scholarly journals Extraction of Quasi-Monochromatic Gravity Waves from an Airglow Imager Network

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 615
Author(s):  
Chang Lai ◽  
Wei Li ◽  
Jiyao Xu ◽  
Xiao Liu ◽  
Wei Yuan ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Gravity Waves ◽  
Basis Vector ◽  
Discrete Wavelet ◽  
Band Pass Filter ◽  
Monochromatic Wave ◽  
Pass Filter ◽  
Wave Patterns ◽  
Airglow Image ◽  
Band Pass

An algorithm has been developed to isolate the gravity waves (GWs) of different scales from airglow images. Based on the discrete wavelet transform, the images are decomposed and then reconstructed in a series of mutually orthogonal spaces, each of which takes a Daubechies (db) wavelet of a certain scale as a basis vector. The GWs in the original airglow image are stripped to the peeled image reconstructed in each space, and the scale of wave patterns in a peeled image corresponds to the scale of the db wavelet as a basis vector. In each reconstructed image, the extracted GW is quasi-monochromatic. An adaptive band-pass filter is applied to enhance the GW structures. From an ensembled airglow image with a coverage of 2100 km × 1200 km using an all-sky airglow imager (ASAI) network, the quasi-monochromatic wave patterns are extracted using this algorithm. GWs range from ripples with short wavelength of 20 km to medium-scale GWs with a wavelength of 590 km. The images are denoised, and the propagating characteristics of GWs with different wavelengths are derived separately.

A novel variable filter band discrete wavelet transform: Theory and principle

2014 ◽  
Vol 12 (04) ◽  
pp. 1460006
Author(s):  
Zhong Zhang ◽  
Hiroshi Toda ◽  
Takashi Imamura ◽  
Tetsuo Miyake
Keyword(s):  
Wavelet Transform ◽  
Discrete Wavelet Transform ◽  
Perfect Reconstruction ◽  
Discrete Wavelet ◽  
Band Pass Filter ◽  
Mother Wavelet ◽  
Pass Filter ◽  
Signal Characteristics ◽  
Filter Characteristic ◽  
Band Pass

It is well-known that a mother wavelet for the discrete wavelet transform (DWT) has the band-pass filter characteristic with octave width in the frequency domain and can be used for octave analysis. However, it is possible that the octave analysis is not necessarily the most suitable to match the analysis signal. In this study, in order to construct the most suitable basis to match the analysis signal, a novel variable-filter band discrete wavelet transform (VFB-DWT) is proposed. It is achieved by using variable-band filters instead of conventional decomposition and reconstruction sequences, which are designed in consideration of the real signal characteristics. Additionally, it is proven that perfect reconstruction of the analysis signal by VFB-DWT is guaranteed using the perfect shift invariant theorem that underlies the theory of the PTI-CDWT having base DWT.

scholarly journals Artifacts removal from breath sound recordings in pediatric population

2018 ◽  
Vol 154 ◽  
pp. 01046
Author(s):  
Yusuf A Amrulloh ◽  
Jawahir A K Haq
Keyword(s):  
Signal To Noise Ratio ◽  
Pediatric Population ◽  
Breath Sound ◽  
Discrete Wavelet ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Sound Recordings ◽  
Breath Sounds ◽  
Band Pass ◽  
Lower Magnitude

Breath sound recordings from pediatric subjects pose more processing complications. Children, especially the younger ones, are not able to follow instructions to stay calm during recording. This makes their recordings not only contain stationary artifacts but also non-stationary artifacts such as movement of subjects and their heartbeats. Further, the breath sounds from pediatric subjects also have lower magnitude compared to adults. In this work, we proposed to address those problems by developing a method to remove the artifacts from breath sound recordings. We implemented a combination of a Butterworth band pass filter and a discrete wavelet filter. We tested three types of wavelets (Coiflet, Symlet and Daubechies). Ten level decompositions and a set of hard thresholds were implemented in our work. Our results show that our developed method was capable of removing the artifacts significantly while maintaining the signal of interest. The highest signal to noise ratio improvement (10.65dB) was achieved by 32 orders Symlet.

scholarly journals Detect the live after eartquake with CW radar

2009 ◽  
Author(s):  
Seyed Javad Javadi Moghaddam
Keyword(s):  
Wavelet Transform ◽  
Digital Signal ◽  
Radar System ◽  
Analog Signal ◽  
Pass Band ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Portable System ◽  
Band Pass ◽  
Cw Radar

In this paper, new algorithm for Detecting the Live after Earthquake is presented. Here the application of the CW Radar with frequency 2.45GHz in a portable system for detecting the live below a mass of concrete or trash is introduced. The characters of radar hardware are shown too. The software which is used for computer process is LabVIEW, that some part of it is presented. Output of the Radar system which is analog convert to digital signal and enters into PC then for using of continues filtering by a section of the program digital signal is converted to an analog signal again. Now a software band-pass filter with variable pass band is applied, which change the quantity of the system. For the mathematic analyze a special wavelet transform (in-place kind) is applied that its algorithm and its mathematic debate are existed.

OBSERVATION AND SIMULATION OF TSUNAMIS INDUCED BY THE 2003 TOKACHI-OKI EARTHQUAKE (M 8.0)

2015 ◽  
Vol 2 (3) ◽  
Author(s):  
Tatsuo Ohmachi ◽  
Shusaku Inoue ◽  
Tetsuji Imai
Keyword(s):  
Rayleigh Wave ◽  
Water Pressure ◽  
Near Field ◽  
Source Region ◽  
Tsunami Source ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Tsunami Simulation ◽  
Sea Bed ◽  
Band Pass

The 2003 Tokachi-oki earthquake (MJ 8.0) occurred off the southeastern coast of Tokachi, Japan, and generated a large tsunami which arrived at Tokachi Harbor at 04:56 with a wave height of 4.3 m. Japan Marine Science and Technology Center (JAMSTEC) recovered records of water pressure and sea-bed acceleration at the bottom of the tsunami source region. These records are first introduced with some findings from Fourier analysis and band-pass filter analysis. Water pressure disturbance lasted for over 30 minutes and the duration was longer than those of accelerations. Predominant periods of the pressure looked like those excited by Rayleigh waves. Next, numerical simulation was conducted using the dynamic tsunami simulation technique able to represent generation and propagation of Rayleigh wave and tsunami, with a satisfactory result showing validity and usefulness of this technique. Keywords: Earthquake, Rayleigh wave, tsunami, near-field

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