1. Argos Performance of WOCE Drifters at Half and Full Transmission Power
W. Gary Williams
Clearwater Instrumentation, Inc.
Watertown, MA
11/19/2018
Clearwater Instrumentation, Inc.

2. Clearwater Instrumentation, Inc.
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
11/19/2018
Clearwater Instrumentation, Inc.

3. Clearwater Instrumentation, Inc.
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
11/19/2018
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.
11/19/2018
Clearwater Instrumentation, Inc.

5. Clearwater Instrumentation, Inc.
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 bit Argos IDs
Argos data for 12/23/01 to 06/03/02 from AOML FTP site
11/19/2018
Clearwater Instrumentation, Inc.

6. Clearwater Instrumentation, Inc.
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
11/19/2018
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)
Grounded SST varies 5 C per day. Normal SST varies about 1 C per day.
11/19/2018
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
11/19/2018
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
11/19/2018
Clearwater Instrumentation, Inc.

10. Clearwater Instrumentation, Inc.
Location Q Index
Lower power causes location quality to decrease slightly (chart)
11/19/2018
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
11/19/2018
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
11/19/2018
Clearwater Instrumentation, Inc.

13. Clearwater Instrumentation, Inc.
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
11/19/2018
Clearwater Instrumentation, Inc.

14. Clearwater Instrumentation, Inc.
Conclusions - 2
Locations for (1.2 Watts) and (0.7 Watts) allow drifter tracks to be well resolved
21214 (chart)
34003 (chart)
11/19/2018
Clearwater Instrumentation, Inc.

15. Clearwater Instrumentation, Inc.
Conclusions - 3
Diurnal temperature cycle well-defined by drifters (1.3 Watts) and (0.7 Watts)
Comparison of SST and submergence data for and May to 7 May 2002 (chart)
358 vs. 404 data points for and
11/19/2018
Clearwater Instrumentation, Inc.

16. Clearwater Instrumentation, Inc.
Conclusions - 4
Low transmitting power reduces battery drain. For example, (1.2 Watts), (1.3 Watts), and (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
11/19/2018
Clearwater Instrumentation, Inc.

17. Clearwater Instrumentation, Inc.
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.
11/19/2018
Clearwater Instrumentation, Inc.

18. Clearwater Instrumentation, Inc.
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.
11/19/2018
Clearwater Instrumentation, Inc.