Bistatik yapay açıklıklı radar yardımıyla görüntüleme

Abstract

Bu tezde bistatik Yapay Açıklıklı Radar (Y.A.R.) yardımıyla görüntülemede ters dönüşüm algoritmasının oluşturulması üzerinde çalışılmıştır, ilk olarak yapay açıklıklı radar kavramı kısa olarak anlatılmıştır. Daha sonra monostatik yapay açıklıklı radarda ters dönüşüm bağıntısı elde edilmiştir. Buna bağlı olarak bistatik radar içinde ters dönüşüm bağıntısı ve algoritması üzerine çalışılmıştır. Burada elde edilen dönüşüm yöntemi, bistatik oluşturulan dizi bilgisinin Fourier analizine ve Doppler bilgisinin faz modülasyon analizine dayan maktadır. Bu yaklaşım gönderilen ve sonuçta yansıyan küresel dalgaların faz bilgisi analizini içermektedir. Doppler bilgisi bistatik açı ve mesafelere bağlı olan bir band içinde yansıma fonksiyonunun uzaysal Fourier dönüşümünün örnekleriyle belirlenmektedir. Elde edilen bistatik yapay açıklıklı radar dönüşümü kullanılarak, hareketli bir cismin görüntüsü tek transmisyon durumu için incelenmiştir. Monostatik ve bistatik Y.A.R. ters dönüşüm algoritmaları ifade edilmiştir. Daha sonra ters dönüşüm algoritmaları ile ilgili uygulama örnekleri gerçekleştirilmiştir.

The aim of this thesis is to show that an algorithm for mon- static and bi static synthetic aperture radar inversion in object imag ing. The synthetic aperture radar can be regarded as a particular kind of high resolution imaging system operating in the microwave re gion. Its high resolution is achieved in range direction by compres sion of a chirp pulse, and in azimuth direction by using the synthetic aperture principle. Synthetic aperture radar can be mounted either on an airplane, a spacecraft or on a space shuttle. These vehicles move with respect to the detected targets as shown as Fig 1, then collect and process the echo reflected by them by means of digital or optical processing technique. Finally such radar system can generate a two dimensional image, which is similar to the optical photograph, of reflectivety distribution of the detected targets. One dimension of the image is proportional to slant range and the other dimension to along track koordinate position. Synthetic aperture radar has its unique characteristics, that is, synthetic aperture radar use its own energy to illuminate the detected surface, and it generates an image from the backs catter echoes. Therefore SAR is not dependent on illumination from the sun, it means that the weather changes (such as rain, clowd and mist take place) almost do not effect on imaging of synthetic aperture radar. In not limited by and weather factor. In addition, the illumination angle and illumination direction of synthetic aperture radar can be controlled and selected, whereas in optical system these parameters conserained by the sun's location. Consequently, synthetic aperture radar is an all time, all-weather microwave remote sensor. According to the wave theory, though the target is buried the hideaway under ground, the synthetic aperture radar is still able to observe to a limited depth. In fact, the depth D of the penetration depends on frequency and pal ari zati on of incident waves. The image resolution of synthetic aperture radar is independant of the lenght of micro wave, the altitude of the vehicle and the maximum detected range of radar, with the size of a resolution element being 1x1 m to 10x10 m. Synthetic aperture radar employs wavelengths different from photo graphic sensor, and thus provides information on surface rouhness, dielectric properties, moisture. Synthetic aperture radar can ope rate simultaneously in several wavelengths, and thus has a multi- spectral potential. IV Carl Wiley, Goodyear Aerospace Corporation, first put foward Doppler beam-sharpening concept in June 1951. University of Illinois demonserated the above concept in 1952 and produced first synthetic X=Vat *Y s r Transmitting RcrcİMns Radar Fig. 2. Imaging Geometry for a Monostatic SAR vn Transmitting Radar's Flight Path (X,.Y,.L) | K. < "2 «,*,> _ Transmitting Radar | (X"Y,*o) f, S J. -' (X..Y.-L) Receiving Radar's Flight Path (X2,Y,»U 1 * (XjY,-») _ S I Receiving Radar T (X2,Yj4.) Fig. 3. Imaging Geometry for a Bi static SAR. The bistatic SAR formulation also brings out certain functi onal properties of a physical array's data that is useful for dev- loping inversion in multi static echo imaging problems. An dynamic object with a single transmission and makes multiple (multistatic) measurements of resultant echoed signal along a physical linear array is discussed in this thesis. It is shown that such multistatic measurements can be translated into the data from a monostatic syn thesized linear array. Reconstruction of simulated targets in the above mentioned imaging problems are presented.