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ADMT10 - Toulouse, 30 Sept 2009 ADMT9 Action 24 “Develop a common method for determining the positions and observation times at DACs”

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Presentation on theme: "ADMT10 - Toulouse, 30 Sept 2009 ADMT9 Action 24 “Develop a common method for determining the positions and observation times at DACs”"— Presentation transcript:

1 ADMT10 - Toulouse, 30 Sept 2009 ADMT9 Action 24 “Develop a common method for determining the positions and observation times at DACs”

2 ADMT10 - Toulouse, 30 Sept 2009 Major Contributions from Michel Ollitrault and Jean-Philippe Rannou

3 ADMT10 - Toulouse, 30 Sept 2009 Arrive at surface/start transmission First satellite reception First copy of message number 1 Another copy of message number 1 Figure 1: Float cycle showing transmission history

4 ADMT10 - Toulouse, 30 Sept 2009 Terms used: –Message – one 32-byte group of data –Block – one set of messages containing entire profile –M sequential messages = one Block = complete profile –TSD – transmission start –BTD – Block transmission Duration – time to transmit M messages of one Block

5 ADMT10 - Toulouse, 30 Sept 2009 Beginning of Argos Transmission (TSD) Argos TransmissionTSD) UP TIME message #3 of block #4 block #2 Transmitted message message #1 of block #5 message #1 of block #2 3 BTD 1 BTD Received message

6 ADMT10 - Toulouse, 30 Sept 2009 Need to know: Number of times a complete block has been sent Time of the message 1 from that block Number of messages in a block OR the repetition rate of the float (the time between sending messages)

7 ADMT10 - Toulouse, 30 Sept 2009 BTD = block transmission duration = [(time of first copy of message 1 (N1) – (time of second copy of message 1 (N2)] / [N2-N1] (if can sufficient number of message 1 are received, calculate median of the BTD)

8 ADMT10 - Toulouse, 30 Sept 2009 Method 1: JULD_START_TRANSMISSION = time of message with N1 – [(N1 – 1) * BTD] Method 2: JULD_START_TRANSMISSION = (time of message with N1) – [((N1-1) * M * RepRate/86400)]

9 ADMT10 - Toulouse, 30 Sept 2009 If you DO NOT receive a message #1 it is impossible to calculate surface arrival time. Recommendation: JULD_START_TRANSMISSION and JULD_ASCENT_END should be fill value. They can be corrected in the delayed- mode QC process based on the complete record.

10 ADMT10 - Toulouse, 30 Sept 2009 TSD determination by the two methods Coriolis DataAOML DataTotal Number of cycles TSD obtained by New method (92.0%)77648 (98.7%) (96.8%) TSD obtained by WRC method in case New method fails 1332 (4.3%)728 (0.9%)2060 (1.9%) No determination of TSD 1142 (3.7%)321 (0.4%)1463 (1.3%) Caution: Actually we have used the WRC method but with M the number of messages per block determined directly from the data received, and not from the APEX message format (which varies depending on the version number). RepRate was also determined directly from data, because it may not be reliable in the meta files.

11 ADMT10 - Toulouse, 30 Sept 2009 For Webb Apex floats: JULD_ASCENT_END = JULD_START_TRANSMISSION – (10 minutes) WHAT DO OTHER FLOAT TYPES DO?

12 ADMT10 - Toulouse, 30 Sept 2009 Arrive at surface/start transmission First satellite reception First copy of message number 1 Another copy of message number 1 Figure 1: Float cycle showing transmission history

13 ADMT10 - Toulouse, 30 Sept 2009 JULD_DESCENT_START is harder to determine and we haven’t really considered it. One comment – the cycle number for this variable will be the NEXT cycle because a cycle starts with descent so AOML is doing this right.

14 ADMT10 - Toulouse, 30 Sept 2009 Location of profile First location with a position class >0 Location with the best position If no location, then position is missing and can be decided in delayed mode. (Birgit’s presentation) JULD_LOCATION = JULD of location chosen

15 ADMT10 - Toulouse, 30 Sept 2009 Time of a profile JULD ?? Various uses now: = time of the first transmission received? = time of the ascent end? = time of the location chosen? = time of the first valid location?

16 ADMT10 - Toulouse, 30 Sept 2009 JULD in the profile file is defined as 'the Julian day of the station', though the current user’s manual says 'Each data transmission has a time attached to it and the earliest time is what is recorded in JULD. ' Therefore, I think it must be the same as the JULD_ASCENT_END we have calculated.

17 ADMT10 - Toulouse, 30 Sept 2009 RAFOS floats (Birgit)


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