Middle East Technical University
Profiling Drifters

Table of Contents

  1. Introduction
  2. Automatic data processing & web-page generation
  3. Reliability statistics
  4. Argos Data Telemetry
  5. GTS publication of float profiles
  6. Contact Information
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Welcome to the Web Site for the Middle East Technical University profiling drifter study.

Automatic data processing, data distribution, & web-pages generation

This web site contains thousands of dynamic objects that must be updated as new data become available. Examples include postscript files, jpeg images, tables, HTML files, hydrographic profile data, and data distribution services. These objects are automatically generated or maintained in quasi-real-time by an extensible system of autonomous software. Consequently, maintaining this web site requires no regular manual intervention.

Reliability Statistics

The reliability of the floats can be measured in terms of the number of profiles expected during a specified time period as compared to the number actually executed. These statistics are presented in the following table (updated daily).

Profiling Drifter Reliability
Profiler Reliability Statistics
for the period from Jan 01 00:01 GMT 2000 to Jul 20 20:32 GMT 2006.
Group Size Profiles Executed Profiles Expected Reliability (%)
APEX260 5 443 721 61.4
APF8 5 443 721 61.4
Total 5 443 721 61.4

Argos Data Telemetry

The data are recovered from the floats via the Argos system. These floats spend 7 to 8 hours transmitting on the surface with one message transmitted every 46 to 54 seconds. This means that each float transmits from 470 to 530 messages for each profile. Most of these transmissions are lost because no satellite happens to be overhead. In fact, telemetry statistics below show that only 7 to 10 percent of these messages are transmitted when a satellite is overhead. Some statistics have wider appeal and we have collected several of them in the table below (updated daily). All of these statistics were computed on a per-profile basis.

Middle East Technical University Profiling Drifter ARGOS Receipt Statistics
As of 21:04 GMT on Dec 17, 2011 Average Per-Profile Statistics for ARGOS Data Telemetry
0587 73 3 4.1% 16 42% 239 158 66% 80 34% 102 64% 57 36%
0631 115 0 0.0% 18 44% 250 171 69% 78 31% 109 63% 63 37%
0634 125 18 14.4% 16 35% 226 133 62% 92 38% 75 56% 58 44%
1325 187 15 8.0% 18 35% 261 153 62% 108 38% 88 57% 65 43%
1550 173 18 10.4% 16 39% 264 160 61% 104 39% 102 63% 57 37%
2206 129 16 12.4% 12 35% 197 113 61% 84 39% 66 57% 47 43%
2619 173 14 8.1% 13 36% 215 134 62% 82 38% 79 57% 55 43%
Ensemble Average: 8.2% 15 38% 236 146 63% 90 37% 89 59% 57 41%
Standard Deviation: 4.9% 2 4% 25 20 3% 12 3% 16 3% 6 3%

Publication of Profiles to the Global Telecommunications System (GTS)

The profiles from these floats are published in quasi-real-time via the GTS system using TESAC/KKXX format. Each float is assigned a unique WMO identifer that can be found on our Present Status web page. The status of each profile with respect to GTS publication is also available on our GTS Status web page.

Quality control of profile data is managed automatically by a QC module that is integrated into the GTS publication software. Each profile must pass a number of quality control criteria in order to be published via GTS. If even a single observation in the profile violates any of the criteria then publication of the entire profile is inhibited. The following criteria are used to inhibit publication of rejected profiles.

  1. A profile that is older than 30 days will be rejected as required for GTS publication.

  2. A profile that does not have a valid location fix will be rejected as required for GTS publication. This might happen if ARGOS reception is poor.

  3. A profile with a gap between adjacent observations that exceeds 300 decibars will be rejected. A profile with the shallowest observation deeper than 300 decibars will also be rejected. This is to maintain reasonable accuracy in the pressure to depth conversion calculation as required for GTS publication. This might happen if ARGOS reception is poor.

  4. A profile with an observation where the pressure is reported to be less than zero or greater than 3000 decibars will be rejected as indicative of a pressure sensor problem or malfunction.

  5. A profile with deepest observation less than 50 decibars is rejected. For example, this might happen if the float drifts into shallow water or becomes entangled in mats of surface-drifting seaweed.

  6. A profile with pressures that are not monotonic will be rejected. This is intended as a general criterion that a properly collected profile should satisfy.

  7. A profile with fewer than 5 observations will be rejected. This is intended as a general criterion that a properly collected profile should satisfy.
This list is exhaustive in the sense that any profiles that do not violate these criteria will be published via GTS. In the absence of established GTS quality control criteria, the approach of caveat emptor has been assumed with respect to the hydrographic data.

Contact Information: Please note that the data and material on this web site are the property of the Middle East Technical University. Questions concerning the information available here can be addressed to Mr. Temel Oguz, (email: oguz@ims.metu.edu.tr).

This web site was developed and is maintained by Dana Swift (email:swift@ocean.washington.edu) of the University of Washington, Seattle, Washington.

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