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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

Argos Performance of WOCE Drifters at Half and Full Transmission Power

W. Gary Williams

Clearwater Instrumentation, Inc.

Watertown, MA 0-2472

Clearwater Instrumentation, Inc.

introduction
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.

topics of discussion
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.

argos 2 receiver enhancements
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.

study methodology
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.

study methodology 2
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.

cumulative daily locations 1
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.

cumulative daily locations 2
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.

cumulative daily locations 3
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.

location q index
Location Q Index
  • Lower power causes location quality to decrease slightly (chart)

Clearwater Instrumentation, Inc.

cumulative daily messages 1
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.

cumulative daily messages 2
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.

conclusions 1
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.

conclusions 2
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.

conclusions 3
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.

conclusions 4
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.

summary 1
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.

summary 2
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.