Computer Engineering and Intelligent Systems, 2016
The Global Positioning Satellite System (GPS) Continuously Operating Reference Stations (CORS) ar... more The Global Positioning Satellite System (GPS) Continuously Operating Reference Stations (CORS) are popular and have become increasingly dense throughout the world. One of the important factors affecting the GPS accuracy is the ionosphere Total Electron Content (TEC). The hardware Differential Code Biases (DCB), inherited in both Global Positioning System satellites and receivers, influence the total electron content estimation accuracy. DCB can be estimated using GPS data themselves or during the GPS data processing. The effect of DCB on CORS results are studied here using nine CORS stations from the Egyptian Permanent GPS Net (EPGN). Bernese software version 5.0 is used for data analysis. Three strategies are applied to the data. The first strategy is using a special MATLAB code to estimate DCB which in turn is introduced as known input in Bernese. Using Bernese itself to estimate the DCB along with the ionosphere is the second method. The third way is to totally ignore the DCB. The three solutions are compared based on ratio of ambiguity resolutions, standard deviations, error ellipse, and closure errors. The results indicate that the worst solution is obtained when ignoring the DCB. Both Bernese estimation and known DCB solutions are similar and gives good results. For example, the ratio of un-resolved ambiguity for baseline between Marsa-Alam and Arish is about 0.3096 for Bernese estimated DCB while it is about 0.5643 when ignoring DCB. Hence it is recommended to consider the DCB when processing GPS data for precise applications.
Down-looking (DL) Global Positioning System (GPS) radio occultation can produce an estimate of th... more Down-looking (DL) Global Positioning System (GPS) radio occultation can produce an estimate of the atmospheric refractivity profile. The main observations are the bending angle as a function of the impact parameter. DL provides both negative as well as positive elevation angle measurements. Abel inversion can be operated on a profile of partial bending angle found by subtracting the positive elevation measurement from the negative one with the same impact parameter. Abel inversion requires the spherical symmetrical assumption. Basically, partial bending calculation removes the ionospheric bending and hence it is possible to use a single frequency GPS receiver. The current paper introduces a simulation data for the case of a receiver on mountain top. The simulation uses model refractivity from MSISE-90 model as well as radiosonde data. Random noises are added to the bending angle profile before inversion. The result shows that it is possible to produce accurate vertical refractivity profile below the receiver altitude. The calculation of the water vapor profile is also made using temperature profile information from the MSISE-90 model as well as radiosonde. The errors in the retrieved vapor profile are always less than 0.1 mbar.
Port-Said Engineering Research Journal, Aug 24, 2020
Many earthquakes with moderate magnitude have occurred in many areas of the world. The common pro... more Many earthquakes with moderate magnitude have occurred in many areas of the world. The common procedures to extract the dynamic responses mainly depend on monitoring the change of the points in a time interval. This method could not be used to fully extract all dynamic parameters accompanied by the earthquake. To overcome these defects, and to analyze the seismic wave of those earthquakes, the GNSS precise point positioning (PPP) can be an effective tool for getting the values of the displacement of the point more accurate up to millimeters. In this paper, we apply the PPP technique to evaluate the station's displacement components and the station's heights in three different periods from the earthquake, Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) is used here [1]. Bernese GNSS 5.2 software is used as a reference to evaluate the PPP results [2]. Finally, it was found that PPP is an important tool for obtaining a high accuracy of our needed observations.
Port-Said Engineering Research Journal, Aug 24, 2020
Nowadays, detecting the response level of ground shaking and studying its effect on the measureme... more Nowadays, detecting the response level of ground shaking and studying its effect on the measurements of the surface motion are considered very important, because of the spread of natural disasters, such as earthquakes, volcanoes, and tsunamis. Such disasters lead to changes in the Earth's crust and hence movements of some points. Therefore, studying these movements has great benefits, such as the ability to predict the occurrence of an earthquake, which helps to control and minimize human and economic damages. It is possible to evaluate accurately the magnitude of point displacements and to find the factors affecting these displacements. In this research work, we explain the seismic monitoring techniques using the global navigation satellite system (GNSS), which considered a powerful tool for monitoring the ground points displacements, Bernese GNSS Software 5.2[4], was used to obtain high-precision of the results of the IGS stations data and their displacements, with the application on the network stations in the study area of Turkey,(Aegean sea earthquake).
NRIAG Journal of Astronomy and Geophysics, Jan 2, 2019
Nowadays, a GNSS application is one of the main backbones of lifestyle. The GNSS signal that come... more Nowadays, a GNSS application is one of the main backbones of lifestyle. The GNSS signal that comes from space satellites to receivers on Earth suffers some delays. The troposphere layer is one of the basic sources of delay to signals. To detect the delay, many models have been produced taking into account the receiver location and satellite zenith angle. Most of these models give vertically perfect representation without accounting the horizontal asymmetry effect. The horizontally graded difference "azimuth asymmetry" is negligible at high elevation angles up to 10°. At low elevation angles, the asymmetry is significant. At 2°elevation angle, the asymmetry is about 72 mm for east and west and about 66 mm for south. Using the Precise Tropospheric Delay Database (PTD), the difference in horizontal plane delays is studied. A new model is proposed and compared to PTD calculations. The model has three coefficients obtained for high zenith angles (70°to 88°). These coefficients are modelled as a function of zenith angle and used to give a horizontal gradient factor which is multiplied by the northern mapping function to map it to any azimuth. The proposed model makes significant improvement. For east and west directions, the model decreases the bias from around 72 mm to be about 1.0 mm. For the southern direction, the produced model needs an improvement to get closer to the true asymmetry.
Characteristics of Wet Tropospheric Delay Deduced from Water Vapor Radiometer Data and Their Implications for GPS Baseline Solution Accuracy(水蒸気ラジオメータによる観測資料から得られた対流圏における水蒸気遅延の特性とそのGPSによる基線解精度への関連性)
Refractivity Profiles Obtained by Abel Inversion from a Down Looking GPS Radio Occultation Experiment at Mt. Fuji: Preliminary Results and Future Plan
... 106: 11875-11889 Kursinski ER, Hajj GA, Hardy KR, Schofield JT. ... try of a Mountain top GPS... more ... 106: 11875-11889 Kursinski ER, Hajj GA, Hardy KR, Schofield JT. ... try of a Mountain top GPS Receiver, ION GPS 2001 proceedings, 1117-1126 Mousa AK, Tsuda T (2002) Refractivity profile retrieved from Down-looking GPS radio Occultation using Abel Inversion: simulation ...
NRIAG Journal of Astronomy and Geophysics, Jun 1, 2018
For space geodetic measurements, estimates of tropospheric delays are highly correlated with site... more For space geodetic measurements, estimates of tropospheric delays are highly correlated with site coordinates and receiver clock biases. Thus, it is important to use the most accurate models for the tropospheric delay to reduce errors in the estimates of the other parameters. Both the zenith delay value and mapping function should be assigned correctly to reduce such errors. Several mapping function models can treat the troposphere slant delay. The recent models were not evaluated for the Egyptian local climate conditions. An assessment of these models is needed to choose the most suitable one. The goal of this paper is to test the quality of global mapping function which provides high consistency with precise troposphere delay (PTD) mapping functions. The PTD model is derived from radiosonde data using ray tracing, which consider in this paper as true value. The PTD mapping functions were compared, with three recent total mapping functions model and another three separate dry and wet mapping function model. The results of the research indicate that models are very close up to zenith angle 80°. Saastamoinen and 1/cos z model are behind accuracy. Niell model is better than VMF model. The model of Black and Eisner is a good model. The results also indicate that the geometric range error has insignificant effect on slant delay and the fluctuation of azimuth anti-symmetric is about 1%.
Although the Cairo region is classified as low and moderate seismological area, the frequent eart... more Although the Cairo region is classified as low and moderate seismological area, the frequent earthquakes (M=2-4) and the largest one at 12th October 1992 (M=5.9) prove the recent seismotectonic activity of the area, which is connected to the known fault systems. To monitor the tectonic changes GPS network was established in Cairo region and analyzed between 1986 and 2003. Because of technical reason the network was updated in 2011 and the data processing methods were reconsidered. The application of usual methods require a very careful approach since the Cairo Network is very fare from the known fiducial GPS stations at the African plate, the nearer fiducial stations are at different plates and the network is near to the plate borders. For the investigation of these circumstances UNAVCO plate motion calculator was used to simulate coordinate changes, and the impact of the chosen plate motion on the result of intra-plate deformations monitoring were analyzed. New data processing approach and integrated baseline adjustment and similarity transformation method is proposed as an alternative strategy for the regional size Cairo Network to estimate intraplate deformations using GPS observations. The proposed method is demonstrated to estimate coordinate changes, global rotations and scale parameters in one computational step. The proposed method is used to investigate the significance of the impact of global plate motions on regional crustal movement network. Simulated data of the regional Cairo network is used for this evaluation. The estimated plate motions, simulated scale bias (due to miss-modeling of troposphere effect on GPS data) and baseline noise proved that the impact of plate motions have to be taken into account in the case of Cairo network if the investigation period is near or larger than ten years.
Journal of the Meteorological Society of Japan, 2004
Downward-looking (DL) Global Positioning System (GPS) occultation experiments from the top of Mt.... more Downward-looking (DL) Global Positioning System (GPS) occultation experiments from the top of Mt. Fuji were carried out as a joint project between Kyoto University, Meteorological Research Institute in Japan, and the Jet Propulsion Laboratory (JPL) in the U.S.A. from July 10 to September 25, 2001, in order to obtain temperature, water vapor and pressure profiles near the Earth's surface. A TurboRogue SNR-8000 GPS receiver and a choke ring antenna were installed at the Mt. Fuji weather station located at an altitude of about 3.8 km. Applying an Abel inversion, these DL observations can provide refractivity profiles over an area south of Mt. Fuji. This paper shows temperature, relative humidity, and pressure profiles derived from these refractivity profiles using a one-dimensional variational technique (1D-Var). The derived profiles show agreement with the Mt. Fuji weather station observations within 1.7 C, 1.2%, and 1.0 hPa at the receiver altitude.
This paper proposes to determine the GPS satellites DCB using nine GPS receivers located in the m... more This paper proposes to determine the GPS satellites DCB using nine GPS receivers located in the middle of Egypt. During four seasons and 36 days characterized by quiet geomagnetism, the performance of the proposed method is examined. The dual GPS data selected is used and applied to the GPS receiver chain notes. The Bernese program V.5 is used to estimate DCBs from the data of a single GPS station where the results of the algorithm operation are compared to the CODE DCB data and the main differences in GLONASS data are recorded. According to the comparison of the results between the proposed method and the currently existing methods, it can be shown that the accuracy of the DCB estimates is at a level of about 0.31 and 0.17 ns.
NRIAG Journal of Astronomy and Geophysics, Jun 1, 2016
The tropospheric delay is a serious error source for positioning using Global Navigation Satellit... more The tropospheric delay is a serious error source for positioning using Global Navigation Satellite Systems (GNSS). Since the scientific applications of GNSS positioning such as crustal deformation studies and earthquakes prediction require high accuracy in positioning, analysis of tropospheric delay calculation is necessary to improve GNSS positioning accuracy. In this study data from ground based GNSS receivers are used to evaluate effect of the tropospheric delay in position determination accuracy. These data are also used to study the tropospheric delay characteristics. The collected GNSS data are for the year 2013, taken from 8 stations from Egypt Permanent GNSS Network (EPGN) and 13 IGS stations. The GNSS data were processed using advanced GNSS software called Bernese V 5.0. The results show that the RMS of the coordinates is better in case of making estimation for the troposphere ZWD and bad in case of ignoring the troposphere. Also there is a correlation between the troposphere and the height component. The troposphere ZWD values have daily, temporal and spatial variation, depending on time in the day, day in the year, geographic location of the station and how near it to water. The ZWD values also go upward from the start to the end of the year, and also it shows high correlation with the water vapor content in the troposphere.
Space-based Radio Occultation (RO) measurements using a GPS receiver on a low Earth orbiter (LEO)... more Space-based Radio Occultation (RO) measurements using a GPS receiver on a low Earth orbiter (LEO) provide accurate atmospheric refractivity profiles. EQUatorial Atmospheric Research Satellite (EQUARS) is a planned satellite mission carrying a GPS receiver for RO measurements, whose main focus is to study the vertical coupling process in the equatorial atmosphere and ionosphere through upward propagating atmospheric waves. This paper presents a model simulation to determine the best practical orbital parameters of a LEO satellite for GPS occultation, which provides dense occultation coverage from 20 • S to 20 • N and sparser coverage extending to 30 • S and 30 • N. Constellations of 29 GPS satellites are computed every 10 sec using the six Keplerian parameters based on real almanac data, while various orbits of LEO satellite are computed by varying orbital parameters, especially orbital altitude and inclination. Then, the occultation events are simulated under the assumption that the ray path between the occulting GPS and LEO satellites is a straight line. The simulation analysis shows that altitude and inclination angle of orbit are considered as principal parameters among the Keplerian parameters to accomplish the RO measurements in the equatorial region. Taking into account the long-lived mission, an avoidance of ionospheric F-layer influences, and practical antenna field of view, the best practical orbit for RO measurement in the equatorial region has an altitude of 750 km and an inclination of 20 •. LEO on this orbit is expected to provide 530 RO events per day. The analysis also shows that three LEOs in that orbit with 120 • separation can provide atmospheric profiles at least once every 6 h within 1000 km from an arbitrary station in the equator.
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Papers by Ashraf Mousa