Assessing the performance of IRI-2016 and IRI-2020 models using COSMIC-2 GNSS radio occultation TEC data under different magnetic activities over Egypt
Journal of Applied Geodesy
Variations in Total Electron Content (TEC) between the COSMIC-2, IRI-2016, and IRI-2020 are consi... more Variations in Total Electron Content (TEC) between the COSMIC-2, IRI-2016, and IRI-2020 are considered under different levels of geomagnetic storm activity: minor, moderate, and severe. TEC values are scrutinized at three levels of the Kp index, which serves as a metric for gauging the strength of a magnetic storm (Kp = 3.0, Kp = 6.0, Kp = 8.0) and across four-time intervals throughout 24 h to understand the performance of the models during both day and night-time conditions. Statistical analysis reveals that the standard deviation of TEC variations is lower during minor storms than moderate and severe. The comparison of variations between COSMIC-2 Radio Occultation TEC and both IRI-2016 and IRI-2020 models revealed more substantial discrepancies during day-time intervals; This was likely attributed to the dynamic and complex nature of the ionosphere influenced by solar radiation and other factors. Comparative analysis across the three levels of storm activity demonstrated that IRI2...
Land deformation monitoring by GNSS in the Nile Delta and the measurements analysis
Arabian Journal of Geosciences
Nile Delta, one of the most populated deltas around the world, is suffering from subsidence due t... more Nile Delta, one of the most populated deltas around the world, is suffering from subsidence due to the natural compaction of its sediment. Land subsidence has a great impact on the infrastructure, economic, and social. This study investigatesthe evaluation of the land subsidence in Nile Delta using GNSS measurements. Eight stations of GNSS points through period 2013–2015 distributed around Nile Delta and the Northern part of Egypt are utilized using differential GPS with nine IGS stations by GAMIT/GLOBK V. 10.61. The main objective is to monitor the spatiotemporal variations of land surface within the Nile Delta by time series analysis of the ellipsoidal height. The northern part of Egypt can be divided into three major parts; the western part shows subsidence rate of 2 mm/year downward; Nile Deltaof 2.5 to 10 mm/year downward from west to east and the eastern part shows an uplift.
Sea level analysis using tide gauge observations at the northern delta coast, Egypt
NRIAG Journal of Astronomy and Geophysics
ABSTRACT The current study focuses on the analysis of observed sea level in the northern delta co... more ABSTRACT The current study focuses on the analysis of observed sea level in the northern delta coast, which is considered the most important region in Egypt. The used sea-level data are records of three tide gauge stations located on the north of the delta, on Alexandria, Damietta, and Port Said. Different periods of sea-level records had been used to be analyzed to get the astronomical tide and surge heights. Geotide software had been used to obtain the tidal harmonic constituents. The tidal cycle sort at the three locations of the tide gauges had been calculated and the results were as follows: a mixed semidiurnal tidal type in Alexandria and Damietta, and a semidiurnal tidal type in Port Said. The Mean Sea Level (MSL), referred to the Egyptian Survey Authority datum (ESA-1906), had been calculated, and the tidal datums of each station referred to the International Terrestrial Reference Frame (ITRF-2014) had been calculated else. Ten groups of tidal constituents had been obtained and two of them have the largest amplitudes and they are M2 (Principal lunar), S2 (Principal solar). The amplitudes and percentages of astronomical tide and surge, in the observed sea level data, will be shown in the results section.
Determination of local geometric geoid model for Kuwait
Journal of Applied Geodesy
Determining a precise local geoid is particularly important for converting the Global Navigation ... more Determining a precise local geoid is particularly important for converting the Global Navigation Satellite System (GNSS) heights to orthometric heights. The geometric method for computing the geoid has been extensively used for a comparatively small region, which, in some points, interpolates geoid heights based on GNSS-derived heights and levelling heights. Several considerations should be considered when using the geometric method to increase the accuracy of a local geoid. Kuwait is used as a test area in this paper to investigate several features of the geometric method. The achievable precision is one of these aspects, the role of the interpolation method, global geopotential models, and the influence of the topographic effect. The accuracy of the local geoid can be substantially enhanced by integrating a geopotential model with a digital terrain model of the research region. It is possible to get a precision of 2–3 cm.
Accuracy assessment of available airborne gravity data in the central western desert of Egypt
Journal of Applied Geodesy
In the current study, the accuracy of airborne gravity data is evaluated based on the most recent... more In the current study, the accuracy of airborne gravity data is evaluated based on the most recent Global Geopotential Models (GGM) and terrestrial gravity data to find out to what extent these data are acceptable to be used in multi-applications (e. g., geodesy and geophysics). To achieve this goal, the remove-compute-restore (RCR) scheme, upward, and downward continuation operational methods (least square collocation and fast Fourier transform procedures) are applied. The airborne gravity data had been acquired by the Egyptian Nuclear Material Authority (ENMA) in the central-western desert for geological applications. Firstly, three GGMs models (EGM2008, EIGEN-6C4 and XGM2019e up to various degrees) are used to compare with the free-air airborne gravity anomaly, The EGM2008 model up to degree 720 produces the smallest mean and STD difference values with 2.59 and 3.07 mGal, respectively. The terrestrial gravity data are compared with the airborne gravity anomaly at both flight and g...
Establishing a Marine Gravity Database around Egypt from Satellite Altimetry-Derived and Shipborne Gravity Data
Marine Geodesy, 2021
Abstract For the purpose of marine geoid modeling and many other geodetic and geophysical applica... more Abstract For the purpose of marine geoid modeling and many other geodetic and geophysical applications, a marine gravity map around Egypt is established by the integration of gravity data provided by satellite altimetry and shipborne gravimetric observations. Firstly, the collected shipborne data were compared with GO_CONS_GCF_2_TIM_R6 and XGM2019e GGMs and with SSv29.1 and DTU17 altimetry models. Then, a pre-refinement of ship marine surveys was done with a rigorous condition, in which a number of 6525 points have been removed from the dataset. After that, 87709 points were deducted from the pre-filtered shipborne dataset to fit the study area and the cross-validation approach with the kriging interpolation algorithm were applied. A rigorous level of confidence was decided in this step where the points which have differences between the estimated and the observed values more than twice the STD of the residuals were removed until the STD reached a value less than 1 mGal. Finally, the filtered shipborne gravity data were combined with DTU17 (the best evaluation model) using the least-squares collocation technique (LSC). The final gravity map was tested using 8000 randomly chosen shipborne stations, which were not included when applying LSC, revealing the significant enhancement gained after the integration process.
Geodetic-Based Estimation of the Geostrophic Currents for Semi-Closed Waterbodies. Case Study: The Red Sea
The estimation of sea currents circulation for semi-closed waterbodies is a challenge for GOCE be... more The estimation of sea currents circulation for semi-closed waterbodies is a challenge for GOCE because the spatial scales of their structures are smaller than both these of open ocean and the expected resolution of GOCE models. An attempt to compute the Sea currents circulation model for the Red Sea implementing the geodetic methods is made. Such a model has been developed exploiting a combination of heterogeneous datasets, i.e., the GOCE-based DIR-R5 and EGM2008 gravity contributions, DTU13 altimetric gravity, Bureau Gravimétrique International (BGI) shipborne gravity observations, and SRTM15_Plus topography data. In the beginning, the quality of shipborne gravity data, provided by the BGI, has to be assessed, therefore the leave-one-out cross-validation integrated with the Kriging prediction method was chosen to ensure that the shipborne gravity observations are both consistent and gross-errors free. A confidence level of 95.4% was implemented to filter the shipborne data while the cross-validation algorithm was repeatedly applied until the standard deviation (STD) of the residuals, between the observed and estimated gravitational values, are less than 1.5 mGal, which led to the exclusion of about 17.7% of the total shipborne gravity data. Then, the least-squares collocation (LSC) was implemented to sew the shipborne and the DTU13 gravity data in order to create a unique and consistent gravity field over the Red Sea with no data voids. The combined data were independently tested using a random extraction of a total of 95 shipborne gravity stations. Comparing the extracted shipborne gravity data with the corresponding DTU13 altimetry anomalies, before and after applying the LSC, revealed that significant improvements are achievable using the combined dataset, where the mean value dropped from-3.6 to-0.39 mGal and STD dropped from 9.31 to 2.04 mGal. At this point, a statistical comparison has to be made between various, i.e., satellite-only and combined, global geopotential models (GGMs) and the shipborne gravity data. Also, the GOCE satellite-only GGMs were evaluated via the spectral analysis and by cross-comparing them to the shipborne free-air gravity anomalies over the Red Sea. On the one side, the EGM2008 combined model manifested the best results with a mean and STD values of 1.35 and 10.11 mGal, respectively. On the other side, the DIR-R5 GOCE-only model synthesized up to degree/order 160 showed the overall best results. At this point, the Red Sea gravimetric geoid model is computed using the DIR-R5 synthesized up to degree/order 160, EGM2008, and combined gravity dataset (the integrated shipborne observations with DTU13 model). The gravimetric geoid computation methodology is based on the Remove-Compute-Restore technique with residual terrain model (RTM) reduction, and the 1D-FFT technique with Wong-Gore modification. Finally, the mean dynamic topography (MDT) is simply computed as the difference between the DTU13 mean sea surface (MSS) and the gravimetric geoid. All regions with depth values less than 200 m are excluded and the Gaussian filter with a 1.25 o width is used to remove the high-frequency noise that contaminate the final MDT model and accordingly, the geostrophic currents model for the semi-closed Red Sea is estimated.
A Proof of Concept: Exploiting GOCE Data to Enhance the Estimation of Geostrophic Currents for Semi-Closed Waterbodies
Exploiting GOCE data to estimate sea geostrophic currents for Open Ocean has been a success due t... more Exploiting GOCE data to estimate sea geostrophic currents for Open Ocean has been a success due to the competent and cross-comparable spatial resolution of the open ocean structure and the resolution of GOCE. On contrary, exploiting GOCE data to properly estimate sea Geostrophic Currents for semi-closed waterbodies has been a great challenge because the spatial resolution of GOCE models is higher than those of the semi-closed waterbodies' structures. A proof of concept research on the gain of using GOCE data for a better estimation of the sea currents circulation model for the Red Sea implementing the geodetic methods is made. Such a model has been developed sewing together heterogeneous gravity-based datasets, i.e. the GOCE-based DIR-R5 and EGM2008 models, DTU13 alti-metric gravity, the Bureau Gravimétrique International (BGI) shipborne gravity observations, and SRTM15_Plus topography data. First, a quality assessment step for the gravity data has been made, then the leave-one-out cross-validation integrated with the Kriging prediction method was chosen to guarantee that the gravity data are consistent and free of gross-errors. The cross-validation algorithm was repeatedly applied until the standard deviation (STD) of the residuals, differences between observed and estimated values, are less than 1.5 mGal. Then, the least-squares collocation (LSC) was executed to combine the shipborne and DTU13 gravity data in order to create a unique and consistent gravity field over the Red Sea with no data voids. The combined data were tested using independent gravity dataset. Testing the gravity data, before and after applying the LSC, revealed a significant improvement, as the mean and STD values dropped from-3.6 to-0.39 mGal and from 9.31 to 2.04 mGal, respectively. At this point, a statistical-based comparison has to be made between the satellite-only and combined global geopo-tential models (GGMs) and shipborne data campaign. The GOCE satellite-only GGMs were assessed via the spectral analysis and cross-comparison to the shipborne free-air anomalies over the study area. On the other hand, the EGM2008 combined model manifested the best results with a mean of 1.35 mGal and a STD of 10.11 mGal. Accordingly, the DIR-R5 GOCE-only model synthesized up to degree/order 160 revealed the best results. Consequently, the Red Sea gravimetric geoid model is computed, applying the Remove-Compute-Restore technique with residual terrain model (RTM) reduction, and the 1D-FFT technique with Wong-Gore modification, utilizing the synthesized DIR-R5 (degree/order 160), EGM2008, and combined gravity dataset, i.e. integrated shipborne and DTU13. Finally, the mean dynamic topography (MDT) is computed evaluating the differences between the DTU13 mean sea surface (MSS) and the gravimetric geoid. Regions with depth values below 150 m were excluded and a Gaus-sian filter with a 1.25o width is used to remove the high-frequency noise that contaminate the final MDT model and correspondingly, the geostrophic currents model for the semi-closed Red Sea is estimated.
Assessment of the latest release of GOCE satellite-only global geopotential models over the Red Sea
The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission launched on March 20... more The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission launched on March 2009 has successfully concluded its mission on October 2013 after collecting leading gravity gradient measurements. Such unprecedented GOCE data made it possible to improve the determination of the geoid over our study area, namely the Red Sea. The performance of GOCE global gravity field models (GGMs), at the end of its mission that lasted for 42 months, is evaluated using shipborne free-air gravity anomalies over the Red Sea. Seven recent GOCE-based GGMs, namely the DIR_R5, ITU_GGC16, SPW_R5, TIM_R5, NULP_02S, GOCO05C and GGM05G are assessed by means of the Spectral Enhancement Method (SEM) as well as the EGM2008 model. The evaluation focused the light on spherical harmonics degree/order (d/o) ranging from 100 to the maximum degree of the model with an incremental step of 20 d/o. SEM has been exploited in order to fill in the existing spectral gap between satellite and terrestrial data. Then, the combined model resulted from integrating GOCE data with EGM2008 is enhanced by accounting for the very high-frequency components, associated with the terrain effects, the so-called Residual Terrain Model (RTM). The results show that GOCE-based GGMs can improve the free-air gravity anomalies over the Red Sea, where such improvements are highly evident between d/o 140 and 160, where the performance of EGM2008 surpasses GOCE GGMs beyond these d/o. The best GOCE-only GGMs results were delivered by the SPW_R5 at d/o 160 with a mean and standard deviation of 2.06 and 9.90 mGal, respectively.
Validation of Global TEC Mapping Model Based on Spherical Harmonic Expansion towards TEC Mapping over Egypt from a Regional GPS Network
Unlike the interpolation process of Total Electron Content (TEC) maps made by Ionospheric Associa... more Unlike the interpolation process of Total Electron Content (TEC) maps made by Ionospheric Associate Analysis Centers (IAAC) over areas have no International GNSS Service (IGS) stations, A TEC mapping tool with a temporal resolution of 1 h based on GPS dual frequency observations was developed. This tool was written under MATLAB environment and can be used globally to produce GIMs from local GPS networks in several areas with low number of IGS stations or without. As the geomagnetic storm field affect directly on the TEC, three stormy days and other three quiet days were chosen for validating the developed model. The estimated TEC resulted from the model firstly was compared with Center for Orbit Determination in Europe (CODE) TEC results using the RINEX data of ten Eurobian IGS stations. The comparison of the results shows a convergence between CODE and GTM estimated TEC. The maximum differences were 2.52 TECU and 1.31 TECU for the stormy and quiet days, respectively. Then the new m...
Assessment of NRCAN PPP online service in determination of crustal velocity: case study Northern Egypt GNSS Network
Arabian Journal of Geosciences, 2021
Precise point positioning (PPP) has the ability to give precise positioning with high accuracy. T... more Precise point positioning (PPP) has the ability to give precise positioning with high accuracy. That may be an alternative to precise Deferential GNSS (DGNSS), in addition to being a low-cost alternative among all processing strategies of Global Navigation Satellite System (GNSS), especially when online services are used. To see the assessment study of PPP in the determination of crustal velocity, 66 days of GNSS data distributed in the period 2013–2015 were used. Composing a network of eight stations called the Northern Egyptian Permanent GNSS Network (N-EPGN) with nine IGS stations was processed. Scientific software GAMIT/GLOBK and Bernese used to calculate the final precise coordinate and the associated velocity of each station in the International Terrestrial Reference Frame (ITRF 2008). Each campaign consists of 3 days. These data were processed by PPP approach. The final precise coordinate and the associated velocity of each EPGN station estimated. The final results compare to...
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Papers by Mostafa Rabah