The National Geodetic Survey began publishing a series of experimental geoid (xGEOID) models annually since 2014. The latest experimental model is xGEOID20. The San Joaquin Experimental Range (SJER) in Fresno County, California is surveyed using Static GPS and precise levelling and a local geoid (SJER Geoid) is created. In this study, SJER Geoid is compared against xGEOID20A&B models and the results are tabulated. The results indicate that xGEOID20A&B slopes agree with the GPS/levelling data well even in such a small area. SJER Geoid model agrees with the xGEOID20 models at 7 mm level. The biases about 80 cm are within the expected range between the North American Vertical Datum of 1988 (NAVD88) and North American-Pacific Geopotential Datum of 2022 (NAPGD2022).

RTKLIB which is an open source Global Navigation Satellite Systems (GNSS) software has gained rapid acceptance among Surveying professionals thanks to recent developments in UAS (Unmanned Aerial System) technology. RTKLIB enables standard and precise point positioning (PPP) in real-time and post-processing modes to be performed. As such, UAS users utilize this software to analyze GNSS data collected by GNSS systems on UAS. By being versatile and free, RTKLIB is commonly used by many; however, it is not the only freely available GNSS software. There are also freely available online GNSS data processing software running on servers. These online GNSS data processing services provide data processing in static, kinematic and rapid static modes. Because UAS collect data in kinematic mode, in this study, kinematic data processing by aforementioned software (CSRS-PPP, GAPS and APPS) is analyzed. The results coming from these software are compared against the results produced by photogrammetric software (Agisoft Metashape and Pix4Dmapper). The aim of this practical project is to produce generalizable knowledge about the performance of these software. It is found out that RTKLIB and CSRS-PPP achieved cm-level precision. Yet, GAPS and APPS achieved dm-level precision both for horizontal and vertical coordinates. This study demonstrates the precision and accuracy expected from these software if they are used for kinematic GNSS data processing.

In the recent past, the information and analysis centre of Russia began providing GNSS static data processing operating in experimental mode. Since this service processes data in static mode only, the service is compared with the OPUS static service. OPUS produces better results for the points in the USA. OPUS produced slightly better results for the point with nearby ITRF reference stations than for a point far away from the ITRF reference stations. The Russian system did not differentiate between the point with nearby ITRF reference stations and the point which is far away from ITRF reference stations. In addition, for both services, having a longer observation period did not substantially improve the quality of the solutions for all coordinates. Additionally, coordinate differences between OPUS results and the Russian system results are in the order of decimetres.

Post Processed Static (PPS) and Precise Point Positioning (PPP) techniques are not new; however, they have been refined over the decades. As such, today these techniques are offered online via GPS (Global Positioning System) data processing services. In this study, one Post Processed Static (OPUS) and one Precise Point Positioning (CSRS-PPP) technique is used to process 24 h GPS data for a CORS (Continuously Operating Reference Stations) station (P565) duration of year 2016. By analyzing the results sent by these two online services, subsidence is determined for the location of CORS station, P565, as 3-4 cm for the entire year of 2016. In addition, precision of these two techniques is determined as similar to 2 cm. Accuracy of PPS and PPP results is 0.46 cm and 1.21 cm, respectively. Additionally, these two techniques are compared and variations between them is determined as 2.5 cm.

The source of deformations in one of the most densely populated residential areas of the city of Zonguldak is studied using InSAR techniques. During the investigations, it is discovered there had been mining acitivites underway under the city during the time period that the InSAR images were taken. Approximately 8 years of this time period is examined, and in total a maximum 41 cm subsidence is discovered in the area of coal mining. In addition, the vertical motion coefficient for the area of interest is calculated as 1.6.

Today rapid-static GPS is an alternative surveying technique among other fundamental GPS surveying methods such as real-time kinematic and static GPS. It usually finds application areas in engineering surveying and monitoring of ground deformation for example landslides. Web-based GPS software such as OPUS-RS which was developed by the National Geodetic Survey (NGS) promoted further the use of the technique. NGS also provides its users the obtainable accuracy of the OPUS-RS derived solutions. Minimum 15 min of GPS data is recommended for rapid-static positioning and the accuracy is given accordingly. In this study, we go beyond the typically recommended 15 min observations and examine the accuracy variation of rapid-static OPUS positioning solutions over 8-118 min interval. Seven Continuously Operating Reference Stations from the US are selected, and their data are segmented into the above-mentioned shorter sessions. Statistical analyses of the CORS stations revealed that solutions from 15 min or shorter sessions contain outliers, and this degrades the efficiency of the technique. By extending the typical 15 min observation length up to 60 min perfectly eliminates the outliers, and the accuracy on the average is improved by about 5-20 mm for horizontal and about 25 mm for vertical components.

Except some special cases, commonly used volume computation methods are grids method, contours method and volume computations by utilizing TIN (Triangulated Irregular Network). In this study, to investigate the precisions of these techniques, a grid system is established in an undulating area and volume of the mound is determined by using these three volume computation methods. It is found out that contour method results were not as price as the other two methods. Thus, a precise formula for volume computations using contours method is proposed.

GALILEO (Europe's Global Navigation Satellite System) is going full speed ahead to achieve full constellation by 2020. Since GALILEO is currently an emerging system, the contribution of these satellites to GNSS (Global Navigation Satellite System) solutions needs to be investigated. For this purpose, GNSS data collected at three IGS (International GNSS Service) MGEX (Multi GNSS Experiment) stations are analyzed. For the analyses, GPS (Global Positioning System) only, GLONASS (Russia's Global Navigation Satellite System) only, GALILEO-only and combined solutions are tested and also effect of baseline length is examined. The results indicate that compared to GPS, GLONASS and ALL (GPS+GLONASS+GALILEO) solutions, GALILEO results vary greatly. When GALILEO observations are combined with other observations, the precision goes down. That is to say, for short baseline solution, GALILEO results fluctuate around 1 cm in the horizontal plane and in the vertical plane variations are mostly within 3-5 cm. For long baseline solution, GALILEO results are going up and down in the horizontal between 2 and 3 cm and in the vertical roughly 10 cm. In terms of accuracy, for short baseline solution, GALILEO-only solution is close to GPS-only solution; yet, we cannot say the same thing for long baseline solution.

In this study, a hydrographic map of a South Florida canal is prepared using RTK GPS (Real Time Kinematic Global Positioning System) measurements combined with a hydrolite (single beam echo sounder). RTK GPS measurements are made using both single RTK and Network RTK systems. Digital sounding measurements taken by hydrolite are compared to manual lead line measurements. Single RTK and Network RTK results differed in the order of tenth of a foot accuracy for horizontal coordinates and for height measurements variations can go up to several tenths. Sounding results indicate a best-fit trend line with a slope of 0.993, and an R squared value of 0.972, demonstrating that hydrolite measurements and manually collected depths at this site are well correlated.

Free access online GNSS (Global Navigation Satellite System) data processing services are becoming popular since only a single GNSS receiver can do the job. These services are user friendly and easy to use. Thus, no training and a GNSS software package purchase are needed. This means less cost to users. Currently, three online GNSS data processing services provide kinematic data processing option. In this study, GNSS data collected for hydrographic surveying is processed using these online services and positioning precision of these services are compared. The results indicate that with 1s data, decimeter to meter precision can be achieved for both horizontal and vertical coordinates.

Commonly used real time kinematic (RTK) network (RTK Network) techniques, i.e., MAX, I-MAX, FKP and VRS, are tested by taking monthly measurements for a year in Florida. Additionally, RTCM message versions 2 and 3 are used with I-MAX and VRS measurements. The results revealed that mostly, horizontal coordinates vary a few centimeters and generally changes in vertical coordinates are less than two decimeters. In terms of horizontal coordinates, the best results are produced by I-MAX3 method and FKP yielded the worst results. In terms of vertical coordinates, almost all results look alike; however, the best results are produced by VRS3 method. It appears that I-MAX3 performed better than I-MAX2 and VRS3 performed better than VRS2. Yet, MAX did not stand out among other techniques.

After geodetic networks (e.g., horizontal control, leveling, GNSS etc.) are established, they are measured and point coordinates are estimated by the method of Least Squares. If one or more observations are burdened with errors, these contaminated observations affect the other good observations and may produce incorrect estimates of the parameters. Thus, these contaminated observations should be detected and corrected. Generally, in practice, they are removed and the network is readjusted. To detect the outliers among the observations statistical tests are performed. Yet, reliability measures should be accompanied to statistical tests to find out more about the ability of error detection and the effects of errors on the solutions. Now it is possible that reliability measures can be calculated for the cases of single or multiple outliers. In this paper, a GNSS network is analyzed using reliability measures in both cases. The results show that in the case of multiple outliers reliability measures worsen.

A complete deformation analysis process requires adequate consideration of all sources of errors from the initial design of the network to the parameter estimation. In this study, during deformation analysis, effect of having more object points in geodetic networks is researched. Numerical results confirm the theory that having more object points is also an important factor for deformation analysis.

Robustness Analysis is a natural merger of reliability and strain and defined as the ability to resist deformations caused by the maximum undetectable errors. Internal reliability criterion describes maximum undetectable errors in observations, which would not be detected by Baarda's statistical testing method (data snooping) based on the chosen Type I and II error probabilities. The non-centrality parameter is a function of probability levels and it plays an important role in Robustness Analysis. In this paper, it is aimed to show the impact of non-centrality parameter on the displacements and the relationship between the selected confidence level for confidence regions and threshold values in a geodetic network. For a geodetic network example, a GPS network is chosen and computations of displacements and threshold values (derived from confidence regions) have been carried out for both in-context and out-of context approaches. According to our results, the non-centrality parameter controls the magnitudes of displacements without affecting their relative behaviours. Statistically, lower probability levels are desired. However, if error probabilities are decreased, the non-centrality parameter increases. Since, the non-centrality parameter scales the displacements, a balance between both types of decision error is needed to obtain displacement values that are smaller than threshold values in order to reach a totally robust network at the required level of probability.

Recently, many organizations have begun providing online GNSS (Global Navigation Satellite System) data processing services. Currently, only one of these organizations i.e., OPUS (On-line Positioning Users Service) provides a rapid static data processing option. In case of static online data processing, the users are required to submit at least two hours of data to get reasonably precise results. To provide processing option with less than two hours of data, NGS (National Geodetic Survey) developed OPUS–RS for rapid static data processing so that usersmay submit as little as 15 minutes of dual frequency GNSS data. In this study, multiple observation sessions are conducted at the same locations to compare OPUS-RS generated coordinates among the different sessions to see whether separate values agree with each other. The results indicate that with OPUS-RS results the differences in horizontal coordinates agree with each other within 3.5 cm and vertical coordinates agree within 7.2 cm. For an independent check, OPUS-RS results are also compared against LGO(Leica Geo Office) produced Static results; this comparison yielded up to 4.5 cm variations among horizontal coordinate differences and variations among vertical coordinate differences are up to 11.4 cm.

Robustness analysis is a natural merger of reliability and strain and defined as the ability to resist deformations induced by the maximum undetectable errors as determined from internal reliability analysis. Thus far, robustness analysis has been carried out using reliability theory based on the assumption of a single outlier. However, in practice, there might be multiple outliers in a data set. Therefore, measures of reliability for multiple outliers ought to be used. This paper extends robustness analysis so that it can determine the deformation induced by multiple undetected errors through the evaluation of a strain matrix using the proper external reliability measure. In this study, the question of whether a network is robust against deformations induced by two or more undetected outliers is investigated. The results indicate that in the case of multiple outliers, robustness of geodetic networks decreases.

The consistency of the Chang’E-1 and SELENE reference frames as realized by the footprint positions of laser altimetry measurements of the lunar surface during both missions was analyzed using a global 12-parameter model for small (with respect to unity) deformations and rigid body motions. The rigid body motion and deformation parameters between the two reference frames estimated from nearly-colocated without tie measurements are found to be consistent, i.e., nearly zero for the estimates of the translations, rotations and shear parameters. However, the estimated three strain parameters, which are similar in magnitude and sign, reveal a prominent scale difference, between the Chang’E-1 and SELENE reference frames, of about 0.9 × 10 −5 . The scale difference can be attributed to calibration of the data sets using the known coordinates of the lunar laser ranging stations all located on the near side of the Moon.