JOURNAL OF GEOMATICS SCIENCE AND TECHNOLOGY
Year:2013 | Volume:3 | Issue:2|Papers Count:8

To estimate the unknown parameters in a linear model in which the observations are linear functions of the unknowns, one of the conventional methods is the least-square estimation. The best linear unbiased estimation (BLUE) is achieved when the inverse of the variance covariance matrix of the observables is considered as the weight matrix in the estimation process. Therefore having a realistic assessment of the precision of the observations is an important issue. One of the methods to reach this goal is the use of the least-square variance component estimation (LS-VCE). However, in this method, it is not impossible to estimate negative variances. But, they are not acceptable from the statistical point of view. In this paper, numerical methods such as genetic algorithm and also iterative methods based on LS-VCE are presented for non-negative estimation of variance components. By using non-negative variance components estimation methods not only one guarantees the non-negative variance components but also one can investigate to incorporate different noise components into the stochastic model. Those components that are not likely present are automatically estimated zeros. In this paper, using the above-mentioned methods, we assess the noise characteristics of time series of GPS permanent stations. The data used in this research are the coordinates of IGS stations located in Mehrabad-Tehran and also two other stations in Ahvaz and Mashhad (2005-2010). To deal with this amount of data, the iterative methods are superior over the numerical methods such as the genetic algorithm. The results indicate the noise of GPS position time series are a combination of white noise plus flicker noise, and in some cases combined with random walk noise.

Ray-tracing is a solution for tropospheric delay estimation, which recently has found an important role in space geodesy techniques. There are different data sets, which can be considered as input of this method, for example numerical weather models, rdiosonde observations and direct measurements. We have developed a constrained ray-tracing method for estimation of tropospheric total delay based on surface meteorological parameters, radiosonde observations and numerical weather models. We show results of two different methods (regional and zonal) and compare with ray-tracing using only numerical weather models. We can find that discrepancies between these methods come mainly from no hydrostatic component, which means uncertainty in wet observations. In addition, as validation of methods, we compare our results with results of a comparison campaign, which was carried in first half of 2010 under umbrella of the IAG working group 4.3.3. The comparison shows an agreement between results, particularly in terms of slant factors.

This paper evaluates moving objects database (MODs) data models and data structures by focusing on history management approach for MODs. MODs algorithms and their complexity are being discussed. By introducing benchmarks as conventional tools for comparison of MODs, we use queries and data utilized within Berlin Mod benchmark for evaluation and analysis. Finally, we propose methods to enhance queries performance.

In most applications of GPS time series, white noise is considered as a covariance matrix, while over 20 years of GPS time series, white noise is not enough for unwanted signals and on the other hand white noise is unavoidable part of realistic noise model. Selecting of a prepare noise model assure us to considering all unwanted signals which GPS have been involved during its time series. In order of comparison between two modes, white noise and realistic noise, we considered one of the most important of application of GPS time series. For this purpose, strain analysis was selected, but, in additional of considering noise model, for better comparison, we introduces Normalized Strains which could help us for the comparison in two different states, realistic noise and white noise. California Network with more than 10years continuous GPS data with proper density is appropriate criteria to assessment of efficacy of time series duration and No discontinuity GPS data on final results. Beside, Azerbaijan Network is one of the most regular and most dense of Iranian Networks which its obtained noise model can be considered as Iranian Geodynamic Network’s noise model. By comparing of these two networks results, there are some useful suggestions to improve the Iranian Geodynamic Network’s future outcomes.

To investigate Caspian Sea level changes, sea surface height (SSH) data obtained from satellite altimeters, Topex/Poseidon, Jason1 and Jason2, between 1992 and 2011 were used. The data between 1992 and 2002 were obtained from T/P, between 2002 and 2008 were obtained from Jason1, and between 2008 and 2011 were obtained from Jason2. Finally, in almost 19 years, 9 passes and in average over each pass 680 cycles of data have been observed. According to this fact that the orbit of these satellites in the mentioned years are the same, time series for the points over passes have been produced. Time series on points over passes and in the crossover of passes have been produced and Least Squares Spectral Analysis have been performed on them. For further comparison and investigation of Caspian Sea level changes, tide gauge records in Neka and Anzali stations have been used. The correlation coefficient between tide gauge time series of Neka and the altimetry time series of one point on Caspian Sea were calculated 0.6663 and for tide gauge time series of Anzali and the altimetry point, correlation coefficient was 0.8198. Between Neka and Anzali, correlation coefficient was 0.7919. Spectral analysis on these time series showed a period of 1 year over all of them. Some of periods such as 6.7 years have been observed in Neka and altimetry that they didn’t exist in Aanzali, that there is no physical justification for them. Between 1992 and 2011 Caspian Sea level dropped about 2.5 cm per year.

Considering ongoing developments in Photogrammetry and Remote Sensing and attending to their applications such as digital true orthophoto generation from high resolution images, have already proven the urgency and necessity of approaches for generating DEM as input of these applications. In this research we describe a novel method for automatic DEM generation. We describe “Semi-Global Matching” algorithm then implement and test it for generating an initial disparity image from high resolution stereo satellite images. Furthermore, post-processing steps for removing outliers, recovering from specific problems of structured environments and the interpolation of gaps are needed, to generate an accurate disparity map. With generating a clear disparity map we can generate 3d point clouds. Then these point clouds are used for generating a precise DEM for other applications.

With the appearance of the satellite altimetry in 1973, a new window was opened in the oceanography, marine sciences and Earth-related studies. Advances in the sensors technology and different satellite altimetry missions in the recent years led to a great evolution in geodesy and the gravity field modeling studies. Satellite altimetry provides a huge source of information for the geoid determination with high accuracy and spatial resolution. The information from this approach is a sufficient alternate for the marine gravity data in the high frequency modeling of the Earth’s gravity field in marine areas. Marine gravity observations always carry a high noise level due to the environmental effects. Moreover, it is not possible to model the high frequencies of the Earth’s gravity field in a global scale using these observations. The gravitational gradient tensor, as the second order spatial derivatives of the gravitational potential, provides more information than other measurements from the Earth’s gravity field such as the gravity anomaly. In this paper, a new approach is introduced for the determination of the gravitational gradient tensor at sea level based on the satellite altimetry and using two modeling techniques, namely radial base functions and harmonic splines. As a case study, the gravitational gradient tensor is determined in Persian Gulf based on the satellite altimetry data, and the results are presented. By the investigation of the results for the gravitational gradient tensor, it is concluded that modeling of the Earth’s gravity field using radial base functions leads to better results compared to the modeling based on the harmonic splines.

Urban land-use expansion is a challenging issue in developing countries. The expansion usually deteriorates other land-uses such as agriculture and natural resources. Urban expansion is unavoidable, thus, urban planners are always estimating the optimum regions for development. Due to the spatial component of this issue, GIS is widely used. The complexity of urbanization may not be well-handled using simple GIS functions such as overlay. Land-use development may also use advanced functions of optimizations that are integrated in a GIS environment. Such optimization considers numerous conflicting criteria. Even with taking all of the probable assumptions and constraints into account, it is possible that optimum result is not doable. Thus, it is desirable to suggest more than one (semi) optimum solutions. If the implementation of one solution is complex, other ones should be examined. In this study, Modeling to Generate Alternatives (MGA) is used to determine the best sites for future urban land-uses in the vicinity of Qazvin with 1620 squared kilometers. This method which is based on linear programming (binary integer programming) can result in proper alternatives. The characteristic of the performed method is the use of Density- Based Design Constraint (DBDC) as a constraint that guaranties the contiguity and compactness of the suggested sites and prevents scattered developments. The results of this study not only offered the optimum sites for future urban land-use developments but also determined some other options to be chosen if the optimum solution is not admired.