River drifter with Salinity sensor installed
- GPS based tracking
- Iridium Short Burst Data (SBD) telemetry
- Nortek 4-beam ADCP (1Mhz or 2Mhz head available)
- Sea Surface Temperature
- Sea Surface Salinity (BTO)
- Directional Wave Spectrum (BTO)
- Variable sampling rate down to 5 minutes
The River Drifter (RD) stems from the CODE drifter design and was conceived and designed at Scripps Institution of Oceanography. This development originated from the need to have a Lagrangian drifter capable of operating in calm and shallow water bodies, such as lagoon and estuaries, or in the surf-zone, while also measuring the water depth and vertical shear of the three-dimensional currents underneath. A fleet of RDs can be used, for example, to study the dispersion of near-surface water and pollutants and their dependence on bed-forms and on the vertical shear of the horizontal currents.
The central body of the RD is 0.6 m long and the cross-sectional area of the sails and hull combined is 0.39 m2 (Figure 8). As for the CODE drifter, the hull contains the battery pack and the LDL controller to manage the sensors, the data acquisition and telemetry. The sensors suite include a GPS engine, data logger, as well as a specially designed acoustic Doppler current profiler (ADCP) by Nortek. The ADCP has 4 transducers, three to measure the three-dimensional water velocity and the fourth to measure the water depth. Two versions of the RD ADCP exist, 1 Mhz and 2 Mhz, which allow operations at different water depths and with different vertical resolutions of the current. The data telemetry options include a direct RF link and the Iridium (Short-burst Data -SBD- modem) for global applications. A direct data link is also available through a wet-pluggable connector located next to the dual Iridium/GPS antenna which allows direct communications with the instrument for ADCP calibration, sensor configuration, data retrieval and diagnostic output via RS-232 protocol.
Depending on the duty cycle type of batteries, the endurance of the RD can vary from 1 to 7 days. A full description of the instrument and examples of applications can be found in Postacchini et al. (2016).
Heart of the River drifter is the LDL buoy controller, enabling a number of sensor payloads. The basic sensor suite includes a GPS engine, Nortek ADCP, and SST but ancillary Sea Surface Salinity measurements are also available.