Design of global positioning system (GPS) networks using different artificial intelligence techniques

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 high accuracy. The results showed that the BOA method was more efficient than the traditional ones by 19.2%. It was better than the artificial methods in terms of length. Asit enhanced (SA) method by 21.7% and (PSO) method by 4.6% . Consequently, the use of the BOA is proven to be more effective and applicable.

Total Electron Content (TEC) estimation over Pakistan from local GPS network using spherical harmonics

Many organizations allow GNSS users to access Global Ionosphere Maps (GIMS). However, the TEC estimates derived from GIMs are of insufficient quality to describe small-scale TEC variations over Pakistan. In this paper, the first local TEC map over Pakistan for the year 2019, derived from a regional GPS network, is presented. Spherical harmonics expansion is employed to estimate TEC with the spatial resolution of latitude 0.2° x longitude 0.2° and temporal resolution of 5 minutes. The impact of changing the degree/order of harmonics is assessed and it is determined that harmonic expansion up to 6 degrees is sufficient for estimating accurate TEC map for the region of interest. We have demonstrated that the TEC maps of Pakistan generated by local model conform better to the GIM by Center of Orbit Determination (CODE) (RMS = 5.83) as compared to International Reference Ionosphere (IRI-2016) (RMS = 7.18). We found that the TEC estimated by the local model shows a better correlation to measured TEC; CODE-GIM overestimated TEC, while IRI-2016 underestimates it. Moreover, it was observed that TEC peaks during noon (1100-0100 LT) and Equinox (April). The residuals of local TEC estimates with respect to TEC obtained from CODE- GIM indicate the inaccuracy of CODE-GIM over the region of Pakistan: highest deviation of TEC from local model with respect to CODE –GIM was observed in April (RMS = 8.73) and minimum in October (RMS = 2.78). We have also analyzed the performance of our maps in geomagnetically disturbed days. The research presented in this paper will contribute towards the ionosphere study over Pakistan, where limited research is available currently.

The new tiltmetric network of Tenerife: technical and scientific issues

<p>Since 2004, the Instituto Tecnológico y de Energías Renovables (ITER) in collaboration, since 2011, with the Instituto Volcanológico de Canarias (INVOLCAN), are monitoring Canary Islands archipelago with a network of more than 30 differential GPS stations. Specifically, in Tenerife island alone there are 12 permanent GPS receivers. Data are processed automatically using Bernese software, constituting an important tool for the geodetic monitoring of Tenerife.</p><p>Since 2016, the volcanic system of Tenerife is experiencing a hydrothermal unrest, with a marked increase of the diffuse CO<sub>2</sub> flux from the crater of Mt. Teide, the major volcanic edifice of the island. This increased flux is likely to be related to the injection of fluids of magmatic origin within the hydrothermal system of Tenerife. The subsequent pressurization of this system is reflected also by the increase in the background microseismicity observed since July 2017. Until now, the GPS network has not recorded significant ground deformation above the instrumental error.</p><p>With the aim of improving the geodetic monitoring of Tenerife, detecting possible small ground deformation below the sensitivity of the GPS network, INVOLCAN has recently started deploying, since June 2019, high-gain tiltmeters (Jewell Instruments A603-C) in the surrounding of Mt. Teide. Currently the tiltmetric network consists of 3 tiltmeters, located close to existing seismic or GPS stations. Data are automatically downloaded via UMTS connection and processed daily.</p><p>The nominal sensitivity of such instruments is less than 2.5 nradians, hence their installation and calibration require very careful operations. The sensors are equipped with leveling worm-gear feet to guarantee a perfect levelling. However, the high sensitivity of the instrumentation makes adjustments made manually totally useless. The tilt change caused by the weight of the human operator during the levelling is enough to drive the instrument out of scale. For this reason, INVOLCAN developed a robotic system to perform the required adjustments from remote. The system is based on Arduino Mega 2560, driving two servomotors to adjust the leveling worm-gears. Another servomotor allows switching the gain level. The system can be accessed and operated through an internal web page, which allows driving the servomotors and checking the leveling of the tiltmeter platform by using an Arduino Ethernet.</p>

Towards a new generation of Generic Atmospheric Correction Online Service for InSAR (GACOS 2.0)

<div>The tremendous development of InSAR missions (e.g., Sentinel-1A/1B, ALOS-2, TerraSAR-X/TanDEM-X, COSMO-SkyMED, RADARSAT-2, and Gaofen-3) in recent years facilitates the study of smaller amplitude ground deformation using longer time series and over greater spatial scales. This poses new challenges for correcting interferograms for atmospheric (tropospheric) effects especially the dominant long wavelength effect and the spatial-temporal correlated topographic related effect, resulting the atmospheric effect being distance-dependent with larger interferograms experiencing greater contamination and preventing deformation mapping of large scales deformation phenomena such as inter-seismic tectonic strain accumulation, post-seismic relaxation of fault systems and Glacial Isostatic Adjustment (GIA). </div><div> </div><div>To overcome this, we have released the Generic Atmospheric Correction Online Service (GACOS) whose notable features comprise: (i) global coverage, (ii) all-weather, all-time usability, (iii) correction maps available in near real-time, and (iv) indicators to assess the correction performance and feasibility. The model applies operational high resolution ECMWF data (0.125-degree grid, 137 vertical levels, 6-hour interval) using an iterative tropospheric decomposition model and its performance for InSAR atmospheric correction was tested using globally-distributed interferograms, encompassing both flat and mountainous topographies, mid-latitude and near-polar regions, monsoon and oceanic climate systems, achieving a phase precision and displacement accuracy of approximately 1 cm for the corrected interferograms. Indicators describing the model’s performance including (i) ECMWF cross-RMS, (ii) phase-delay correlations, (iii) ECMWF time differences, and (iv) topography variations, were developed to provide quality control for subsequent automatic processing and provide insights of the confidence level with which the generated atmospheric correction maps may be applied. </div><div> </div><div>To further improve the performance of GACOS to better serve the InSAR community, a new generation (GACOS 2.0) is being developed by: (i) improving the temporal resolution by integrating the newly published 1-hour ERA-5 weather model and the 5-minute GPS tropospheric delay estimates; (ii) developing an API system to facilitate automatic data processing; and (iii) enhancing GACOS based on regional/local datasets (such as national weather model and regional GPS network). The ERA-5 product and global GPS tropospheric delay estimates are carefully validated in order to achieve a robust integration. Based on the globally distributed GPS network and the MODIS PWV product, the performance of GACOS 2.0 in different regions of the world is evaluated with its elevation and latitude dependency being concluded which could be served as another performance indicator. All these features will contribute to a simplified time series analysis method (i.e. relying less on spatial-temporal filters) to reduce the computational burden, provided that the majority of the atmospheric error has been mitigated by GACOS 2.0. </div><div> </div>