure lines measurement, Cape Kennedy launch support, and studies in air pollution, The Products and Services Exhibit showcased new sensor and image processing technologies, aircraft data collection services, unmanned vehicle technology, platform equipment, turn-key services, software a workstations, GPS services, publications, and processing and integration systems by 58 exhibitors. The participation of aircraft users and crews provided unique dialogue between those who plan data collection a operate the remote sensing technology, and those who supply the data processing and integration equipment. Research results using hyperspectral imagery, radar and optical sensors, lidar, digital aerial photography, a integrated systems were presented. Major research and development programs and campaigns we reviewed, including CNR's LARA Project and European Space Agency's 1991-1995 Airborne Campaign. The pre-conference short courses addressed airborne video, photogrammetry, hyperspectral data analysis, digital orthophotography, imagery and GIS integration, IFSAR, GPS, and spectrometer calibration.