Topic
Spatial filter
About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: The proposed method can be applied to measurements performed in semi-anechoic chambers, outdoor systems or even an echoic environments with a poor reflectivity level to remove reflected components and to retrieve the results one would obtain in an ideal anechoic chamber.
Abstract: A new method to reduce the unwanted reflection effects in antenna measurements is presented. The proposed method can be applied to measurements performed in semi-anechoic chambers, outdoor systems or even anechoic environments with a poor reflectivity level to remove reflected components and to retrieve the results one would obtain in an ideal anechoic chamber. The method is based on spatial filtering over the plane where the antenna under test (AUT) is placed. To calculate the field in this plane, a diagnostic technique is employed. However, in contrast to classic application (error source identification), the reconstructed field has to be obtained in a zone larger than the antenna dimensions. Thus, it is possible to identify virtual sources out of the antenna aperture, which appear due to the presence of reflections (image theory). Then, by cancelling the virtual and unwanted sources, the related reflected components can be suppressed. Finally, by employing this filtered reconstructed field, a new radiation pattern similar to the one obtained in a fully anechoic environment is calculated. To verify the effectiveness of the method, three examples are presented.
33 citations
TL;DR: It is shown that various types of correlation signals can be produced simply by varying the severity of the nonlinearity and without the need to synthesize the specific matched filter.
Abstract: We describe a multifunction nonlinear optical processor that can perform various types of operations such as image deconvolution and nonlinear correlation. This processor is joint power spectrum based and does not use any filters. In this technique both the input signal and the processing function are displayed side by side at the input plane of the processor. The joint power spectrum of the input signals is thresholded with varying nonlinearity to produce the specific operation. In image deconvolution the joint power spectrum is modified and hard clip thresholded to remove the amplitude distortion effects and to restore the correct phase of the original image. An amplitude mask averaged over an ensemble of images is assigned to the thresholded power spectrum to provide the amplitude magnitude of the restored image. In optical correlation, the Fourier transform interference intensity is thresholded to provide higher correlation peak intensity and a better defined correlation spot. We show that various types of correlation signals can be produced simply by varying the severity of the nonlinearity and without the need to synthesize the specific matched filter. For example, a phase-only correlation signal is produced by selecting the appropriate nonlinearity. An analysis of the nonlinear processor for image deconvolution is presented. Computer simulation of the proposed technique for a linearly smeared image is provided.
33 citations
TL;DR: A new algorithm used to adaptively filter a remote-sensing data set based on signal-to-noise ratios (SNRs) once the maximum noise fraction has been applied, which improves image quality and classification accuracies.
Abstract: This paper describes a new algorithm used to adaptively filter a remote-sensing data set based on signal-to-noise ratios (SNRs) once the maximum noise fraction has been applied. This algorithm uses Hermite splines to calculate the approximate area underneath the SNR curve as a function of band number, and that area is used to place bands into ldquobinsrdquo with other bands having similar SNRs. A median filter with a variable-sized kernel is then applied to each band, with the same size kernel used for each band in a particular bin. The proposed adaptive filters are applied to a hyperspectral image generated by the airborne visible/infrared imaging spectrometer sensor, and results are given for the identification of three different pine species located within the study area. The adaptive-filtering scheme improves image quality as shown by estimated SNRs. Classification accuracies of three pine species improved by more than 10% in the study area as compared to that achieved by the same discriminant method without adaptive spatial filtering.
33 citations
TL;DR: In this paper, the relationship between solid particles mean velocity in a pneumatic pipeline and the power spectrum of the output signal of an electrostatic sensor was mathematically modeled and the effects of the length of the sensor, the thickness of the dielectric pipe and its length on the spatial filtering characteristics of sensor were also investigated using the finite element method.
Abstract: The spatial filtering method for particle velocity measurement has the advantages of simplicity of the measurement system and convenience of data processing. In this paper, the relationship between solid particles mean velocity in a pneumatic pipeline and the power spectrum of the output signal of an electrostatic sensor was mathematically modeled. The effects of the length of the sensor, the thickness of the dielectric pipe and its length on the spatial filtering characteristics of the sensor were also investigated using the finite element method. As for the roughness of and the difficult determination of the peak frequency fmax of the power spectrum characteristics of the output signal of the sensor, a wavelet analysis based filtering method was applied to smooth the curve, which can accurately determine the peak frequency fmax. Finally, experiments were performed on a pilot dense phase pneumatic conveying rig at high pressure to test the performance of the velocity measurement system. The experimental results show that the system repeatability is within ±4% over a gas superficial velocity range of 8.63–18.62 m s−1 for a particle concentration range of 0.067–0.130 m3 m−3.
33 citations
Patent•
08 May 2009TL;DR: In this article, a system and method for tracking an airborne target including an illumination source (e.g., a diode laser array) is used to enhance a target signature and a detector (i.e., a passive high-speed camera) was used to detect to electromagnetic radiation reflected off the target, where the received electromagnetic radiation was processed by a digital computer and passed through a spatial filter that implements a band limited edge detection operation in the frequency domain.
Abstract: A system and method for tracking an airborne target including an illumination source (e.g., a diode laser array) is used to enhance a target signature and a detector (e.g., a passive high-speed camera) is used to detect to electromagnetic radiation (e.g., infrared radiation) reflected off the target. The received electromagnetic radiation may be processed by a digital computer and passed through a spatial filter that implements a band limited edge detection operation in the frequency domain. The filter may remove low spatial frequencies that attenuate soft edged clutter such as clouds and smoke as well as filter out artifacts and attenuated medium to high spatial frequencies to inhibit speckle noise from the detector as well as speckle from the laser return off the target.
33 citations