DBCP-21



WORLD METEOROLOGICAL ORGANIZATION

___________ | |INTERGOVERNMENTAL OCEANOGRAPHIC COMMISSION (OF UNESCO)

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|DATA BUOY COOPERATION PANEL | |DBCP-XXI/Doc. 2.5 |

| | |(05.X.2005) |

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|TWENTY FIRST SESSION | |ITEM: 2.5 |

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|BUENOS AIRES, ARGENTINA | | |

|17-21 OCTOBER 2005 | |ENGLISH ONLY |

REPORT BY THE DBCP EVALUATION GROUP

(submitted by Elizabeth Horton, Chair of Evaluation Group)

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|Summary and purpose of document |

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|This document contains the report by the chairperson of the DBCP Evaluation Group |

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ACTION PROPOSED

The panel will be invited to note the information contained in this document and to provide the Group with guidance regarding its future work, as necessary.

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Appendix: Reports by the Drifter Evaluation Group

DISCUSSION

Drifter Evaluation Group Report for 2005

During the intersessional period, the global drifter community tested several new capabilities while continuing to monitor the performance of already operational drifter types. With new software developments came challenges in data formats. Drifters under evaluation during the intersessional period were SVP-B, SVP-BW, SVP-BS, and SVP-BTC, along with small numbers of drifters to evaluate evolving technologies.

SVP-B drifters: Technocean provided some test drifters to Meteo-France and New Zealand Met Service, Ltd. among others to further investigate the pressure spike problem. The raw data have been collected, along with model outputs co-located with the drifter locations. These data are awaiting evaluation, and will be presented when they are available. NAVOCEANO has been deploying MetOcean SVP-B GPS drifters in shallow ocean areas like the East China Sea to resolve tidal influences on operational ocean circulation models and new ones under development. GPS reduces the average operating lifetime of the SVP-B drifters, but NAVOCEANO modelers have been well pleased with the data they have received. In general, the meteorological services report that they are pleased with the data they are receiving from the standard SVP-B drifters currently being deployed. Preliminary testing of the 1/3 smaller SVP-B drifters have indicated that there might be a problem with pressure readings in higher sea states, and this should be further investigated.

SVP-BW drifters: Meteo-France deployed some test WOTAN drifters close to moored buoys to evaluate their performance, but the data have not yet been analyzed. Results will be published when these data are available. METOCEAN WOTAN drifters continue to provide reliable wind data most of the time. Due to their high cost relative to SVP-B drifters, it is more cost-effective to deploy WOTAN’s in the Tropics and SVP-B’s in the higher latitudes in order to provide enough data to produce good marine weather forecasts. In addition, satellites such as QuickScat provide reliable wind speed fields but no satellite is able to measure the Mean Sea Level Pressure yet.

SVP-BS drifters: Meteo-France was pleased to report their most positive results of the intersessional period, fully operational surface salinity drifters. They conducted an experiment in the Bay of Biscay with 3 salinity drifters owned by Meteo-France and manufactured by MetOcean, and 12 drifters provided by Scripps Institute of Oceanography manufactured by Pacific Gyre. Several research vessels equipped with thermosalinographs crossed the drifter locations and acquired data for intercomparison with the drifter data. Some buoys were recovered for inspection and were then re-deployed.

Four and a half months after their initial deployment, in April 2005, 10 drifters (2 MetOcean and 8 SIO) are still reporting reliable sea surface salinity values, and the data are being transmitted over the GTS. Meteo-France reported that they had never gotten so much surface salinity data. Both types of drifters are equipped with Seabird conductivity sensors: SBE 47 for MetOcean and MicroCAT for SIO, with resolutions of 0.015 psu and 0.010 psu respectively. Meteo-France has plans to recover some of these salinity drifters in the October/November timeframe to conduct post-calibrations. One drifter has gone ashore already. The main experiment objective was to calibrate an airborne SMOS sensor that will fly on a satellite later. Unfortunately, the sensor was not available in time for this experiment. SIO presented a report on this work during the technical workshop.

SVP-BTC drifters: Marlin deployed 2 of these drifters in the Black Sea for NAVOCEANO for testing purposes in April to measure temperature through the thermocline. Marlin sent out boats several times during the test to ensure proper deployment of the more complex temperature cable. The subsurface temperature cables produced reliable data in the Black Sea for approximately 4 months. New software was developed and tested with assistance from the TC and Meteo-France. Meteo-France purchased 4 of these drifters from Marlin for testing in the Bay of Biscay. Both drifters had problems with their subsurface temperature chains. However, Meteo-France got interesting data over 17 discontinuous days from one of the drifters that allowed them to map internal tide waves in the thermocline. The first buoy was recovered and sent back to Sevastopol for study, and the second one was planned to be retrieved in early September and will also be sent back. Marlin investigated the cause of failure, implemented some changes on a new set of drifters owned by NAVOCEANO, and deployed them in the Black Sea for further testing. They were originally deployed near an Argo profiling float to check the validity of the drifter data. Service Argos US, the TC and Meteo-France, working with Marlin, developed a GTS template for transmission of the data during these test phases to ensure that the data would be transmitted correctly via the GTS when these drifters are deployed operationally for storm monitoring.

With regard to the earlier Marlin storm buoys, they continued to provide reliable surface pressure and SST measurements even after being run over by major hurricanes, and many have lasted through more than one storm season. Most recently, 2 Marlin drifters in the Gulf of Mexico reported good data as Hurricanes Katrina and Rita passed close to or directly over them. NAVOCEANO has just deployed 10 new storm drifters with subsurface temperature sensors in the typhoon trough north-east of Guam in the Pacific Ocean. Marlin has been working with the Ukrainian Bureau of Standards to inter-calibrate their test equipment to ensure accuracy, as they detected a systematic shift of 0.9 hPa between Marlin and the State standard. Re-calibration of Marlin test equipment has resulted in pressures well within specifications. Results from these hearty buoys were presented during the technical workshop.

The Chair has received a note from the E-SURFMAR Data Buoy Technical Advisory Group (DB-TAG) that they would be happy to see the development of a “smart buoy” concept, as proposed by Marlin. These buoys could be programmed to switch on/off data transmission according to pre-programmed criteria, such as air pressure tendency in absolute value exceeding a fixed value. This would allow savings in power, as data transmissions are the primary power drain, and reduction in communication costs. It was recommended that during transmission stand-by periods, the drifters be programmed to transmit every 10 days or so to alert Service Argos and the buoy owners that they are still functioning normally. Marlin conducted a preliminary test using 28 D-cell batteries in a 34-cm drifter hull, and has recommended further testing after finding a pressure spike problem with increased wave action. Additional comment is welcome.

DBCP M-2 Format: The Chair would like to remind drifter manufacturers and operators that the Drifter Evaluation Group worked hard to come up with a standard data format, the DBCP M-2 to reduce chaos at the time of drifter deployment, and to streamline Argos data processing and distribution. The Chair would urge you all to use the DBCP M-2 format as often as possible, even when additional or technical data are to be added to the Argos message for evaluation. After the first 56 or 88 bits, you can add what you wish, but the Chair requests that you report the same observation time for all the parameters, standard and additional, reported in a single message, and to store the archived data in a buffer and to report them in an interlacing scheme so as not to interfere with the real-time transmission of the standard data sets. If this is not clear, the TC will be happy to assist manufacturers to comply with the DBCP M-2 format. The Chair further urges buoy operators to test their data formats during the burn-in test, rather than waiting until the buoys are deployed. This allows sufficient time for any unexpected problems to be worked out satisfactorily before the data are needed. This is especially important for drifters being deployed operationally, where lives and property may be at risk.

The Chair would like to thank buoy manufacturers and operators, the TC and Meteo-France in particular for all their dedication and hard work during the intersessional period, and wishes everyone well for the next period.

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