Software development for deformation analysis with GNSS measurements

Determination of deformations in the earth's crust and structures is one of the important subjects of engineering surveys. Geodetic network method is generally used in deformation determination studies with geodetic methods. Today, GNSS techniques are also preferred in the measurement of deformation-purpose geodetic networks due to their short measurement time and high accuracy. There are many scientific and commercial software used to process GNSS measurements, and there is no open source software to perform deformation analysis. Considering the possible damages caused by deformations, analyzes should be completed as soon as possible. The high calculation load in the deformation analysis makes it difficult to complete the analysis in a short time. In order to reach the analysis results in a short time and accurately, deformation analysis software is needed. Iteratively Weighted Similarity Transformation (IWST) is a robust method used in deformation analysis. The advantage of the method is that it can be applied in 1D, 2D, 3D networks and does not require prior knowledge about unstable points in the network. In addition, the results obtained with this method reflect the actual deformation model and provide the best datum to be determined since it has the least distortion effect on the displacement vector. The method is useful and programmable for performing deformation analysis in GNSS networks. Today, there are open-source technological programming languages used in the field of science and engineering. The fact that the R-programming language has free and ready libraries makes it stand out among programming languages. In this study, a program called DefAn-for-GNSS-networks has been developed for deformation analysis with IWST method in R-language, using the result products obtained by processing the measurements performed in periods with the static GNSS technique. In the prepared program, there is no limit on the number of measurement periods to be used as input data. Solution-independent data exchange format (SINEX) files and result (OUT) files, which are obtained from Bernese v5.2 software as input data and contain the coordinates of the points in the geodetic network and the covariance matrix elements related to the unknowns, can be used directly. Deformation analysis can also be performed by arranging these data obtained from different GNSS processing software according to the format recognized by the program. The developed program can work independently of operating systems and can detect deformation points in a GNSS network as robust. The results are provided to the user in two different formats, HTML and PDF, and the motion sizes are presented graphically. In addition, since it is the first open-source software developed for deformation analysis with the result products obtained as a result of the processing of GNSS measurements, it is a pioneer for new studies to be carried out in this field. In order to test the developed program, a micro geodetic GNSS network was established in the Selçuk University campus and GNSS measurements were made by creating 1 cm virtual deformations in the north, east and upward directions on the designed measurement mechanism. The measurements were processed with GPS only (G) and GPS+GLONASS (G+R) satellite combinations in Bernese v5.2 software, and geodetic deformation analyses were carried out in the prepared program. As a result of 44 static deformation analyses (22 G, 22 G+R), 1 cm virtual deformations at the object point were tried to be determined. However, in some baseline vectors in the deformation network, when the ambiguity resolution (AR) rates decreased below 20% or the number of observations in the measurements decreased, it was observed that the determined deformation amounts moved away from the virtual deformation amount. As a result, deformations of 1 cm were determined between 0.7 cm and 1.8 cm. It has been determined that the vectorial deformation magnitudes are generally in agreement with the virtual deformation value. The displacements calculated as a result of the analyses have been converted into the local geodetic coordinate system and revealed in the relevant axis direction, thanks to the prepared program. With the prepared program, the geometric dimensions of the deformations and statistically significant point movements could be detected practically in the micro geodetic network used in the application. For this reason, it has been seen that the prepared program provides a great deal of convenience in determining the geometric dimensions of the deformations. Although the deformations are determined to a large extent with the prepared program, it is important to check the AR rates and the number of observations, which affect the processing results of the GNSS measurements, before the analysis and to proceed to the analysis after the appropriate conditions are obtained.