Denoising Methods for Underwater Acoustic Signal

Underwater ambient noise is primarily a background noise which is a function of time, location, and depth. It is of prime importance to detect the signals such as sound of a submarine or echo from a target surpassing this ambient noise. It is also defined as the residual noise that remains after all easily identifiable sound sources are eliminated. In the absence of the sound from ships and marine life, underwater ambient noise levels are dependent mainly on wind speeds at frequencies between 500 Hz and 50 KHz.The detection of background noise is essential to enhance the signal‐to‐noise ratio of acoustic‐based underwater instruments. Since there is a possibility of signal and noise present in the same frequency, it becomes essential to find out a suitable algorithm to perform denoising. In this chapter, various denoising techniques such as wavelet, empirical mode decomposition (EMD) in time domain, ensemble empirical mode decomposition (EEMD), and frequency domain‐based EMD are studied, and the results are compared. The proposed frequency domain algorithm produced better results in the frequency ranging from 50 Hz to 25 KHz, with less signal error

Underwater Ambient Noise

Underwater ambient noise is primarily a background noise which is a function of time, location, and depth. Background baseline of the noise in ocean is represented by ambient noise generated from the ocean surface due to wind and rain. This understanding pertained to ambient noise under various conditions will help in improving the signal-to-noise ratio (SNR) of marine instruments. It is of prime importance to detect the signals such as sound of a submarine or echo from a target surpassing this ambient noise. Ambient noise excludes all forms of self noise, such as the noise of current flow around the measurement hydrophone and its supporting structure. It should also exclude all forms of electrical noise. It is also defined as the residual noise that remains after all easily identifiable sound sources are eliminated. In the absence of sound from ships and marine life, underwater ambient noise levels (NL) are dependent mainly on wind speeds at frequencies between 100 Hz and 25 KHz

Comparison of Fourier Bessel (FB) and EMD-FB Based Noise Removal Techniques for Underwater Acoustic Signals

756-762The purpose of this paper is to compare the efficacy of two algorithms used for denoising underwater acoustic signals affected by ambient noise. The two denoising techniques are, (i) Fourier Bessel (FB) expansion based denoising algorithm and (ii) Empirical Mode Decomposition (EMD)-Fourier Bessel (FB) based denoising algorithm<span style="mso-fareast-font-family: Calibri" lang="EN-GB">. Sea water normally contains unwanted background noise called ambient noise which is non-stationary produced by man-made or natural sources. In practical applications it is absolutely necessary to denoise underwater acoustic signals. The information that will be received through hydrophones shall be unaffected, pristine and original. In this paper, initially the two techniques are applied to a stationary input and the outcomes of both the techniques are compared. Later the two methods are once again applied to anon-stationary input and the results are then compared. </span

Formulation and Evaluation of Gastro-retentive Floating Multi-particulate System of Metoprolol Tartarate

Purpose: To develop a floating multiparticulate unit system for metoprolol tartarate, using a porous carrier, with an outcome for delayed gastric emptying. Methods: Dried microparticles of metoprolol tartarate were prepared by solvent evaporation using Eudragit® RS-PO, polypropylene foam powder, and dichloromethane as release-rate modifying polymer, floating aid and solvent respectively. The surface topography of the particles was assessed by SEM while the physical state of the drug within the developed system was characterised by DSC and XRD. Drug release was investigated by in vitro dissolution test. Tc99m sulfur colloid radio-labelled microparticle formulation was administered to fasting rabbits and their transit behavior was monitored using gamma scintigraphy. The anterior and posterior images recorded were computed to determine the geometric mean counts, enabling quantitative estimation of gastric emptying rate. Results: Dried free-flowing, white coloured microparticles were obtained. They were highly porous and also irregular in shape. The drug in the microparticles was partly amorphous, showing a decrease in crystallinity. In vitro drug release from the particles followed a biphasic pattern with zero-order kinetics. The microparticulate system exhibited good floating ability with t1/2 of 300 min over the duration of the in vivo study (6 h). Conclusion: The developed microparticles showed suitable release properties, were free-flowing and exhibited good floating ability in rabbit stomach. Therefore, the formulation is capable of being further processed into tablet and/or capsule dosage forms for oral administration as a gastro-retentive controlled delivery system

Formulation and Evaluation of Gastro-retentive Floating Multi-particulate System of Metoprolol Tartarate

Purpose: To develop a floating multiparticulate unit system for metoprolol tartarate, using a porous carrier, with an outcome for delayed gastric emptying. Methods: Dried microparticles of metoprolol tartarate were prepared by solvent evaporation using Eudragit® RS-PO, polypropylene foam powder, and dichloromethane as release-rate modifying polymer, floating aid and solvent respectively. The surface topography of the particles was assessed by SEM while the physical state of the drug within the developed system was characterised by DSC and XRD. Drug release was investigated by in vitro dissolution test. Tc99m sulfur colloid radio-labelled microparticle formulation was administered to fasting rabbits and their transit behavior was monitored using gamma scintigraphy. The anterior and posterior images recorded were computed to determine the geometric mean counts, enabling quantitative estimation of gastric emptying rate. Results: Dried free-flowing, white coloured microparticles were obtained. They were highly porous and also irregular in shape. The drug in the microparticles was partly amorphous, showing a decrease in crystallinity. In vitro drug release from the particles followed a biphasic pattern with zero-order kinetics. The microparticulate system exhibited good floating ability with t1/2 of 300 min over the duration of the in vivo study (6 h). Conclusion: The developed microparticles showed suitable release properties, were free-flowing and exhibited good floating ability in rabbit stomach. Therefore, the formulation is capable of being further processed into tablet and/or capsule dosage forms for oral administration as a gastro-retentive controlled delivery system