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Utilization of Satellite Geophysical Data as Precursors for Earthquake Monitoring
Published in Ramesh P. Singh, Darius Bartlett, Natural Hazards, 2018
The study area and the generalized geological map over Gujarat are shown in Figures 4.1 and 4.2, respectively. The details of high-resolution satellite-derived gravity data have been discussed by Hwang et al. (2002). They carried out very detailed data assimilation for calculation of the deflection of the vertical and then generated a 2 × 2 min (4 × 4 km) grid over oceans and geoidal gravity using a high-resolution geoid, for example, Earth Gravitational Model 1996 (EGM96), over land (Majumdar et al. 2001; Hwang et al. 2002). Detailed quality evaluation of marine gravity (Hwang et al. 2002) over the Indian offshore has been discussed elsewhere (Chatterjee et al. 2007a,b). Root mean square errors (RMSEs) for various satellite-derived profiles with ship-borne gravity over the Arabian Sea and the Bay of Bengal have been found to be within ±3–6 mGal, which is quite satisfactory (Chatterjee et al. 2007b). The National Geophysical Research Institute (NGRI), Hyderabad, has taken several in situ gravimeter surveys over Kachchh and other places in Gujarat and generated an in situ gravity map over this region (NGRI Map Series 1978). The NGRI land gravity data grid size is approximately 0.5° × 0.5°. Recently, Gravity Recovery and Climate Experiment (GRACE) gravity data (grid size ~0.1° × 0.1°) have been generated over land which are utilized over the Kachchh region (GRACE website 1). Figure 4.7a–c shows various gravity images over the Kachchh region after superimposition with the tectonic map.
Position
Published in W. Schofield, M. Breach, Engineering Surveying, 2007
The most precise global geoid is the Earth Gravitational Model 1996 (EGM96). However, it still remains a complex, undulating figure which varies from the GRS80 ellipsoid by more than 100 m in places. In the UK the geoid–ellipsoid separation is as much as 57 m in the region of the Hebrides. As a 6-m vertical separation between geoid and ellipsoid would result in a scale error of 1 ppm, different countries have adopted local ellipsoids that give the best fit in their particular situation. A small sample of ellipsoids used by different countries is shown below: When f = 0, the figure described is a sphere. The flattening of an ellipsoid is described by f = (a – b)/a. A further parameter used in the definition of an ellipsoid is e, referred to as the first eccentricity of the ellipse, and is equal to (a2 − b2) ½ /a.
Usefulness of Remotely Sensed Data for Extreme Flood Event Modeling
Published in George P. Petropoulos, Tanvir Islam, Remote Sensing of Hydrometeorological Hazards, 2017
Sebastien Pinel, Joecila Santos Da Silva, C. R. Fragoso, J. Rafael Cavalcanti, Jeremie Garnier, Frederique Seyler, Stephane Calmant, David Motta Marques, Marie-Paule Bonnet
Besides the bias introduced by interferometric errors, the SRTM data present an elevation ranging above the bare earth and below the maximum canopy height (Brown et al. 2010; Carabajal and Harding, 2006), because of the incapacity of C-band radar in reaching the bare earth. (Carabajal and Harding, 2006) estimated the vertical height accuracy to 22.4 m in the lowland Amazon basin. Original data are referenced to the World Geodetic System 84 (WGS84) ellipsoid and the Earth Gravitational Model 1996 (EGM96) geoid. The EGM96 geoidal undulations were replaced by the EGM08 ones (Pavlis et al. 2013).
Correction of global digital elevation models in forested areas using an artificial neural network-based method with the consideration of spatial autocorrelation
Published in International Journal of Digital Earth, 2023
Yanyan Li, Linye Li, Chuanfa Chen, Yan Liu
SRTM is a cooperative project sponsored by the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA) (Farr et al. 2007). It was launched in February 2000 for 11 days and collected topographic data between 60° N and 56° S latitude using InSAR with C- and X-band. Thus, SRTM data was collected in winter in the northern hemisphere when the deciduous trees have defoliated. At present, many versions of C-band SRTM DEMs have been released, and the most popular version (V4.1) was produced by the Consortium for Spatial Information using a void-filling interpolation method (Reuter, Nelson, and Jarvis 2007). The specified vertical accuracy of the 1 arc-second SRTM (SRTM1) at 90% confidence level is 16 m and horizontal accuracy is 20 m (Rodriguez, Morris, and Belz 2006). Becek (2008) reported that the root mean square error (RMSE) of SRTM was less than 2 m when compared with runway elevation data around the world. The horizontal datum of SRTM is the World Geodetic System 1984 (WGS84), and the vertical datum is the Earth Gravitational Model of 1996 (EGM96). SRTM1 has been freely available worldwide since September 2014 (González-Moradas and Viveen 2020). SRTM1 was used in this study, which was downloaded from CGIAR-CSI (http://srtm.csi.cgiar.org/).
Global DEMs vary from one to another: an evaluation of newly released Copernicus, NASA and AW3D30 DEM on selected terrains of China using ICESat-2 altimetry data
Published in International Journal of Digital Earth, 2022
Hui Li, Jiayang Zhao, Bingqi Yan, Linwei Yue, Lunche Wang
The Copernicus DEM is a 1-arcsec Digital Surface Model (DSM) based on the two radar satellite data acquired from December 2010 to January 2015 during the TanDEM-X mission. The primary goal of the mission is to create a worldwide, consistent and high-precision DSM using Synthetic Aperture Radar (SAR) interferometry (Fahrland et al. 2020). The mission provides DSM products at three resolutions (0.4″, 1″ and 3″). The 3″ Copernicus DEM was released in 2019, and 1″ DEM in late 2020, while the 0.4″ DEM was commercially available in 2016. The Copernicus DEM contains significant terrain correction and hydrological editing, such as spikes and holes removal, identification and filling of voids, edits of shore and coastlines, as well as correction of implausible terrain structures and random biases. The Copernicus DEM has been assessed against ICESat measurements, which indicates a vertical RMSE of 1.68 m (Leister-Taylor et al. 2020). The products are provided in Geographic Coordinates, with the horizontal reference datum of the World Geodetic System 1984 (WGS84), and the vertical reference datum of the Earth Gravitational Model 2008 (EGM2008).
Using advanced soft computing techniques for regional shoreline geoid model estimation and evaluation
Published in Marine Georesources & Geotechnology, 2018
Mosbeh R. Kaloop, Mostafa Rabah, Jong Wan Hu, Ahmed Zaki
Geoid undulation N is the difference between ellipsoid surface, ellipsoidal height h, and the geoid surface, orthometric height H. The accurate estimation of N can be used to detect H based on h deduced from satellite measurements which decreases the cost of the shorelines geoid heights monitoring. Nowadays, the shoreline monitoring is an effective way to study the climate changes. Therefore, many monitoring points are selected along shorelines to measure the shorelines changes using long-term monitoring periods for the horizontal directions. Many previous studies evaluated the shorelines and mean sea level changes to study the climate change factor (Klemann and Wolf 2005; Kaloop, Rabah, and Elnabwy 2016). The regional shorelines geoid models are a novel application study for the lines geoid, while no specific shorelines geoid models are studied before especially in Egypt (Roman et al. 2010). Gikas, Mpimis, and Androulaki (2013) evaluated the geoid model of railway line (101 km) in Greece based on dense point spacing of the global navigation satellite system (GNSS)/leveling measurements. Dawod et al. (2010) evaluated the geoid model of Earth Gravitational Model 2008 (EGM2008) for the north of Nile valley, Egypt, using 320 global positioning system (GPS)/leveling observations points. The current study aims to model the north shorelines (900 km) geoid of Egypt with low number (95 points) of GNSS/leveling (GNSS/L) measurements.