Development of Lagrangian Drifter for ocean mapping, and the collection of ocean data to support research in ocean visualization, circulation and acidification.

Student: Om Deshmukh

Supervised by: Dr. Chrys Chrysostomides and Dr. Thomas Consi 

Abstract

Technological advancements have opened opportunities for new ways of observing the ocean. The overall goal of this project is to develop a cost-effective hardware technology (ocean drifters), which will enable scientists to design, build, operate, and maintain a portable observatory. This observatory will be capable of providing a continuous data-stream for analysis, interpretation, and communication to scientists who are researching ocean circulation and acidification among other parameters.

The autonomous mobile drifters developed will be equipped with sensors to sample various water parameters (including Temperature, pH, Conductivity, Dissolved Oxygen levels, and Turbidity) and components for the satellite communication link to send and receive short messages from anywhere on Earth. 

Objective

The ocean is defining the future of our planet and it is critical to maintaining the health of our oceans. By developing our own drifter, we not only reduce the total costs but allow the general public to develop their own self-made drifters– adding their data to the Sea Grant database. This cost-effective solution will help gather important information about our oceans at a larger scale and take proactive actions wherever needed to save our oceans.

The goal of this project is to develop a cost-efficient Lagrangian ocean drifter to log various water parameters – pH, temperature, conductivity, dissolved oxygen levels, and turbidity, and integrate it into an Ocean Mapping Interface (OMI) for ocean mapping and making the data easily available in the public domain in real-time.

Project Overview

A surface drifter is an oceanographic device floating on the surface to investigate ocean currents and other parameters like temperature or salinity. The drifter approximately follows the current at the ocean surface and can be used in oceanographic research.

Modern drifters are typically tracked by satellite, often GPS1. They are known as Lagrangian drifters as the location of the measurement reading moves with the currents. They have been used to help map out the ocean base.

This project consists of two separate devices, the Microstar Drifter and Independent Drifter – an original self-assembled drifter based on an initial design at MIT Sea Grant.

INDEPENDENT DRIFTER

The objectives for the Independent Drifter were familiarization with the Rockblock satellite communication module and Atlas Scientific sensors, power optimization, programming and testing the ability for the sensor to sample and transmit data through the Iridium satellite network. 

There are three main reasons to develop the independent Drifter at MIT Sea Grant

Hardware Implementation

All the components used in the Independent drifter are off the shelf and low-cost which are available widely and can be used to build similar drifters by anyone to help MIT Sea Grant develop a robust data-driven regional forecasting system of aragonite and other quantities of interest (QoI) – an acidification learning system – that will be continuously updated and improved in time.

 Rockblock 9603 – Iridium SatComm Module

The RockBLOCK 9603 receives and sends messages anywhere on Earth from the drifter. At the core of RockBLOCK 9603 is an Iridium 9603 modem. The RockBLOCK contains the 9603 modem and provides it with an antenna and power supply requirements. It connects the modem’s serial interface via a breakout connector over serial, and has an SMA connector for external antenna usage [7]. 

Key features

Power Requirements – RockBLOCK 9603 runs on a 5v DC power input & also has the ability to run from a 3.7v DC LiPo/LiIon source. It requires a minimum of 100mA for operation, but has a sleep state to conserve power between transmissions if required.  

 Atlas Scientific Sensors [5]

Ph Sensor: The Ph Probe can be fully submerged in the fresh and saltwater indefinitely. 

Dissolved Oxygen:  Use the Dissolved Oxygen Probe to determine the concentration of oxygen in aqueous solutions in the field or in the laboratory.

Temperature Sensor: Temperature Sensors measure the amount of heat energy or even coldness that is generated by an object or system, allowing us to “sense” or detect any physical change to that temperature producing either an analogue or digital output.

Conductivity Probe: The Conductivity Probe can be used to measure either solution conductivity or total ion concentration of aqueous samples being investigated in the field or in the laboratory. Conductivity is one of the most common environmental tests of aquatic samples.

software algorithm

cost efficiency

One of the goals of this project was to create a design that was cost-friendly drifter design that could easily be built by anyone without expertise. A standard Surface Velocity Program (SVP) drifter costs roughly US $1,800, with additional expenses for added sensors (e.g., ~US$1,300 for a barometer, ~US$6,000 for salinity, ~US$4,500 for wind speed and direction, etc.). The device that this report is proposing has an estimate of around $700 including the sensors.

 Challenges & Solutions

Issues that needed to be resolved included those of the Rockblock 9603, Atlas scientific sensors. 

A surface drifter is an oceanographic device floating on the surface to investigate ocean currents and other parameters like temperature or salinity. The drifter approximately follows the current at the ocean surface and can be used in oceanographic research.

Modern drifters are typically tracked by satellite, often GPS1. They are known as Lagrangian drifters as the location of the measurement reading moves with the currents. They have been used to help map out the ocean base.

This project consists of two separate devices, the Microstar Drifter and Independent Drifter – an original self-assembled drifter based on an initial design at MIT Sea Grant.

The Microstar Drifter’s drag area ratio is 40. It follows water with a slip of less than 2 cm/s in winds up to 10m/s.

 The Microstar drifter uses a GPS sensor to determine its position, and the Mobitex terrestrial cellular communications system to communicate the position information in real-time. This configuration allows position data with accuracy to be sampled every few minutes and communicated inexpensively. The real time communication of highly accurate position data enables the drifters to be retrieved and redeployed, further increasing the economy. [1]

drifter deployment & testing

A Series of Drifter deployments were conducted in the lab, and in the external environment – i.e. off Charles River in Boston, MA to test several ocean parameters and the location tracking.

The experiments were run in various locations with a river bottom varying between 15 to 30 meters depths. 

drag

The drag force is the force acting against the motion of a body traveling through a fluid. By increasing the ratio of the drag force of the drouge to the surface float, the drifter will more accurately follow the flow of water at the depth of the drouge, and will thus provide a better representation of the ocean currents. The drag force of the Drifter can be calculated using the equation:

D = ½ CpAv^2

Where

C is the drag coefficient

p is the fluid density

A is the cross sectional area

v is the velocity of the object through the fluid

The Microstar Drifter’s drag area ratio of a drogue to surface float is 40. It follows water with a slip of less than 2 cm/s in winds up to 10 m/s.

ocean mapping interface

The vast majority of our oceans are still virtually unmapped and unexplored. Ocean Mapping2 Interfaces gives us a capability to create a map out of the ocean using this innovative technology and sensors on the drifters. MIT Sea Grant seeks to encourage collaborative ocean research with its mapping technology to better understand our oceans and create awareness of the advantages of data sharing to mitigate environmental impacts. 

MIT Sea Grant is developing the “Digital Ocean”, a marine data storage, analysis, and visualization system for use by scientists and the public. It helps provide essential tools for ensuring the healthy sustainment of our economic and marine resources by gathering, analyzing and making data widely available [6].

Next Steps

Before the end of this year, the current generation drifter will be complete, with the additions of the external encasing to waterproof the design, formatting of data into a .csv format, and adding the dissolved oxygen sensor (and additional sensors if needed). Next-generation improvements are promising: to design the second-generation surface float with a probe that once deployed, can detect ocean properties, and descend to a controllable (depth) to gather data at various ocean layers. An even further generation of this design would be to control the drogue, which allows the device to control the currents (at a specific depth) it is following.

Working with Sea Grant Researcher Ben Bray to create a specific visualization software for our drifters, thus enabling a network of public drifters built by those interested, who can then adopt the design and code, and contribute their data to the Sea Grant database. 

Conclusions

The Microstar Drifter was assembled and deployed in the Charles River. The RTD sensor then underwent testing, in a temperature-controlled water bath, for both accuracy and precision. The self-assembled drifter is able to sample, transmit, and print the values that it is receiving in 5 minute to 12 hour intervals. 

Upon completion, the self-designed drifter functioned flawlessly– data was received sustainably at 5 minute intervals. Probes were then tested for pH, GPS, and conductivity (which determines the concentration of pollution in the water). Currently, the device transmits data through the Iridium satellite network, which currently can be received and displayed onto the serial monitor. Upon receipt of the dissolved oxygen sensor, which is currently programmed, testing of the sensor will begin and the drifter deployed. 

This deployment of the Microstar Drifter and lab testing of the self-made drifter is promising for its deployment, which will occur following the assembly of the watertight enclosure. This is a positive step towards the rectification of the natural balance within biodiversity, through expanding our current understanding of the ocean. 

This deployment of the Microstar Drifter and lab testing of the self-made drifter is promising for its deployment, which will occur following the assembly of the watertight enclosure. This is a positive step towards the rectification of the natural balance within biodiversity, through expanding our current understanding of the ocean. 

This system will help support research in ocean circulation and acidification and will integrate into research Ben Bray is working on: developing a visual representation of ocean data that is easily available for the general population to access and understand. This will have a dual purpose, to provide reliable data for scientists to use, and to be a data-driven collaboration for the public, to build, understand and advocate for the care of the ocean.