An imaging algorithm for spaceborne high-squint L-band SAR based on time-domain rotation

For spaceborne high-squint L-band synthetic aperture radar (SAR), the long wavelength and high-squint angle result in strong coupling between the range and azimuth directions. In conventional imaging algorithms, linear range walk correction (LRWC) is commonly used to correct linear range cell migration which dominates the coupling. However, LRWC introduces spatial variation in the azimuth direction, limits the depth-of-azimuth-focus (DOAF) and affects the imaging quality. This article constructs a polynomial range model and develops a modified omega-k algorithm to achieve spaceborne high-squint L-band SAR imaging. The key to this algorithm is to rotate the two-dimensional (2-D) data after LRWC in the time domain by a proposed time-rotation (TR) operation that eliminates the DOAF degradation caused by LRWC. The proposed algorithm, which is composed of LRWC, bulk compression, TR, and modified Stolt interpolation, achieves well-focused results at a 1-m resolution and a swath of 4 km × 4 km at a squint angle of 45°

A Beam-Segmenting Polar Format Algorithm Based on Double PCS for Video SAR Persistent Imaging

Video synthetic aperture radar (SAR) is attracting more attention in recent years due to its abilities of high resolution, high frame rate and advantages in continuous observation. Generally, the polar format algorithm (PFA) is an efficient algorithm for spotlight mode video SAR. However, in the process of PFA, the wavefront curvature error (WCE) limits the imaging scene size and the 2-D interpolation affects the efficiency. To solve the aforementioned problems, a beam-segmenting PFA based on principle of chirp scaling (PCS), called BS-PCS-PFA, is proposed for video SAR imaging, which has the capability of persistent imaging for different carrier frequencies video SAR. Firstly, an improved PCS applicable to video SAR PFA is proposed to replace the 2-D interpolation and the coarse image in the ground output coordinate system (GOCS) is obtained. As for the distortion or defocus existing in the coarse image, a novel sub-block imaging method based on beam-segmenting fast filtering is proposed to segment the image into multiple sub-beam data, whose distortion and defocus can be ignored when the equivalent size of sub-block is smaller than the distortion negligible region. Through processing the sub-beam data and mosaicking the refocused subimages, the full image in GOCS without distortion and defocus is obtained. Moreover, a three-step MoCo method is applied to the algorithm for the adaptability to the actual irregular trajectories. The proposed method can significantly expand the effective scene size of PFA, and the better operational efficiency makes it more suitable for video SAR imaging. The feasibility of the algorithm is verified by the experimental data

Synthetic Aperture Radar (SAR) data processing

The available and optimal methods for generating SAR imagery for NASA applications were identified. The SAR image quality and data processing requirements associated with these applications were studied. Mathematical operations and algorithms required to process sensor data into SAR imagery were defined. The architecture of SAR image formation processors was discussed, and technology necessary to implement the SAR data processors used in both general purpose and dedicated imaging systems was addressed

Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems

Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne or on a space-borne vehicle. The relative motion between the targets on ground and the platform causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves. In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically, thus allowing even a radar discrimination capability in the range direction (i.e. in distance). For side-looking acquisition geometries, the along-track and the range directions are almost orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to produce images of the illuminated area on ground. A side-looking geometry consists in the radar antenna to be, either mechanically or electronically, oriented perpendicular to the observed area. Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack and range directions in the order of few tenths of centimeters. Since the SAR is a microwave active sensor, this technology assure the possibility to produce images of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR a very useful instrument for monitoring and mapping both the natural and the artificial activities over the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them which are briefly listed below: a) the performance achievable in terms of resolution are usually paid in terms of system complexity, dimension, mass and cost; b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally radio-frequency interferences which might limit normal system operability; c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from moving targets. These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system

Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems

Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne or on a space-borne vehicle. The relative motion between the targets on ground and the platform causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves. In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically, thus allowing even a radar discrimination capability in the range direction (i.e. in distance). For side-looking acquisition geometries, the along-track and the range directions are almost orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to produce images of the illuminated area on ground. A side-looking geometry consists in the radar antenna to be, either mechanically or electronically, oriented perpendicular to the observed area. Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack and range directions in the order of few tenths of centimeters. Since the SAR is a microwave active sensor, this technology assure the possibility to produce images of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR a very useful instrument for monitoring and mapping both the natural and the artificial activities over the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them which are briefly listed below: a) the performance achievable in terms of resolution are usually paid in terms of system complexity, dimension, mass and cost; b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally radio-frequency interferences which might limit normal system operability; c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from moving targets. These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system

SAR (Synthetic Aperture Radar). Earth observing system. Volume 2F: Instrument panel report

The scientific and engineering requirements for the Earth Observing System (EOS) imaging radar are provided. The radar is based on Shuttle Imaging Radar-C (SIR-C), and would include three frequencies: 1.25 GHz, 5.3 GHz, and 9.6 GHz; selectable polarizations for both transmit and receive channels; and selectable incidence angles from 15 to 55 deg. There would be three main viewing modes: a local high-resolution mode with typically 25 m resolution and 50 km swath width; a regional mapping mode with 100 m resolution and up to 200 km swath width; and a global mapping mode with typically 500 m resolution and up to 700 km swath width. The last mode allows global coverage in three days. The EOS SAR will be the first orbital imaging radar to provide multifrequency, multipolarization, multiple incidence angle observations of the entire Earth. Combined with Canadian and Japanese satellites, continuous radar observation capability will be possible. Major applications in the areas of glaciology, hydrology, vegetation science, oceanography, geology, and data and information systems are described

Motion Compensation for Near-Range Synthetic Aperture Radar Applications

The work focuses on the analysis of influences of motion errors on near-range SAR applications and design of specific motion measuring and compensation algorithms. First, a novel metric to determine the optimum antenna beamwidth is proposed. Then, a comprehensive investigation of influences of motion errors on the SAR image is provided. On this ground, new algorithms for motion measuring and compensation using low cost inertial measurement units (IMU) are developed and successfully demonstrated

Highly Resolved Synthetic Aperture Radar with Beam Steering

The present work deals with a highly resolved radar with a synthetic aperture (synthetic aperture radar - SAR), which uses a beam steering to improve performance. The first part of this work deals with the influence of various effects occurring in the hardware of the High-Resolution Wide-Swath SAR (HRWS SAR) system. A special focus was set to single bit quantization in multi-channel receiver. The second part of this work describes SAR processors for Sliding Spotlight mode

Highly Resolved Synthetic Aperture Radar with Beam Steering

Diese Arbeit beschäftigt sich mit einem hochauflösenden Radar mit synthetischer Apertur. Der erste Teil dieser Arbeit beschreibt mögliche Auswirkungen verschiedener Effekte in dem Empfänger des High-Resolution Wide-Swath SAR (HRWS SAR) Systems. Darüber hinaus wird ein Konzept zu Reduktion von Quantisierungsbits in Systemen mit mehreren Empfangskanälen untersucht. Der zweite Teil der Arbeit betrifft die Datenverarbeitung eines hochauflösenden SAR-Systems in Sliding Spotlight Mode