Remote sensing
Masoud Dehvari; Saeed Farzaneh; Mohammad Ali Sharifi
Volume 15, English Special Issue , May 2022, , Pages 15-24
Abstract
In this research, three-dimensional and four-dimensional tomography is used to demonstrate the distribution of wet refractivity index of the troposphere. In this model, spherical cap harmonics are used for the horizontal distribution of the wet refractivity index, and empirical orthogonal functions are ...
Read More
In this research, three-dimensional and four-dimensional tomography is used to demonstrate the distribution of wet refractivity index of the troposphere. In this model, spherical cap harmonics are used for the horizontal distribution of the wet refractivity index, and empirical orthogonal functions are used for the vertical distribution of the index. The region of study is in the west California State, and the wet refractivity index is retrieved from the wet tropospheric delay measurements. to validate the results, radiosonde profiles were compared to the tomographically retrieved profiles. The result shows that wet refractivity indices can be retrieved using functional models with RMSE about 2.4 ppm till 3.9 in four-dimension method. The comparisons show that the four-dimensional retrieved profiles shows improvement up to 34 and 42 percentage in mid-day tomography epochs compare to three-dimensional tomography results. Also it can be seen that in mid-night epochs three-dimensional tomography has higher accuracy compare to four-dimension method because of low variation of wet refractivity indices
F. Nobakht-Orsi; M. A. Sharifi; A. R. Safari
Volume 4, Issue 1 , July 2011, , Pages 15-22
Abstract
In this paper, Hilbert Huang transform (HHT) for time series analysis of the status of permanent GPS stations can be provided. Hilbert Huang transform and its, related spectrun is a new method for the analysis of nonlinear processes.This method represents not only a precision analysis in the time-frequency ...
Read More
In this paper, Hilbert Huang transform (HHT) for time series analysis of the status of permanent GPS stations can be provided. Hilbert Huang transform and its, related spectrun is a new method for the analysis of nonlinear processes.This method represents not only a precision analysis in the time-frequency space, but also it declares the physics of the dynamic processes. This method has two speps. At the first step, the data is disintegrated into IMF elements by EMD method. At the second step Hilbert transform is applied for IMF elements and distribution of the time-frequency –Hilbert energy spectrum is then determined. In this spectrum, Location, frequency and energy defined by time events for the Hillbert transform will be reserved. So instantaneous frequency will have a major role in this method.
M. A. Sharifi; F. Samadzadegan; Saeed Saeed Farzaneh
Volume 2, Issue 2 , July 2009, , Pages 27-38
Abstract
Celestial positioning has been used for navigation purposes for many years. Stars as the extra-terrestrial benchmarks provide unique opportunity in absolute point positioning. However, astronomical field data acquisition and data processing of the collected data is very time-consuming. The advent of ...
Read More
Celestial positioning has been used for navigation purposes for many years. Stars as the extra-terrestrial benchmarks provide unique opportunity in absolute point positioning. However, astronomical field data acquisition and data processing of the collected data is very time-consuming. The advent of the Global Positioning System (GPS) nearly made the celestial positioning system obsolete. The new satellite-based positioning system has been very popular since it is very efficient and convenient for many daily life applications. Nevertheless, the celestial positioning method is never replaced by satellite-based positioning in absolute point positioning sense.The invention of electro-optical devices at the beginning of the 21st century was really a rebirth in geodetic astronomy. Today, the digital cameras with relatively high geometric and radiometric accuracy has opened a new insight in satellite attitude determination and the study of the Earth’s surface geometry and physics of its interior, i.e., computation of astronomical coordinates and the vertical deflection components. In the automatic star detection, high precision and reliable in extraction of the star’s centers from the captured images and corresponding them with the astronomical coordinates is the most important point. In this article, the star’s centers are extracted by the advanced image processing technique with sub-pixel precision. Relating the parameters of the presented technique to star’s Mag is one of it’s exclusive properties
