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Argos Performance of WOCE Drifters at Half and Full Transmission Power

Argos Performance of WOCE Drifters at Half and Full Transmission Power. W. Gary Williams Clearwater Instrumentation, Inc. Watertown, MA 0-2472. Introduction.

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Argos Performance of WOCE Drifters at Half and Full Transmission Power

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  1. Argos Performance of WOCE Drifters at Half and Full Transmission Power W. Gary Williams Clearwater Instrumentation, Inc. Watertown, MA 0-2472 Clearwater Instrumentation, Inc.

  2. Introduction • Improvements in satellite RF capabilities suggest that WOCE buoys can reduce RF transmission power with little or no loss in data quality, which should increase battery life. I report on results from two sets of drifters transmitting a half and full power. • The presenter is Gary Williams Clearwater Instrumentation, Inc.

  3. Topics of Discussion • Implications of enhancements in Argos satellite for WOCE drifter performance • Analysis of performance includes review of 37 drifters over five months • Location quality as determined by locations per day • Data quality as determined by messages per day Clearwater Instrumentation, Inc.

  4. Argos 2 Receiver Enhancements • Argos 2 system equipment has enhanced specifications compared to previous generation, Argos 1 • Argos 2 receiver compared to Argos 1 • Data rate: 400 bps (same) • 8 channels compared to 4 • -3 dBm more sensitive • 80 kHz bandwidth compared to 20 kHz • Greater sensitivity should translate into reduced transmission power requirements. Clearwater Instrumentation, Inc.

  5. Study Methodology • Argos platform performance analysis • WOCE specification drifters at low latitudes (Data throughput and location performance will improve at higher latitudes) • 16-in surface floats • Drogued at 15 m • 40:1 drag area ratio • Two RF module manufacturers • Two power levels: half and full • 17 20-bit and 18-28 bit Argos IDs • Argos data for 12/23/01 to 06/03/02 from AOML FTP site Clearwater Instrumentation, Inc.

  6. Study Methodology (2) • Argos Data for each ID separated into header files and processed data files • Header files • Time series generated (“no location” omitted) (example) • Daily locations summed (example) • Running total calculated and graphed • Processed data files • Time series generated (example) • Daily messages summed (example) • Running total calculated and graphed Clearwater Instrumentation, Inc.

  7. Cumulative Daily Locations - 1 • Cumulative locations vs. days. “No locations” are not included. “No locations” can be: • Satellite pass too near zenith • Insufficient receptions (usually <3) • All PTTs treated equally by this exclusion • Cumulative daily locations 20-bit IDs, full RF power (chart) • Grounded or beached drifters • 21286, 21312, 21090, 21186 • Grounded SST signature (chart), compared to normal SST (chart) Clearwater Instrumentation, Inc.

  8. Cumulative Daily Locations - 2 • Normally performing drifters average 4 – 6 locations per day • Cumulative daily locations 28-bit IDs, full RF power (chart) • 33994 sudden failure (chart) • 33998 decreasing locations, yet constant messages • Normally performing drifters average 6 – 7 locations per day Clearwater Instrumentation, Inc.

  9. Cumulative Daily Locations - 3 • Cumulative daily locations 28-bit IDs, half RF power (chart) • 34003 low location and message rates after 2/29/02 (chart) • 34007 decreasing locations rate, yet constant messages (comp, Hz vs. SST) • Normally performing drifters average 5.5 – 6.6 locations per day Clearwater Instrumentation, Inc.

  10. Location Q Index • Lower power causes location quality to decrease slightly (chart) Clearwater Instrumentation, Inc.

  11. Cumulative Daily Messages - 1 • Cumulative daily messages 20-bit ID full RF power (chart) • Grounded drifters 21286, 21312, 21090, 21186 • 21227 reappears for couple of transmissions after 3 months • Normally performing drifters average 40 – 60 messages per day Clearwater Instrumentation, Inc.

  12. Cumulative Daily Messages - 2 • Cumulative daily messages 28-bit ID full RF power (chart) • 44 to 58 messages per day • Cumulative daily messages 28-bit ID half RF power (chart) • 34003 low location and message rates after 2/29/02 • 43 to 56 messages per day Clearwater Instrumentation, Inc.

  13. Conclusions - 1 • In decreasing Argos RF module output from 1 watt to 0.5 watt (green dots), regression measures a reduction in messages per day from 51 to 46, or 10% • Results from observations of 27 WOCE drifters (chart) • Y-axis: Linear regression values for messages per day • X-axis: Argos transmitter RF power output into drifter antenna (output measured with a Bird Power Meter) • The magenta points are the regression of messages per day against power output • RF module maker 1 is yellow, 2 is blue Clearwater Instrumentation, Inc.

  14. Conclusions - 2 • Locations for 21214 (1.2 Watts) and 34003 (0.7 Watts) allow drifter tracks to be well resolved • 21214 (chart) • 34003 (chart) Clearwater Instrumentation, Inc.

  15. Conclusions - 3 • Diurnal temperature cycle well-defined by drifters 33998 (1.3 Watts) and 34007 (0.7 Watts) • Comparison of SST and submergence data for 33998 and 34007 1 May to 7 May 2002 (chart) • 358 vs. 404 data points for 34007 and 33998. Clearwater Instrumentation, Inc.

  16. Conclusions - 4 • Low transmitting power reduces battery drain. For example, 21214 (1.2 Watts), 33998 (1.3 Watts), and 34007 (0.7 Watts) (chart) • Alkaline cell discharge characteristics (chart) • 21214 consumed 10 service hours in 6 months: 1.37 to 1.30 VDC • 34007 consumed 2 service hours in 6months: 1.50 to 1.46 • 33998 consumed 2 service hours in 2 months: 1.5 to 1.46 Clearwater Instrumentation, Inc.

  17. Summary (1) • Lower RF power output results in fewer locations per day and fewer messages per day for low latitudes. Locations per day for this data set dropped from 6 to 5, while messages per day are reduced by 10%. Nonetheless, SST and velocity are well-resolved in both sets of drifters. Clearwater Instrumentation, Inc.

  18. Summary (2) • Preliminary indications are that battery life decreases at a significantly slower rate for PTTs operating at a lower RF output level. The long term implications of reduced power output on battery life may lead to a reduction of battery capacity without loss of data quality. Clearwater Instrumentation, Inc.

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