A.S. Petrov – Dr.Sc. (Eng.), Professor, Chief Research Scientist, 

Lavochkin Association (Moscow region, Khimki)

Е-mail: as-petr@yandex.ru

The longitudinal or azimuthal resolution in synthetic aperture radar (SAR) is determined by a signal with Doppler modulation of the carrier frequency, which is characterized by two main parameters: the Doppler centroid and the Doppler frequency rate. The peculiarity of the space-based SAR is that these two main parameters constantly change during the flight of the platform in orbit, as well as with variations in its angular orientation. Therefore, it is necessary to fix them as accurately as possible at each time. There are two main methods for determining these parameters: calculation using kinematic parameters of a moving platform and spectral analysis of the received signal.

In this article, a method for evaluating Doppler parameters (DP) using both methods is developed for the use of personal computers. The results of its application are illustrated by graphical dependencies.

The first section provides a complete summary of the relations used in the kinematic part of the technique, which are necessary for its implementation in the form of algorithms and software modules. The graphical dependencies given for three typical RSA systems clearly illustrate the behavior of the DP in the entire range of variation of the orbital anomaly of the platform (0º…360º) and changes in the angles of incidence of the wave from 10º to 80º. The influence of changes in the angular orientation of the platform in space by roll, pitch and yaw on the DP is also analyzed.

In the second section, DP's are analyzed using spectral methods. A correlation method for determining the Doppler centroid is described using three options for choosing the weighing function, as well as evaluating the phase of the correlation function. Two numerical examples are given that demonstrate the application of the method when selecting three options for implementing the weighing function and two values of the noise-to-signal ratio. A sub-aperture method for estimating the rate of change of the Doppler frequency is described in a compact way.

In the third section, we analyze the effect of errors in the Doppler centroid setting and the Doppler frequency rate on the SAR response function, taking into account the apodization of the amplitude distribution of the signal at the antenna aperture, which leads to the suppression of the side lobes of its directional diagram. The results of the analysis are presented in a clear normalized form, which allows us to make generalized conclusions about the tolerances for the Doppler parameters of the SAR.

Petrov A.S. Doppler parameters modeling of spaceborn synthetic aperture radars. Achievements of modern radioelectronics. 2020. V. 74. № 7. P. 18–31. DOI: 10.18127/j20700784-202007-02. [in Russian]

1.  
2. Verba V.S., Neronskiy L.B., Turuk V.E. Perspektivnye tekhnologii tsifrovoy obrabotki radiolokatsionnoy informatsii kosmicheskikh RSA. M.: Radiotekhnika. 2019. [in Russian]
3. Tomiyasu K. Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface. Proc. IEEE. 1978. V. 66. May. P. 563–583.
4. Li F.-K., Held D.N., Curlander J.C., Wu C. Doppler Parameter Estimation for Spaceborne Synthetic-Aperture Radars. IEEE Transactions On Geoscience And Remote Sensing. V. Ge-23. № 1. January, 1985. P. 47–56.
5. Bamler R. Doppler Frequency Estimation and the Cramer-Rao Bound. IEEE Transactions On Geoscience And Remote Sensing. 1991. V. 29. № 3. P. 385–390.
6. Cumming I.G., Wong F.H. Digital processing of synthetic aperture radar data: algoritms and implementation. Artech House. 2005.
7. Renga A., Moccia A.G. Use of Doppler parameters for ship velocity computation in SAR images. IEEE Trans. Geosci. Remote Sens. 2016. V. 54. № 7. P. 3995–4011.
8. Petrov A.S., Prilutskiy A.A., Chikov V.A., Volchenkov A.S. K voprosu rascheta geometricheskogo razresheniya i energeticheskogo  potentsiala kosmicheskogo radiolokatora s sintezirovannoy aperturoy, raspolozhennogo na geosinkhronnoy orbite i rabotayushchego v bistaticheskom rezhime. Vestnik NPO im. S.A. Lavochkina. 2019. №4. S. 57–66. [in Russian]
9. Pitz W., Miller D. The TerraSAR-X Satellite. IEEE Transactions On Geoscience And Remote Sensing. 2010. V. 48. № 2. P. 615–622.
10. Volchenkov A.S., Petrov A.S., Prilutskiy A.A., Chikov V.A. Pobochnye glavnye maksimumy v subaperturnykh antennykh reshetkakh kosmicheskogo bazirovaniya. Vestnik NPO im. S.A. Lavochkina. 2018. № 2. S. 100–106. [in Russian]
11.