Middle East Technical University
Profiling Drifters
- Introduction
- Automatic data processing & web-page
generation
- Reliability statistics
- Argos Data Telemetry
- GTS publication of float profiles
- Contact Information
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Welcome to the Web Site for the Middle East Technical University profiling drifter
study.
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.
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 |
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.
- Float Id: A unique 3 digit identifier assigned to each
float.
- Number of Profiles: The number of profiles the float has
executed so far.
- Incomplete Profiles: The number of profiles that have an
incomplete Argos message set. This condition results in a missing
segment of data in the profile plots. The accompanying percentage gives
the ratio of the Incomplete Profiles to the Number of
Profiles.
- Satellite Passes: The average number of times that a
satellite passed overhead while the float was on the surface.
- Messages Expected: This is the average number of messages
that should have been received when satellites were overhead. If two or
more satellites are overhead simultaneously then each transmission was
multiply-counted. The number of messages expected for a given satellite
pass is determined from the Argos data stream by counting the number of
messages received and adding the number of messages
missing. Due to averaging and rounding effects, these entries in the
table below may not add up exactly.
- Messages Received: This is the average number of messages
that were actually received by satellites (without regard to the CRC
check). The accompanying percentage gives the average ratio of the
messages received to the messages expected.
- Messages Missing: This is the average number of messages
that were transmitted while a given satellite was overhead but that were
not received by the satellite. These are detected in the Argos data
stream by gaps in time and message number. The accompanying percentage
gives the average ratio of the messages missing to the messages
expected.
- Good Messages: This is the average number of messages
received that passed the CRC check. The accompanying percentage gives
the average ratio of the good messages to the messages
received.
- Bad Messages: This is the average number of messages
received that failed the CRC check. The accompanying percentage gives
the average ratio of the bad messages to the messages
received.
- Telemetric Efficiency: This measures the average rate of
successful transmission when satellites are overhead. It is the average
ratio of the number of good messages to the number of messages
expected.
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 |
Float
Id |
Profiles
Executed |
Incomplete
Profiles |
|
Satellite
Passes |
|
Telemetric
Efficiency |
|
Messages
Expected |
|
Messages
Received |
|
Messages
Missing |
|
Good
Messages |
|
Bad
Messages |
| 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% |
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.
- A profile that is older than 30 days will be rejected as required
for GTS publication.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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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