CTD Profiling from a moving vessel
Achieve over 500m vertical profiles while underway at 10kts
Convenience of expendables without the environmental impact
High quality SeaBird Electronics freefall CTD data
Compact and portable for deployment on multiple vessels

The Oceanscience UnderwayCTD provides research grade CTD (conductivity, temperature, and depth) profiles while underway at up to 20kts. The unique freefall profiler offers researchers vertical profiles even as the ship is moving away from the deployment location. The innovative deployment winch and re-spooling mechanism allows the probe to be recovered and re-launched time after time without ever needing to stop or slow down. Profiles are gathered quickly, allowing excellent spatial resolution for CTD transects. The UnderwayCTD can be installed on practically any vessel. The small footprint winch can be mounted on a post or rail, and can be set up and operated by one person. The UnderwayCTD components can be transported from ship to ship with ease, making the system ideal for gathering high quality data from vessels of opportunity.
The UnderwayCTD in Action
An evening on board the R/V Knorr with the UnderwayCTD

Deployment of the UnderwayCTD in 45 kt North Atlantic winds (April 2011). Courtesy of Dave Ullman, Mark Harris, and Emily Dougan (University of Rhode Island). Warning: not for the faint hearted.
An UnderwayCTD Deployment in the tropical Pacific with WHOI

Researchers at Woods Hole Oceanographic Institution using the UnderwayCTD for the fourth straight year on STRATUS cruises (April 2011). Courtesy of Sean Whelan (WHOI).
UnderwayCTD Data Examples

The fast sampling rate and highly accurate sensors used in the UnderwayCTD probe generate excellent data adequate for the most exacting scientific research programs. Compared to expendable probes such as XBTs and XCTDs, the data are of significantly greater accuracy. A plot of raw, uncorrected data from a 400m UnderwayCTD cast conducted while at 12kts is shown below.

The fast turnaround between profiles allows extremely detailed CTD transects to be completed. A high resolution hydrographic section derived from CTD data gathered using the UnderwayCTD deployed at 10kts is shown below.

Extracted from Rudnick, D. L., and Klinke, J., "The Underway Conductivity-Temperature-Depth
Instrument,"Journal of Atmospheric and Oceanic Technology, 2007.

Principle of Operation

The UnderwayCTD uses a freefall data-logging probe that is tethered to the ship by high strength line and not a conducting cable. To achieve deep vertical profiles, a special tail spool on the probe is pre-loaded with line from the UnderwayCTD winch before every cast. As the probe falls, the line on the tail spool is paid out at the same time as line is paid out from the winch on the ship, similar to the operation of an XBT or XCTD. As the probe drops with very little drag to slow it down, very deep profiles are possible even with the ship moving at over 10kts.

The UnderwayCTD deployment consists of four stages:

  1.   Deployment Probe dropped from aft deck. Line simultaneously spools off the winch and the probe tail spool
  2.   Recovery Probe recovered to the ship using high speed winch
  3.   Respooling Line is reloaded onto the probe tail spool ready for the next cast
  4.   Downloading Fast Bluetooth data transfer extracts data in seconds

Probe motion is completely decoupled from the ship throughout the downcast, leading to fast and highly accurate profiles.

Click here to learn more about how the Oceanscience Underway profilers work.

CTD Probe Specifications

The UnderwayCTD uses a custom freefall CTD probe manufactured by industry leader Sea Bird Electronics. Using field-proven and highly accurate conductivity, temperature, and pressure sensors, exceptional quality results are obtained. The internal electronics and exposed sensor components are carefully designed to withstand deployment and recovery at up to 20kts. Sampling at 16Hz, overall depth resolution of below 25cm is attained at a drop speed of about 4m/s. The specifications of the CTD probe sensors are shown below.

  Conductivity (S/m) Temperature
Resolution 0.0005 0.002 0.5 0.005
Accuracy - Raw Data 0.03 0.01 - 0.02 4 0.3
Accuracy - Processed Data 0.002-0.005 0.004 1 0.02 - 0.05
Range 0 - 9 -5 - 43 0 - 2000 0 - 42

UnderwayCTD Configurations

Several configurations of the UnderwayCTD are available. The tether line thickness and length can be customized for each cruise requirement, and line sections are easily replaced as necessary. Longer line setups give deeper profiling for blue water oceanography; for shallow coastal work the UnderwayCTD can be configured with shorter lengths of thicker line for maximum probe security. For the available standard configurations, download the configurations options information sheet. The general purpose configuration is shown below.

  Profile Depth (m)
Speed (kts) 300 400 500 600 700 800 900 1000

Click here to download the configuration options information sheet.

UnderwayCTD Deployment in Shallow Water

Although developed for profiling in the open ocean, the UnderwayCTD has been adapted to allow successful use in the coastal environment. For profiling down to 250m or less, the tail spool reloading phase may be omitted and the probe simply dropped from the ship with line spooling off the main winch only. For shallow water deployment, this basic configuration represents a cost-effective means to gather high quality CTD profiles very rapidly.

For deployment in 15-100m water depth, the "Slow-Fall" profiler option can be specified. Properly selected buoyancy modules are simply installed on the tail spool to slow the probe descent rate from 4m/s to 1m/s.

Deployment of the "Slow-Fall" UnderwayCTD profiler

A slower descent rate maximizes data quality and offers safe use of the UnderwayCTD in shallow water, even estuaries.

UnderwayCTD Cruise Reports

Oceanscience customers are generating unique datasets with the UnderwayCTD in all of the major world oceans. Some information about particularly interesting projects is included in the application notes below.

  NOAA National Data Buoy Center Deep-ocean Assessment and Reporting of Tsunamis (DART) Program

NOAA Breaks Record Research Grade Profile Depth in Only 50 minutes with the UnderwayCTD - 2,041m!

Woods Hole Oceanographic Institution

Four years of UnderwayCTD Success Stories

University of Washington, Applied Physics Lab

Record-breaking 3,000 UnderwayCTD Profiles Completed in 20 days!

EMAM (Portugal)

First UnderwayCTD Cruise Completed

Frequently Asked Questions

Have a question about the UnderwayCTD? If frequently asked, the answer will be in the FAQ!
Click here for the FAQ Page


TECHNICAL PAPER - Rudnick and Klinke, 2007
TECHNICAL PAPER - WHOI Technical Note 2007
TECHNICAL PAPER - Eddies in the South East Pacific 2009