Eddy Covariance Tilt Corrections over a Coastal Mountain Area in South-east China:Significance for Near-Surface Turbulence Characteristics

Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation： double rotation （DR）, triple rotation （TR）, and classic planar-fit rotation （PF） were examined in terms of correction of eddy covariance flux. Using the commonly used DR and TR methods, unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics. The PF method rotates the coordinate system to an ensemble-averaged plane, and shows large tilt error due to an inaccurate fit plane over variable terrain slopes. In this paper, we propose another coordinate rotation scheme. The observational data were separated into two groups according to wind direction. The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s-1. Then, the coordinate systems were rotated to their respective best- fit planes for all available hourly observations. We call this the PF10 method. The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics, the spectra of wind-velocity components, and sensible heat and momentum fluxes under various atmospheric stabilities. Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality. The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes.

Movement Invariants-based Algorithm for Medical Image Tilt Correction

In this paper, the edge detection for a medical image is performed based on Sobel operator, and the bounding box is obtained, by which the effective medical sub-image is extracted. Then, the centroid and the normalized central moments of the medical sub-image are calculated, and the rotation angle a is obtained by minimizing the second-order central moment based on its rotation invariance. Finally, the whole medical image is rotated around the centroid by --a to correct the tilted image. F^rthermore, inspired by the uniformity degree of the image, the rotation angle ct is revised, which achieves a better correction effect and performance. The experimental results show that the proposed algorithms are fairly reliable and accurate for the determination of tilt angles, and are practical and effective tilt correction techniques.

Study on the vehicle license plate tilt correction

The shortage of current different approaches of the vehicle license plate(VLP) tilt correction is analyzed in the paper and a new rotary correction method put forward based on the former ways of the VLP tilt correction in the horizontal direction and the vertical direction Owing to the VLP tilt taking place in the vertical direction,the array of the image’s pixels of the same column is broken,and even different rows come into being superposition.The VLP tilt taking place in the horizontal direction,by which the array of the image’s pixels of the same row broken,and so much as different columns come into being superposition.

A New Method for Correcting Vehicle License Plate Tilt

In the course of vehicle license plate （VLP） automatic recognition, tilt correction is a very crucial process. According to Karhunen-Loeve （K-L） transformation, the coordinates of characters in the image are arranged into a two-dimensional covariance matrix, on the basis of which the centered process is carried out. Then, the eigenvector and the rotation angle α are computed in turn. The whole image is rotated by -α. Thus, image horizontal tilt correction is performed. In the vertical tilt correction process, three correction methods, which are K-L transformation method, the line fitting method based on K -means clustering （LFMBKC）, and the line fitting based on least squares （LFMBLS）, are put forward to compute the vertical tilt angle θ. After shear transformation （ST） is imposed on the rotated image, the final correction image is obtained. The experimental results verify that this proposed method can be easily implemented, and can quickly and accurately get the tilt angle. It provides a new effective way for the VLP image tilt correction as well.