University of Washington
North Atlantic PALACE Floats

Introduction

This project, sponsored by the US National Science Foundation, is designed to examine the formation and circulation of the so-called "18-degree water" of the North Atlantic, using the technique of profiling ALACE (PALACE) floats. Components for these instruments are purchased from Webb Research, Inc., of Falmouth, MA, USA, and final assembly, calibration, and ballasting operations are carried out at the University of Washington in Seattle. In all, approximately 72 PALACEs have been deployed as part of this project. Other NSF-sponsored projects in the N. Atlantic using PALACE floats are also underway, in both the subarctic gyre and in the subtropical gyre, under the direction of scientists from other institutions, including Woods Hole Oceanographic Institution, Scripps Institution of Oceanography, the University of Miami, and the NOAA/AOML Laboratory. All of these projects are part of the Atlantic Climate Change Experiment (ACCE), a 5-year program sponsored by NSF to examine ocean-atmosphere interaction in the N. Atlantic region and the ocean's effect on climate change.

The first PALACEs were launched in the 18° C water region (20°-40° N, 40°-80° W) in July and August of 1997 from the R/V Knorr. Beginning in November of 1997, most floats were deployed from Voluntary Observing Ships (VOS). Between November, 1997 and March, 1998 a total of 43 VOS deployments of PALACE floats were successfully executed.

Reliability Statistics

The reliability of the buoyancy engine can be measured in terms of the number of profiles expected during a specified time period as compared to the number actually executed. The hydrographic data are not used to qualify or disqualify profiles and therefore these statistics are properly interpreted as measuring the reliability of the buoyancy engine as an elevator. However, the buoyancy engine does depend on the sensor module for pressure data in order to function properly.

Heterogeneous Reliability Statistics

The following table (updated daily) tabulates the number of profiles expected from the ensemble of Atlantic floats versus the number executed since deployment. Each Atlantic float was expected to serve a two-year mission after deployment but many continue to function well past their two-year mission has expired. The phrase Heterogeneous Reliability Statistics refers to the inclusion of all floats without regard to how long each has been in the field. Newly deployed floats are included and even the floats that have completed their two-year missions are counted as if they are still expected to continue to profile.

UW 18 Degree Water PALACE Float Reliability
Profiler Reliability Statistics
for the period from Jul 01 12:01 GMT 1997 to Jan 23 11:23 GMT 2002.
Group Size Profiles Executed Profiles Expected Reliability (%)
APEX180 10 638 995 64.1
APF-2 61 5557 6283 88.4
APF-3 4 289 412 70.1
APF-5 8 467 789 59.2
R1 63 5675 6489 87.5
Total 73 6313 7484 84.4

The R1 PALACE Float: The R1 model of PALACE has reached a mature phase of the development cycle and has proven its reliability. A total of 41 of the R1 floats in the table were deployed using the VOS method. The remaining 22 R1 floats were deployed from research vessels. The R1 model of PALACE is manufactured by Webb Research Corporation (WRC).

The APEX Float: The APEX is a newer model of profiling float that has been tested in the subtropical North Atlantic since 1997. Seven Atlantic VOS deployments of APEX instruments equipped with Sea-Bird CTD modules were conducted between September, 1998 and February, 1999. These trials were designed to test the APEX in preparation for the Japan/East Sea experiment. The APEX is also manufactured by WRC.

Argos Data Telemetry

The data are recovered from the floats via the Argos system. Most of our floats spend 11.5 to 15 hours transmitting on the surface with one message transmitted each 84 to 96 seconds. This means that the floats transmit from 430 to 645 messages for each profile. Most of these transmissions are lost because no satellite happens to be overhead. In fact, telemetry statistics show that only 7 to 10 percent of these messages are transmitted when a satellite is overhead. We are experimenting with various factors that affect data telemetry and evaluate the results using many different types of statistics.

Status Table with engineering information.


The Lagrangian component of the 71 PALACE floats available, as compiled by the Subsurface Float DAC, consists of the surface locations recorded by Service Argos, with no smoothing or extrapolation to predicted surfacing or sinking locations.


Link to the webpage for this experiment.