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Utilizing the frequency-dependent beam pointing characteristics of phased array antenna, frequency scanning (F-SCAN) spaceborne SAR can realize the smooth beam scanning from the far to the near edge of the observation scene. This property could enhance the wide-swath imaging performance in terms of signal-to-noise ratio (SNR) and side lobe suppression. Besides, it can achieve the constant and high image quality independent of target position within the scene. In this paper, we make a thorough investigation into this novel operation mode and present the overall and detailed system design procedure. In addition, the system performance evaluation approach is also given and its differences from that of conventional spaceborne SAR are emphasized. At last, an exemplary spaceborne SAR system operating in F-SCAN mode is brought forward and corresponding simulation results validate the effectiveness of our system design scheme as well as advantages of F-SCAN SAR.

This paper focuses on the design of a new optical cone and pendulum scanning imaging mode for micro-nanosatellites. This kind of satellite uses a high-resolution camera with a small imaging plane to achieve high-resolution and ultra-wide coverage imaging through the three-dimensional motion of the camera's wobble, satellite spin, and satellite orbital motion. First, this paper designs a single-camera constant speed OCPSI (optical cone and pendulum scanning imaging) mode. On the premise of ensuring coverage, the motion parameters and imaging parameters are derived. Then, in order to improve the performance and imaging quality of the system, a dual-camera variable speed OCPSI mode is designed. In this method, in order to reduce the overlap ratio, the camera is oscillated at a variable speed. Turn on the cameras in turn at the same time to minimize the overlap. This paper details these working modes. The simulation experiment is carried out using the satellite orbit of 500 km, the focal length of 360 mm, the pixel size of 2.5 μm, the resolution of [5120 × 5120], the number of imaging frames in the pendulum scanning hoop of 10, and the initial camera inclination angle of 30°. The single-camera constant speed OCPSI mode has an effective swath of 1060 km at a ground sampling distance of 5.3 m. The dual-camera variable speed OCPSI mode has an effective width of 966 km under the same conditions. Finally, the ground experiment prototype of OCPSI imaging theory is designed. We choose a camera with a pixel size of 3.45 μm, a resolution of [1440 × 1080], and a focal length of 25 mm. The ground experiment was carried out at the initial camera inclination angle of 10°, the number of imaging frames in the pendulum scanning hoop of 3, and the orbit height of 11 m. The experimental result is that the effective width of OCPSI imaging mode reaches 10.8 m. Compared with the traditional push-broom mode using the same camera, the effective width of 1.64 m is increased by seven times, and the effective width of 3.83 m is increased by three times compared to the traditional whisk-broom imaging mode. This study innovatively integrates three-dimensional motion imaging into aerospace remote sensing and provides a reference for the research on the realization of high-resolution and ultra-wide coverage of micro-nano remote sensing satellites. [ABSTRACT FROM AUTHOR]

This paper focuses upon the novel optical conical scanning imaging working mode design for small satellites. This kind of satellite employs only one inclined optical camera achieving wide-swath imaging via a rotational motion about the nadir axis either by the camera or by the satellite. Three working modes are designed, i.e., high-speed rotational mode, low-speed rotational mode, and variable-speed rotational mode. For the high-speed and low-speed working modes, the camera rotates at a constant speed and the corresponding angular velocity is derived under the consideration of guaranteed coverage and minimized overlap. To improve the system performance, an enhanced working mode taking advantages of both the high-speed rotational mode and low-speed rotational mode is proposed. Working in this variable-speed rotational mode, the camera rotates slowly to get high-quality pictures when it works, while it rotates rapidly to reduce the energy consumption and save the storage during which period the camera is turned off to minimize the overlap. All these working modes are illustrated in detail, and numerical simulation tests are conducted to validate their effectiveness. [ABSTRACT FROM AUTHOR]

With the development of the Moon exploration, the concept of deploying sensors of synthetic aperture radar based on the Moon (Moon-based SAR) to fully and constantly observe the Earth is gaining increased attention. The Moon-based SAR has the advantages of long-term, large-scale and continuous observation, and it may provide a new way for macro-scale solid Earth monitoring. Here, the system parameters theoretically are analyzed and simulated considering at the requirements of large-scale Earth observation. In addition, the actual relative motion parameters of the Earth-Moon system and the performance of the Moon-based SAR imaging are taken into account. The results show that the Moon-based SAR has the potential of ultra-wide observation applications. It can form an imaging swath of thousands of kilometers by using multi-beam SAR with good imaging performance. [ABSTRACT FROM AUTHOR]

Conventional single antenna synthetic aperture radar (SAR) has a conflict between wide imaging swath width and fine cross-range resolution. Single input multiple output (SIMO) and multiple input multiple output (MIMO) radars are the two methods to overcome this limitation. In order to separate the signals of MIMO radar, the codes are expected to be orthogonal for all delays. This is impossible in SAR. Due to the special imaging geometry of SAR, short-term shift orthogonal (STSO) codes were proposed to be used in MIMO SAR. This letter compares the SIMO SAR structure and MIMO SAR structure using STSO codes. We draw a conclusion that the number of receivers of MIMO structure is less than that of SIMO structure. [ABSTRACT FROM AUTHOR]

The successful launch of the GF-4 satellite has greatly enhanced wide-swath and high-frequency imaging capabilities, both of which are urgently needed in the fields of ship detection and monitoring. In this letter, the applicability of GF-4 satellite data for ship recognition and maritime traffic surveillance was investigated. It is concluded that the movement of ships, the velocity and direction, for instance, can be detected by using either a single GF-4 image that has short time lags between bands, or time-series GF-4 images that have a short interval between their acquisition times, implying that GF-4 satellite images have the potentiality for the monitoring of moving ships. [ABSTRACT FROM PUBLISHER]

Circular-transmit/linear-receive compact polarimetry synthetic aperture radar systems combine coherent dual polarization with wide-swath imaging. The polarization information in these data may be represented as a Stokes vector, or one can reconstruct several quadpolarized covariance elements. Two reconstruction algorithms have been published in the literature: one by Souyris and a refined algorithm by Nord We investigated the application of these two algorithms for reconstructing ocean clutter for the purpose of detecting targets. We tested the assumptions underlying these algorithms and found that they were not valid for ocean scenes. We present a simple empirical reconstruction model whose reconstruction and target detection performance is superior to the two published algorithms. [ABSTRACT FROM PUBLISHER]

Since the range swath width in the conventional single channel spaceborne synthetic aperture radar (SAR) is restricted by the system parameters, there is a trade-off between the azimuth resolution and the swath width in order to satisfy the Nyquist sampling criterion. In this paper, we propose a novel spaceborne SAR wide-swath imaging scheme based on compressive sensing (CS) for the sparse scene. The proposed method designs a Poisson disk-like nonuniform sampling pattern in the azimuth direction, which meets the demand of wider swath by restricting the smallest time interval between any two azimuth samples, with the conventional sampling pattern preserved in the range direction. By a similar way to the processing procedure of spectral analysis (SPECAN) algorithm, the linear range migration correction (RMC) is realized while carrying out range compression, which can meet the demand for focusing with middle level resolution. To reduce the computation load of CS reconstruction, we propose a novel fast reconstruction algorithm based on nonuniform fast Fourier transform (NUFFT), which greatly reduces the computation complexity from O(2 MN) to O(4 N log N). Experiment results validate the effectiveness of the proposed methods via the point target simulation and the Radarsat-1 raw data processing in F2 mode. [ABSTRACT FROM AUTHOR]