Mohamed Doma - Academia.edu (original) (raw)
Papers by Mohamed Doma
Texture plays an important role in many machine vision tasks such as surface inspection, scene cl... more Texture plays an important role in many machine vision tasks such as surface inspection, scene classification, and surface orientation and shape determination. For example, surface texture features are used in the inspection of semi-conductor wafers, gray-level distribution features of homogeneous textured regions are used in the classification of aerial imagery, and variations in texture patterns due to perspective projection are used to determine three dimensional shapes of objects. In this study, the effect of using auxiliary data in the classification results was investigated using the SVM classifier and specified training sample size, with generated Co-occurrence matrix attributes. Three investigations have been implemented: 1) using single attribute of each band. 2) Using the group attributes of each band. 3) Using the all attributes of bands and comparing the results with the case of RGB image only. The results showed that, the group of attributes of Blue band performed the b...
ERJ. Engineering Research Journal, 2009
In the case that more constraints than necessary to remove the network datum defect< have been de... more In the case that more constraints than necessary to remove the network datum defect< have been defmed, a new type of geodetic network will be obtained " overconstrained geodetic network ". Datum changes may be obtained by Similarity Transformations in order to select the proper coordinate datum for geodetic networks as well as to analyse the stability of the reference points. The purpose of this research paper is to choose the optimal fixed points for overconstrained geodetic networks by using Similarity Transformation. A numerical example is presented. b% si JLJy >I &.&I\ a&) 2 4 1 \6!
ERJ. Engineering Research Journal, 2012
Geodetic networks are very important tools used to monitor earth and/or structural deformations. ... more Geodetic networks are very important tools used to monitor earth and/or structural deformations. However, a geodetic network must be designed to meet sufficiently some network quality requirements such as precision, reliability, or sensitivity. This is the subject of geodetic network optimization. The determination of the observation weights problem in the deformation monitoring networks can be dealt with as an optimization procedure, this problem can performed by solving the second-order design (SOD) problem. Traditional methods have been used for geodetic optimization tasks. On the other hand, some heuristic techniques have been started to be used recently in geodetic science such as the Particle Swarm Optimization (PSO) algorithm. The general purpose optimization method known as Particle Swarm Optimization (PSO) has received much attention in past years, with many attempts to find the variant that performs best on a wide variety of optimization problems. In this paper, the PSO algorithm, a stochastic global optimization method, has been employed for the determination of the optimum observation weights to be measured in the field that will meet the postulated criterion matrix at a reasonable precision. The fundamentals of the method and a numeric example are given.
ERJ. Engineering Research Journal, 2014
Thematic maps representing the characteristics of the Earth's surface have been widely used as a ... more Thematic maps representing the characteristics of the Earth's surface have been widely used as a primary input in many land related studies. Classification of remotely sensed images is an effective way to produce these maps. The value of the map is clearly a function of the accuracy of the classification. Selecting proper size of samples and classification method are essential issues to produce accurate thematic maps. In the present study, training data sets at various sizes used to investigate the effect of the training set size on the classification accuracy. Six supervised classification methods with different characteristics were applied to produce land use/land cover thematic map of the study area. The used classifier include: Parallelepiped, Minimum Distance, Mahalanobis Distance, Maximum Likelihood, Neural Network and Support Vector Machine (SVM). The results showed that optimum sample size differs from classifier to another. In the case of limited number of training pixels, SVM and maximum likelihood classifiers produced higher classification accuracies than the rest of classifiers.
Journal of Geodetic Science, 2013
The Global Positioning System (GPS) is increasingly coming into use to establish geodetic network... more The Global Positioning System (GPS) is increasingly coming into use to establish geodetic networks. In order to meet the established aims of a geodetic network, it has to be optimized, depending on design criteria. Optimization of a GPS network can be carried out by selecting baseline vectors from all of the probable baseline vectors that can be measured in a GPS network. Classically, a GPS network can be optimized using the trial and error method or analytical methods such as linear or nonlinear programming, or in some cases by generalized or iterative generalized inverses. Optimization problems may also be solved by intelligent optimization techniques such as Genetic Algorithms (GAs), Simulated Annealing (SA) and Particle Swarm Optimization (PSO) algorithms. The purpose of the present paper is to show how the PSO can be used to design a GPS network. Then, the efficiency and the applicability of this method are demonstrated with an example of GPS network which has been solved previously using a classical method. Our example shows that the PSO is effective, improving efficiency by 19.2% over the classical method.
Nowadays the Global Positioning System (GPS) is one of the most favorite techniques in practical ... more Nowadays the Global Positioning System (GPS) is one of the most favorite techniques in practical geodesy. A major dilemma in GPS surveying lies in its ellipsoidal-based type of heights, while in engineering practice orthometric heights are usually utilized. Thus, it is important to convert GPS heights into orthometric heights through applying an accurate geoid model. The objectives of this paper are to model a local geoid in the study area using GPS/levelling technique, and to evaluate the performance of several Global Geopotential Models (GGMs) particularly the OUS-91A, EGM96 and EGM2008 in the study area, which is located in the northern Egypt at Rosetta zone area. The accomplished results show that the EGM 2008 represents the most precise global geopotential model to be used for geoid determination in Egypt. Furthermore, the achievable accuracy of local geoid determination in the study area after using regression method models is ranges between 0.059 meter to -0.083 meter, with a...
Advances in Space Research
Global Positioning System (GPS) is being used in aviation, nautical navigation and the orientatio... more Global Positioning System (GPS) is being used in aviation, nautical navigation and the orientation ashore. Further, it is used in land surveying and other applications where the determination of the exact position is required. Although GPS is known as a precise positioning system, there are several error sources which are categorized into three main groups including errors related to satellites, propagation and GPS receivers. In this paper we focus on the estimation of the receiver coordinates of a fixed point based on pseudorange measurements of a single GPS receiver. The estimation of the unknowns is achieved by introducing an Extended Kalman Filter (EKF) and Iterative Least Square (ILS) that processes. Kalman filter is the method most often used nowadays. It is based on some assumptions and if all the assumptions are met it can offer optimal estimation and prediction. A navigation filter is commonly designed by use of a EKF to estimate the vehicle state variables and suppress the...
Digital Elevation Models (DEMs), which can come in the form of digital surface models or digital ... more Digital Elevation Models (DEMs), which can come in the form of digital surface models or digital terrain models, are key tools in land analyses and other purposes. Classical methods such as field surveying and photogrammetry can yield high-accuracy terrain data, but they are time consuming and labor-intensive. Nowadays, different modernistic height-finding methods have emerged, including Global Positioning System (GPS) and airborne methods. In contrast to the airborne ways that are suited to gain highly precise, fine-resolution DEMs at a local scale. The airborne ways are complementary to their space-borne matches, such as Light Detection and Ranging (LiDAR), Shuttle Radar Topography Mission (SRTM), Advanced Spaceborne Thermal Emission and Reflection RadiometerGlobal Digital Elevation Model (ASTER GDEM) and Advanced Land Observing Satellite (ALOS). LiDAR data acquisition has become the standard approach for collecting point data to interpolate high-resolution ground and aboveground ...
Journal of Engineering Research
The most prominent spatially correlated errors in GNSS observations are well known to be atmosphe... more The most prominent spatially correlated errors in GNSS observations are well known to be atmospheric effects. The ionosphere and troposphere are the two main layers of the Atmosphere that cause delays in GNSS observations. A linear combination of the dual-frequency data can be used to reduce ionospheric delay. Unlike the ionospheric delay, the tropospheric delay cannot be eliminated using the same methods. The troposphere is primarily associated with GPS. The delay it causes in GPS signals is regarded as one of the primary sources of errors that must be eliminated to determine accurate positions. This paper's main purpose is to develop a new source code that can estimate the effect of tropospheric delay over any GPS station. The tropospheric delay in this proposed code is estimated utilizing sequential least-squares adjustment using a model depending on Niell Mapping Function (NMF). This model, known as the Tropospheric Delay Estimation program, was created in the MATLAB® enviro...
Journal of Applied Geodesy, 2021
Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to rem... more Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, an analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stor...
Global Positioning System (GPS) results are suffering from one of the major errors in high precis... more Global Positioning System (GPS) results are suffering from one of the major errors in high precision GPS positioning, the ones caused by reflections, known as Multipath error. Here, we study some of the multipath factors affecting on the accuracy observables obtained from GPS measurements. This will be achieved through monitoring and record the multipath effect according to different types of surface which reflected the signals specific set of generating and monitoring systems for multipath signal is established and a series of controlled experiments are carried out. Experimental results show that Aluminium caused the highest amount of multipath. This is followed by Glass and Wood.
7 Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal reso... more 7 Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolution of Global Ionosphere 8 Maps (GIMs). Receivers and Satellites Differential Code Biases (DCBs) are one of the main error sources in estimating precise 9 TEC from Global Positioning Systems (GPS) data. Recently, researchers are interested in developing models and algorithms 10 to compute DCBs of receivers and satellites close to those computed from the Ionosphere Associated Analysis Centers 11 (IAAC). Here we introduce a MATLAB code called Multi Station DCB Estimation (MSDCBE) to calculate satellites and 12 receivers DCBs from GPS data. MSDCBE based on spherical harmonic function and geometry free combination of GPS 13 carrier phase and pseudo-range code observations and weighted least square were applied to solve observation equations, to 14 improve estimation of DCBs values. There are many factors affecting estimated value of DCBs. The first one is the 15 observations weighting fun...
Journal of Engineering Research, 2021
The selection of optimal GPS baselines can be realized by solving the geodetic second-order desig... more The selection of optimal GPS baselines can be realized by solving the geodetic second-order design (SOD) problem. Basically, there are two techniques to be used for selecting optimal baselines in GPS network, namely traditional techniques and artificial techniques. Traditional techniques include the method of trial and error and the analytical method, while artificial methods include both local and global optimization techniques. The global optimization techniques, such as Genetic Algorithms (GAs), Simulated Annealing (SA) method, Particle Swarm Optimization (PSO) Algorithm, and Butterfly Optimization Algorithm (BOA) have been used recently in geodesy. In the current study, (BOA) has been used for the selection of the optimal GPS baselines to be measured in the field that will meet the postulated criterion matrix, at a reasonable cost. Ithas been tasted on a GPS network. The BOA is already designed and it determined the number of baselines that would be observed due to obtaining hig...
Journal of Applied Geodesy, 2019
An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the ... more An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. The ionospheric delay is the most predominant of all the error sources. This delay is a function of the total electron content (TEC). Because of the dispersive nature of the ionosphere, one can estimate the ionospheric delay using the dual frequency GPS. In the current research our primary goal is applying Precise Point Positioning (PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB and was named VI...
Arabian Journal of Geosciences, 2017
The differential code bias (DCB) is the differential hardware (e.g., the satellite or receiver) d... more The differential code bias (DCB) is the differential hardware (e.g., the satellite or receiver) delay that occurs between two different observations obtained at the same or two different frequencies. There are two approaches used to estimate DCBs for receivers and satellites: the relative and absolute methods. The relative method utilizes a GPS network, while the absolute method determines DCBs from a single station (zero difference). Three receiver types based on the pseudo-range observables were used here to collect the GPS data: Codeless Tracking, Cross Correlation, and Non-Cross Correlation styles. According to its types, GPS receivers have responded to restrictions on the GPS signal structure in different ways. The main goal of the current research is providing a method to determine the DCBs of GPS satellites and dual frequency receivers. The developed mathematical model was based on spherical harmonic function and geometry-free combination of pseudo-range observables (C/A or/and P-code) according to receiver type. A new elevationdependent weighting function with respect to GPS satellites in our algorithm was applied. The applied weighting function was used to consider the quality variation of satellite DCBs, which is caused by pseudo-range measurement errors. The code of the proposed mathematical model was written using MATLAB and is called Bzero difference differential code bias estimation (ZDDCBE)^. This code was tested and evaluated using data from IGS GNSS stations and different types of GPS stations out of IGS network installed in Egypt and Saudi Arabia. The estimated values from the ZDDCBE code show a good agreement with the IGS analysis centers with a mean error of estimation for the receiver DCB equal 5.94%. Therefore, the ZDDCBE code can be used to estimate the DCB for any type of receiver regardless if the receiver is from IGS network or not.
Journal of Applied Geodesy, 2014
ABSTRACT Deformation monitoring is a kind of continuous recording positions (horizontal and verti... more ABSTRACT Deformation monitoring is a kind of continuous recording positions (horizontal and vertical coordinates) precisely regardless the deformation pattern and instrument used. In general, a deformation monitoring network can be designed using the trial and error method or analytical methods such as linear programming and nonlinear programming. Recently, a deformation monitoring network may also be designed by heuristic optimization algorithms such as Genetic Algorithms (GAs), Particle Swarm Optimization (PSO) and Simulated Annealing (SA). In this paper, GAs and PSO, which are heuristic optimization techniques, are applied to a geodetic horizontal deformation monitoring networks to solve second-order design problem. The results proved that both GAs and PSO can be used as alternative methods in place of the traditional optimization techniques with high eficiency.
Annales Geophysicae Discussions, 2018
Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolu... more Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolution of Global Ionosphere Maps (GIMs). Receivers and Satellites Differential Code Biases (DCBs) are one of the main error sources in estimating precise TEC from Global Positioning Systems (GPS) data. Recently, researchers are interested in developing models and algorithms to compute DCBs of receivers and satellites close to those computed from the Ionosphere Associated Analysis Centers (IAAC). Here we introduce a MATLAB code called Multi Station DCB Estimation (MSDCBE) to calculate satellites and receivers DCBs from GPS data. MSDCBE based on spherical harmonic function and geometry free combination of GPS carrier phase and pseudo-range code observations and weighted least square were applied to solve observation equations, to improve estimation of DCBs values. There are many factors affecting estimated value of DCBs. The first one is the observations weighting function which depending on the satellite elevation angle. The second factor concerned with estimating DCBs using single GPS Station Precise Point Positioning (PPP) or using GPS network. The third factor is the number of GPS receivers in the network. Results from MSDCBE were evaluated and compared with data from IAAC and other codes like M_DCB and ZDDCBE. The results of weighted (MSDCBE) least square shows an improvement for estimated DCBs, where mean differences from CODE less than 0.746 ns. DCBs estimated from GPS network shows a good agreement with IAAC than DCBs estimated from PPP where the mean differences are less than 0.1477 ns and 1.1866 ns, respectively. The mean differences of computed DCBs improved by increasing number of GPS stations in the network.
Accurate and high spatial resolution digital elevation models (DEMs) are in increasing demand for... more Accurate and high spatial resolution digital elevation models (DEMs) are in increasing demand for a growing number of mapping and GIS tasks related to applications such as forest management, urban planning, bird population modelling, ice sheet mapping, flood control, road design, etc. Airborne Light Detection and Ranging (LiDAR) has become the preferred technology for digital elevation data acquisition in a wide range of applications. DEMs quality relies on the quality of elevation data and the process of converting discrete elevation points to a continuous surface represented by a DEM through an interpolation operation. LiDAR technology provides high-density and high-accuracy three-dimensional terrain point data acquisition, however, the quality of the DEM generated from LiDAR is affected directly by the interpolation process. In this study, the Ordinary Kriging (OK), the Local Ploynomial (LP) and the Inverse Distance Weighting (IDW) interpolation methods working under ArcGIS 10.1 ...
Annales Geophysicae Discussions, 2018
An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the ... more An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. the ionospheric delay is the most predominant of all the error sources. Thisidelay is a function of theitotalielectronicontent (TEC). Because ofithe dispersive nature of the ionosphere, one caniestimateitheiionosphericidelay using the dual frequency GPS. In the current research our primary goal is applying PreciseiPointiPositioningi(PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB. The proposed Algorithm depends on the geometry-free carrier-phaseiobservations afteridetectingicycle slip to estimates the ionosphericidelayiusingia spherical ionospheric shell model, in which the vertical delays are described by means of a zenithidelayiatitheistationipositioniandilatitudinaliandilongitudinal gradients. geometry-free carrier-phase observations were applied to avoid unwanted effects of pseudorange measurements, such as code multipath. The ionospheric estimation in this algorithm is performed by means of sequential leastsquares adjustment. Finally, an adaptable user interface MATLAB software are capable of estimating ionosphere delay, ambiguity term and ionosphere gradient accurately.
Texture plays an important role in many machine vision tasks such as surface inspection, scene cl... more Texture plays an important role in many machine vision tasks such as surface inspection, scene classification, and surface orientation and shape determination. For example, surface texture features are used in the inspection of semi-conductor wafers, gray-level distribution features of homogeneous textured regions are used in the classification of aerial imagery, and variations in texture patterns due to perspective projection are used to determine three dimensional shapes of objects. In this study, the effect of using auxiliary data in the classification results was investigated using the SVM classifier and specified training sample size, with generated Co-occurrence matrix attributes. Three investigations have been implemented: 1) using single attribute of each band. 2) Using the group attributes of each band. 3) Using the all attributes of bands and comparing the results with the case of RGB image only. The results showed that, the group of attributes of Blue band performed the b...
ERJ. Engineering Research Journal, 2009
In the case that more constraints than necessary to remove the network datum defect< have been de... more In the case that more constraints than necessary to remove the network datum defect< have been defmed, a new type of geodetic network will be obtained " overconstrained geodetic network ". Datum changes may be obtained by Similarity Transformations in order to select the proper coordinate datum for geodetic networks as well as to analyse the stability of the reference points. The purpose of this research paper is to choose the optimal fixed points for overconstrained geodetic networks by using Similarity Transformation. A numerical example is presented. b% si JLJy >I &.&I\ a&) 2 4 1 \6!
ERJ. Engineering Research Journal, 2012
Geodetic networks are very important tools used to monitor earth and/or structural deformations. ... more Geodetic networks are very important tools used to monitor earth and/or structural deformations. However, a geodetic network must be designed to meet sufficiently some network quality requirements such as precision, reliability, or sensitivity. This is the subject of geodetic network optimization. The determination of the observation weights problem in the deformation monitoring networks can be dealt with as an optimization procedure, this problem can performed by solving the second-order design (SOD) problem. Traditional methods have been used for geodetic optimization tasks. On the other hand, some heuristic techniques have been started to be used recently in geodetic science such as the Particle Swarm Optimization (PSO) algorithm. The general purpose optimization method known as Particle Swarm Optimization (PSO) has received much attention in past years, with many attempts to find the variant that performs best on a wide variety of optimization problems. In this paper, the PSO algorithm, a stochastic global optimization method, has been employed for the determination of the optimum observation weights to be measured in the field that will meet the postulated criterion matrix at a reasonable precision. The fundamentals of the method and a numeric example are given.
ERJ. Engineering Research Journal, 2014
Thematic maps representing the characteristics of the Earth's surface have been widely used as a ... more Thematic maps representing the characteristics of the Earth's surface have been widely used as a primary input in many land related studies. Classification of remotely sensed images is an effective way to produce these maps. The value of the map is clearly a function of the accuracy of the classification. Selecting proper size of samples and classification method are essential issues to produce accurate thematic maps. In the present study, training data sets at various sizes used to investigate the effect of the training set size on the classification accuracy. Six supervised classification methods with different characteristics were applied to produce land use/land cover thematic map of the study area. The used classifier include: Parallelepiped, Minimum Distance, Mahalanobis Distance, Maximum Likelihood, Neural Network and Support Vector Machine (SVM). The results showed that optimum sample size differs from classifier to another. In the case of limited number of training pixels, SVM and maximum likelihood classifiers produced higher classification accuracies than the rest of classifiers.
Journal of Geodetic Science, 2013
The Global Positioning System (GPS) is increasingly coming into use to establish geodetic network... more The Global Positioning System (GPS) is increasingly coming into use to establish geodetic networks. In order to meet the established aims of a geodetic network, it has to be optimized, depending on design criteria. Optimization of a GPS network can be carried out by selecting baseline vectors from all of the probable baseline vectors that can be measured in a GPS network. Classically, a GPS network can be optimized using the trial and error method or analytical methods such as linear or nonlinear programming, or in some cases by generalized or iterative generalized inverses. Optimization problems may also be solved by intelligent optimization techniques such as Genetic Algorithms (GAs), Simulated Annealing (SA) and Particle Swarm Optimization (PSO) algorithms. The purpose of the present paper is to show how the PSO can be used to design a GPS network. Then, the efficiency and the applicability of this method are demonstrated with an example of GPS network which has been solved previously using a classical method. Our example shows that the PSO is effective, improving efficiency by 19.2% over the classical method.
Nowadays the Global Positioning System (GPS) is one of the most favorite techniques in practical ... more Nowadays the Global Positioning System (GPS) is one of the most favorite techniques in practical geodesy. A major dilemma in GPS surveying lies in its ellipsoidal-based type of heights, while in engineering practice orthometric heights are usually utilized. Thus, it is important to convert GPS heights into orthometric heights through applying an accurate geoid model. The objectives of this paper are to model a local geoid in the study area using GPS/levelling technique, and to evaluate the performance of several Global Geopotential Models (GGMs) particularly the OUS-91A, EGM96 and EGM2008 in the study area, which is located in the northern Egypt at Rosetta zone area. The accomplished results show that the EGM 2008 represents the most precise global geopotential model to be used for geoid determination in Egypt. Furthermore, the achievable accuracy of local geoid determination in the study area after using regression method models is ranges between 0.059 meter to -0.083 meter, with a...
Advances in Space Research
Global Positioning System (GPS) is being used in aviation, nautical navigation and the orientatio... more Global Positioning System (GPS) is being used in aviation, nautical navigation and the orientation ashore. Further, it is used in land surveying and other applications where the determination of the exact position is required. Although GPS is known as a precise positioning system, there are several error sources which are categorized into three main groups including errors related to satellites, propagation and GPS receivers. In this paper we focus on the estimation of the receiver coordinates of a fixed point based on pseudorange measurements of a single GPS receiver. The estimation of the unknowns is achieved by introducing an Extended Kalman Filter (EKF) and Iterative Least Square (ILS) that processes. Kalman filter is the method most often used nowadays. It is based on some assumptions and if all the assumptions are met it can offer optimal estimation and prediction. A navigation filter is commonly designed by use of a EKF to estimate the vehicle state variables and suppress the...
Digital Elevation Models (DEMs), which can come in the form of digital surface models or digital ... more Digital Elevation Models (DEMs), which can come in the form of digital surface models or digital terrain models, are key tools in land analyses and other purposes. Classical methods such as field surveying and photogrammetry can yield high-accuracy terrain data, but they are time consuming and labor-intensive. Nowadays, different modernistic height-finding methods have emerged, including Global Positioning System (GPS) and airborne methods. In contrast to the airborne ways that are suited to gain highly precise, fine-resolution DEMs at a local scale. The airborne ways are complementary to their space-borne matches, such as Light Detection and Ranging (LiDAR), Shuttle Radar Topography Mission (SRTM), Advanced Spaceborne Thermal Emission and Reflection RadiometerGlobal Digital Elevation Model (ASTER GDEM) and Advanced Land Observing Satellite (ALOS). LiDAR data acquisition has become the standard approach for collecting point data to interpolate high-resolution ground and aboveground ...
Journal of Engineering Research
The most prominent spatially correlated errors in GNSS observations are well known to be atmosphe... more The most prominent spatially correlated errors in GNSS observations are well known to be atmospheric effects. The ionosphere and troposphere are the two main layers of the Atmosphere that cause delays in GNSS observations. A linear combination of the dual-frequency data can be used to reduce ionospheric delay. Unlike the ionospheric delay, the tropospheric delay cannot be eliminated using the same methods. The troposphere is primarily associated with GPS. The delay it causes in GPS signals is regarded as one of the primary sources of errors that must be eliminated to determine accurate positions. This paper's main purpose is to develop a new source code that can estimate the effect of tropospheric delay over any GPS station. The tropospheric delay in this proposed code is estimated utilizing sequential least-squares adjustment using a model depending on Niell Mapping Function (NMF). This model, known as the Tropospheric Delay Estimation program, was created in the MATLAB® enviro...
Journal of Applied Geodesy, 2021
Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to rem... more Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, an analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stor...
Global Positioning System (GPS) results are suffering from one of the major errors in high precis... more Global Positioning System (GPS) results are suffering from one of the major errors in high precision GPS positioning, the ones caused by reflections, known as Multipath error. Here, we study some of the multipath factors affecting on the accuracy observables obtained from GPS measurements. This will be achieved through monitoring and record the multipath effect according to different types of surface which reflected the signals specific set of generating and monitoring systems for multipath signal is established and a series of controlled experiments are carried out. Experimental results show that Aluminium caused the highest amount of multipath. This is followed by Glass and Wood.
7 Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal reso... more 7 Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolution of Global Ionosphere 8 Maps (GIMs). Receivers and Satellites Differential Code Biases (DCBs) are one of the main error sources in estimating precise 9 TEC from Global Positioning Systems (GPS) data. Recently, researchers are interested in developing models and algorithms 10 to compute DCBs of receivers and satellites close to those computed from the Ionosphere Associated Analysis Centers 11 (IAAC). Here we introduce a MATLAB code called Multi Station DCB Estimation (MSDCBE) to calculate satellites and 12 receivers DCBs from GPS data. MSDCBE based on spherical harmonic function and geometry free combination of GPS 13 carrier phase and pseudo-range code observations and weighted least square were applied to solve observation equations, to 14 improve estimation of DCBs values. There are many factors affecting estimated value of DCBs. The first one is the 15 observations weighting fun...
Journal of Engineering Research, 2021
The selection of optimal GPS baselines can be realized by solving the geodetic second-order desig... more The selection of optimal GPS baselines can be realized by solving the geodetic second-order design (SOD) problem. Basically, there are two techniques to be used for selecting optimal baselines in GPS network, namely traditional techniques and artificial techniques. Traditional techniques include the method of trial and error and the analytical method, while artificial methods include both local and global optimization techniques. The global optimization techniques, such as Genetic Algorithms (GAs), Simulated Annealing (SA) method, Particle Swarm Optimization (PSO) Algorithm, and Butterfly Optimization Algorithm (BOA) have been used recently in geodesy. In the current study, (BOA) has been used for the selection of the optimal GPS baselines to be measured in the field that will meet the postulated criterion matrix, at a reasonable cost. Ithas been tasted on a GPS network. The BOA is already designed and it determined the number of baselines that would be observed due to obtaining hig...
Journal of Applied Geodesy, 2019
An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the ... more An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. The ionospheric delay is the most predominant of all the error sources. This delay is a function of the total electron content (TEC). Because of the dispersive nature of the ionosphere, one can estimate the ionospheric delay using the dual frequency GPS. In the current research our primary goal is applying Precise Point Positioning (PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB and was named VI...
Arabian Journal of Geosciences, 2017
The differential code bias (DCB) is the differential hardware (e.g., the satellite or receiver) d... more The differential code bias (DCB) is the differential hardware (e.g., the satellite or receiver) delay that occurs between two different observations obtained at the same or two different frequencies. There are two approaches used to estimate DCBs for receivers and satellites: the relative and absolute methods. The relative method utilizes a GPS network, while the absolute method determines DCBs from a single station (zero difference). Three receiver types based on the pseudo-range observables were used here to collect the GPS data: Codeless Tracking, Cross Correlation, and Non-Cross Correlation styles. According to its types, GPS receivers have responded to restrictions on the GPS signal structure in different ways. The main goal of the current research is providing a method to determine the DCBs of GPS satellites and dual frequency receivers. The developed mathematical model was based on spherical harmonic function and geometry-free combination of pseudo-range observables (C/A or/and P-code) according to receiver type. A new elevationdependent weighting function with respect to GPS satellites in our algorithm was applied. The applied weighting function was used to consider the quality variation of satellite DCBs, which is caused by pseudo-range measurement errors. The code of the proposed mathematical model was written using MATLAB and is called Bzero difference differential code bias estimation (ZDDCBE)^. This code was tested and evaluated using data from IGS GNSS stations and different types of GPS stations out of IGS network installed in Egypt and Saudi Arabia. The estimated values from the ZDDCBE code show a good agreement with the IGS analysis centers with a mean error of estimation for the receiver DCB equal 5.94%. Therefore, the ZDDCBE code can be used to estimate the DCB for any type of receiver regardless if the receiver is from IGS network or not.
Journal of Applied Geodesy, 2014
ABSTRACT Deformation monitoring is a kind of continuous recording positions (horizontal and verti... more ABSTRACT Deformation monitoring is a kind of continuous recording positions (horizontal and vertical coordinates) precisely regardless the deformation pattern and instrument used. In general, a deformation monitoring network can be designed using the trial and error method or analytical methods such as linear programming and nonlinear programming. Recently, a deformation monitoring network may also be designed by heuristic optimization algorithms such as Genetic Algorithms (GAs), Particle Swarm Optimization (PSO) and Simulated Annealing (SA). In this paper, GAs and PSO, which are heuristic optimization techniques, are applied to a geodetic horizontal deformation monitoring networks to solve second-order design problem. The results proved that both GAs and PSO can be used as alternative methods in place of the traditional optimization techniques with high eficiency.
Annales Geophysicae Discussions, 2018
Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolu... more Precise Total Electron Content (TEC) are required to produce accurate spatial and temporal resolution of Global Ionosphere Maps (GIMs). Receivers and Satellites Differential Code Biases (DCBs) are one of the main error sources in estimating precise TEC from Global Positioning Systems (GPS) data. Recently, researchers are interested in developing models and algorithms to compute DCBs of receivers and satellites close to those computed from the Ionosphere Associated Analysis Centers (IAAC). Here we introduce a MATLAB code called Multi Station DCB Estimation (MSDCBE) to calculate satellites and receivers DCBs from GPS data. MSDCBE based on spherical harmonic function and geometry free combination of GPS carrier phase and pseudo-range code observations and weighted least square were applied to solve observation equations, to improve estimation of DCBs values. There are many factors affecting estimated value of DCBs. The first one is the observations weighting function which depending on the satellite elevation angle. The second factor concerned with estimating DCBs using single GPS Station Precise Point Positioning (PPP) or using GPS network. The third factor is the number of GPS receivers in the network. Results from MSDCBE were evaluated and compared with data from IAAC and other codes like M_DCB and ZDDCBE. The results of weighted (MSDCBE) least square shows an improvement for estimated DCBs, where mean differences from CODE less than 0.746 ns. DCBs estimated from GPS network shows a good agreement with IAAC than DCBs estimated from PPP where the mean differences are less than 0.1477 ns and 1.1866 ns, respectively. The mean differences of computed DCBs improved by increasing number of GPS stations in the network.
Accurate and high spatial resolution digital elevation models (DEMs) are in increasing demand for... more Accurate and high spatial resolution digital elevation models (DEMs) are in increasing demand for a growing number of mapping and GIS tasks related to applications such as forest management, urban planning, bird population modelling, ice sheet mapping, flood control, road design, etc. Airborne Light Detection and Ranging (LiDAR) has become the preferred technology for digital elevation data acquisition in a wide range of applications. DEMs quality relies on the quality of elevation data and the process of converting discrete elevation points to a continuous surface represented by a DEM through an interpolation operation. LiDAR technology provides high-density and high-accuracy three-dimensional terrain point data acquisition, however, the quality of the DEM generated from LiDAR is affected directly by the interpolation process. In this study, the Ordinary Kriging (OK), the Local Ploynomial (LP) and the Inverse Distance Weighting (IDW) interpolation methods working under ArcGIS 10.1 ...
Annales Geophysicae Discussions, 2018
An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the ... more An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. the ionospheric delay is the most predominant of all the error sources. Thisidelay is a function of theitotalielectronicontent (TEC). Because ofithe dispersive nature of the ionosphere, one caniestimateitheiionosphericidelay using the dual frequency GPS. In the current research our primary goal is applying PreciseiPointiPositioningi(PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB. The proposed Algorithm depends on the geometry-free carrier-phaseiobservations afteridetectingicycle slip to estimates the ionosphericidelayiusingia spherical ionospheric shell model, in which the vertical delays are described by means of a zenithidelayiatitheistationipositioniandilatitudinaliandilongitudinal gradients. geometry-free carrier-phase observations were applied to avoid unwanted effects of pseudorange measurements, such as code multipath. The ionospheric estimation in this algorithm is performed by means of sequential leastsquares adjustment. Finally, an adaptable user interface MATLAB software are capable of estimating ionosphere delay, ambiguity term and ionosphere gradient accurately.