Periodic noise corrupts digital images during acquisition and transmission stages by adding repetitive patterns. This study introduces a new adaptive Gaussian notch filter (AGNF) in Fourier transform domain for effectively restoring images contaminated with periodic, quasi-periodic and Moire pattern noises. Since periodic noises are sinusoidal functions added to the uncorrupted images, Fourier transform of images make these noisy functions to concentrate as easily distinguishable conjugate peaks in frequency domain. The proposed AGNF effectively identifies the noisy peak positions and adaptively quantifies the associated noisy areas by analysing the ratio of averages of frequencies from adaptively varying neighbourhoods. These identified noisy peaks are then diffused by Gaussian notch filter of adaptively varying sizes. The proposed filter ensures maximum diffusion of identified noisy peak areas by maintaining the minimum frequency values from the outputs of overlapping notch filters. Visual and quantitative experimental analysis of the proposed algorithm with mean absolute error, peak signal-to-noise ratio, mean structural similarity index measure and computation time reveals that AGNF is better in restoring images contaminated with periodic noises when compared to other methods.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-ipr.2018.5707

Adaptive Gaussian notch filter for removing periodic noise from digital images

In view of the special properties of the upper atmosphere at the altitude of 80-120 km, a ground-based passive remote sensing instrument ground-based airglow volume emission rate and temperature imaging interferometer (GBAVTII) is built to detect the atmospheric temperature used O 2(0-1) spectral line of night airglow at the altitude of 94 km. In the process of photographing the upper atmosphere airglow with the GBAVTII, the stray light (white noise) such as moonlight, city lights, and starlight will be affected. In this paper, the theoretical expression of denoising is derived based on the rotational line temperature measurement of diatomic O 2(0-1) airglow. Through a slight adjustment of different parameters in the forward equation of the GBAVTII and noise reduction in laboratory flat-field fine calibration, and other denoising methods in the GBAVTII image processing process, the maximum accuracy of the GBAVTII detection of the upper atmospheric temperature is enhanced to 2.4 K. Also, the minimum error of the GBAVTII detecting data with the satellite instrument sounding of atmosphere using broadband emission radiometry is 0.4 K. Thus, the absolute accuracy of the GBAVTII in detecting the upper atmospheric temperature can be improved to ±(0.4-2.4)K through the theory and method studied in this paper.

Improving the upper atmospheric temperature accuracy of the ground-based instrument by eliminating noise ways.

Being susceptible to the change of atmospheric conditions, the volume emission rate (VER) is very suitable to be used as a light source by passive remote sensing for measuring atmospheric wind and temperature. Thus, the VERs emitted from O2(0-1) and O(S1) of the nightglow at 80-120 km are studied in this paper. Based on the Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model data and the ground-based airglow imaging interferometer (GBAII) instrument observation for a local time and place, simulated VER profiles represented by four layers are obtained for the nightglow of O2(0-1) and O(S1). The O2(0-1) nightglow model peak values at 94 km on 6 December 2013 and 8 November 2011 are 8111  photons·cm-3·s-1 and 8406  photons·cm-3·s-1, respectively; however, the O(S1) VER peak at a higher altitude of about 96 km on 18 December 2011 is only 338  photons·cm-3·s-1. The upper atmospheric VER values have been derived to transfer into the ground-based detected column intensities by our GBAII prototype. The calculated column integrated emission rates (IERs) of O2(0-1) for 0° and 45° zenith angles are 1.48×107 and 1.91×107  photons·cm-2·s-1, respectively; the calculated column IERs of O(S1) are 5.53×105 and 7.03×105  photons·cm-2·s-1, respectively. Correspondingly, the detected column IERs obtained by GBAII are 2.43×107 for O2(0-1) and 6.57×105  photons·cm-2·s-1 for O(S1).

Qingsong Liu

Papers

Simulation and observation for volume emission rates emitted from O2(0-1) and O(1S) nightglow in northwest China.

Beyond the partial light intensity imager: Eliminating Moiré patterns