Using NI LabVIEW to Enhance an Ocean Buoy Monitoring System

Author(s):
Stephen Boronkay - Blaton Technologies

Industry:
Water/Wastewater

Products:
LabVIEW

The Challenge:
Creating a Windows-based software program to work with an offshore stationary ocean buoy.

The Solution:
Using NI LabVIEW, we created a system providing ease of communication among instruments, versatile file-handling capabilities, and powerful built-in analysis functions.

A Windows-Based System that Acquires, Analyses, and Presents Data
An offshore stationary ocean buoy monitors water temperatures, currents, waves, and wind, along with other parameters. It sends the readings back to an onshore station via a radio-modem multiplexer. A computer at the onshore station reads the transmitted data from the multiplexed radio link, saves the data to files, performs partial analysis, and dispatches the data to computers at other sites for further analysis and report generation. Previously, programs written in Fortran carried out these tasks, and we wanted to replace this software with a program that could run under Windows. In addition to replacing the existing software, we optimised the data path and its associated components. We chose NI LabVIEW, because it is particularly well suited to communicate with instruments, and to analyse to present data.

Acquiring Various Data
The buoy has two data acquisition instruments onboard. One reads water temperatures (14 sensors), wind speed, and direction (2 anemometers), buoy compass heading, and the battery voltage every 30 seconds. The radio/modem transmits the results on one of the multiplexed channels back to shore. The second reads an accelerometer every second yielding water elevation, which transmits to shore at eight-second intervals. Two current meters immerse at 17 and 52 meters depth and measure ocean current vectors, water temperature, and conductivity every 30 seconds.

Intuitively Analysing Data
The computer at the onshore station reads the transmitted data from four asynchronous serial ports and stores the raw data received every 30 seconds in a set of 24-hour files. The program then averages the water temperature, wind, current, buoy heading, and battery voltage every five minutes. It also performs wave analysis in the time and frequency domain every five minutes on the previous 34 minutes of wave elevation data. Then it stores the resulting, five-minute, analysed data in 24-hour files.

Key five-minute data appear on the front panel as indicators and 24 plots for viewing by coast guard personnel. The computer has three serial output ports for disseminating data. The first connects to a permanent line through which the program sends five-minute averaged data to the Bureau of Meteorology. The other two ports connect to dial-up modems, so remote computers can download the previous day’s 24-hour files and optionally access the five-minute averaged data as it arrives.

Enhancing Reliability with LabVIEW
We designed the onshore computer LabVIEW program for 24-hour, seven-day-a-week operation. It uses a state-machine architecture with a predefined sequence of operations, except for start-up and shutdown. We wrote the RS-232 communication sub-VIs entirely using VISA for reliability and consistent error handling. The program, as well as the tasks defined above, must take into account and recover from sometimes quite serious data disruptions inherent in the system. These include the nonsynchronous multiplexed radio links, dropouts, non uniform data rate, and more serious data loss depending on weather conditions (such as high seas or rain). Another difficulty is the infrequent access to the buoy (only a few times a year), which means that if any sensors drift or fail, the program that accepts manual correction offsets to each sensor. Also, if a sensor fails the program, the system has a control on the front panel to turn the sensor "off."

The computer at this station monitors the operation of the system, downloads and archives 24-hour files, performs quality assurance on the previous days data, and calculates and collates summary files for use by environmental and meteorological models. To accomplish these tasks, we wrote a suite of VIs in LabVIEW. The most significant and challenging programs were the ones that perform automatically and unattended. Each day a suite of quality assurance criteria to the previous day’s five-minute averaged data and prepare summary files that by FTP transfers to a remote computer for environmentalmodelling.

Quality Assurance
With the LabVIEW program written to automatically apply quality assurance criteria to the previous day’s five-minute data, we replaced anomalous values using interpolation from values deemed good. This involved adaptive threshold testing of every point and an interpolation mechanism. We filled in missing data using various predictive algorithms to either interpolate data when only part of an hour’s worth of data was missing, or to insert null values when whole hours worth of data was absent. After the
above two operations prepared the fiveminute data, we filtered the data using the Lancos Cosine filter and reduced to hourly values. We combined the hourly data with tide and sewage flows from three treatment plants sent by FTP to a remote computer for environmental modelling.

We developed a variant of this program to perform post QA analysis and correct for errors missed with the automatic program. As quite a significant quantity of data generates each day, these programs resulted in significant time savings compared to manual techniques.

Easy, Versatile, and Powerful Solution
We modernized the ocean reference station ocean buoy monitoring program using the highly productive graphical development environment of LabVIEW. It is particularly suitable for the task because of its ease of communication with instruments, versatile file-handling capabilities, and powerful builtin analysis functions. Additionally, with its open development environment, we could take advantage of technologies like FTP and its ability to create intuitive user interfaces that can effectively display graphical data.

For more information, contact
Stephen Boronkay
Balaton Technologies
24 Boundary Street
Paddington, NSW 2021, Australia
Tel: 61-2-9358-4374
Fax: 61-2-9358-6370
E-Mail: balaton@bigpond.net.au

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