Computationally Efficient Algorithm for Frequency Estimation of a Two-Dimensional Sinusoidal Model

The spatial evolution of three-dimensional disturbances in an attachment-line boundary layer is computed by direct numerical simulation of the unsteady, incompressible Navier–Stokes equations. Disturbances are introduced into the boundary layer by harmonic sources that involve unsteady suction and blowing through the wall. Various harmonic-source generators are implemented on or near the attachment line, and the disturbance evolutions are compared. Previous two-dimensional simulation results and nonparallel theory are compared with the present results. The three-dimensional simulation results for disturbances with quasi-two-dimensional features indicate growth rates of only a few percent larger than pure two-dimensional results; however, the results are close enough to enable the use of the more computationally efficient, two-dimensional approach. However, true three-dimensional disturbances are more likely in practice and are more stable than two-dimensional disturbances. Disturbances generated off (but near) the attachment line spread both away from and toward the attachment line as they evolve. The evolution pattern is comparable to wave packets in flat-plate boundary-layer flows. Suction stabilizes the quasi-two-dimensional attachment-line instabilities, and blowing destabilizes these instabilities; these results qualitatively agree with the theory. Furthermore, suction stabilizes the disturbances that develop off the attachment line. Clearly, disturbances that are generated near the attachment line can supply energy to attachment-line instabilities, but suction can be used to stabilize these instabilities.

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An Efficient Signal Reconstruction Algorithm for Stepped Frequency MIMO-SAR in the Spotlight and Sliding Spotlight Modes

International Journal of Antennas and Propagation ◽

10.1155/2014/329340 ◽

2014 ◽

Vol 2014 ◽

pp. 1-8

Author(s):

Jiajia Zhang ◽

Guangcai Sun ◽

Mengdao Xing ◽

Zheng Bao ◽

Fang Zhou

Keyword(s):

Efficient Algorithm ◽

Low Cost ◽

Signal Reconstruction ◽

Multiple Input Multiple Output ◽

Reconstruction Algorithm ◽

Synthetic Aperture ◽

Two Dimensional ◽

Multiple Input ◽

Input Multiple Output ◽

Stepped Frequency

Multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) using stepped frequency (SF) waveforms enables a high two-dimensional (2D) resolution with wider imaging swath at relatively low cost. However, only the stripmap mode has been discussed for SF MIMO-SAR. This paper presents an efficient algorithm to reconstruct the signal of SF MIMO-SAR in the spotlight and sliding spotlight modes, which includes Doppler ambiguity resolving algorithm based on subaperture division and an improved frequency-domain bandwidth synthesis (FBS) method. Both simulated and constructed data are used to validate the effectiveness of the proposed algorithm.

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An Adaptive Tracking Algorithm for Convection in Simulated and Remote Sensing Data

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-20-0119.1 ◽

2021 ◽

Vol 60 (4) ◽

pp. 513-526

Author(s):

Bhupendra A. Raut ◽

Robert Jackson ◽

Mark Picel ◽

Scott M. Collis ◽

Martin Bergemann ◽

...

Keyword(s):

Simulated Data ◽

Remote Sensing Data ◽

Life Cycles ◽

Tracking Algorithm ◽

Two Dimensional ◽

Computationally Efficient ◽

Convective Systems ◽

Object Based ◽

Modular Platform ◽

Convective Cells

AbstractA robust and computationally efficient object tracking algorithm is developed by incorporating various tracking techniques. Physical properties of the objects, such as brightness temperature or reflectivity, are not considered. Therefore, the algorithm is adaptable for tracking convection-like features in simulated data and remotely sensed two-dimensional images. In this algorithm, a first guess of the motion, estimated using the Fourier phase shift, is used to predict the candidates for matching. A disparity score is computed for each target–candidate pair. The disparity also incorporates overlapping criteria in the case of large objects. Then the Hungarian method is applied to identify the best pairs by minimizing the global disparity. The high-disparity pairs are unmatched, and their target and candidate are declared expired and newly initiated objects, respectively. They are tested for merger and split on the basis of their size and overlap with the other objects. The sensitivity of track duration is shown for different disparity and size thresholds. The paper highlights the algorithm’s ability to study convective life cycles using radar and simulated data over Darwin, Australia. The algorithm skillfully tracks individual convective cells (a few pixels in size) and large convective systems. The duration of tracks and cell size are found to be lognormally distributed over Darwin. The evolution of size and precipitation types of isolated convective cells is presented in the Lagrangian perspective. This algorithm is part of a vision for a modular platform [viz., TINT is not TITAN (TINT) and Tracking and Object-Based Analysis of Clouds (tobac)] that will evolve into a sustainable choice to analyze atmospheric features.

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Computationally efficient algorithm for multifocus image reconstruction

10.1117/12.476754 ◽

2003 ◽

Cited By ~ 48

Author(s):

Helmy A. Eltoukhy ◽

Sam Kavusi

Keyword(s):

Image Reconstruction ◽

Efficient Algorithm ◽

Computationally Efficient

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Hyers-Ulam Stability of Lagrange’s Mean Value Points in Two Variables

Mathematics ◽

10.3390/math6110216 ◽

2018 ◽

Vol 6 (11) ◽

pp. 216 ◽

Cited By ~ 2

Author(s):

Soon-Mo Jung ◽

Ji-Hye Kim

Keyword(s):

Efficient Algorithm ◽

Mean Value ◽

Two Dimensional ◽

Ulam Stability

Using a theorem of Ulam and Hyers, we will prove the Hyers-Ulam stability of two-dimensional Lagrange’s mean value points ( η , ξ ) which satisfy the equation, f ( u , v ) − f ( p , q ) = ( u − p ) f x ( η , ξ ) + ( v − q ) f y ( η , ξ ) , where ( p , q ) and ( u , v ) are distinct points in the plane. Moreover, we introduce an efficient algorithm for applying our main result in practical use.

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