جستجوی مقالات مرتبط با کلیدواژه « interferometry » در نشریات گروه « فنی و مهندسی »

Metal and especially aluminum mirrors have wide applications in the optical industry due to their desirable properties, hence requiring very high polished surfaces. One of the methods of preparing aluminum mirrors is single-point diamond turning. In this research, the manufacturing process of 6061-grade aluminum mirrors has been studied using diamond turning and consequent polishing process in order to reach surfaces with acceptable optical properties. In the first part, the effective range of turning parameters was determined. The results showed that the feed values less than 5 µm/rev, the cutting edge radius between 0.2 and 0.8 mm, and the rotational speed of 2250 rpm have a greater effect on the surface roughness. In the second part of the research, initially, the turning process was performed with effective parameters and then the polishing process was applied as the final finishing process. Surface finish is evaluated by surface roughness and surface interferometry parameters. The results showed that the smaller surface roughness after the diamond tool turning process led to higher optical properties after the final polishing process. The lowest PV value equal to 0.293 µm was obtained by diamond turning with 1.5 µm/rev and a cutting edge radius of 0.8 mm.

Metal and especially aluminum mirrors have wide applications in the optical industry due to their desirable properties, hence requiring very high polished surfaces. One of the methods of preparing aluminum mirrors is single-point diamond turning. In this research, the manufacturing process of 6061-grade aluminum mirrors has been studied using diamond turning and consequent polishing process in order to reach surfaces with acceptable optical properties. In the first part, the effective range of turning parameters was determined. The results showed that the feed values less than 5 μm/rev, the cutting-edge radius between 0.2 and 0.8 mm, and the rotational speed of 2250 rpm have a greater effect on the surface roughness. In the second part of the research, initially, the turning process was performed with effective parameters and then the polishing process was applied as the final finishing process. Surface finish is evaluated by surface roughness and surface interferometry parameters. The results showed that the smaller surface roughness after the diamond tool turning process led to higher optical properties after the final polishing process. The lowest PV value equal to 0.293 μm was obtained by diamond turning with 3 μm/rev and a cutting-edge radius of 0.8 mm.

Determining the third dimension of the underwater targets, by the sonar system, can play an important role in three dimensional imaging and target recognition. In this paper, by applying the inverse synthetic aperture sonar and using the seabed virtual source and a second sensor, the third dimension of the targets is obtained. For obtaining the third dimension, we use the distance between the scatterer and its two main corresponding artifacts in the two dimensional image. In the case of having two sonar systems, with both the transmitting and receiving roles, the third dimension resolution is increased obviously, compared to the monostatic case explained in our previous paper. In addition, because of having these two sensors, more target scatterers will be in the view of sensors. By using the information obtained in this way, it is possible to achieve more accuracy in calculating the third dimension and create a three-dimensional image of the target.  Because of the importance of the underwater monitoring, using the proposed scenario, we can use this system for more accurate identification of the targets to counter the threats and for the defence applications.

Introduction Persistent Scatterer Interferometry (PSI) is a technique to detect and analysis of a network of coherent pixels referred as Permanent/Persistent scatterer (PS) which are stable throughout time-series of SAR images. This technique has been applied to monitor and measure phenomena such as earth subsidence fault movements and earthquake volcanic activity and other geological and environmental studies. In all PSI techniques, the processing is carried out only on the PS pixels. Therefore, high density and phase quality of these pixels are the most effective factors on the results of these techniques. The main challenge of this technique is to detect the coherent pixels over non-urban areas which suffer from the temporal decorrelation. Nowdays and with the development of polarimetric SAR sensors, polarimetric radar data are available. Polarimetric data consist of several conventional SAR acquisitions, usually addressed as channels. Each channel in a PolSAR acquisition is sensitive to different geometric characteristics of the scene. This additional redundancy over the scene may allow to increase both quality and density of the PS pixels. Therefore, the combination of polarimetry and interferometry enables to improve the effectiveness of PSI techniques, especially in non-urban areas. In this paper, we employ a method to improve the conventional PSInSAR algorithm for detecting PSC by using polarimetric optimization method on dual-pol SAR data. The improvement of this research is based on minimizing ADI criterion by means of an Exhaustive Search Polarimetric Optimization method to increase the number of PSCs. Materials & Methods 2.1 Dataset Description   The proposed method is tested using a dataset of 17 dual-pol SAR data (VV/VH) acquired by Sentinel1-A satellite March 2017 and October 2017.    2.2 Polarimetric SAR Interferometry   A general formulation for polarimetric SAR interferometry was proposed in (Cloude & Papathanassiou, 1997). The scattering matrix S represents the polarimetric information associated to each pixel of the scene. Considering a monostatic configuration, the scattering matrix S is defined as follows:   (1) where , are copolar terms,  is the cross polar term. This can be represented with the target scattering vector  using the Pauli basis as: (2) where  is the transpose operator. In Sentinel-1configuration (VV/VH), where there is no knowledge of  , scattering vector  can be written as: (3) In order to generate an interferogram, each target vector  can be projected onto a unitary complex vector  . Result of this step obtains the scattering coefficient μ defined as: (4) where i corresponds to two images, and * represents the conjugate operator. The scattering coefficient μ is a new channel or polarization state which is a linear combination of the Pauli vector elements. In this regard, all interferometry techniques can be extended from single-pol configuration to a desired polarization state by using (4) and (5). The projection vector for dual-pol data defined as:   (5) where  and  are two real parameters whose ranges are finite and known and are related to the geometrical and electromagnetic properties of the targets. The parameter  represents the type of scattering mechanism and  corresponds to orientation of scattering. In our research, the main purpose of polarimetric optimization is to search in a two-dimensional space,  and , to find an optimum projection vector, .   2.3 Amplitude Dispersion Index Optimization   In order to generate a polarimetric form of , it is sufficient to replace scattering coefficient, , in (6) by  as define in (4):       (6)       (7)   The main issue in the ADI optimization is finding a projection vector  for each pixel, which leads to minimize the  value. Results & Discussion Our results confirm that the algorithm substantially improves the PSInSAR performance, increasing the number of PS pixels with respect to standard PSI, and increasing the phase quality of selected pixels. The results reveal that using the optimum scattering mechanism increases the number of PSC about 2.6 times and PS density about 2 times than using single channel datasets. Also, the effectiveness of the method is evaluated in urban and non-urban regions. The experimental results showed that the method was successful to increase the final set of PS pixels in both regions significantly. Conclusion In summary, it can be inferred that the polarimetric optimization method is successful to increase the number of the final set of PS pixels in different regions, significantly.

In this study, the thermal characteristics of two impinging flame jets are investigated. For the flame structure and temperature field analysis, a non-contact method named Mach-Zehnder Interferometry is used. Mach zehnder method is utilized to determine the effective parameters of flame structure in different amount of Reynolds number and equivalence ratio. The hydraulic diameter of the burners is considered 1.3 mm with 20 mm length and 10 mm width. The angle between two burners is 77 degree. The effect of fuel/air ratio is investigated, when Reynolds number is 70 and equivalence ratio varies between 0.8 and 2.5. Maximum temperature and velocity occurs in equivalence ratio of 1 but at this point, increasing of Reynolds number leads to enhance the maximum temperature and at the same time the growth of the maximum temperature domain.

High energy electron beams are one of those ionizing radiation beams that are being widely used in nuclear medicine for treatment of cancerous tumors. However, these beams may also harm the healthy cells in traversing the patient body. Accordingly, knowing the dose distribution in a tissue-equivalent phantom is the main requirement in an electron therapy treatment design. In recent years, great interest is attracted toward the application of digital holography method for accurate three dimensional measurement and monitoring of the absorbed dose. In this work, design and modelling of a mobile dosimetric instrument, which works based on the digital holography principles, are studied and a new approach is developed for measuring the absorbed dose of electron radiation using the digital holography technique with a laser beam. The proposed method for measuring the absorbed dose is also developed to be immune against the environmental noises that are present in difficult situations. Monte Carlo and numerical modelling of the instrument, demonstrate its capability in accurate measurement of the absorbed dose.

Today''s digital elevation models have many applications in various fields including engineering projects and management of natural resources and etc. One of these applications is a topographic correction in InSAR to find the amount and rate of displacements. The purpose of this paper is to compare the effects of two digital elevation models with a resolution of 30 m and 90 m in order to obtain displacement rates from radar images. Persist Scatterer and Small Baselines methods were used to compute the displacement rate in the region. Processing was performed with both models SRTM and ASTER. The maximum difference between the results from two elevation models is observed in areas with a high elevation difference. In both methods، the number of persist scatterers in the case of model ASTER is less than model SRTM. In areas with low elevation differences، the results of two elevation models are very similar to each other. But in areas with high topography، the low resolution elevation model does not have the ability to deliver results with appropriate accuracy. In PS method there are 0. 2 mm difference in maximum and 1. 1 mm in minimum of displacement rate field and in Small Baselines method، these rates were 4 and 1 mm respectively. In order to better evaluate the results، six points in the region were examined. The maximum difference between the results was 4 mm. This difference is significant at the ten percent level of confidence. As a result، in areas of high topography، it is necessary to use the more accurate digital elevation model to achieve higher accuracy.

Nowadays، SAR imaging systems have become more interesting for scientists. high spatial resolution of recent SAR images has become a key factor for their accurate applications such as interferometry، radargrammetry and change detection. In these applications، SAR image matching procedure is a critical step for conjugate point extraction which is much more difficult than the optical images. The main reasons are both high radiometric speckle noise and high geometric distortions defining by layover، shadow، and foreshortening. Therefore، utilizing efficient methods to achieve a more favorable result in the SAR image matching، could help us to get better output in various applications. Among the SAR images، study about TerraSAR-X is so important، because TerraSAR-X sensor acquires high spatial resolution images. In this paper، we used various textural image features including contrast، correlation، dissimilarity، entropy، homogeneity، optimal gradient filter، mean، second moment، variance، high pass filter and edge images. The main aim of our research was to determine how much can these features improve the SAR image matching process? In our experiments، we used a small urban part of pair of TerraSAR-X single-look slant-range complex (SSC) images that were acquired over the city of Jam، southern Iran، in spotlight mode. The result shows that for some image areas with low texture، the conventional image matching algorithm (here Lucas-Kanade’s optical flow) is not able to detect corresponding points، while using the above textural features in image matching process causes to extract appropriate numbers of matched points.

SAR Image matching is a critical step in the radargrammetry, interferometry, DSM Generation and change detection applications of SAR image data. Image matching procedure in these images is much more difficult than the optical images due to high speckle noise and geometric distortions defining by layover, shadow, and foreshortening. Therefore, study on an efficient SAR image matching could be useful. In this paper, a multi-step strategy for this issue is proposed. These steps include SAR image despeckling, point feature extraction, feature allocation, local image matching and global image matching. In the proposed multi-step method we used current algorithms in photogrammetry and computer vision. In each step, several algorithms are experimented and compared to specify the final algorithm for that step. In our experiments, we used a pair of TerraSAR-X single-look slant-range complex (SSC) images with short and long baselines that were acquired over the city of Jam, southern Iran, in spotlight mode. The result shows that the proposed method could match appropriate number of points in both images with high accuracy and reliability. For example it could match 211 points with 1.9 pixel accuracy for long base line image pair with size of 700×700 pixels and 1603 points with 1.22 pixel accuracy for short base line image pair with size of 400×400 pixels. Therefore, the proposed SAR multi-step image matching strategy is appropriate for coarse matching level.