Development of compact, low-cost GNSS drifters at SAC

Realized Drifters ready for deployment at RK Beach, Visakhapatnam

GNSS Antenna

Rip currents are dangerous strong narrow seaward flow of waterusually found in surf zone of many beaches worldwide.

Drifters are very efficient way of measuring dangerous Rip currentsin the high energy surf zone.

They record Latitude, Longitude, velocity and time at 4 Hz rateusing multi-channel GNSS receiver.

The raw data from the drifters are post-processed using a staticBase receiver (installed near the site), to get a very precise position(Kinematic mode H= ± 7mm (DGPS); V= ± 14mm (DGPS))

Under SAMUDRA TDP R&D project, new state-of-art multi-purpose compact and low-cost GNSS drifters have been designed andfabricated at SAC to measure sea surface currents, primarily used for Rip current studies.

GNSS Drifter

Disc to reduce the wave impact

Fins to increase the current drag

Minimal surface area to reduce the wind impact

Net weight (incl. electronics) ~ 6 kg in Air

Team: Surisetty V V Arun Kumar, GSD/GHCAG/EPSA

Jishad. M, OSD(E)/AOSG/EPSA

Ratheesh R, GSD/GHCAG/EPSA

Prof. KVSR Prasad, Andhra University

JRFs, Andhra University

1.0

m

Water level

Design by S V V Arun Kumar (EPSA) and Rakeshkumar Luhar (PFSF-MESA)

Field Photos (14 May 2018) at RK Beach, Visakhapatnam

GNSS AntennaGNSS Receiver

Battery

Flash Memory

Controller

Base Station

Drifter

Rhodamine-B Dye & drifter moving along the rip current

Electronics inside

GNSS AntennaGPS GLONASS

GALILEO

Professional Swimmer released the drifter in mid surf zone

NOTE: Non-swimmers.. Please don’t attempt it

Drifter-A

Schematic of Rip current Experiment

Drifter-B

Spatially averaged nearshore currents from Two drifters

• Rip currents are very strong near the coast and become weak towards theoffshore.

• Currents with speeds ranging from 1.0-1.3 m/s were recorded in the Rip neckduring the experiment.

• They became weak to the order of 0.5-0.7 m/s in the Rip Head.• More number of drifters help us to generate a detailed spatial structure of rip

currents.• Similar experiments will be conducted at every fortnightly interval and the

data will be used as inputs in numerical modelling to understand the Ripcurrent dynamics.

• Future drifters will include compact NaVIC receivers.

Rip Head

Rip Neck

Source: Internet

Rip Head

Rip Neck

Drifter track

These GNSS drifters emerge a technological advancement in many fields of applications including

Rip current dynamics (spatial & temporal structure) Search and Rescue Oil spill monitoring Bloom tracking Pollution dispersion monitoring in the surf zone Bathymetry mapping Nourishment effects River and estuarine flood monitoring Forensic investigation Military and Naval Coast Guard application Coastal research

Source: Grant et al. 2005

Source: Roeland et al. 2012Acknowledgements:Shri. Tapan Misra, Director, SACDr. Raj Kumar, DD, EPSADr. A.S. Rajawat, GD, GHCAG, EPSAShri. Arun Kumar Sharma, Head, GSD, GHCAG, EPSADr. Rashmi Sharma, Project Leader SAMUDRA, Head, OSD(E), AOSG, EPSAShri. Rakeshkumar Luhar, PFSF, MESA for the design and fabricationShri. Nitin P Thacker, General Manager, PFSF, MESA