Customer Solutions
Measuring Underwater Radiated Noise with PXI and LabVIEW
Author(s):
Mark Trotman, ICON Technologies Pty Ltd, Australia; Paul Cornes, ICON Technologies Pty Ltd, Australia; Kurt Friday, ICON Technologies Pty Ltd, Australia; Alex Le Dain, ICON Technologies Pty Ltd, Australia; James Stewart, ICON Technologies Pty Ltd, Australia
Industry:
Telecommunications
Product:
LabVIEW, LabVIEW Real-Time, PXI/CompactPCI
The Challenge:
Developing a cost-effective system for measuring underwater radiated noise.
The Solution:
Building a custom data acquisition system based on NI PXI hardware and NI LabVIEW software that offers the optimum combination of input signal resolution and integrity, compact and robust form factor for seabed installation, and full PC programmability plus network support.
Introduction to Underwater Radiated Noise
Naval operations and the oil and gas industry use applications in monitoring underwater radiated noise for the characterization and tracking of underwater vehicles such as submarines and ROVs. In a broader sense, it is a subset of a much larger range of marine applications for high-resolution multi-channel data acquisition systems capable of continuous logging at sample rates up to 200 kHz. Dynamic range is particularly important in the marine environment where signals are acquired in a complex background that ranges from very large amplitude, low frequency swell events to low amplitude, high frequency transients – both natural and man-made.
No standard off-the-shelf systems exist that encompass all requirements in the field. Almost all applications require at least some degree of system design and physical installation customization. With tight coupling between PXI and LabVIEW, PXI hardware offers the optimum combination of technical characteristics to suit the task, which ensures that the custom integration could be completed in a timely and cost-effective manner.
Submerged PXI
The underwater radiated noise measurement system consists of a hydrophone array, which floats suspended above a data acquisition pod that sits up to 150 m deep on the ocean floor. The pod is a watertight steel cylinder that contains a real-time PXI data acquisition unit comprising a PXI-1000B chassis, PXI-8176 RT 1.26 GHz embedded controller, PXI-4472 dynamic signal acquisition module(s), and PXI-6052E multifunction I/O module. Up to 2 km of cable incorporating Ethernet link tether the pod to a monitoring vessel on the surface.
In a typical operation, the data acquisition system is exposed to the noise source for a period ranging from a few minutes to nearly an hour, depending upon the nature of the source. During the exposure, the local PXI disk continuously logs and samples all hydrophone inputs in the pod at 24-bit resolution and 96 kSa/s sample rate. Any one of the inputs can be selected from the monitoring vessel and retransmitted as audio over the Ethernet link to provide direct feedback to the operator. A link from LabVIEW to Microsoft DirectX audio-streaming technology then implements the retransmission. At the end of the exposure period, the binary data file is transferred through FTP from the pod to the master server on the monitoring vessel for long-term archiving and analysis. The binary data file is typically sized at 100 MB. The cycle then repeats as required.
LabVIEW is a client-server architecture, such that the pod client and remote control station log onto the DAS server automatically. In addition to its main task of acquiring and logging the hydrophone data, the pod client monitors the pod environment and controls the hydrophone transducer interface. During an acquisition run, the pod client streams audio packets to the DAS server and environment and status packets to the remote control station. The remote control station provides the operator interface to the DAS server and pod client. It sends control packets to the pod and initiates the FTP data transfer from the pod to the DAS server once the run is complete.
A Great Solution to a Generic Problem
Measuring underwater radiated noise is a specific application of the more general problem of high-resolution, multichannel data acquisition in the marine environment. Resolution is a particular issue given that signals are acquired within a complex background that ranges from high amplitude swell effects at frequencies of several hertz, to a multitude of low amplitude, natural and man-made signals at kilohertz and higher frequencies.
The client identified the PXI platform as offering the optimum mix of capabilities to address the requirements of the task. In general terms, PXI offered a robust, compact form factor with modest power requirements that made it suitable for encapsulation within the submerged pod without compromising data acquisition speed and computer processing power. The PXI-4472 24-bit dynamic signal acquisition module offers a combination of dynamic range, channel density, and sample rate that makes it ideally suited to many underwater data acquisition tasks. Each PXI-4472 module includes eight simultaneously-sampled channels, so the existing system could be upgraded to 56 input channels without significantly affecting the pod architecture.
By using LabVIEW Real-Time, the pod client takes advantage of the additional power by running under a fully deterministic, embedded real-time operating system without compromising programming power. This is important, given that retrieval of the pod from the seabed to address any computer-related issues is a major logistical task. The client and server applications running in the less demanding environment of the monitoring vessel are Windows-based, enabling them to take maximum advantage of the many industry-standard productivity tools available for the Windows desktop.
While the ability of each hardware and software component to meet the requirements of the task was critical, the tight level of integration between the NI hardware and LabVIEW Real-Time was equally important in the choice of platform architecture. The close coupling of software and hardware gave the client a high degree of confidence that the custom system could be designed, built, and deployed in a cost-effective and timely manner.
For more information, contact:
Mark Trotman,
ICON Technologies, 1st Flr, Alberman House, 20 Teddington Rd., East Vic. Park, WA, 6100 Australia
Tel: +618 9470 4275
E-mail: mt@icon-tech.com.au
