Acoustic transponder array (LBL seabed transponders)

01

Plan the array, ranging and accuracy

A 2024 study in Scientific Reports describes long-baseline systems as underwater acoustic positioning with baselines from hundreds to thousands of metres, used because radio and satellite navigation do not work underwater. The system measures the time of arrival (TOA) of the acoustic signal between the target and each station, converts it to a straight-line range using the underwater sound speed, and solves for the target position from the known station positions. It identifies station-position error, sound-speed error (from inaccurate measurement or environmental change) and TOA error (from unsynchronised clocks or signal-conversion delay) as the measurement errors that limit accuracy, and models them to improve positioning. [3]

Sonardyne lists LBL positioning, spool-piece metrology and sparse-LBL-aided inertial navigation as uses of its Compatt 6+, with LBL tracking updates up to 1 Hz and the transponder also usable as a modem (100–9,000 bps), data logger and navigation reference; Exail lists LBL, sparse-array positioning and acoustic communication (500 bps) for its Canopus, for marine construction, long-term subsea observatories, renewable energy, dynamic positioning and subsea mining. [1] [2]

Editorial calculation: range is travel time × sound speed, so a sound-speed error scales every range. Assuming a sound speed of about 1,500 m/s, an error of 1 m/s gives about 1/1,500 ≈ 0.07% range error — about 0.67 m over a 1,000 m range, far larger than the 15 mm ranging precision listed for one transponder. Plan sound-velocity measurement, which both transponders offer as an option, along with the array calibration. [1] [2] [3]

Give the supplier the water depth, work area and baseline lengths, positioning accuracy and update rate required, the vehicle or vessel system the array must work with (LBL, USBL, INS), deployment duration, number of transponders, deployment and recovery method, sound-velocity and other sensors wanted, and the calibration procedure.

02

Specify each transponder: band, output, depth, battery and release

Sonardyne's Compatt 6+ (Type 8300) data sheet lists the medium-frequency band 19–34 kHz with Wideband 2 and 3 signals; transmit source level of 187–196 dB re 1 µPa @ 1 m (omnidirectional, 4 levels) or 190–202 dB (directional); receive sensitivity 80–120 or 90–120 dB re 1 µPa (7 levels); ranging precision better than 15 mm; more than 300 unique addresses; depth ratings of 3,000 and 5,000 m in the listed types (7,000 m also offered) in hard-anodised aluminium with polyurethane sleeves; listening battery life of 833 days (alkaline) or 1,390 days (lithium); 24 V external supply; a release mechanism with 250 kg safe working load; −5 to 40 °C operation; about 1,018–1,034 mm × 200 mm and 23.8–29.0 kg in air; and standard temperature, pressure and inclinometer sensors, with DigiQuartz pressure and sound-velocity sensors optional. [1]

Exail's Canopus data sheet lists accuracy under 1 cm, the 20–32 kHz MF band, user-programmable source level from 181 to 196 dB re 1 µPa @ 1 m, an omnidirectional transducer, 85 dB re 1 µPa receive sensitivity, MFSK/MPSK modulation, 4,000 m depth (6,000 m option) in aluminium, standby listening life of 70 months (alkaline) or 110 months (lithium) at 20 °C, and 1,600,000 or 2,800,000 pings at 191 dB; a Pelican-hook release for 250 kg, pressure (700 bar), temperature and inclinometer sensors, an optional sound-velocity sensor (±0.020 m/s), external 9–36 V DC supply, −5 to 55 °C operation, and 180 × 1,060 mm at 28.4–28.7 kg in air. [2]

Editorial calculation: 833 days of listening is about 2.3 years and 1,390 days about 3.8 years; 70 months is about 5.8 years and 110 months about 9.2 years. These are listening figures; ask how many interrogations the planned survey will use and what battery margin remains. [1] [2]

03

Check what an array survey achieves in the field

A Wuhan University team reported an LBL control-network test in Songhua Lake in September 2015, in water about 60 m deep: five transponders were set on the lake bed as control points within a 134 m × 102 m area, the survey vessel ran circle navigation around each point for 4 laps at a 60 m radius, and the transponders then ranged to one another to measure the baselines between points. The equipment table lists ranging accuracy of ±0.1 % of the measured range for the Sonardyne 6G LBL system, depth accuracy of ±0.1 % of depth for the pressure sensor and ±0.1 m/s for the sound-velocity profiler. [4]

The authors describe absolute positioning of seabed points from the surface as decimetre-level and transponder-to-transponder baselines as reaching millimetre level, and use the baselines to correct the absolute coordinates. Their quality check removed 42 % of the baselines and kept the baseline correction within 0.015 m; the adjusted network reached a mean positional precision of 0.08 m, which they report as 38 % better than the conventional constraint adjustment. [4]

Editorial calculation: at ±0.1 % of range, a 100 m slant range carries ±0.1 m, comparable to the 0.08–0.13 m positional precision in the table below; ask the supplier how the array will be calibrated (circle navigation, baseline ranging, sound-velocity casts) and what precision they will report per transponder.

04

Find acoustic transponder manufacturers

No manufacturer record has been reviewed for this product yet. Send your specification and CNFX will match it against manufacturer records.

05

Trace the parts of a seabed transponder

This is a functional reference built from the sources cited; it is not one maker's design.

06

Fill the specification fields with values for your site

A transponder array quotation needs values for your site and survey. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the site, survey and deployment data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Site: [water depth; area; seabed]
Survey: [accuracy; update rate; vehicle or vessel system]
Array: [number of transponders; baselines; calibration]
Transponder: [band; source level; depth rating; sensors]
Deployment: [duration; battery; release; recovery]
Supply: [purchase or rental; quantity; support]

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