Year:2007 | Volume:40 | Issue:8 (102)|Papers Count:10

In this paper a new approach for producing precise hydrographic charts is addressed. This goal is achieved by solving the problem of removing tidal and heaves effects from hydrographic depth sounding without applying costal tide gauge observations which could be quite erroneous at places with complicated tidal regimes like the gulfs. Two driving forces of our machinery are (1) precise 3-D GPS positions during the hydrographic operations, and (2) application of tidal models derived from satellite altimetry missions. For the precise GPS positioning double difference carrier phase observations can be used. The tidal models derived from satellite altimetry could be used to compute precise Local Chart Datum (LCD). Here we define the Local Chart Datum as the lowest sea water level due to tide at the sounding point. Having, (1) the precise position {λ,φ,h} of depth sounding transducer, (2) measured depth d from sounding, the local chart datum CD h can be derived for the coordinates {λ,f,h} of sounding location, by using the tidal model derived from satellite altimetry. Next, using the aforementioned pieces of information the sounding depth with respect to local chart datum CD h can be derived as follows: dcd =d−h+hcd . It is important to note that in this way we are not only reducing the soundings to the chart datum, but also removing the effect of heaves during the sounding process. This procedure, specially, in waterways connected to oceans, and with low depth of water, like Persian Gulf can be very helpful for producing accurate and reliable hydrographic charts. As the case study, 11- years of Topex-Poseidon satellite altimetry data is used to produce a hydrographic chart for a test region at Persian Gulf. It is important to note that the average depth in Persian Gulf is 20 meters and the tide effect in some places can reach to 4 meters, therefore could be regarded as challenging test areas for improving the water depth information presented in a hydrographic chart. Our numerical tests indicate a considerable improvement in the produced hydrographic chart based on our proposal. In summary, main achievements of this study could be listed as: (1) removal of the heave effect from the soundings, (2) removal of the tidal effect from the soundings, and (3) a new proposal of definition of chart datum, i.e. Local Chart Datum.

Tide is the main deriving force of sea level variations. Accurate information about tide is needed for oceanographic studies, correction of satellite altimetry observations, removal of tidal effect from the observations of superconducting gravimeters, and removal of tidal effects from the geographical coordinates computed by Global Navigation Satellite Systems (GNSS) and the heights by precise leveling. Engineering activities at sea, such as building harbors, offshore oil platforms, placing under water pipelines, and many other applications require accurate knowledge about sea level and currents, which could not be derived without having a thorough knowledge on tide. The information about the tide, currents and seawater circulations are also of great importance for sea navigation. Due to importance of tidal information, analog computers are developed especially for tidal analysis, years before the advent of electronic computers. At the coastal area, tidal information can be obtained by coastal tide gauge stations. However, at the offshore there is not such possibility. There are various methods for offshore sea level measurements, but among  them satellite altimetry is proven to be the most efficient one. Altimetry satellites are providing sea level variations in global scale and therefore are widely used in oceanic sciences. Modern altimetry satellites are equipped with range measuring instruments, which can measure the distance between satellites to the sea surface up to few centimeters accuracy. Thanks to positioning systems such as SLR, GPS and DORIS the geocentric position of the altimetry satellites can be determined to a very high degree of precision, that is why altimetry satellites are nowadays so versatile in oceanic sciences. In this paper we are aiming at a global 4-D time and space tidal model by taking advantage of high quality satellite altimetry data. The constant and the harmonic parts of the global ocean tide are modeled up to 9 major tidal constituents, namely, S2, M2, N2, K1, P1, O1, Mf, Mm, and Ssa. The computations are started by the Fourier sine and cosine series expansion for the aforementioned tidal constituents including the constant part, while the frequencies of the tidal constituents are considered known, and the coefficients of the sine and cosine functions are assumed as unknown quantities. Next, the coefficients of sine and cosine functions as well as the constant part of the Fourier expansion are expanded into spherical harmonics up to degree and order n , where n corresponds to the number of linearly independent spherical harmonic base functions needed for the modeling of the tidal constituents, determined via independent columns of the Gram matrix. The unknown coefficients of the spherical harmonic expansions are computed using sea level observations within cycles 1-350 of the Topex/Poseidon satellite altimetry during 11 years of its mission. A set of orthonormal base functions is generated for the sea areas covered by Topex/Poseidon observations from the spherical harmonics by Gram-Schmidt orthogonalization process and used for modeling the aforementioned tidal constituents. The computed models based on orthonormal base functions for the 9 tidal constituents and the constant part of the Fourier expansion, are tested numerically for their validity and accuracy. Numerical tests proved centimeter accuracy of the computed tidal model. The major contributions of this work can be summarized as: (1) Number of tidal constituents, determined from the satellite altimetry observations. (2) Use of orthonormal base functions at the sea area to present MSL and tidal constituent models.

Clear and justifiable analysis and decision making approaches play critical roles in acceptability of the results by managers and decision makers for optimum information management. This research follows these fact in providing a suitable spatial decision making approach for weighing earthquakes' vulnerability.We developed the well known analytic hierarchical process (AHP) method using basic concepts of fuzzy logic to overcome AHP's high sensibility against uncertainties in an earthquake vulnerability study. The mentioned development is carried out by substituting the simple binary questions in contemporary AHP questionnaires with three-value fuzzy questions. It enabled us to define a triangular fuzzy membership function for the questions. The simple fuzzy structure is adopted here to ensure the least perturbation of intrinsic simplicity of AHP method. Then the relevant analyzes of the AHP are replaced with their fuzzy counterparts.  The method has been implemented in this research for weighing of human-loss related vulnerability factors in city of Tehran. Buildings' condition and population are considered as the main factors. The buildings' condition is defined by age, structure and number of floors. These factors are categorized as follow:• Building age: Built before 1966, between 1966 and 1975, and after 1975 University College of Engineering, University of Tehran 3 • Building structure: Very weak, not stabilized, stabilized, and highly stabilized • Building floor number: 1 to 3, 4-15, and more than 15 floors These factors are evaluated for three earthquake scenarios as follow:• Scenario A: A weak to strong earthquake• Scenario B: A strong to severe earthquake• Scenario C: A severe to fatal earthquake The questionnaires were filled by twelve experts in seismology, geology, civil engineering and building structure. The results were analyzed by the contemporary AHP method and the modified one presented in this paper. Analogy of these results showed that the proposed modified AHP has been successful in reduction and absorption of uncertainty. Besides that, interpretation of the results of the proposed approach is closer to objective parameters which can be evaluated by the concerned managers. It also provides our desired level of clarity and justifiability, mostly preserved from AHP as well as considering the concepts and effects of spatial uncertainties in the achieved results.

This paper presents behavioral aspect of the spatio-temporal databases for managing and querying moving objects. The objectives of this paper are to evaluate the current states of the Object-Relational Database Management System and extend the selected system in such a way to support modeling and querying moving objecs. More than thirty five paprameters have been identified to evaluate the existing DBMSs namely; Oracle10g, DB2, MS SQL Server, MySQL, and Postgre SQL. Spatial and Temporal data models are assessed and the needs for a novel spatio-temporal data model have been recognized. It is concluded that the existing DBMSs lacks the required capabilities for handling moving objects. The optimum platform for extending the spatiotemporal capabilities is identified as Oracle10g. The developed extension supports spatio-temporal objects that change position or extent continuously as well as all pure spatial and temporal data types. In this research an extension to the selected DBMS has been developed using C++ language that supports moving objects. In order to examin the developed system, the querries posed by fleet management companies are selected. The results have been evaluated and showed the superior functionalities of the system. The resulted system supports a wide set of object methods that extend Oracle’s query language PL/SQL with spatio-temporal semantics. Throgh many practical examples, it has been shown that applications such as vehicle tracking can be handled more efficiently, as temporal queries can be answered directly. This research concerned only 2-Dimensional spatial objects as well as the change and motion of such geometries in the 2D Cartesian plane.

Tin Plate Spline (TPS) firstly introduced by j. Duchon (1976). These days TPS have been found so many uses, as an example, geophysical applications in aeromagnetic & gravimetric surveying, modeling of fingerprints, medical researches, converting elevation contours to a grid. In this paper, we used TPS for constructing digital elevation model.Thin plate spline is a physically based 2D interpolation witch represents a thin metal sheet that is constrained not to move at grid points and free from any external force relied upon control points from this sight it should have minimum bending energy in control points. This bending energy function is show as follow:I[¦(X,Y)]=òRò2¦2XX+2¦2XY+¦2YYThat f represents a height in 3D model. This equation is invariant under translation, rotation, or scaling of either set of control points, support second norm of surface and when it is minima it means that bending of surface in control point got to be minimized and slope variation in tangential plates reduced to minimum.From another point of view Thin Plate Splines as an approximation of a real surface of control point must cross this points as near as possible. Therefore a constraint of distance between control points and the surface also must have been minimized. We showed that the TPS as density independence method can be used for construction of surfaces in new brand geomatics because of miscellaneous of data sources and difference in their density’s, note that weights is always of concern of surveys. From other side using TPS, without Voronoi algorithms whereby produced limitations in number of control points and reduce speed of operation, one can create a surface in contrary to other surface simulation methods such as BS plines all at once. Because of density independence mathematical form of straigh method, one can use it in CAD/CAM softwares.It is certain that independency of density must to be of specifications of thin plate spline thus purpose other research on other solutions of TPS. Because at least one can prove that in dense and bare zones it can be used with comparable error results. By results of this article we purpose using of TPS for mountainous-flat areas because variations of one zone don’t affect other zones so much.

Advances in 3D data-acquisition hardware have facilitated the more widespread use of scanning to document the geometry of physical objects for archival purposes or as a step in new product design. A typical 3D data acquisition pipeline consists of the following steps:canning: Acquisition of surface samples with a measurement device, such as a laser range scanner or a stereographic system.Data registration: Alignment of several scans into a single coordinate system.Data integration: Interpolation of the measured samples, or points derived from the measured samples, with a surface representation, usually a triangle mesh.Model conversion: Mesh decimation/optimization, fitting with higher-order representations etc.This paper focuses on the data integration phase. We present a method for finding a triangle mesh that interpolates an unorganized set of points. The method is α-shapes. An α-shape is a polytope that is neither necessarily convex nor connected and can be derived from the Delaunay triangulation of the point set, with a parameter controlling the desired level of detail. The set of all values leads to a discrete family of shapes capturing the intuitive notion of "crude" versus "fine'' shapes of a point set.The main application of α -shapes is the reconstruction of objects which have been sampled by points. For instance, a 3D-scanner provides points on the surface of a humanbeing or so.In this paper we used the α-shapes for reconstruction of a Digital Terrain Model (DTM). Delaunay interpolation method is usually used as an approach for reconstruction a DTM. This algorithm has some limitations in expression of complex objects for example break lines in DTM. Therfore α-shapes can be improved the limitations and fill the gapes derived from delaunay interpolation.

Shortest path selection is known as one of the most important functions in geo-spatial information system (GIS) network analysis. It is classified into two types; one is single criterion shortest path problems (SSP) and the other is multi-criteria shortest path problems (MSPP). The current GIS usually confronts the University College of Engineering, University of Tehran 5 lack of powerful tools in spatial analysis for MSPP, so the suitable solution for MSPP is one of the current major needs for GIS. Urban multi-objective optimized routing problems are called both NP-Hard problems and one of the branches of MSPP.Algorithmic and approximation schemes are available to solve MSPP; unless they meet some problems such as the complexity of these approaches often prohibits their implementation in large urban route networks, they are limited to a few numbers of criteria, each criterion is independent with no weight of importance and it is needed to select one solution from Pareto-optimal solutions. These categories of optimization problems can not be solved practically and therefore an approximation of the general optimum has to be considered.During the last decades, genetic algorithm (GA) has been one of the most important references in artificial intelligent (AI) for multi-objective complex optimization problems. By proposing a novel approach on the bases of route guidance navigation system principles, virus theory (viral infection and local infection) and by GIS and GA utilization, this paper is come up to rate search improvement in urban multi-objective routing problems on real networks with multiple dependent criteria. For the purpose of the innovative approach capability proof, it has been discussed the achieving results in each step of approach improvement from generic GA to proposed an innovative approach in a case of four experiments. As in the first experiment, we have done generic GA design and implementation for quasi multi-objective optimal urban route selection. In the second experiment, generic GA is improved due to Minimal Generation Gap (MGG) model utilization. In the third experiment, virus theory and viral infection improved the second experiment and finally in the fourth experiment by adding local infection we have come up to third experiment improvement.Moreover, all these experiments have been implemented in a part of North-West of Tehran traffic network by considering and modeling four criteria of route including length, time, congestion and degree of difficulty.Accepting unlimited criteria, being "range (scale)-independent ranking" method, taking the "importance" of each objective chosen by driver, utilizing priority knowledge with viral infection and local infection, converging GA to "best compromise" solution and proposing a quality metric for assessing the best compromise solution are the major characteristics of this innovative approach. Furthermore, the achieved results ineach step of the algorithm improvement, from generic GA to novel approach are the evidences of high capability of the proposed method.

With the ever increasing the number of remote sensing satellites, advances in data fusion and the functionality of modern geographic information systems, the use of multi-image spatial information products is swiftly becoming commonplace. However, in order to meet the requirements of the user, each individual image making up the multiimage product needs to be expressed in the same geometric reference frame. This means the images have to be accurately registered to geodetic co-ordinate system (e.g. Digital maps).Automatic Geo-Referencing involves a search to find the transform that yields the highest similarity between the input and the Geo-Referenced data. It has been known that there is no single best registration technique for all types of data and applications. Due to the tremendous complications and complexities associated with the natural scenes appearing in satellite imageries and digital vector maps, fully automatic Geo-referencing process have faced serious obstacles and thus, only in a relatively simple imaging environment a reliable result is normally expected.Proposed registration procedure of this paper matches satellite images with GIS data of the same scene that have been taken at different times, geometric structure and data types. The present approach is designed to be completely independent from the sensor type and any a prior information on the exterior orientation.The overall strategy for our proposed registration method may be expressed by the following interrelated three phases:1- Multi-resolution Representation2- Feature Extraction3- Registration based on Genetic algorithm.In this method, key features (salient points, intersections, and corners) in the reference and data based have been detected based on a multi-resolution representation of information. By construction of image and feature pyramids, in this stage, for each feature in the left feature pyramid, based on corresponding mathematical model, a search area is constructed on the corresponding right feature pyramid. Now to identify the conjugate features the Genetic algorithm is employed. The Genetic algorithm starts with the selection of population of features followed by the determination of a so called criterion function which can comprise different similarity measures (e.g. geometric discrepancy). Using this criterion function a new population is constructed by decomposition of the old population using a so called Cross-Over operator. The procedures are repeated until a small subset of the population with a specific pattern best satisfies the criterion function. The main advantage of Genetic algorithm is its fast rate of convergence compared to the other searching methods.The potential of the proposed method is evaluated using IKONOS imagery and corresponding digital map in the urban and suburban area of Tehran City. Registration process is performed hierarchically using five– layer pyramids.The proposed automatic registration method discussed in this paper, has proved to be very efficient and reliable for automatic registration of different satellite imageries with GIS data.The implemented methodology has the following characteristics:• Utilization of a multi-resolution representation of information and mathematical models.• Employing a Genetic algorithm for conjugate feature identification and modeling.In spite of the success which is gained in the implementation of the presented method, the topic by no means is exhausted and still a great deal of research works are needed. These research works should be focused mainly on the development of a more sophisticated Genetic algorithm, interest operator and matching strategy. All of these are currently under investigation in our institute.

Short-time detection and forecasting of fog and low stratus clouds have wide application in aviation. Meteorological satellites have created vast hopes for meteorologists. The present number of observing stations in land and sea are not adequate in determination of actual fog corona. To compensate for the lack of information, deployment of remote sensing technology especially at nighttime seems necessary. During the daytime, due to the high contrast of fog and low St Albedos, their detection is relatively simple. In the nighttime and in the absence of sunlight, however, the contrast due to thermal radiation and consequently different brightness's could be a tool in distinction of these kinds of clouds.Due to the same temperature of fogs and land surfaces, their distinctions in the thermal channels are not always possible. Consequently, differences in their spectral emissivities will be used in distinguishing fogs from land and water surfaces.In this research, five techniques in detection of fogs and low clouds using different channels of SEVIRI sensor on board of Meteosat Second Generation (MSG-1) have been offered. These techniques are 1- Brightness Temperature Difference Technique, 2- Band 4 and 5 day and night technique, 3- Daytime band 1 and 3 indices, 4- Ratio of band 3 to band 1 and band 9 during the daytime, 5- Ratio of band 4 to band 1 and band 9 during the daytime. The percentages of low cloud and fogs coverage in the scene detected in these techniques are 91, 76.8, 81.66, 95.85 and 88.95 respectively.Results of different methods are in an acceptable agreement with each other. As a University College of Engineering, University of Tehran 7 result, 2nd technique for the nighttime and 4th technique for the daytime is recommended.A satellite of this kind will be flying soon over Indian Ocean over 63E longitude on a geostationary orbit, that the use of its images in extracting meteorological parameters over Iran’s plateau is strongly recommended. In this paper, a new method for detection of snowcovered surfaces is also introduced.