GNSS precise positioning

Multispectral cameras on-board an Unmanned Aerial System (UAS) can acquire imagery at ultra-high spatial and temporal resolution for efficient, non-destructive analysis of vegetation. Whilst this can produce meaningful data for Precision Agriculture, the ability to detect change requires imagery which is positioned accurately and referenced to a real-world coordinate system. A traditional method of doing this is to place and register the location of Ground Control Points (GCPs) in the scene of interest. However, continued advances in Global Navigation and Satellite System (GNSS) technology is now enabling the ability to accurately observe and record UAS camera position at the time of image capture. This technique is known as Direct Georeferencing (DG) and has the advantage of decreased reliance on GCPs, which are often time-consuming and costly to use. The recent announcement of a Satellite-Based Augmentation System (SBAS) in Australia is opening further opportunities to do this, particularly due to the availability of standalone (no reference station required) solutions such as Dual-Frequency Multi-Constellation (DFMC) and real-time Precise Point Positioning (PPP). As part of a nationwide SBAS test-bed project, this study aimed to test the accuracy and reliability of this next-generation positioning technique in a DG workflow. To determine if multispectral orthomoasics could be useful in Precision Agriculture, two prototype SBAS receivers were mounted on a DJI Matrice600 UAS and airframe position was observed throughout six independent flights. Positions as a function of each SBAS solution were later synchronised with image acquisition and subsequently used in photogrammetric processing software (Agisoft Metashape), to produce georeferenced multispectral outputs of varying geometric accuracy. DG orthophoto accuracy was then validated using 14 GCP checkpoints, which had been placed throughout the study area. In addition, SBAS accuracy was assessed relative to a Post-Processed Kinematic (PPK) GNSS solution, using a dual-frequency carrier-phase receiver also mounted on the UAS airframe and processed differentially using a local reference station.
Error analysis of DG outputs show that resultant orthophoto accuracy is inherently related to the performance of the SBAS solution used to define camera position during UAS flights. Based on mean horizontal GCP checkpoint offsets, orthophotos georeferenced using a real-time PPP solution produced the highest accuracy of ~0.28 m (std. deviation of ~0.11 m), compared to code-based DFMC solutions, which produced an orthophoto accuracy of ~0.81 m (std. deviation of 0.40 m). Whilst more accurate, real-time PPP is limited by its long convergence time (>1 hour) and remains less accurate than orthophotos georeferenced using a dual-frequency PPK solution (~0.17 m). Overall SBAS solution performance is also affected by time-varying influences caused by changing satellite geometry. This degrades the precision of DG outputs, producing inconsistent results across different observation windows. Accordingly, photogrammetric products georeferenced using SBAS positioning may not be suitable for change detection at the scale of individual plants, though may be useful in crop areas where variability exceeds the geometric error of DG orthophotos.

Se entiende por levantamiento Topográfico al conjunto de actividades que se realizan en el campo con el objeto de capturar la información necesaria que permita determinar las coordenadas rectangulares de los puntos del terreno, ya sea directamente o mediante un proceso de cálculo, con las cuales se obtiene la representación gráfica del terreno levantado, el área y volúmenes de tierra cuando así se requiera. Aun cuando las nuevas tecnologías han impactado en el cómo se capturan y se procesan los datos, el conjunto de las actividades que contempla el levantamiento topográfico puede discriminarse en las mismas etapas que la topografía clásica tradicionalmente ha considerado, entre las que se puede mencionar la selección de equipos, planificación, señalización y captura de datos.

The market for Global Navigation Satellite System (GNSS) based applications requiring accurate positioning information has been steadily growing over the recent years. As a consequence of technological advances in GNSS technology, single-frequency, navigation-grade receivers capable to provide carrier phase data can be a cost-effective alternative to the high-professional, geodetic-grade receivers. Navigation-grade receivers are mainly attractive as their cost ranges around of few hundred euros. In addition, the carrier phase measurements are the most accurate observables collected from a GNSS system. As a result, the positioning accuracy obtained with navigation-grade receivers can reach levels that may raise interest various communities that use positioning information. The main purpose of this study is to analyze the performance of high-sensitivity carrier phase-based positioning using navigation-grade equipment. A few static tests covering different time intervals and various baselines with different lengths are investigated. In addition, several kinematic tests are also conducted. The obtained positioning solutions and baseline lengths are compared to the corresponding ones derived from observations collected with professional equipment. The test results demonstrate that cm-level accuracy can be achieved with navigation-grade equipment when it can output carrier phase data. This level of accuracy may be attractive to various applications, such as land, marine or aerial surveying, structural monitoring or early warning systems.

Precise Point Positioning requires precise knowledge of the satellite position and satellite clock offsets, which are nowadays provided by the Analysis Centers of the International GNSS Service. The knowledge of the satellite phase biases is crucial to achieve the ultimate positioning accuracy and a short convergence time, as these hardware-induced delays affect the ability to successfully resolve the integer carrier phase ambiguities. In this study, a new method for the estimation of these parameters with a global network of multi-frequency reference stations is proposed. In its first part, the thesis introduces the proposed parameter mapping in the state space of the GNSS observation model that allows for an undifferenced and uncombined PPP-RTK model. First,
individual satellite phase biases, position and clock corrections are derived for each cluster of stations. Then, the solutions of each cluster are combined into a multi-cluster solution, in order to acquire global estimates of the aforementioned parameters. Based on this concept, an independent and complete system has been developed and implemented
for GNSS satellite phase bias estimation in post-processing mode. Apart from the satellite-only related parameters, the system provides receiver clock offsets and phase biases, and tropospheric zenith and ionospheric slant delays. The performance of the proposed method is first analyzed with simulated Galileo measurements on E1 and E5a acquired from the IGS global network, split into 16 clusters. The achieved accuracy
of the multi-cluster derived satellite phase biases is better than 2 and 4 cm for almost all epochs and satellites with and without integer ambiguity fixing, respectively. Finally, the proposed concept is validated with real GPS measurements on L1 and L2 acquired from stations of the IGS Multi-GNSS network. The single-cluster derived satellite phase biases
show a stability of 2-8 cm/hour and a precision varying between 1 and 6 cm, depending on the observational session duration and cluster size. The precision of the phase biases reaches the 5-9 mm level within a few hours in the multi-cluster combined solution, while an improvement on their stability is not observed.

Precise Point Positioning (PPP) has been one of the major research areas in surveying in
recent years to obtain cost effectively coordinates using one dual frequency GNSS instrument.
The purpose of this study is to investigate the accuracy of the kinematic PPP solution using
Bernese software for hydrographic applications. This PPP solution was compared with the
double-difference solution from Bernese software. The Virtual SAPOS
(SAtellitenPOSitionierungsdienst der deutschen Landesvermessung) reference station was
considered as a reference station.
Two kinematic trajectories have been observed within project “HydrOs (Integrated
Hydrographic Positioning System) on the Rhine River, Duisburg, Germany. This project is
launched in co-operation of the department M5 (Geodesy) of the German Federal Institute of
Hydrology (BfG) and the Institute of Engineering Geodesy at the University of Stuttgart
(IIGS).
The first kinematic trajectory shows a standard deviation for the kinematic PPP solution of 6
cm in East, 2.1 cm in North, and 6.8 cm in height. If the 5% of the measurements are
eliminated as outliers, the standard deviation values for a confidence level of 95% (SD95%)
are 5 cm in East, 1.2 cm in North and 5 cm in height. The second trajectory, which started
with 40 minutes of quasi-static observation time (non-moving vessel), achieves a more precise
solution. The standard deviation values of all measurement are 1.7 cm in East, 2.6 cm in
North, and 4.9 cm in height. For a confidence level of 95%, the PPP solution provides a
standard deviation (SD95%) of 1.5 cm for the East and North directions. Moreover, it delivers
3 cm for the height.

Precise Point Positioning (PPP) has been proved by many researchers in the last decade as a cost-effective alternative for Differential GPS (DGPS) with an estimated precision sufficient for many applications. PPP implementation needs state-of-art software to correct GNSS observations from different types of errors. Several online PPP services have been developed recently by government agencies, universities, industries and individuals. The PPP software centre managed by University of New Brunswick (UNB), Canada is offering the user four online PPP services (CSRS-PPP, GAPS, APPS and magicGNSS) (UNB-PPP, 2015). This research presents an accuracy assessment evaluation study for those services by processing 3h 52min. dual frequency-static GPS observations which were divided into 10 sessions with different observation duration (10min, 20min, 30min, 45min., 1 hr, 1.5 hr, 2 hr, 2.5 hr, 3 hr and 3hr 52min.)

— The concept of Precise Point Positioning (PPP) for Global Navigation Satellite System (GNSS) technology was introduced in 1976, however it took until the 1990s for PPP to generate interest amongst the greater GNSS community. In order to evaluate the performance of PPP and its uses for CORSs Network definition, data collected from geodetic receivers belonging to permanent stations of Nigeria network (NIGNET-http://www.nignet.net/) were used. PPP was chosen as an option because the stations belong to the network are still sparsely distributed and the data are not available on a perfect continuous basis. However, the PPP approach could form basis for the mass-market sensor data acquisition since it works using the principles of relative positioning. Therefore, to test the algorithm of the PPP, there is the need for using best set of data available. Considering some software freely available online and others available offline, each file for each day is processed using different strategies, and results were obtained for each method for the entire fifteen days. Some statistical analysis and comparisons between obtained results were computed thanks to a routine written in Matlab, in order to obtain the overall average for the entire fifteen days. The procedure was repeated for all the stations used and the outcome is shown. From the result obtained in this paper, it can be deduced that the online processing software provide still highly reliable solutions. Differences between estimated and reference positions are in the other of 1-10 cm, in both horizontal and vertical components, for almost all software. In this context, PPP can be considered an interesting technique to determine the CORS' reference coordinates. Despite the sessions length (very long), PPP can be considered a great alternative respect to the relative techniques for many applications (e.g. cadastral applications) where high accuracy is required.

GLONASS pseudorange observations are affected by inter-frequency channel biases (ICBs) due to the frequency division multiple access (FDMA) satellite signal structure. This research estimated the GLONASS pseudorange inter-frequency channel biases using 350 IGS stations, based on 32 receiver types and over 11 antenna types over a period of 1 week, DOY 195 to 201 in 2013. An improvement of 19% and 1% was observed after calibrating out the pseudorange ICBs, in the horizontal and vertical components, respectively, considering a 20-min convergence period. Two major contributions are presented. The first contribution is the presentation of the four different scenarios involving varying different receiver and antenna types and how that variability affects the characteristics of ICBs. Attention is also drawn to the characteristics of the Analysis Center (AC) satellite common mean errors. In relation to the antipodal nature of the GLONASS satellites, the correlation of the GLONASS frequency numbers with the AC-satellite common mean errors is addressed.

Global Positioning System (GPS) technology is ideally suited for inshore and offshore positioning because of its high accuracy and the short observation time required for a position fix. Precise point positioning (PPP) is a technique used for position computation with a high accuracy using a single GNSS receiver. It relies on highly accurate satellite position and clock data that can be acquired from different sources such as the International GNSS Service (IGS). PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of observations among other factors. PPP offers comparable accuracy to differential GPS with safe in cost and time. For many years, PPP users depended on GPS (American system) which considered the solely reliable system. GLONASS's contribution in PPP techniques was limited due to fail in maintaining full constellation. Yet, GLONASS limited observations could be integrated into GPS-based PPP to improve availability and precision. As GLONASS reached its full constellation early 2013, there is a wide interest in PPP systems based on GLONASS only and independent of GPS. This paper investigates the performance of kinematic PPP solution for the hydrographic applications in the Nile river (Aswan, Egypt) based on GPS, GLONASS and GPS/GLONASS constellations. The study investigates also the effect of using two different observation types; single-frequency and dual frequency observations from the tested constellations.

In this paper, an improved Precise Point Positioning GPS/MEMS-based integrated system is introduced for precise positioning applications. Un-differenced ionosphere-free linear combinations of carrier phase and code measurements are processed. Tropospheric delay, satellite clock, ocean loading, Earth tide, carrier-phase windup, relativity, and satellite and receiver antenna phase-center variations are accounted for using rigorous modeling. Tightly coupled mechanism is adopted, which is carried out in the raw measurements domain. Both Extended Kalman filter (EKF) and Unscented Kalman filter (UKF) are developed to merge the GPS and inertial measurements. The performance of integrated system is analyzed using a real test scenario in downtown Kingston. It is shown that both Extended Kalman and Unscented Kalman filters have comparable performance. The positioning results of the integrated system show that decimeter-level accuracy is achievable. During the GPS outages, the integrated system showed meterlevel accuracy when a 60-second outage was introduced. However, the positioning accuracy was improved to sub-decimeter and centimeter level when 30- and 10-second GPS outages were introduced, respectively.

Commonly, kinematic PPP techniques employ un-differenced ionosphere-free linear combination of GPS observations. This, however, may not provide continuous solution in urban areas as a result of limited satellite visibility. In this paper, the traditional un-differenced as well as between-satel- lite single difference (BSSD) ionosphere-free linear combinations of GPS and GLONASS measure- ments are developed. Except GLONASS satellite clock products, the final precise GPS and GLONASS satellites clock and orbital products obtained from the multi GNSS experiment (MGEX) are used. The effects of ocean loading, earth tide, carrier-phase windup, sagnac, relativity, and satellite and receiver antenna phase-center variations are rigorously modeled. Extended Kalman filter (EKF) is developed to process the combined GPS/GLONASS measurements. A comparison is made between three kinematic PPP solutions, namely standalone GPS, standalone GLONASS, and combined GPS/ GLONASS solutions. In general, the results indicate that  the addition of GLONASS observations im- proves the kinematic positioning accuracy in comparison with the standalone GPS PPP positioning accuracy. In addition, BSSD solution is found to be superior to that of the traditional un-diffe- renced model.

The positioning by GNSS is based on solving a mathematical problem involving the observation of the ranges from the user to a set of satellites with known coordinates. The position can be computed in absolute or in relative mode. The absolute positioning relies solely on a single receiver for the position determination. The relative positioning, however, depends on reference stations and involves the use of more receivers other than the one belonging to the user himself. Thus, the methods used in determining the position of a mobile platform, with accuracy in the order of centimetres, are based on this latter type of positioning. However, they have the disadvantage of being dependent on reference stations, with a limited range and they also require simultaneous observations of the same satellites by the reference station and the receiver. A new GNSS absolute positioning method was developed by computing or completely removing most of the errors associated with each component of the observation equations, using precise ephemeris and clock corrections for the satellites. This method is known as Precise Point Positioning (PPP) and allows the user to achieve an accuracy equivalent to relative positioning systems.

In this work, after a thorough research on this subject, a PPP application was developed for academic purposes, to process GNSS data using the GPS Toolkit C++ class library, which allows to compute the position and speed of the receiver in kinematic mode and in real time. This was tested using observation data from a static station (processed in kinematic mode) and from the Portuguese Navy’s survey ship NRP Auriga. The results showed a precision at decimetre level for the position and at cm/s for the velocity.

The mitigation of ionospheric delay is still of crucial interest in GNSS positioning, especially in precise solutions such as instantaneous RTK positioning. Thus, several effective algorithms and functional models were developed, and also numerous investigations of ionospheric correction properties in RTK positioning have been performed so far. One of the most highly effective approaches in precise relative positioning is the application of the ionosphere-weighted model with network-derived corrections. This contribution investigates the impact of the accuracy of the network ionospheric corrections on time-to-fix in RTK-OTF positioning. Also, an attempt has been made to estimate the desirable accuracy of the network ionospheric corrections, allowing for reliable instantaneous ambiguity resolution. The experiment is based on a multi-baseline GPS RTK positioning supported with network-derived ionospheric corrections for medium length baselines. The results show that in such scenario, the double-differenced ionospheric correction residuals should not exceed $1/3 of the L1 wavelength for successful single-epoch ambiguity resolution.

With the advent of quad‐constellation, triple‐frequency and external atmospheric constraints being provided to the PPP user, the novelty and focus of this paper is in the quest to answer the question: Do we really need ambiguity resolution in multi‐GNSS PPP for accuracy or for integrity? To address the first component of the question, which is also an area of research that has lacked attention, is an examination of the significance between the float and ambiguity resolved PPP user solution. Is the improvement significant enough for applications such as precision agriculture and autonomous vehicles to justify the additional cost and computational complexity of producing a multi‐GNSS PPP‐AR solution? Results consist of solution analysis of convergence time (time to a pre‐defined performance level), position precision (repeatability), position accuracy (solution error with respect to analysis centre's weekly Site Independent Exchange (SINEX) solution) and residual analysis. Pre‐defined user thresholds were selected based on specifications for lane navigation and machine guidance for agriculture. A novel component within the realm of PPP‐AR is the analysis of ambiguity resolution as a metric to examine the integrity of the user solution. The role of ambiguity resolution relies primarily on what are the user specifications. If the user specifications are at the few cm‐level, ambiguity resolution is an asset, as it improves convergence and solution stability. Whereas, if the user's specification is at the few dm‐level, ambiguity resolution offers limited improvement over the float solution. If the user has the resources to perform ambiguity resolution, even when the specifications are at the few dm‐level, it should be utilized. To have a high probability of correctly resolving the integer ambiguities, the residual measurement error should be less than a quarter of a wavelength. Having a successfully resolved and validated solution can indicate to user the solution strength and reliability.

GNSS users use Differential positioning technique for high accuracy but with high cost. Precise Point Positioning (PPP) is an enhanced single point positioning technique for code or phase measurements using precise orbits and clocks. To compensate for ionospheric effects, dual frequency measurements are used for an ionosphere free combination. PPP provides comparable positioning accuracy to Differential GPS (DGPS) with safe in cost and time. PPP precision varies based on the used constellation, positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of observations among other factors. Kinematic-PPP has many applications in fields such as; infrastructure, hydrography and precision Agriculture. Kinematic-PPP using single frequency observations is an efficient low cost system for users in developing countries as dual frequency receivers have high cost comparing with single frequency receivers. During this research, a 637 m track was observed on (10/9/2015-18614 GPS day) at Aswan; a city sited in south Egypt (using GPS single frequency ProMark3 receiver using (stop and go) and kinematic positioning techniques. The track positions were obtained using four techniques namely; DGPS (stop and go), DGPS (kinematic), PPP (stop and go) and PPP (kinematic). Evaluation the accuracy of PPP solutions comparing with differential solution yield mean height difference of 2.988 m for (stop & go) positioning technique while the mean height difference was 4.666 m for kinematic positioning technique. PPP solutions for the two types of observations provide similar accuracies with an average error mean for latitude, longitude and height of 3.15, 2.60 and 7.1 m respectively.

GPS-Differential is the default positioning technique for GPS users with high cost as it requires two receivers. Precise Point Positioning (PPP) is a technique that can compute positions with a high accuracy using a single receiver. It relies on highly accurate satellite position and clock data that can be downloaded from different sources. PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency), constellation (GPS or GLONASS or combined GPS/GLONASS) and the duration of observations among other factors. Kinematic-PPP has many applications in fields such as; infrastructure, hydrography and precision Agriculture. This research presents feasibility study for kinematic-PPP precision based on different observations types; single and dual frequency from different constellations; GPS, GLONASS and combined GPS/GLONASS under low visibility environment conditions. Low cost kinematic PPP technique using single frequency receivers under non-ideal environment conditions could provide a precision of a few meters for Hz. coordinates and from 10m to 20 meters for Height coordinate. High cost kinematic PPP technique using dual frequency receivers could provide a precision of few centimeters for Hz. coordinates and about 50 cm or less for Height coordinate.

This paper presents an original navigation algorithm intended to push the accuracy of standalone positioning beyond the limitations imposed by GPS system biases (errors of broadcast orbits and clocks).  The proposed algorithm is based on the processing of iono-free carrier-phase combination with floating ambiguities by the Kalman filter. Unlike traditional phase processing, ambiguities are essentially modeled as dynamic values intended to absorb long-term range errors, of which GPS system biases are the most essential. The model, which describes the behavior of ambiguities, has been optimized using both experimental and simulated data sets. The acronym DARTS reads as Dynamic Ambiguities Real-Time Standalone.
The accuracy of DARTS is close to typical accuracies of code-based DGPS. Standard deviations for position are within the range of 1.0-1.3m for heights, and 0.6-0.8 m for horizontal coordinates. This level of accuracy has been proven for a variety of applications. DARTS has been designed having in mind its application in GNSS receivers.

A set of Continuously Operating Reference Stations (CORS) distributed all over Nigeria constitutes the Nigerian GNSS Reference Network referred to as NIGNET. Global Navigation Satellite System (GNSS) is a system that uses satellites for autonomous position determination, and is a critical component of the modern-day geodetic infrastructure and services. Using CORS provide geodetic controls of comparable accuracy and a better alternative to the classical geodetic network. As the NIGNET infrastructure is utilised for different geodetic applications, it has become necessary to evaluate the suitability of the network data for the definition of a geodetic reference frame (GRF). This study utilised the technique of Precise Point Positioning (PPP) in position estimation, and time series analysis for temporal monitoring of the network. The sufficiency and adequacy of the NIGNET data archive was also evaluated against that of an International GNSS Service (IGS) Station. The temporal stability of the station coordinates measured in terms of standard deviations varied between 10 mm and 22 mm. This analysis suggests a relative stability required for Tiers 1 and 2 CORS in line with the IGS standards. Based on this reported stability, it is concluded that NIGNET is fit for purpose in defining the Nigerian Geodetic Reference Frame. However, despite the good data quality observed, the adequacy of the network has been compromised by infrastructural failures and lack of continuity in data transmission. Accordingly, it is recommended that both practical and policy measures required to ensure the realisation of the goal of the network should be implemented.

A new high accuracy technique using one dual frequency GNSS receiver, precise point positioning (PPP) offers the possibility of cost effectively obtaining coordinates. This study investigates the accuracy of kinematic PPP for hydrographic applications on rivers, and shows results comparable to double-difference solutions.

This paper presents a first analysis on the positioning performance using raw GNSS dual-frequency measurements acquired by the Xiaomi Mi 8 smartphone. In our study, we used the code-only-based Single Point Positioning technique for epoch-by-epoch positioning , and the Precise Point Positioning technique, which is based on both code and carrier-phase measurements, on precise satellite orbit and clock corrections, as well as on a dynamic model to exploit the time-constant property of the phase ambiguities. The functional model used in both our own SPP and PPP algorithms is based on the uncombined GNSS observation equations. As the Xiaomi Mi 8 smartphone is able to track both GPS and Galileo systems in two frequencies, we will present results based on single and combined GNSS solutions in single-and dual-frequency mode. The performance of these solutions will be assessed in terms of their repeatability and accuracy with respect to the ground-truth, while the improvement in Android-based positioning with multiple frequencies and GNSSs will be assessed compared to the GPS L1-only SPP case. An optimal combination of the elevation cutoff angle and the carrier-to-noise density ratio mask will be explored in order to have a reasonable balance between availability and quality of observations. Both real-time and post-processing positioning results will be presented.

Precise point positioning with integer ambiguity resolution requires precise knowledge of satellite position, clock and phase bias corrections. In this paper, a method for the estimation of these parameters with a global network of reference stations is presented. The method processes uncombined and undifferenced measurements of an arbitrary number of frequencies such that the obtained satellite position, clock and bias corrections can be used for any type of differenced and/or combined measurements. We perform a clustering of reference stations. The clustering enables a common satellite visibility within each cluster and an efficient fixing of the double difference ambiguities within each cluster. Additionally, the double difference ambiguities between the reference stations of different clusters are fixed. We use an integer decorrelation for ambiguity fixing in dense global networks. The performance of the proposed method is analysed with both simulated Galileo measurements on E1 and E5a and real GPS measurements of the IGS network. We defined 16 clusters and obtained satellite position, clock and phase bias corrections with a precision of better than 2 cm.

Topcueri M, Muharrem Keskin. 2019. Effectiveness of GNSS-based tractor auto steering systems in crop spraying. Mustafa Kemal University Journal of Agricultural Sciences, Special Issue, 24:78-90. ........ ....... ...... ...... ...... ....... ....... ...... ....... ...... Abstract: This study aimed to compare pass-to-pass overlaps and spacings in adjacent parallel passes in spraying with and without tractor automatic steering (AS). The data were obtained from 13 farmer fields (cotton, corn and peanut) to assess the performance of AS systems in real farmer conditions. Root mean square errors (RMSE) of overlaps and spacings were determined on the maps generated from the coordinates of the tractor recorded while spraying. Variations between the fields were also examined. The RMSE was lowest (7.5 ± 1.7 cm) in the fields on which farmers used AS (with RTK correction signal) in all three operations of tillage, sowing and spraying. RMSE values were comparatively higher for the fields on which farmers used AS only in ridge tillage but not in sowing and spraying (CORS-GSM: 46.1 ± 6.5 cm, SBAS: 76.5 ± 13.9 cm). The fields with manually-steered ridge tillage, sowing and spraying (all three) had the highest RMSE value of 100.8 ± 27.8 cm (p<0.05). The mean RMSE in the manual spraying (without AS) were found to be significantly higher than those using the AS (p<0.05). Conclusions: AS systems were found to be beneficial in reducing the mean pass-to pass overlap and spacing errors (RMSE) in spraying. However, most of the farmers used AS only in soil ridge tillage and made the spraying without AS by referencing marking flags and/ or soil ridges which were formed using AS. Main reason of this is the high cost of the AS systems and farmers cannot afford to equip all of their tractors. The use of AS systems not only in ridge tillage but also in planting and spraying reduced the errors and increased the benefit of AS usage. The level of benefit from the AS could change from farmer to farmer; thus, farmers should use the AS systems carefully with appropriate equipment settings to obtain a higher level of benefits. Appropriate use of AS systems in spraying offers benefits to reduce overlap and gaps and the amount of pesticides resulting in lower amount of environmental pollution and pesticide residues on crops, lower application time, lower fuel and labor consumption. ........ ....... ...... ...... ...... ....... ....... ...... ....... ...... İlaçlama işleminde GNSS esaslı traktör otomatik dümenleme sistemlerinin etkinliği....... ..... ...... ..... ....... ....... ...... ....... ...... ...... Özet: Bu çalışmada, traktör otomatik dümenleme (OD) sistemi ile ve manuel dümenleme ile yapılan ilaçlamada yan yana paralel geçişlerdeki örtüşme ve boşluk miktarları karşılaştırılmıştır. Veriler, OD sistemlerinin gerçek çiftçi koşullarındaki performansını değerlendirmek için 13 çiftçi tarlasından (pamuk, mısır ve yerfıstığı) elde edilmiştir. İlaçlama sırasında traktörün izlediği noktaların koordinatları kayıt altına alınmış, bu noktalardan oluşturulan haritalar üzerinden ortalama örtüşme ve boşluk hata değerleri (Hataların ortalama kare kökü; Root mean square error: RMSE) belirlenmiş ve analiz edilmiştir. Tarlalar arasındaki değişkenlik de incelenmiştir. RMSE değerinin çiftçilerin sırta toprak işleme, ekim ve ilaçlama işlemlerinin her üçünde OD kullandığı (RTK düzeltme sinyaliyle) tarlalarda en düşük değerde (7.5 ± 1.7 cm) olduğu gözlemlenmiştir. Çiftçilerin sadece sırta toprak işlemeyi OD sistemiyle, ekim ve ilaçlamayı manuel olarak (OD kullanmadan) yaptığı tarlalarda ortalama hata değerinin daha yüksek olduğu tespit edilmiştir (CORS-GSM: 46.1 ± 6.5 cm, SBAS: 76.5 ± 13.9 cm). Sırta toprak işleme, ekim ve ilaçlamanın hepsinin manuel dümenleme ile yapıldığı tarlalarda ise ortalama hata değerinin en yüksek düzeyde olduğu (100.8 ± 27.8 cm) görülmüştür (p<0.05). Manuel ilaçlama durumunda (OD kullanılmadan) ortalama hata değerinin OD kullanılan tarlalara göre önemli derecede daha yüksek olduğu bulunmuştur (p<0.05). OD sistemlerinin, ilaçlamada yan yana paralel geçişlerdeki ortalama ötüşme ve boşluk hata değerini azaltmada yararlı olduğu tespit edilmiştir. Ancak, çiftçilerin çoğunun OD sistemini sadece toprak sırtı oluşturmada kullandığı, ekim ve ilaçlamayı toprak sırtlarını referans alarak OD kullanmaksızın elle dümenleme ile yaptığı belirlenmiştir. Bu durumun temel nedenlerinden biri, OD sistemlerinin maliyetinin yüksek olması ve çiftçilerin tüm traktörlerini OD sistemi ile donatacak mali gücünun olmamasıdır. OD sistemlerinin sadece sırta toprak işlemede değil, aynı zamanda ilaçlamada da kullanımının örtüşme ve boşluk hatalarını azalttığı ve OD kullanımının yararını arttırdığı gözlenmiştir. OD'den elde edilen fayda düzeyinin çiftçiden çiftçiye değişebildiği tespit edilmiş olup, daha yüksek düzeyde faydalar elde etmek için çiftçilerin OD sistemlerini uygun ekipman ayarlarıyla dikkatli bir şekilde kullanmaları gereklidir. OD sistemlerinin ilaçlama işleminde uygun şekilde kullanımı, örtüşme ve boşluk miktarında azalmaya bağlı olarak tarım ilacı kullanımında azalma, bitkiler üzerinde daha az toksik etki, ürün üzerinde daha düşük miktarda pestisit kalıntısı, daha az çevre kirliliği, daha düşük ilaçlama süresi, daha düşük yakıt tüketimi ve daha düşük işçilik masrafı potansiyeline sahiptir.

Galileo satellites 5 and 6 (E18, E14), erroneously launched into elliptical orbits, were commissioned into service on Nov 30, 2020, but already on Feb 16, 2021 were again declared unusable in a wake of reports indicating repeatable daily problems with RTK, a precise phasedifferential positioning technology. This decision stripped Galileo users of two apparently usable satellites even though RTK does not belong to the list of Galileo services and its availability and accuracy mostly depend upon base-rover interaction. In this study, we explore possible impact of deviant elliptical orbits on the performance of RTK. The statement of this paper is as follows: if the implementation of RTK algorithms is generally correct and follows Galileo ICD as well as good practices of GNSS theory, there is no reason to expect any anomalies caused by high orbit eccentricity per se. However there exists a limited range of problems caused by a combination of high eccentricity with high age of ephemeris, which occurs few times a year due to limited uplink capacity of Galileo's ground control segment. The impact of these extra errors on standard RTK services with baselines of about 10 km is almost negligible except for the cases of delayed reception of differential corrections. In such cases an extra time-linear term is added to the error budget, particularly significant when time latencies reach values of 10 seconds or longer. In summary, we conclude that there is no reason to declare elliptical Galileo satellites unhealthy, but it is recommended to broadcast appropriate values of the SISA index (I/NAV word 3, F/NAV p. 1) to indicate degraded accuracy of orbit predictions.

One of the most crucial issues in engineering of structure and investigating ground deformation is deformation monitoring. The only thing which is strongly required is to create microgeodesy networks. An essential issue in microgeodesy networks is detecting unstable points of network. L1-Norm minimization and the global congruency can be noted as one of the classical methods for identifying network unstable points. In all previously conducted studies regarding this issue, results distinctly demonstrates that when displacement point vector is small, the number of points which have really displaced is more than that of true detection of displaced points using common deformation analysis ways. The probable reason for that can refer to spreading nature of the least squares estimation. Considering the results of recent studies in the detecting the network unstable points, to tackle the limitation the idea of subnetwork analysis is offered. In this case, some subnetworks including a subject point and the other source points appeared from dividing the deformation monitoring network. According to the unstable points, subnetworks will be there. This method will enable us to investigate the stable and unstable points. Having divided whole network to subnetworks, each network would be adjusted and unstable points of it would be detected. So, unstable points and their relations are cutoff and spreading effect of the least squares is fallen. This paper is on effort to evaluate the method in a simulated and a real network. The results prove that in a better and correct detection of unstable point can be successfully achieved by using subnetwork analysis compared to global congruency test all stimulates states proved the 35% of improvement on average. One percent of improvement in the results of subnetwork method to L1-Norm minimization cannot be acceptable. The algorithms of detecting unstable points in common methods and the method of analyzing subnetwork were conducted on a real network and the results are in line with simulated network results.

This paper presents a dual-band RF front-end architecture designed for simultaneously receiving the L1 and L5 signals of the Global Positioning System (GPS). The use of the new L5 signal can improve the accuracy and reliability of the typical mass-market receivers that rely only on the L1 signal. The proposed architecture is based on a compact microstrip diplexer that separates the two bands of interest providing the necessary filtering. Each band is down-converted independently and then both are combined at intermediate frequency (IF) in order to obtain one analog output. This front-end architecture is suitable for implementing a programmable high accuracy GPS receiver using a generic digital signal processing platform. The current work focuses on the diplexer design as well as the selection of the sampling rate and frequency plan required to avoid band overlapping before and after the analog to digital conversion. Satisfactory measurement results of the diplexer are presented.

Continuously operating reference stations (CORS) are permanent GNSS stations that log and disseminate GNSS observations continuously to meet various user needs. CORS networks have been going up all over the world in
the last decade to help establish geodetic reference frames, monitor tectonic movement as well as helping surveyors to do real-time positioning. This article zooms in on Corsmap, an initiative that was founded by three geomatic professionals to be a one-stop shop for all CORS installations in Africa.

n processing and interpreting the data collected during FALCON airborne gravity gradiometry surveys it is necessary to carefully compensate for topographic features. So that surveys may be performed even in areas where accurate DEMs (Digital Elevation Maps) are unavailable, the FALCON aircraft have been fitted with laser scanners, providing ground return data across a sufficiently wide swathe so that very adequate DEMs over the whole survey area can be produced. Additionally, in one aircraft, a laser profilometer has been fitted adjacent to the scanner, providing independent data to monitor the scanner integrity throughout a survey. This paper briefly describes the scanner features and details the post processing of the scanner ground returns through to gridded DEM format. The intrinsic accuracy of the scanner at low scan angles is demonstrated to be very good, accounting for a ground height error of less than 0.1m standard deviation. Taking into account that DGPS height errors are about 0.15m, the resulting ground height error is estimated as 0.2m standard deviation, which is confirmed by the analysis of height differences in the overlapping areas between adjacent lines. This estimate is characteristic of a lightly vegetated terrain. This level of topographic error will have a negligible impact on our ability to identify target anomalies arising from geological variations

The study introduces an efficient methodology to perform the transformations between station coordinate and velocity
solutions where either minimum or redundant datum constraints have been imposed employing the estimated state vector
and the covariance matrix thereof. The analytical methodology presented herein facilitates the datum alignment of largenetwork
solutions, especially for the GNSS technique. The computational complexity reduction is achieved by avoiding the
expensive normal equation system reconstruction and the subsequent inversion thereof, which is the current norm, in favor
of an elegant approach involving the inversion of an up to 14-order matrix. All information parsed in our algorithm is readily
available in the widely used space geodetic solution files following the Solution Independent Exchange (SINEX) format. Our
transformation approach is evaluated in two globally distributed GNSS-derived solutions and one terrestrial reference frame
with a spatial concentration in South America. The results prove the equivalence of the current and proposed algorithm and
that our approach is at least an order of magnitude faster. In addition, we test the Fast Constraints Transformation (FCT)
through simulated networks, with a size of up to 5000 stations. The FCT presented here accelerates the transformation by
almost 140 times compared to the commonly used strategy.

The oscillators, which are essential for precise timing, are at the heart of a satellite-based navigation system. The purpose of this research is to investigate the crucial role that space-borne oscillators play in increasing the performance of GNSS and satellite-based augmentation systems (SBAS). The African contribution to the SBAS, the NIGCOMSAT-1R navigation payload, which uses externalised 10 MHz Master Oscillators in a 3 X 4 hybrid array configuration, examines the efficacy of Location Based Services using Navigation for Emergency and Crisis Management, among other applications.

New technologies and services are being developed every day to support the evolution of automated vehicles (AVs). The ultimate goal is to provide safety features and driving automation systems to enable driverless operation resulting in more efficient transportation. A reliable navigation system relies on the information from both positioning and warning systems, and can even integrate both to provide a robust solution with high integrity. The Global Positioning System (GPS) is the first fully operational global navigation satellite system (GNSS) that provides all-weather worldwide coverage. An inertial navigation system (INS) is a navigation system that includes a navigation processor and an inertial measurement unit (IMU). The IMU consists typically of accelerometers to measure specific forces (acceleration) and gyroscopes to measure angular rotation rates. Odometry is the calculation of the change in position and the speed of an object using motion sensors.

Processing of Global Navigational Satellite System (GNSS) data forms the basis for the usage of differential systems for obtaining spatial data. All open sources or commercial software packages developed for data processing give specific details to suit the intended purpose of the software. To obtain a uniform format for submitted survey data, Survey and Mapping Division (SMD) in various jurisdictions have specified formats for data submission for all kinds of surveys. In this regard, "GNSS Ghana" Software (GGS), a GNSS standalone Windows-based application with a modern user-friendly interface was developed for geodetic applications such as, projection and datum transformation worldwide, GNSS data post-processing of Receiver Independent Exchange Format (RINEX) files, and generating reports to meet Ghana SMD reporting standards including cadastral computations and reports for submission. To assess the developed software, GNSS data from two International GNSS Service (IGS) stations (BJCO and YKRO) were processed using GGS and three other commercial software such as GNSS Solution Software (GSS), Spectrum Survey Software (SSS), and Leica Geo Office (LGO), and the positional results compared against the existing coordinate. The results revealed that the GGS outperformed the remaining three commercial software packages with a sub-meter level of accuracy. Further assessment was conducted on datum transformation using the coordinates of 21 existing geodetic control points in Ghana. Utilizing the 7-transformation parameters of Ghana, the results gave uncertainties of [0.10ft. ± 0.99ft.] in the eastings and [0.02ft. ± 1.61ft.] in the northings with a 99% confidence level.