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Image classification is a hot topic in computer vision and pattern recognition. Feature coding, as a key component of image classification, has been widely studied over the past several years, and a number of coding algorithms have been proposed. However, there is no comprehensive study concerning the connections between different coding methods, especially how they have evolved. In this paper, we first make a survey on various feature coding methods, including their motivations and mathematical representations, and then exploit their relations, based on which a taxonomy is proposed to reveal their evolution. Further, we summarize the main characteristics of current algorithms, each of which is shared by several coding strategies. Finally, we choose several representatives from different kinds of coding approaches and empirically evaluate them with respect to the size of the codebook and the number of training samples on several widely used databases (15-Scenes, Caltech-256, PASCAL VOC07, and SUN397). Experimental findings firmly justify our theoretical analysis, which is expected to benefit both practical applications and future research. [ABSTRACT FROM AUTHOR]

A new cross-channel interference suppression method based on the fractional Fourier transform (FRFT) is proposed to eliminate the effect due to cross-channel interference when a full-polarimetric radar adopts the opposite-slope linear frequency modulation transmit signals and de-ramping processing in the simultaneous measurement mode. The FRFT with an appropriate order is operated on the signals in the cross-interference interval. Such order is obtained via the calculation of the frequency-modulation slope of transmitted signals. The cross-channel interference is changed into sinc functions that are detected by a designed threshold and filtered out in the FRFT domain to suppress the cross-channel interference. The simulations show that the proposed method can obviously reduce the peak sidelobe levels and the integrated sidelobe levels of targets in range profiles compared with the traditional method, which is benefit to improve the detection and measurement performances of weak polarimetric scattering components. The proposed method is suitable for stable or slow-moving targets. [ABSTRACT FROM PUBLISHER]

The 2-D image of a spinning target obtained by monostatic radar is modified by the angle between the spinning axis and the radar line of sight, so it usually cannot describe the real size of the target. The T/R-R bistatic radar is proposed to solve this problem. First, the bistatic geometry and bistatic echo signals of a spinning target are modeled. Then, a novel 2-D imaging algorithm is presented based on the connections between the mono- and bistatic echoes of the same scatterer and the classical Hough transform, allowing both the mono- and bistatic 2-D images of the spinning target to be obtained simultaneously. The theoretical analysis is carried out by the electromagnetic calculation and numerical simulations. [ABSTRACT FROM PUBLISHER]

Antenna polarization states always vary with scan direction. Here this phenomenon is called spatial polarization characteristic (SPC) of antenna. Based on the single polarized radar antenna, by sufficiently utilizing of the inherent polarization property of antenna (i.e. the property that polarization state is not a constant but a function of antenna's spatial scanning direction), a novel polarization scattering matrix (PSM) measurement method is established. This method has the following advantages: (i) It does not need dual orthogonal polarization channels; (ii) the PSM of target can be obtained just by using the prior knowledge of SPC and by improving the signal processing mode of received radar signal. The modern radar systems can make use of this property in its measurement of target polarization scattering property in the searching or angle tracking stage. [ABSTRACT FROM PUBLISHER]

The biologically inspired model (BIM) proposed by Serre presents a promising solution to object categorization. It emulates the process of object recognition in primates' visual cortex by constructing a set of scale- and position-tolerant features whose properties are similar to those of the cells along the ventral stream of visual cortex. However, BIM has potential to be further improved in two aspects: mismatch by dense input and randomly feature selection due to the feedforward framework. To solve or alleviate these limitations, we develop an enhanced BIM (EBIM) in terms of the following two aspects: 1) removing uninformative inputs by imposing sparsity constraints, 2) apply a feedback loop to middle level feature selection. Each aspect is motivated by relevant psychophysical research findings. To show the effectiveness of the EBIM, we apply it to object categorization and conduct empirical studies on four computer vision data sets. Experimental results demonstrate that the EBIM outperforms the BIM and is comparable to state-of-the-art approaches in terms of accuracy. Moreover, the new system is about 20 times faster than the BIM. [ABSTRACT FROM AUTHOR]

Simultaneous polarimetric radars can measure the polarization scattering matrix (PSM) of moving targets within one pulse. The key point is the orthogonal waveform design to reduce the interference caused by the simultaneous transmission and reception. Meanwhile, to ensure the measurement accuracy of moving targets, the Doppler tolerance of the transmitted waveforms is also important. In this article, first, a matched filter (MF) at the receiver is considered and a unified framework with a newly proposed objective function to design Doppler resilient sequences under several constraints is described. The proposed objective function contains the widely used peak sidelobe level (PSL) and the integrated sidelobe level (ISL) as special cases. Meanwhile, a series of constraint conditions, including the unimodular constraint, the uncertainty modulus constraint, and the PAR constraint, is considered. Thereafter, a mismatched filter is considered for further improving the correlation properties and a similar framework for designing the optimal receiving filter at the expense of a controllable signal-to-noise ratio (SNR) loss is proposed. Numerical results are presented to verify the performance of the proposed methods. The designed sequence pair is also implemented on a fully polarimetric system to measure the PSM of a canonical target in the anechoic chamber, and the effectiveness of the proposed framework is verified by using the simultaneous polarimetric radar. It is predicted that the framework has the potential to be applied for other multichannel systems. [ABSTRACT FROM AUTHOR]

High cross-polarization isolation (CPI) is crucial to the accurate polarization measurement using polarimetric phased array radar (PPAR). In this article, we propose an adaptive direction-dependent polarization state configuration (AD2PSC) method to improve the polarization isolation. Compared with the conventional fixed polarization state of radiated wave whether it is linear, circular, or elliptical polarization state, our AD2PSC approach configures the polarization state on basis of beam steering. To achieve the adaptive configuration of magnitude and phase of the dual-polarization antenna, an improved steepest descent algorithm is put forward. To facilitate the uniform representation for the polarization measurement application of PPAR, the universal expressions of intrinsic and measured backscatter matrices are derived for arbitrary polarization state. The dual-polarization dipole array is used to assess the priority of our proposed method. Compared with the conventional approaches, our approach could obtain higher CPI while being available for a larger scanning range. The configured CPI meets the specific polarization requirement for PPAR. [ABSTRACT FROM AUTHOR]

Microcavity-feedback fiber-loop laser gives a promise for single-mode and tunable lasing. Here, a whispering gallery mode(WGM) microcavity-feedback fiber-loop laser is constructed and dynamic lasing mechanisms are investigated by rate equation models. For the single-mode lasing, the results show that the lasing efficiency can be maximized by tuning the coupling of waveguide and WGM microcavity, and two critical coupling rates exist for a fixed internal coupling coefficient of clockwise and counter-clockwise WGMs. By simply increasing the total length of fiber-loop laser, multi-mode lasing originated from one WGM feedback of a silica microsphere is explored, the lasing behaviors are well predicted by the rate equations and the WGM resonance linewidth can be effectively evaluated from the beat notes bandwidth of multiple lasings. We wish the results demonstrated here can be used for optimization on the lasing output of a fiber-loop laser with an external feedback mirror. [ABSTRACT FROM AUTHOR]