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TAO Mooring information
Go to:Historical Standard ATLAS Moorings - Surface Mooring Hardware - Sensor Heights and Depths - ADCP Current Meter Moorings - Historical Current Meter Moorings - TRITON Moorings

Schematic of Next generation ATLAS mooring Design of the relatively inexpensive ATLAS (Autonomous Temperature Line Acquisition System) mooring was initiated by PMEL's Engineering Development Division (EDD) in 1984 (see Standard ATLAS Moorings, below). By the mid-1990's, a reengineering effort was underway to modernize the ATLAS mooring with emphasis on:
  • improving data quality
  • adding new sensors
  • increasing temporal resolution of internally recorded data
  • improving reliability to extend system life
  • simplifing fabrication procedures
  • reducing costs
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This effort used as many of the components and procedures of the existing system as possible, thereby minimizing the impact on the infrastructure that supported the array.The first NextGeneration systems were deployed in the array in May 1996. The transition to NextGeneration systems throughout the array was completed in November 2001.

picture of module installationA significant Next Generation ATLAS improvement over the Standard ATLAS is the incorporation of inductively coupled sensors for subsurface data. The sensors clamp onto the wire rope strength member that serves as one of the inductive elements. This simplifies fabrication, eliminating the themistor cable with its labor-intensive assembly and deployment procedures.
Addressable modules on the cable allow the system to be expanded for new sensors by adding the appropriate hardware and software interfaces. Flexibility in the design also allows the interface of additional sensors including rainfall, short-wave and long-wave radiation, barometric pressure, ocean salinity and currents. Most measurements are made at a sample rate of 10 minutes, with the exception of barometric pressure (1 hour), short-wave and long-wave radiation (2 minutes), and rainfall (1 minute). These high temporal resolution data are recorded internally and available after mooring recovery.


schematic of standard ATLAS mooring After testing and deployment of prototype ATLAS moorings, the first elements of the large scale monitoring TAO array were deployed in the eastern Pacific in November 1984. The full TAO array was eventually completed in December 1994.The standard ATLAS mooring had a design lifetime of one year, and the system proved to be robust and reliable. Over 500 Standard ATLAS moorings were deployed between 1984 and 2001. The final standard ATLAS was recovered in November 2001 and NextGeneration ATLAS moorings are now used exclusively in the TAO array.

Standard ATLAS moorings measured surface winds, air temperature, relative humidity, sea surface temperature, and ten subsurface temperatures from a 500 m long thermistor cable. Daily-mean data were telemetered to shore in near real-time via NOAA's polar-oribiting satellites and Service Argos. A small subset of hourly values (2-3 per day) coinciding with satellite passes were also transmitted in real time. Hourly values of surface data were internally recorded and available after mooring recovery.


The TAO surface buoy is a 2.3 m diameter fiberglass-over-foam toroid, with an aluminum tower and a stainless steel bridle. When completely rigged, the system has an air weight of approximately 660 kg, a net buoyancy of nearly 2300 kg, and an overall height of 4.9 m. The electronics tube is approximately 1.5 m long, 0.18 m diameter, and weighs 27 kg. The buoy can be seen on radar from 4-8 miles depending on sea conditions.

Non-rotating 3/8" (0.92 cm) diameter wire rope jacketed to 1/2" (1.27 cm) is used in the upper 700 meters to guard against damage from fish bite. Standard ATLAS thermistor cables were fixed to the mooring wire with wire rope clamps. Plaited 8-strand 3/4" (1.9 cm) diameter nylon line is used for the remainder of the mooring. Anchors are fabricated from scrap railroad wheels, and typically weight 1900-2000 kg. All hardware is standard equipment as used in other PMEL taut-line moorings and deployments follow the traditional anchor last routine.

Moorings are deployed in water depths between 1500 and 6000m. To ensure that the upper section of the mooring is nearly vertical a nominal scope of 0.985 (ratio of mooring length to water depth) is employed on the moorings in water depths of 1800m or more. At a few sites, slack moorings with scope 1.35 have been deployed due to either shallow bathymetry or severe current regimes. In these cases, the upper portion of the mooring is keep fairly vertical (but less so than taut-line moorings) by using a reverse catenary design.


Standard instrument heights for ATLAS mooring meteorological sensors. LWR is Long Wave Radiation sensor, SWR is Short Wave Radiation sensor, Rain is rain gauge, ATRH is air/relative humidity sensor, BP is Barometric Pressure sensor

Meteorological sensor
Height (m)
4 m
3.5 m
3.5 m
3.5 m
3 m
3 m

Standard instrument depths for ATLAS moorings by ocean basin are listed below: SST/C is Sea Surface Temperature and Conductivity sensor. T1, T2, ...., T10 are subsurface thermistors. TP9 and TP10 are subsurface temperature and pressure sensors. TC1,...,TC6 are subsurface temperature and conductivity sensors. TV1 is a velocity measurement made at 10m depth by a Sontek acoustic Doppler current meter. The current meter is cabled to a temperature module at 13m depth, which relays both velocity and temperature data to the surface buoy.

Pacific Ocean
T1 T2 T3 T4 T5 T6 T7 T8 TP9 TP10
Depths (m) east of 155°W
20 40 60 80 100 120 140 180 300 500
Depths (m) at and west of 155°W
25 50 75 100 125 150 200 250 300 500

Atlantic Ocean
Depths (m), all sites 1 20 40 60 80 100 120 140 180 300 500

Indian Ocean
Depths (m), all sites 1 10 10/13 20 40 60 80 100 120 140 180 300 500


Schematic of current meter moorings ACOUSTIC DOPPLER CURRENT METER MOORINGS

Subsurface Acoustic Doppler Current Profiler (ADCP) moorings are deployed at a few locations to provide velocity profiles the upper 200-300 m of the water column. ADCP moorings are mostly deployed at equatorial locations where geostrophy breaks down and direct velocity measurements are required. ADCPs are usually deployed in tandem with nearby ATLAS moorings, which may also measure velocity as a backup to the ADCP and/or to provide velocity data near the surface where acoustic backscatter from the sea surface interferes with the ADCP signal. The vertical resolution of the ADCP is about 8 m. ADCP data are available only after the subsurface moorings are recovered.


From the 1980s to the mid-1990s, older style current meter moorings were deployed at a few equatorial sites in the Pacific (0-156E, 0-165E, 0-140W and 0-110W). Upper ocean currents were measured at 4 to 7 discrete depths in the upper 300 m using vector-averaging and vector measuring mechanical current meters. In general, these moorings differed from ATLAS moorings in that no subsurface data were telemetered in real time and in that subsurface data were internally recorded at higher sample rates than Standard ATLAS systems. Between 1990 and 1995, current meter moorings included downward looking Acoustic Doppler Current Profilers (ADCP) mounted in the surface toroidal float and were referred to as PROTEUS (PRofile TElemetry of Upper ocean currentS) moorings. PROTEUS mooring deployments stopped in 1995 because fish backscatter interfered with the acoustic signals and seriously contaminated the velocity measurements.

These older style current meter moorings were eventually replaced by Next Generation ATLAS moorings with paired subsurface ADCP moorings. Instrument depths for the older current-meter moorings were different than for ATLAS moorings and varied over time. For graphical information on these instrument depths, see the TAO data availability page. In NetCDF files used for web displays, temperatures from historical current meter moorings have been regridded to standard ATLAS depths.


In October 1999, responsibility for moorings along and to the west of 156E was assumed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) which has deployed Triangle Trans-Ocean Buoy Network (TRITON) buoys at those locations. Data from both ATLAS and TRITON moorings are merged in a common data base and available from both PMEL and JAMSTEC.

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