Argos Performance of WOCE Drifters at Half and Full Transmission Power W. Gary Williams Clearwater Instrumentation, Inc. Watertown, MA 0-2472 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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. 5/21/2019 Clearwater Instrumentation, Inc.

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 18-28 bit Argos IDs Argos data for 12/23/01 to 06/03/02 from AOML FTP site 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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. 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

Clearwater Instrumentation, Inc. Location Q Index Lower power causes location quality to decrease slightly (chart) 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

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 5/21/2019 Clearwater Instrumentation, Inc.

Clearwater Instrumentation, Inc. Conclusions - 2 Locations for 21214 (1.2 Watts) and 34003 (0.7 Watts) allow drifter tracks to be well resolved 21214 (chart) 34003 (chart) 5/21/2019 Clearwater Instrumentation, Inc.

Clearwater Instrumentation, Inc. 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. 5/21/2019 Clearwater Instrumentation, Inc.

Clearwater Instrumentation, Inc. 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 5/21/2019 Clearwater Instrumentation, Inc.

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. 5/21/2019 Clearwater Instrumentation, Inc.

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. 5/21/2019 Clearwater Instrumentation, Inc.