Imaging algorithm for squint sliding spotlight SAR operating in medium-earth-orbit based on polynomial and azimuth resampling method

doi:10.7523/j.ucas.2024.009

Abstract

Abstract:

The medium-earth-orbit synthetic aperture radar （MEO SAR） possesses the capability of short revisit period， high spatial resolution， and wide coverage， which has promising applications in both military and civilian fields. The MEO SAR can improve azimuth resolution by operating in sliding spotlight mode， and can enhance system flexibility through squint imaging mode. However， the increase in orbit height invalidates the assumption of azimuth invariance and the squint mode causes spectrum distortion. In this paper， first， we derive the calculation process of imaging parameters based on the polynomial signal model. Then， by introducing a new model fitting method and a deramp function， we extend the azimuth time-domain resampling method from the stripmap mode to the sliding spotlight mode， correcting the azimuth space-variant characteristics. We further propose a processing flow by combining the two-step method and the non-linear range walk correction to solve the spectrum aliasing in the squint sliding spotlight mode. Finally， the proposed method is verified through simulation experiments.

Key words: spaceborne SAR, medium-earth-orbit（MEO）, azimuth resampling, sliding spotlight mode, squint

CLC Number:

TN957.52

Yiqiong GUO, Mingshan REN, Heng ZHANG, Haixia YUE. Imaging algorithm for squint sliding spotlight SAR operating in medium-earth-orbit based on polynomial and azimuth resampling method[J]. Journal of University of Chinese Academy of Sciences, 2026, 43(1): 61-69.

Figures/Tables 10

Fig.1 Imaging geometry of squint sliding spotlight SAR under curved trajectory

Fig.2 Schematic diagram of beam center crossing time

Fig.3 The first order coefficient of the polynomial model

Fig.4 Algorithm flowchart

Fig.5 The second order coefficients after azimuth resampling

Table1 Simulation parameters of radar

参数类型	参数值
半长轴/km	21 371
偏心率	0
天线长度/m	20
斜视角/（°）	10
俯仰角/（°）	10
雷达载频/GHz	9.6
信号带宽/MHz	70
景中心合成孔径时间/s	26
幅宽（距离向 $×$ 方位向）	30 km $×$ 40 km
分辨率（地距 $×$ 方位向）	1.98 m $×$ 2 m
滑动因子	0.2

Table1 Simulation parameters of radar

参数类型	参数值
半长轴/km	21 371
偏心率	0
天线长度/m	20
斜视角/（°）	10
俯仰角/（°）	10
雷达载频/GHz	9.6
信号带宽/MHz	70
景中心合成孔径时间/s	26
幅宽（距离向 $×$ 方位向）	30 km $×$ 40 km
分辨率（地距 $×$ 方位向）	1.98 m $×$ 2 m
滑动因子	0.2

Fig.6 Distribution of targets

Fig.7 Comparison of spectra

Fig.8 Imaging results of targets

Table 2 Index of imaging processing for point targets

点目标	距离向指标			方位向指标
点目标	PSLR/dB	ISLR/dB	$ρ r$ /m	PSLR/dB	ISLR/dB	$ρ a$ /m
$P 1$	-13.287 6	-9.855 6	1.979	-13.272 4	-9.914 3	2.004
$P 5$	-13.269 7	-9.858 8	1.980	-13.294 0	-9.974 5	2.000
$P 9$	-13.288 3	-9.861 8	1.982	-13.269 7	-9.856 5	1.996
$P 10$	-13.271 5	-9.857 3	1.982	-13.303 6	-9.897 8	1.996
$P 17$	-13.291 3	-9.861 3	1.982	-13.285 2	-9.900 2	1.996

Table 2 Index of imaging processing for point targets

点目标	距离向指标			方位向指标
点目标	PSLR/dB	ISLR/dB	$ρ r$ /m	PSLR/dB	ISLR/dB	$ρ a$ /m
$P 1$	-13.287 6	-9.855 6	1.979	-13.272 4	-9.914 3	2.004
$P 5$	-13.269 7	-9.858 8	1.980	-13.294 0	-9.974 5	2.000
$P 9$	-13.288 3	-9.861 8	1.982	-13.269 7	-9.856 5	1.996
$P 10$	-13.271 5	-9.857 3	1.982	-13.303 6	-9.897 8	1.996
$P 17$	-13.291 3	-9.861 3	1.982	-13.285 2	-9.900 2	1.996

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