In June 2003 a series of acoustic propagation experiments were conducted off the coast of Panama City, Florida. The experiments were designed to measure and provide an understand of signal phase and amplitude fluctuations, and signal spatial and temporal coherence over several large horizontal and vertical arrays. The propagation measurements were conducted in a water depth of 8.8m and at ranges of 70 m and 150 m. The acoustic measurements cover frequencies from 1 to 140 kHz. The propagation measurements were supported by data obtained by wave rider buoys, CTD's, thermister chains and current meters. Bottom penetration data was also obtained using a buried hydrophone array. The experiments will be outlined and the data sets described.
During June 2003, the Naval Research Laboratory conducted a series of acoustic propagation experiments to measure both high (20 to 150 kHz) and low (1 to 10 kHz) frequency spatial and temporal coherence in very shallow water. Environmental data collected to support the acoustic measurements included water column current, bottom current, seasurface wave height, tide height, CTD water column profiles and mid-water time series, twodimensional micro-scale seawater temperature, and weather parameters. Wave periods varied from 3 to7 seconds and wind speeds ranged from 4 to 35 knots throughout the experiment. Temperature and salinity profiles characterized periods when the water column was isovelocity and periods when the water column was stratified with a strong depth dependence of temperature and salinity. Current magnitudes were always less than 25 cm/s. Experimental geometry and methods of environmental data collection are briefly described and environmental conditions and their impact on the propagation environment are emphasized.
Ethernet based list processing controller for high speed data acquisition systems Rev. Sci. Instrum. 77, 096102 (2006); 10.1063/1.2338300Field-programmable data acquisition and processing channel for optical tomography systems Rev. Sci. Instrum. 76, 095109 (2005); 10.1063/1.2042727High speed PC-based data acquisition in ultrasonics AIP Conf.Abstract. The Naval Research Lab is currently conducting research programs in MCM detections and classifications using both low and high frequency acoustics. These include target detections, target imaging, proud and buried target detections and classifications using structural clues. To determine the limitations that a fluctuating environment places on these target detection methods, a data acquisition system was developed. The data acquisition system consists of multi-channel, high-speed A/D's with remote, variable gain control, and FPGA technology. Each A/D is synchronously sampled at a rate of 1 MHz and using time -division multiplexing techniques, is sent down an optical fiber at 1.3 Gbps. The sampled data is then separated back to its original channel and recovered back to an analog signal along with the original clock. Precision filters and high speed transient recorders utilizing fast CAMAC crate controllers are then employed to sample, simultaneously, all data channels with sample rates up to 3Msps. Acoustic and environmental real-time software were developed using National Instruments Labview to generate the CW source signals that went from 10 kHz to 200 kHz, monitor acquired data, and control sample and repetition rates. System DescriptionAn overview of the complete system is shown in Figure 1. The system is divided 438 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions.
This paper is part of a series of papers describing acoustic coherence and fluctuations measurements made by the Naval Research Laboratory in the Gulf of Mexico near Panama City Beach, FL during June 2003. This paper presents low frequency (1-10 kHz) buried hydrophone measurements and preliminary results for two source-receiver ranges with grazing angles less than two degrees (realtive to the direct-path to the seafloor at the receiver location). Results focus on fluctuations after acoustic penetration into the sediment. These fluctuations are correlated with environmental influences.
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