The Iran plateau is located on the earth dust belt. It always has been subject to different dust activities and dust storms that mostly had been originated from dust sources which are located outside of the plateau. Recently we reported that the Mesopotamian region is responsible for more than 80 percent of observed dust events in Northwest Iran. In this work we have used the available aerosol optical dept (AOD) on the MODIS deep blue and the surface soil moisture data (SM) extracted from GLDAS version-1 data set, to look over the evolutions of dust activities and variations of soil moisture in the Mesopotamian region during 2001 to 2012. Recorded monthly values of AOD indicate that most of the annual dust activities had been occurred during April to July but the soil moisture had had its maximum values during December to March. During the considered period of time in this study, dust activities in Northern Mesopotamian area (centered about 35 E, 42 N) have been strengthened considerably and the center of dust activities has been moved about 0.5 degrees to North and the same amount to East. Looking to the annual trend of the AOD (SM) averaged over the months April, May, Jun and July (December, January, February and March), a trend of ~0.030 ± 0.004 (~0.033 ± 0.002 kg/m<sup>2</sup>) per year has been observed for the mentioned time span. Also temporal correlation between annual values of obtained AOD and SM has been investigated in this work. It is found that a strong negative correlation exist between these two parameters and its minimum value (-0.7) occurs when both AOD and soil moisture have been measured in the same year.
The refractive index profile of optical fiber preform is measured by a nondestructive technique based on Talbot interferometry. In this technique the preform is placed between two ronchi ruling gratings of 10 lines/mm and the system is illuminated by an expanded and collimated beam of He-Ne laser. In this arrangement the 2nd grating is positioned in the Talbot image of the 1st grating and the preform axis is parallel to the gratings planes. To eliminate the effect of clad on the light beam deflection during the measurements, the preform is immersed in an index matching liquid. The phase front of the laser light over the 2nd grating can be monitored by analysis of the moire pattern which is formed over there. The analysis is done by means of 4-step phase shift technique. In this technique the second grating is moved in four steps of 1/4 of the grating vector and in each step the intensity profile of the moire pattern is recorded. The phasefront can be specified by using the recorded intensities. The refractive index profile of the preform can be calculated from the changes on phasefront while the preform is placed between the gratings respect to the case when it is absent. The whole procedure is automated and computer controlled by using a CCD camera to record the moire fringes, a stepper motor for linear translation of the 2nd grating and a code in MATLAB to control the system and measurements.
Cloud altitude measurements by a 532nm backscatter Lidar and time lapsed digital photography are combined to monitor the cloud velocity profile. The cloud images are recorded in time steps of two seconds by a Nikon D100 digital camera through a 63° solid angle while the Lidar was measuring the cloud altitude. The images are recorded in 8 bits gray scale JPG format in an array of 2240×1488 pixels. To measure the angular displacement of different parts of the cloud, each image is meshed into an array of 44×29 cells, each cell contains 50×50 pixels. The grayscale density cross correlations between similar cells of successive images are computed using a MATLAB code developed by us for this application. The output products are the direction and the amount of displacement of each cell, in pixels. combining the results on cloud displacement with Lidar measurements enable to calculate the velocity vector in each cell. The resolution in velocity is about 1 ms<sup>-1</sup> and 2° in direction. The calculation technique also is tested by simulating the cloud motion by moving the image pixels with a computer generated Gaussian velocity distribution.
It is shown that when a part of a wave-front bears a sharp change in its phase, the Fresnel diffraction becomes noticeable. To change the phase sharply, one can reflect the wave-front from a step or transmit it through a transparent medium having a sharp change in its thickness or refractive index. The visibility of the corresponding diffraction fringes depends on the amount of phase change and can be varied from zero to one. Since the phase change can be accomplished by various means, the effect renders to measure phase change, refractive index change, displacement, and so on. Here, the change of visibility is the measurement criterion, therefore the fluctuations of the source intensity do not affect the measurement precision. In this paper Fresnel diffraction from one dimensional step, circular step, and single strip are studied, and some of its applications are briefly discussed.
In this work we have introduced a new interferometric technique for measuring the nonlinear refractive index in different samples. Adopting a holographic point of view we have developed a mathematical theory for this technique which is based on the propagation of a Gaussian wave through a small phase aperture.
Fresnel diffraction from a step, in reflection and transmission modes is studied. The study shows that the resulting diffraction pattern is similar to that of a semi- infinite obstacle, but the intensity distribution near the step edge is very sensitive to the step height and is a periodic function of the height. Therefore the effect can be exploited for measuring the heights and optical path differences of the coated films, strips, and small displacements.