The IEEE Seventh Working Conference on Current Measurement Technology

Current and Wave Monitoring and Emerging Technologies

March 13-15 | Bahia Hotel | San Diego, CA, USA

  
     

Development of a Cheap, GPS-Based, Radio-Tracked, Surface Drifter for Closed Shallow-Water Bays

John C. Perez. J. S. Bonner, F. J. Kelly, and C. Fuller

Status: Accepted

Texas A&M University - Corpus Christi
6300 Ocean Drive
Corpus Christi , Texas USA
78412

Phone: (361)-825-5891
Email: perez@cbi.tamucc.edu

This paper describes the development of an inexpensive GPS-based, radio-tracked, surface-drifter system designed to operate within a closed shallow water bay. Texas bays and estuaries are generally shallow, weather/event driven, complex non-linear systems. In spite of the amount of activity that occurs within the bays, very little real-time information is collected. The Conrad Blucher Institute for Surveying and Science (CBI) at Texas A&M University-Corpus Christi is working toward better understanding of these bays by operating a pair of SeaSondeTM HF Radar units within Corpus Christi Bay. This experience has shown the need for a specialized drifter system that can be used in conjunction with the HF Radar operation and along with some of our other bay activities.

The drifter design was broken into two parts, the hardware/software characteristics (including GPS, Radio, Battery, Communication) and the buoy characteristics (drogue design). For this paper, only the hardware components (microprocessor, radio, and GPS) costing around $500, will be discussed.

The design is based on an RCM2300 microprocessor core module from Rabbit Semiconductor. The core module features a 22.1 MHz clock, 256K Flash & 128K SRAM memory, Real-time clock 29 I/O lines, and 4 serial ports. The module is relativity small (41x29x12 mm) and has minimal power consumption (108mA @ 5V) while supporting a real-time operating system utilizing the C programming language.

The radio link used to track the buoys, is based on a 1200 bps, 100mW frequency hopping spread spectrum transceiver manufactured by MaxStream. It has a power requirements are 150 mA @ 5V for transmit and 50 mA for receive. The 1200 bps version was used for its increased range.

The GPS module is manufactured by Liapac and is based on the SiRF star I/LXTM chip set. It is a 12-channel receiver with a position accuracy of 25 m CEP without SA. It uses the standard NMEA output strings and draws 180 mA @ 5V.

The electronics portion of the buoy fit on a 7.5x22 cm board, which makes it capable of being used in a wide variety of drogue designs. A field range test of the radio link (buoy-to-shore/buoy-to-ship) was conducted utilizing various antenna assemblies to determine the best placement. The test application for the buoy system will be verifying aspects of the HF radar system.

Submitted on November 21, 2002