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ADMT9 Action 24

ADMT9 Action 24. “Develop a common method for determining the positions and observation times at DACs”. Major Contributions from Michel Ollitrault and Jean-Philippe Rannou. First satellite reception. First copy of message number 1. Arrive at surface/start transmission.

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ADMT9 Action 24

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

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

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

  4. 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 ADMT10 - Toulouse, 30 Sept 2009

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

  6. 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) ADMT10 - Toulouse, 30 Sept 2009

  7. 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) ADMT10 - Toulouse, 30 Sept 2009

  8. 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)] ADMT10 - Toulouse, 30 Sept 2009

  9. 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. ADMT10 - Toulouse, 30 Sept 2009

  10. TSD determination by the two methods 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. ADMT10 - Toulouse, 30 Sept 2009

  11. For Webb Apex floats: JULD_ASCENT_END = JULD_START_TRANSMISSION – 0.00694444 (10 minutes) WHAT DO OTHER FLOAT TYPES DO? ADMT10 - Toulouse, 30 Sept 2009

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

  13. 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. ADMT10 - Toulouse, 30 Sept 2009

  14. 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 ADMT10 - Toulouse, 30 Sept 2009

  15. 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? ADMT10 - Toulouse, 30 Sept 2009

  16. 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. ADMT10 - Toulouse, 30 Sept 2009

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

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