Model 104 GPS/Argos Drifting Buoy

Model 104 GPS drifter.Drifters can be changed from deep drogue (as shown) to Davis/CODE surface-following configuration in the field.
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Model 104 GPS drifter with extensive external sensor payload. The Model 104 has great flexibility and expandability for specialized applications. This drifter has been customized with 24 external analog channels plus power and control lines to accommodate three Satlantic multichannel irradiance sensors and a Falmouth Scientific salinity/temperature sensor.
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Overview

The Model 104 Autonomous GPS Drifter is a current following (Lagrangian) drifting buoy. It is released in a body of water and moves with the currents over a period of days to months. Onboard electronics acquire a time series of positions using GPS as the drifter moves.

The onboard GPS receiver automatically uses corrections provided by Satellite Based Augmentation Systems to enhance position accuracy in areas of the world served by SBAS. Positions are stored internally in the drifter and telemetered via the worldwide ARGOS satellite network.

Precision Lagrangian current data provided by the Model 104 is useful in current measurement, larval fish studies, oil spill or floating debris tracking, discharge dispersement calculations, and similar studies.

Physical characteristics

Physical drifter design is similar to the Coastal Ocean Dynamics Experiment (CODE) drifter developed at the Scripps Institute of Oceanography. This design (also known as a Davis or SCULP drifter) provides excellent coupling to the surface layer and exhibits little wave rectification. An optional conversion kit allows the drifter to be changed in the field to a deep drogued configuration. The drifters are small and light (14 kg / 30 pounds) and are easily hand-deployed and retrieved by one person.

GPS

The Model 121 features a 12 channel GPS receiver that records position to 0.001 minute of latitude and longitude (1.8 meters). Absolute accuracy of the position is better than 15 meters worldwide. In areas served by one of three Satellite Based Augmentation Systems (WAAS in North America, EGNOS in Europe, and MSAS in East Asia) absolute accuracy is better than 3 meters 2DRMS. Sensor data and positions precise to 0.01 minute of latitude and longitude are telemetered through the Argos data channel. The full acuuracy data is recorded in internal memory for download after drifter retrieval.

Optional Sensors

Temperature: -10 to +40C, resolution 0.01C. Stock accuracy is better than +/-0.5C. Typical postprocessed accuracy with optional individual calibration 0.05C.

Conductivity / temperature: -10 to +40C, resolution 0.01C. 0-60 mmho/cm, resolution 0.01 mmho/cm. Full digital sensor with individual calibration yields typical postprocessed accuracy of 0.05C and 0.05 mmho/cm.

Other analog and digital sensors available upon request.

Setup and operation

Hardwired communication with the drifter is via a standard RS-232 serial interface. An external communications port brings the interface to an underwater connector on the drifter hull, allowing hardwired communications without opening the drifter case. Although the serial interface allows extensive tuning of drifter operational parameters, the drifter can also be operated with a single magnetic switch on the endcap. A "beep code" audible through the case allows personnel without a computer to monitor and confirm proper drifter operation before deployments.

In addition to telemetering data, the Model 104 stores data taken during a deployment in CMOS RAM memory. Even if telemetry coverage is not complete, all deployment data can be retrieved from the Model 104 after recovery.

Telemetry

Argos telemetry provides worldwide data transmission through the US/French Argos satellite system. Data compression allows diagnostic data and up to 25 GPS drifter positions to be encoded in three alternating 256 bit error-checked messages using only one Argos ID number, a technique pioneered by Brightwaters. During deployments at mid latitudes, over 99% of 30 minute positions are typically received through Argos.

Software

Click for sample graphics screen from real time tracking software.

Decoding and tracking software is included with all GPS/Argos drifters at no charge:

Postprocessing software decodes compressed Argos telemetry to flat ASCII files of position and diagnostic data.
Real time software tracks deployed drifters from a ship by monitoring Argos uplink transmissions. Text and graphical screens display drifter tracks, shorelines, ship position, range, bearing, and age of last valid telemetry.

Serviceability

Unlike most competing products, our drifters are designed to be reused. Although Brightwaters offers complete refurbishing services, most routine maintenance can be accomplished by the end user. The drifter hull can be opened to change batteries. Replacement battery packs are simple to make locally or can be ordered from Brightwaters. External parts such as sails or floats are easily replaced if damaged. Many of our customers have used the same drifters for years on multiple research projects.

Custom modification

The design of the Model 104 lends itself well to custom modification of hardware and software to meet individual user's requirements. Generous uncommitted analog and digital interface capability is available to integrate additional sensors. Alternative physical packaging such as WOCE SVP, Draper LCD, or extremely robust "crash cage" and "baseball bat" configurations are possible. There is no minimum quantity for custom modifications, and our wide previous experience often allows us to customize at surprisingly modest cost.

A history of innovation

Brightwaters Instrument Corporation has been building autonomous drifting buoys since 1991, with the Model 104 representing a sixth generation of design. Innovations developed at Brightwaters have been adopted across the drifter industry. Continuous design improvements reflect Brightwaters' commitment to offer the most technically advanced drifters in the world.

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