Why is this instrument called a drifter?
These instruments sit at the surface of the ocean and are transported via near-surface ocean currents. They are not fixed to the ocean bottom, therefore they “drift” with the currents. For this reason, these instruments are referred to as drifters, or drifting buoys.
How do drifters work?
The surface float contains sensors that measure different parameters, such as sea surface temperature, barometric pressure, salinity, wave height, etc. Data collected from these sensors are transmitted to satellites passing overhead, which are then relayed to land-based data centers.
What parameters do drifters measure? / What sensors are possible?
All drifters measure sea surface temperature and location; the locations are used to calculate ocean current velocities. Additional sensors can be added such as barometric pressure, salinity, wave height, wind speed and direction, optical sensors, and internal surface float diagnostic sensors. Each measurement requires an additional sensor, while wave height measurements also require the absence of a drogue.
A barometer on the top of the float is used to measure sea level barometric pressure. These measurements have been shown to significantly improve weather forecasts.
Sea surface temperature is measured by a thermistor (thermometer) on the bottom of the float.
Sea surface current velocities are calculated by the change in position of the drifter over time. The surface float of the drifter is attached to a large holey-sock drogue (also known as a sea anchor) which comprises most of the area of the instrument. The drogue is centered at a depth of 15 meters.
A salinity sensor (specifically, a highly accurate pair of conductivity and temperature sensors) is used to measure sea surface salinity at the base of the surface float. This can also be done deeper on the tether between the float and the drogue.
A sonic anemometer and a wind vane are used to measure wind speed and wind direction.
Do all drifters measure sea surface temperature?
All drifters are equipped with a sea surface temperature sensor at the bottom of the surface float, which sits approximately 15cm below the ocean surface.
Do all drifters measure ocean current velocities?
As long as the drogue remains attached, all drifters measure near-surface ocean current velocities. If the drogue is lost at sea, the wind and waves play a greater role in moving the drifter.
What is a drogue?
The drogue, also known as a sea anchor, extends approximately 20m deep and is designed to move with the near-surface ocean currents. Because the drogue and surface float are connected by a long tether, the surface float is therefore moving with the near-surface currents as well. Without the presence of a drogue, the surface float will also be transported by wind and waves, much as a ping pong ball or beach ball is pushed across the surface of a pool.
Why do drogues have different colors and patterns?
The GDP requires that drogues are made of cordura nylon with rip-stop, with specific dimensions, but the GDP does not require a specific color for their drogues. As a result, drogue manufacturers often use surplus cordura nylon material from other jobs, which may consist of fluorescent pink, neon green, or even camouflage.
What does a drifter look like?
A drifter consists of a surface float, tether, and drogue (i.e., sea anchor). The surface float is buoyant and remains at the ocean surface, while the sub-surface drogue extends to roughly 20m depth (centered at 15 meters). The surface float and drogue are connected by a long, wire rope called a tether, which is encased in a polyurethane sheathing to provide added strength and prevent corrosion.
How large are drifters (weight and dimensions)?
The surface float ranges from 30.5 cm to 40 cm in diameter, while the drogue diameter is approximately 61cm. Total weight (of surface float and drogue) is roughly 50 lbs. Compressed and packaged for shipping/deployment, drifters measure roughly 61cm x 61cm. However, once deployed, the drogue and tether unfurl, extending to roughly 20m beneath the ocean surface.
What are drifters made of?
The surface float is made from form-injected ABS plastic. The surface float contains electronics that acquire and process sensor measurements, D-cell alkaline batteries to power the drifter, and an antenna to transmit the data. The tether is an impregnated polyurethane wire and the drogue is comprised of PVC tubing and nylon cloth material.
How is a drifter powered and how long does it last?
Drifters are powered by battery packs consisting of D-cell alkaline batteries, and are designed to last at least 18 months.
How long does it take to build a drifter?
It takes a considerable amount of time to design the electronic components and computer programs necessary, yet with all materials on-hand, it takes approximately 1 week to assemble each drifter. Of course, manufacturers often build drifters in batches. Therefore, assembling components and testing a larger number of drifters at once increased production and minimizes the amount of time needed to shift from one procedure to another. While drifters are not assembled on a conveyor belt, imagine this process as an assembly line, as each drifter within the batch receives the same components before moving on to the next item on the production checklist.
How much does a drifter cost?
Drifter pricing varies from one manufacturer to another, so we encourage you to contact each manufacturer for a detailed quote. That said, 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.)
Where can you buy a drifter?
Please find contact information for each of the commercial drifter manufacturers at aoml.noaa.gov/phod/gdp/manufacturers
What is the GDP?
The Global Drifter Program is a part of the Global Ocean Observing System, which maintains a 5 x 5 degree array of ~1300 drifters. The program manages the collection, analysis, and distribution of the data acquired by these drifters.
How is the GDP managed? / How is GDP organized?
The GDP is managed with close cooperation between:
Liaisons between the GDP and individual research programs that deploy drifters are maintained by Drs. Rick Lumpkin (AOML) and Luca Centurioni (SIO).
What are the goals of the GDP?
The primary goal of the GDP is to establish a global array of drifters with drifters present in each 5 x 5 degree grid of open ocean and to provide these data in near-real time for weather prediction and ocean state estimation. The Global Drifter Program is also tasked with providing quality controlled data for scientific use.
When will the GDP array be complete?
The GDP array reached its goal size of 1250 drifters in a 5 x 5 degree array on September 18, 2005 and has been maintained since. It was the first component of the Global Ocean Observing System to reach completion.
How do you deploy a drifter?
Complete instructions, in multiple languages, can also be found at
Where are drifters deployed?
Drifters are deployed throughout the world’s open oceans. To view a map of the current drifter locations (updated weekly), please visit aoml.noaa.gov/phod/graphics/dacdata/globpop_countries.
How many drifters are deployed each year?
Approximately 1000 drifters are deployed each year by the GDP and its international partners to maintain the global 5 x 5 degree array of ~1300 drifters. To view the number of deployments per year and their locations, please visit
How are drifter deployment locations determined?
The goal of the drifter program is to implement one drifter in each 5 x 5 degree grid across the globe. Of course, with strong convergent and divergent currents to contend with, as well as limited access to deployment vessels, the GDP works closely with more than fifty domestic and international agencies to coordinate deployment efforts. To maximize spatial drifter coverage and ensure its goals are met, the GDP created a set of Drifter Deployment Value Maps which are used throughout the community to identify the highest value deployment locations.
Who deploys drifters? / Who uses drifter data?
How can students adopt buoys?
If you, or your classroom would like to adopt a drifting buoy, please visit the Adopt a Drifter Program and complete the application under the banner “How to Adopt a Drifter.”
How long does it take to ship drifters across the world?
To minimize costs associated with global transport, drifters are shipped via ocean freight, on large container ships. Therefore, depending on the destination, shipments vary between a couple of weeks to four months for more remote and isolated regions of the world.
Do drifters pose any hazard to people, wildlife, the environment or shipping?
Drifters are not known to harm marine wildlife. Conversely, recovered drifters often contain crustaceans, which are known to attract larger species, creating a micro-habitat.
What’s the longest time a drifter has transmitted quality data?
The longest lasting drifter on record transmitted for 10 years, 4 months, and 21 days.
What should I do if I find a drifter?
If you find a drifting buoy, please Contact a member of the Global Drifter Program with any/all information listed on the surface float. If the drifter remains active, with functional batteries and operational sensors, we’ll attempt to have the drifter re-deployed. If the batteries and/or sensors are no longer operational, the drifter can be disposed. These drifters contain no hazardous material, so simply dispose of the drifter as you would any other alkaline battery product.
What if I have additional questions about drifters?
What if I have questions about drifter data?