TAILIEUCHUNG - Advances in Sonar Technology 2012 Part 4

Tham khảo tài liệu 'advances in sonar technology 2012 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Motion Compensation in High Resolution Synthetic Aperture Sonar SAS Images 49 where a t x y is the spatial-temporal response of the combined transmitter and receiver aperture. The output of the system given by a convolution in along-track emphasize the two main problems faced by the inversion scheme which are the system response is range variant there is a range curvature effect also called range migration. Note that any function with a subscript m implies modulated notation . the analytic representation of the function still contains a carrier term exp ia ot where a 0 represents the carrier radian frequency. Demodulated functions are subscripted with a b to indicate a base band function. The processing of base banded data is the most efficient method as it represents the smallest data set for both the FFT Fast Fourier Transform and any interpolators. Many synthetic aperture systems perform pulse compression of the received reflections in the receiver before storage. The pulse compressed strip-map echo denoted by ssm is given by ss t u Pm t t e1 t u . 12 The temporal Fourier transform of equation 12 is Ss a u Pm a 3 eem t u Pm a Eem to Ù 13 with the Fourier transform of the raw signal Eem a u Pm a j j ff x y A a x y - u exp -i2kựx2 y - u 2 Idxdy 14 with ro and k the modulated radian frequencies and wave-numbers given by ro rob ro0 and k kb k0. Throughout this chapter radian frequencies and wave-numbers with the subscript o refer to carrier terms while radian frequencies and wave-numbers without the subscript b refer to modulated quantities. At this point it is useful to comment on the double-functional notation and the use of the characters e and s like they are appearing in equations 11 till 14 . The character e is used to indicate non-compressed raw echo data while s is used for the pulse-compressed version see equation 13 . Due to the fact that the echo is characterized by a 2D echo matrix . the scattering intensity as a function of azimuth and slant range

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