فصلنامه رادار
سال دوم شماره 2 (پیاپی 4، تابستان 1393)

In this paper, SAR image enhancement and segmentation have simultaneously been considered. Speckle noise inherent in SAR images, is the most important problem for segmentation of these images. Speckle is a multiplying noise with high damaging power which produces intensity inhomogeneity. As a result, usual segmentation methods cannot be applied on SAR images. In this paper, a combinational method is used for SAR image segmentation in order to benefit from the advantages of the pervious techniques and improve their performance. The method uses a suitable feature based on normalized cumulants which is independent of pixel intensity. Also, an image base method is used to model the intensity inhomogeneity resulting in speckle noise reduction. To evaluate the proposed algorithm, it has been tested on a set of simulated and real SAR images. Experimental results applied both on synthetic and real images demonstrate the effectiveness of proposed method.

In this paper، Bam post-seismic deformations during 7 years after earthquake have been extracted using Persistent Scatterer Interferometry technique. Deformation time series have been extracted using the method of constant scattering interferometry techniques. The results illustrate that the maximum amount of uplift and subsidence displacements in Line Of Sight direction during 2004 to 2010 after the earthquake are and centimeters، respectively. The time series are inverted for the afterslip distribution on an extension of the coseismic rupture. The estimated post-seismic slip value is 20. 45±0. 38 cm. Most of the post-seismic displacement field can be explained in terms of fault slip which is the most likely mechanism involved in the post-seismic deformation in the Bam earthquake. The results of post-seismic motion modeling indicate that the poroelastic rebound can be detected using the Line-Of-Sight data and the effect of viscoelastic relaxation in post-seismic displacement is negligible.

Because of having good performance in cancelling the clutter echoes, pulsed-doppler radar is the best solution to some applications. In this paper a new algorithm is developed for signal design and signal processing in high PRF radar. The robust Chinese remainder theorem is the basis for estimating the unambiguous ranges in the proposed algorithm. Two high PRF pulsed-doppler radars are designed to analyze performance of the proposed algorithm. By using mathematical calculation and simulation study, it is shown that it is possible to estimate the unambiguous range in the long range high PRF radars. In this paper, the eclipsing loss, which is the inherent problem in high PRF pulsed-doppler radars, is investigated in more details. Also a method is suggested to overcome the difficulty that the eclipsing loss causes.

The radar tracking is one of the best LEO satellite tracking methods. While Since the tracking filters which are mostly linear, and are not able to have a precise estimation of the objects with nonlinear motion dynamics such as satellite, we should use nonlinear filters. In this paper, firstly, we deal with the problem of the LEO satellites motion path modelling according to the satellite motion emulation with the Cowell equations. Then the observations will be separately fed to non-linear Extended Kalman Filter as well as Unscented Kalman Filter and with studying the RMS position estimation error, their performance for satellite tracking will be evaluated. Simulation results demonstrate that the UKF filter has a better performance in terms of accuracy in comparison with the EKF.

In this paper, the results of design and implementation of the laboratory subsystems are proposed for generating Loran pulse are proposed based on method of carrier’s pulse width change. In order to generate the desired pulse, a PWM signal is generated proportional to output voltage energy in each half-cycle and then it is applied to a class-D switching amplifier. The results show that by generating appropriate pulses in a digital FPGA subsystem for application in switching devices. It is possible to generate Loran pulse using only a single class-D amplifier, and the observed current in the load has the required standards for Loran transmitter. According to the performed measurements and calculations, the maximum zero crossing error in 4th to 12th half-cycle is 45ns and the band width of generated pulse will be 4 kHz. Moreover, MMSE and maximum error of peak points are 0.0092 and 0.025 in 8 first half-cycles, respectively, which they have fulfill the required standards of Loran pulse.