ARGO, Profiling Floats, and Iridium

Stephen C. RiserDana Swift

School of Oceanography, University of Washington

[acknowledgements to NOAA, ONR, NSF, NASA]

Profiling floats…a modern method of observing the state variables of the ocean circulation….

Floats routinely measure T and S as functions of pressure, and absolute velocity at the parking depth, usually 1000-2000 m.

There is great interest in expanding the capabilities of these floats, including the addition of new sensors and communication links and the ability to operate in ice-covered regions.

Issues: power, weight, unattended

Communications: Service Argos (~ 0.1 baud)

ARGO (not to be confused with Service Argos) is an international program designed to deploy 3000 profiling floats in the world ocean, at approximately 300 km resolution, forming the first real-time in situ ocean observing system

Goal: real-time T and S from the subsurface ocean, globally, real-time

All data on GTS < 24 hr

The UW float group has built and deployed over 400 profiling floats in the past 6 years. Components for these floats are purchased from Webb Research Corp.; construction and preparation are done at UW.

ARGO

JES

BLACKSEA

OKHOTSKSEA

Present status of ARGO: 1244 floats deployed by 14 nations. The full, 3000 float array will be implemented by the end of 2006.

Present uses of data from profiling floats….

Mapping regional circulation (JES; N. Atlantic; Labrador Sea) Studies of convection (JES; Labrador Sea) Large-scale water masses, circulation, and climate (ARGO) Studies of mixing by hurricanes (N. Atlantic subtropics)

New features and technological improvements….

Deep (2000 m) capability throughout the world ocean New sensors I (dissolved oxygen) New sensors II (low, high frequency acoustics) Under-ice capability Faster communications (Iridium)

An example of data from profiling floats….

Each profile contains approximately 500 bytes of data (3 variables x 2 bytes x 71 sample depths + engineering data) and requires 6-10 hours per profile transmitting at the sea surface using the Service Argo system.

An example of a profiling float built at the University of Washington

CTD sensors

Argos antenna

Inflatable bladder (inside cowling)

Faster communcations….

We have built several floats that use the Iridium satellite system instead of the usual Service Argos.

2 floats were deployed in the Antarctic Circumpolar Current south of New Zealand in January 2003. They were configured as surface drifters in order to assess the properties of data transfer using the Iridium system.

Results show that data can be transferred using real 2-way communication at nearly 2400 bps. Mission parameters can be changed in real-time. [Dial-up, X-modem]

Cost is comparable to, perhaps somewhat greater than Service Argos.

Argos: 500 byte transfer requires ~9 hr; Iridium: 20 Kb transfer requires < 10 min!

Iridium/GPS patch antenna

Iridium drifter 006, 1/03 – 5/04

Drifter with Iridium unit installed.

Iridium modem (in this case a 9500 phone unit) and GPS unit.

Data from Float 003 show consistent transfer of a 20 Kb file at rates of about 220 bytes/sec (red data). Some handshaking is necessary at the beginning and end of the data transmission. At the end of each data transmission the float uploads a command file (blue data) giving instructions for the next profile.

Usually a connection is established on the first attempt; in a few cases 2 or 3 attempts are necessary. In most cases the full 20 Kb file can be transferred in one connection.

In general, we can obtain a GPS fix and transmit a 20 Kb file in 10 minutes or less.

SUMMARY….

Profiling float technology is advancing rapidly; there are many uses for the data from these floats, including ocean/atmosphere/climate studies using the global ARGO data.

A major improvement in these floats will come if and when the present Service Argos communication system is replaced with Iridium; much faster data transfer rates, and 2-way communication will be possible.

First deployment of ARGO/Iridium float is anticipated in summer of 2004.