Model 115 GPS/Argos Drifting Buoy

Model 115 drifter
Davis/CODE surface rigged
click on image to enlarge

Model 115 drifter
rigged for deep drogue
click on image to enlarge

Overview

The Model 115 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. As the drifter moves, onboard electronics acquire a time series of positions using GPS plus optional sensor data. This data is sent to the end user via the worldwide Argos satellite network.

The Model 115 is a lower cost adaptation of the Model 104 GPS/Argos drifter that provides functionality adequate for many applications while remaining compatible with software, deployment logistics, data format, and drifter characteristics of its more advanced sibling. Additionally, the Model 115 is optimized for simple deployment, allowing drifter launches from ships of opportunity by minimally-trained personnel.

Precision Lagrangian current data provided by the Model 115 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 115 features a 12 channel GPS receiver that records position to 0.01 minute of latitude and longitude (18 meters).

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.

Setup and operation

The Mode 115 is shipped from the factory with the desired customer setup saved in EEPROM, where it persists through battery changes. The drifter can be operated using a magnet applied to two marked areas of the drifter hull. A "beep code" audible through the case allows personnel without a computer to monitor and confirm proper drifter operation before deployments. If desired, an internal RS-232 interface port allows the end user to alter the operational setup and save the changes to EEPROM.

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.

A history of innovation

Brightwaters Instrument Corporation has been building autonomous drifting buoys since 1991, with the current Model 115 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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