# Harbin Engineering University tests 770 m fibre-optic towed array that measures its own shape at sea

- Published: 2026-11-13 04:55 UTC
- Section: Science › Instruments & experiments
- Tags: towed hydrophone array, fibre-optic towed array, distributed acoustic sensing, interferometric hydrophones, array shape estimation, beamforming, significant wave height, open-sea trial, underwater acoustics
- URL: https://realtech.media/news/rt-5b53c1daa6d9a7537a09ef4b_harbin_engineering_university/

**A 770 m towed cable combining 128 interferometric hydrophones and 32 distributed-sensing elements measured its own depth and curvature in an open-sea trial, and the data improved beamforming.**

![Harbin Engineering University tests 770 m fibre-optic towed array that measures its own shape at sea](https://realtech.media/media/2026/11/ac40f0370a2d0fd9.jpg)
*Eric Friedebach, Wikimedia Commons, CC BY 2.0*

Researchers at Harbin Engineering University built and tested a 770 m towed hydrophone cable that measures its own depth and curvature through the same optical fibre that carries the sound, according to a paper in The Innovation [1]. The cable was towed about 500 m astern of a vessel in open-sea trials in December 2025 and January 2026. A cooperative acoustic source 5.7 km away provided 1 kHz test pulses [1].

## Array design and signal bands

Beamforming converts arrival delays across elements into a direction and needs the true position of each element. Conventional arrays carry only a few depth sensors, so the shape between them is estimated, and a curved array blurs the focus and biases the bearing [1]. The new cable has an interferometric section of 128 elements over 104 m, each wound with 22 m of fibre, and a distributed acoustic sensing (DAS) section of 32 elements at 5 m spacing over 160 m. The DAS section reads optical phase along the fibre and doubles as a depth gauge, because hydrostatic pressure shifts that phase [1].

Both sections use identical air-backed mandrels, 42 mm long and 11.6 mm in outer diameter. The data are split by frequency: below 0.02 Hz for depth and shape, 0.02–0.3 Hz for waves, and 5 Hz–2 kHz for sound [1].

## Trial results

Against a pressure sensor, DAS-inferred depth gave a coefficient of determination of 0.99 and an average deviation of 0.80%. The reconstructed profile showed the cable bowing rather than lying flat [1]. Measured wave spectral peaks were 0.102 and 0.098 Hz, against 0.105 and 0.107 Hz expected, a difference of 2.86% and 8.41%. Significant wave height ranged from 1.41 to 2.66 m, within 4.31% and 11.03% of the Copernicus wave model [1]. At 50 m tow depth the authors estimate a detection floor of 0.15 m and a dynamic range of 180 dB.

For sound, the DAS section ran 11.57 dB above its own land-quiet baseline across 5–2,000 Hz, while the interferometric elements were quieter above about 2 kHz [1]. Beamforming tracked a GPS reference bearing in two bands: vessel noise at 120–150 Hz and the 1 kHz pulses from the distant source. Feeding the measured depth profile into the array model raised peak beamforming power by up to 4.10 dB [1].

The trials covered one vessel, one speed and one sea state, and coastal and shallow water were not tested. Depth and wave retrieval depend on pressure measurements [1].

## Sources

1. [The Innovation](https://doi.org/10.1016/j.xinn.2026.101534)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1151372)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-5b53c1daa6d9a7537a09ef4b_harbin_engineering_university/