With the baseline satellite constellation, users with a clear view of the sky have a minimum of four satellites in view. It’s more likely that a user would see six to eight satellites. The satellites broadcast ranging signals and navigation data allowing users to measure their pseudoranges in order to estimate their position, velocity and time, in a passive, listen-only mode.
Applications of GPS positioning abound, with civilian uses far out-weighing military uses. Not only is the number of applications bigger, but the market for hardware is also. By the turn of the century, GPS is expected to be at least a 6 billion dollar industry. GPS has emerged as a "textbook" dual-use technology and "politically correct" use of military funds of which military officials, engineers, and now also politicians are proud Surveyors use GPS to mark legal boundaries and to collect data for Geographic Information Systems (GIS) with electronic data collectors. Today's hunters and hikers use pocket sized GPS receivers to avoid getting lost in the woods.
Receivers in cars supported by digital maps and data bases will take the anxiety out of finding your favorite vacation spot or restaurant whether in rural America or New York City. Engineers will guide machinery and robots with GPS. Farmers already use GPS to map crop yield and correlate it with fertilizer and soil maps. They may soon send their combine to harvest alone!
Fig. 5. A dual frequency GPS receiver used for surveying in common.
Civil aviation will soon go GPS and integrate in-the-air route and on-the-ground airport navigation. The same applies to open ocean, harbor, and inland waterway navigation. GPS will determine positions of other satellites, etc., etc. The imagination is the limit. All you need is an open sky. Generally, when you do not see through it, the GPS signals don't get through.
How does the GSI use GPS to measure fault motion?
We want to know how stations near active faults move relative to each other. Whenwe occupy several stations at the same time, and all stations observe the same satellites, the relative positions of all the stations can be determined very precisely. Often we are able to determine the distances between stations, even over distances up to several 100 kilometers, to better than 5 millimeters.
Fig. 6. Schematic drawings of an active strike-slip fault (right-lateral) with
Geodetic network (rectangle ABCD) around before and after(deformed
rectangle) displacement along the fault plane one year later.
Months or years later we occupy the same stations again. By determining how the stations have moved we calculate how much strain is accumulating and which faults are slipping.
Main goals of Geodynamic department
In fact, day-to-day development and advent of new and amazing satellite- and computer-based methods and technology, especially in last few decades, resulted to variety of approaches to study the geodynamic evolution of our planet and geohazards as well.
Therefore, Geodynamic department plan to work on modern Earth sciences and the methods and apply them to geohazard assessment for the country.
Main goals of Geodynamic department are:
Apply GPS ad its applications to study for earth sciences.
- Performing training courses, representing seminars and workshops.
- Proposing research projects in collaboration with/without domestic and foreign institutes or parties.
- Installing local GPS networks.
- Collecting and processing data extracted from national, local network.
- Interpreting data and information and exchanging with other parties.
- On- & off-shore Navigation of GSI's research parties.
- Developing the real-time digital Geologic Surveying for GSI.
- Developing and Integrating the interferometry (InSar) study with GPS surveying to Geohazard studies in GSI.
- Surveying for the morpho-tectonic proposes of Active tectonic studies using GPS.
- Contributing to the development and site selection of the National Continuous and campaign-mode GPS networks in collaboration with National Cartographic Center (NCC).
Main Resarch projects:
To understand better the geologic activity of the Iranian continental crust and its effects on the habitants accommodated in population centers, especially Tehran region, the capital city with large number of its solar cities where hosted more than 20 millions people, different type of projects have been proposed by the department.
1. Iranian Permanent (Continuous) GPS Network
After powerful earthquake rocked the ancient city of Bam Iran (in southeastern), destroying 70 to 90 percent of the city and killed more than 40- thousand people, National Cartographic Center (NCC) suggested installation of the first Iranian Permanent (Continuous) GPS Network(IPGPSN) consisting of 100 receivers for the country.
Fig. 6. A dual frequency Permanent GPS receiver used for IPGPSN.
The main target of the network was to study a continuous GPS survey for reduction of earthquake hazard risk. IPGPSN is an array of Global Positioning System (GPS) stations distributed throughout the country. The major objectives of the array are:
- To provide regional coverage for estimating earthquake potential of the region.
- To identify active blind/exposed thrust faults and test models of compressional tectonics in the country.
- Although conventional geodetic measurements were made in the past showing a consistent deformation pattern in the region, these measurements have relatively large uncertainties. In contrast, GPS, as a modern geodetic technique, provides the best means for deformation monitoring: higher accuracy, lower cost, more efficient, and near-real time.
- To measure local variations in strain rate that might reveal the mechanical properties of earthquake faults.
- In the event of an earthquake, to measure permanent crustal deformation not detectable by seismographs, as well as the response of major faults to the regional change in strain. These scientific purposes and the network design were developed through several collaborative workshops, as well as by meetings and extensive committee work. Despite the considerable logistical constraints on sitting, the design of the network remained driven by the scientific intent. Data from all IPGPSN stations are freely available on-line, as are coordinate solutions, periodic velocity solutions, and other products. Users of data and products are asked to simply acknowledge IPGPSN and its sponsors.
Fig. 7. Proposed distribution of permanent GPS receivers (shown by blue star) in the country for Iranian Permanent GPS Network is being established by National Cartographic Center(NCC) in collaboration with Geological Survey of Iran(GSI).
2. Central Albourz Geodynamic Network (CAGN)
- Prediction and assessment of earthquake hazard potential: moment rates, Geologic, Seismic, Geodetic.
- Monitoring of the active structures using interferometric method (SAR).
- Applying chronological methods (cosmogenic, luminescence etc. ) to active tectonics
- Geodynamics and Tectonics of Makran Accretionary Prism (MAP project).