In this paper we present a simple and robust method for self-correction of camera distortion using single images of scenes which contain straight lines. Since the most common distortion can be modelled as radial distortion, we illustrate the method using the Harris radial distortion model, but the method is applicable to any distortion model. The method is based on transforming the edgels of the distorted image to a 1-D angular Hough space, and optimizing the distortion correction parameters which minimize the entropy of the corresponding normalized histogram. Properly corrected imagery will have fewer curved lines, and therefore less spread in Hough space. Since the method does not rely on any image structure beyond the existence of edgels sharing some common orientations and does not use edge fitting, it is applicable to a wide variety of image types. For instance, it can be applied equally well to images of texture with weak but dominant orientations, or images with strong vanishing points. Finally, the method is performed on both synthetic and real data revealing that it is particularly robust to noise.

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[1] In this paper we present three methods for evaluating range rates of meteoroids passing through the ionosphere, using linear frequency modulated (LFM) chirped pulse data from the ALTAIR radar. The first method is based on the simple calculation of range differences divided by interpulse intervals. The second method utilizes the dual-frequency capability of ALTAIR to solve for range rates based on the difference in the measured ranges due to range-Doppler coupling. The third method utilizes a simplified form of integer programming in order to unwrap the phase differences of the matched filter time response, with reliance on the rough approximation available from the first method to disambiguate the solution set. The results of the three methods, with error bounds, are given for a large set of meteoroid head echoes taken from a data collection conducted with ALTAIR in 2007.Citation: Loveland, R., A. Macdonell, S. Close, M. Oppenheim, and P. Colestock (2011), Comparison of methods of determining meteoroid range rates from linear frequency modulated chirped pulses,

[1] We describe a new analysis of a set of 32 UHF meteor radar traces recorded with the 422 MHz Advanced Research Project Agency Long-Range Tracking and Identification Radar facility in November 1998. Emphasis is on the absolute velocity measurements and inferences that can be drawn from them regarding the meteoroid masses and mass densities. We find that the 3-D velocity versus altitude data can be fitted as quadratic functions of the path integrals of the atmospheric densities versus distance, and deceleration rates derived from those fits all show the expected behavior of increasing with decreasing altitude. We also describe a computer model of the coupled processes of collisional heating, radiative cooling, evaporative cooling and ablation, and deceleration for meteoroids composed of defined mixtures of mineral constituents. For each of the cases in the data set, we ran the model starting with the measured initial velocity and trajectory inclination and with various trial values of the quantity mr s 2 (initial mass times mass density squared) and then compared the computed deceleration versus altitude curves versus the measured ones. In this way we arrived at the best fit values of the mr s 2 for each of the measured traces. Then further, assuming various trial values of the density r s , we compared the computed mass versus altitude curves with similar curves for the same set of meteoroids determined previously from the measured radar cross sections and an electrostatic scattering model. In this way we arrived at estimates of the best fit mass densities r s for each of the cases.