Sliding Spotlight Mode Imaging with GF-3 Spaceborne SAR Sensor

Zhu

et al. 2018

Sensors

In recent years, multi-input multi-output (MIMO) synthetic aperture radar (SAR) systems, which can promote the performance of 3D imaging, high-resolution wide-swath remote sensing, and multi-baseline interferometry, have received considerable attention. Several papers on MIMO-SAR have been published, but the research of such systems is seriously limited. This is mainly because the superposed echoes of the multiple transmitted orthogonal waveforms cannot be separated perfectly. The imperfect separation will introduce ambiguous energy and degrade SAR images dramatically. In this paper, a novel orthogonal waveform separation scheme based on echo-compression is proposed for airborne MIMO-SAR systems. Specifically, apart from the simultaneous transmissions, the transmitters are required to radiate several times alone in a synthetic aperture to sense their private inner-aperture channels. Since the channel responses at the neighboring azimuth positions are relevant, the energy of the solely radiated orthogonal waveforms in the superposed echoes will be concentrated. To this end, the echoes of the multiple transmitted orthogonal waveforms can be separated by cancelling the peaks. In addition, the cleaned echoes, along with original superposed one, can be used to reconstruct the unambiguous echoes. The proposed scheme is validated by simulations.

Section: Discussionmentioning

confidence: 99%

A Novel Orthogonal Waveform Separation Scheme for Airborne MIMO-SAR Systems

Zhu

et al. 2018

Sensors

“…First, to deal with the wide Doppler bandwidth of the sliding mode data, an azimuth convolution process in the space domain is preceded before performing the FSA. Convolution with the selected chirp signal to avoid aliasing is a widely used technique in full-aperture spotlight SAR processing [27][28][29][30][31], [35][36][37][38][39]. A new signal model is derived after the preliminary azimuth convolution since the dechirped signal model is addressed in this paper.…”

Section: Proposed Full-aperture Frequency Scaling Algorithm For Dechi...mentioning

confidence: 99%

“…This feature produces SAR images with a higher azimuth resolution than the stripmap mode and a wider azimuth extent than the staring mode. Due to these properties, the sliding mode is widely used as one of the main operating modes of modern SAR satellites, such as TerraSAR-X and Gaofen-3 [26][27][28][29]. Accordingly, extensive research has been conducted on the processing of sliding mode SAR data [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

“…As such, although many studies on the full-aperture processing for sliding mode SAR data are being actively conducted [27][28][29][30][31][32][33][34][35][36], most of the studies on full-aperture processing performed so far are based on algorithms that do not consider the dechirped signal model [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. As mentioned above, FSA is a method that efficiently processes the dechirped signal model.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Full-Aperture Frequency Scaling Algorithm for Processing Dechirped Sliding Spotlight SAR Data

Kang,

Park

2023

IEEE Access

This paper proposes a full-aperture method for processing sliding spotlight synthetic aperture radar (SAR) data with dechirp-on-receive. The frequency scaling algorithm (FSA) efficiently processes the dechirped signals because the range cell migration correction (RCMC) process involves removing the residual video phase. However, the conventional FSA combined with the sub-aperture method is unsuitable for processing sliding mode data because the azimuth extent of the SAR image is limited by the system pulse repetition frequency. In addition, the azimuth compression performance deteriorates as the range displacement increases from the center of the SAR image. To address these problems, we developed a modified full-aperture FSA for sliding mode data processing. A complete signal model of the azimuth convoluted sliding mode data with the dechirp-on-receive is newly derived. Based on the signal model, the frequency scaling factor and azimuth-matched filter have been modified to accurately perform RCMC and azimuth compression. Point target simulations demonstrated two advantages of the proposed algorithm over the conventional sub-aperture approach; One is accurate and consistent azimuth compression performance regardless of range displacements, and the other is wide observable azimuth extent. The practicality of the proposed method is further verified through actual SAR raw data experiments. In addition, it is analyzed that the proposed algorithm is specialized in processing dechirped sliding mode data through a characteristic comparison with various traditional sliding spotlight processing methods.INDEX TERMS Azimuth convolution, dechirp-on-receive, frequency scaling algorithm, full-aperture method, sliding spotlight mode, synthetic aperture radar.

“…Spaceborne synthetic aperture radar (SAR) systems play a vital role in tasks like regional mapping, geophysical parameter inversion, and disaster assessment thanks to their all-weather, day-and-night, long-endurance imaging capabilities with fine resolutions [1][2][3][4][5]. In the sliding spotlight SAR mode, the azimuth resolution is improved using azimuth beam scanning, which enlarges the Doppler bandwidth [6,7]. The adjustable squint angle in the squinted spotlight mode provides more flexibility in multi-angle observations and rapid target revisits within one orbital pass [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

System Design and Echo Preprocessing of Spaceborne Squinted Two-Dimensional Beam Scanning Synthetic Aperture Radar

Xu,

Lu,

Huang

et al. 2023

Sensors

Conventional squinted sliding spotlight synthetic aperture radar (SAR) imaging suffers from substantial swath width reduction and complex processing requirements due to the continuous variation in the squint angle and the large range cell migration (RCM) throughout the data acquisition interval. A novel two-dimensional (2D) beam scanning mode for high-resolution wide swath (HRWS) imaging is proposed. The key to the novel imaging mode lies in the synchronous scanning of azimuth and range beams, allowing for a broader and more flexible imaging swath with a high geometric resolution. Azimuth beam scanning from fore to aft was used to improve the azimuth resolution, while range beam scanning was adopted to illuminate the oblique wide swath to avoid the large RCM and the serious swath width reduction. Compared with the conventional sliding spotlight mode, both the swath width and swath length could be extended. According to the echo model of this imaging mode, an echo signal preprocessing approach is proposed. The key points of this approach are range data extension and azimuth data upsampling. A designed system example with a resolution of 0.5 m, swath width of 60 km, and azimuth coverage length of 134 km is presented. Furthermore, a simulation experiment on point targets was carried out. Both the presented system example and imaging results of point targets validated the proposed imaging mode.