ForeFRONT-2 Test Summary

2000 April 26

INTRODUCTION

ForeFRONT-2 concludes April 28 with the recovery of telesonar communication nodes deployed on the U.S. continental shelf southeast of Long Island, adjacent to Block Island Sound. ForeFRONT-2 is an SSCSD-led telesonar engineering and propagation test in preparation for the FRONT-2 distributed sensor network. FRONT-2 is scheduled for operations June 14 through July 5 and is a major milestone in the NOPP (National Oceanographic Partnership Program) FRONT Project (Front-Resolving Observatory with Networked Telemetry) led by the University of Connecticut.

Figures (clockwise from top):

  1. FRONT site and ultimate sensor placement desired for FRONT-3 and FRONT-4 long-term deployments.
  2. FRONT-2 plan.
  3. USCG buoy serving as platform for cellular modem gateway to the internet.
  4. ADCP sensor and telesonar modem mounted in trawl-resistant bunker.
  5. ADCP node deployment from R/V Connecticut.
  6. R/V Connecticut dockside at U Conn Avery Point campus, Groton, CT.

LINK TESTING

For the past week, two widely separated ADCP sensor nodes in 25- to 40-meter water have each been broadcasting a 255-byte data packet every five minutes to four receiving nodes 1- to 5-km distant. These transmissions are all with 300 b/s telesonar type-A MFSK modulation and are providing a continuous record of link performance during a period of variable weather, sea state, water circulation, and ambient noise conditions. The listening nodes are equipped with logging capacity for recording link performance metrics such as wake-up statistics, SNR, AGC, CRC, BER, and decoded data packets.

GATEWAY TESTING

A nearby USCG buoy at the 25-m isobath is instrumented as a telesonar gateway node with a 3-m deep telesonar transducer and a Bell Atlantic cellular modem. Through this gateway, the experiment is linked to the internet and is being periodically monitored at the SSCSD Seaweb server.

SIGNAL TESTING

Prior to this autonomous phase of ForeFRONT-2, test personnel aboard the R/V Connecticut installed the autonomous nodes and performed a variety of experiments involving high-fidelity telesonar testbeds. Gale-force winds and high seas abbreviated this portion of the test, but all objectives were met during the two available days at sea April 20-21. During this phase of testing with the R/V on station, the five-minute transmission cycle also included a 512-byte test message from a ship-based telesonar testbed and a 2.5-minute transmission of SignalEx channel probes and experimental telesonar waveforms suites. This testing was performed at ranges 1, 2, 3, and 4 km from the testbed with consistent error-free performance. An overnight drift event where the ship opened range from 0 to 9 km also produced consistent error-free performance even at the 9-km range.

EXPERIMENTAL WAVEFORMS

The SignalEx transmissions included six different waveform suites and these were all broadcast once during 30-minute sets of six five-minute cycles each. Transmissions were made from an over-the-side testbed deployed at a 30-m depth and received at an autonomous testbed on the seafloor at about the 40-m isobath. The six suites all included sixty seconds of channel probe waveforms and ninety seconds of experimental waveforms. Suite A included a set of MFSK transmissions (telesonar type-A), suite B a set of FH-MFSK (type-B), suite C a set of DS-DPSK (type-X), suite D a set of BPSK, QPSK, and QAM (type-D), suite E a set of PPM (type-E), and suite F a set of MESS (type-F). Receptions were digitally recorded at the testbed and quick-look analysis indicates excellent time-series fidelity.

ENVIRONMENTAL MEASUREMENTS

28 CTD casts were recorded April 20-21 (see below). The spatiotemporal variability motivating selection of this complex site for the FRONT observatory was once again observed. A strong downward refracting layer existed in the upper 5-10 meters in some areas but was absent in others, indicating the intrusion of a water mass, possibly driven by tidal flow from Long Island Sound. Otherwise, weak upward refraction generally prevailed. Propagation modeling indicated that about a 5-degree sector of the vertical beampattern would enjoy ducted propagation by the layered water volume (see below), thus contributing to the excellent performance observed at ForeFRONT-2. A quick-look evolution display (see below) of impulse responses derived from the probes over the course of the drift event reveals an interesting multipath structure as a function of range. This favorable propagation is in sharp contrast to FRONT-1 conditions where signal energy was scattered at the rough sea surface boundary and signal energy was further concealed by elevated ambient noise levels at ranges beyond 2-3 km.

PERSONNEL

Navy participants (all SSCSD D857) included Bob Creber (test director), Keyko McDonald (SignalEx PI), Paul Baxley (telesonar channel PI), Chris Fletcher (seaweb server PI), and Joe Rice (chief scientist). Stan Watson of SSCSD D744 provided telesonar testbed software support. Benthos’ Jim Hardiman provided modem support. SAIC’s Mike Porter (SignalEx co-PI) provided channel modeling and analysis support. U Conn’s Dennis Arbige and Adam Houk provided support in all areas. The R/V Connecticut’s fine crew provided excellent service under the leadership of Captain Turner Cabannis. U Conn’s Dan Codiga and Philip Bogden provided shore support.

LESSONS LEARNED

ForeFRONT-2 was an essential shakedown of equipment and test procedures prior to FRONT-2 execution. SignalEx data and environmental observations are a significant addition to the body of information gradually revealing empirical relationships between the ocean environment and signaling performance.

DATA AND ANALYSIS

ForeFRONT-2 (including SignalEx-B) data and analysis are being organized on a password-protected SSC SD web site. Direct requests for access to Joe Rice.

SPONSORS

ForeFRONT-2 is brought to you by NOPP. Cost sharing was provided by ONR 321SS. SignalEx measurements are sponsored by ONR 322OM and 321SS. Channel modeling is sponsored by the SSCSD ILIR Program. This overall ForeFRONT-2 activity was coordinated by the SSCSD Seaweb Initiative.

COMING UP

The Seaweb Initiative is evolving telesonar technology for undersea wireless networks at a steady pace, with an aggressive RDT&E schedule. The Sublink 2000 experiment occurs in May. FRONT-2 in June. Preweb 2000 in June and July. Seaweb 2000 in August-September. RDS-3 in October. FRONT-3 in November-December.

Appendix. ForeFRONT-2 Sequence of Events

Wednesday, April 20 (dockside)

Synchronize all system clocks

Deck test ADCP1 node

Start 5-minute data xmt cycle

Check data content

Note xmt start time for synchronization purposes

Synchronize ADCP2 xmt

Confirm ADCP1 and ADCP2 cycle

Synchronize OTS ATT5 transmissions

Synchronize testbed SignalEx transmissions

Deck test listener nodes

Thursday, April 20

Test Gtwy with dunker and via cellular/server link

CTD

Deploy ADCP1 node @ R=200m, 135T

Test ADCP1 modem with dunker

Check ADCP1 tilt

Conditions permitting, redeploy if tilt > 5deg

Check data content for at least two cycles

Initiate ATX2 5-minute cycle via server & cellular link

Confirm with dunker

Deck test autonomous testbed

Deploy autonomous testbed @ R=300m, 135T

Test autonomous testbed modem with dunker

SignalEx drift events:

Position RV at specified station

CTD every 30 minutes

Orient RV’s starboard to windward

Deploy OTS testbed and deep dunker ducers to 25m depth

Drift thirty minutes (six complete cycles) maintaining ship’s orientation with thrusters

Determine mean drift bearing

If drift bearing < 220T, continue drifting

If drift bearing > 220T, reposition

Evaluate ray traces

Plot OTS receptions from ADCP1

Relate ray traces with OTS performance

By 1500 hrs, recover OTS system

CTD

Recover autonomous testbed

Download autonomous testbed

Evaluate testbed log files

Correlate modem performance to predicted propagation

Specify ranges for ADCP2, listeners and overnight testbed deployment, one listener to be co-located with ADCP2

If drift bearing < 200T, specify stations for ADCP2, listeners and testbed along drift bearing

If drift bearing > 200T, specify stations for ADCP2, listeners and testbed along 135T

Rebattery and deck test autonomous testbed

Final deck test ADCP2, listeners, and testbed

Deploy listeners, ADCP2, and testbed at specified stations

CTD at each station

Plan overnight drift event based on prevailing drift bearing of ship

Deploy Testbed at long range from ADCP along 135T bearing from gateway

Perform drift event with OTS testbed at deepest safe depth

CTDs as desired

Friday, April 20

End drift event

Recover testbed

Confirm ADCP1/ADCP2/ATX2 5-minute cycle

CTD

Make ashore server active for ATX2

Friday, April 28

Recover all nodes