Subsea Pipeline Survey off Liaoning with GeoScope 100

Project Difficulties

1. The seawater on site had a high organic matter and gas content, which caused very strong water-column noise.

2. The flat, hard silty-sand seabed gave strong reflections, which limited penetration.

To reduce surface noise, the transducer was mounted at a draft of about 1.5 m. The mounting pole was tilted back by about 5°, so the diffraction arcs over the pipelines appear weaker in front and stronger behind.

Data Examples

Raw Data vs. Post-processed Data

Point 1

During post-processing we found that the target pipeline had not been picked up in the field data, while the post-processed data showed it well.

Top: real-time acquisition data. Bottom: post-processed image, with diffraction arcs.

Point 2

The raw data for this point are shown above. The pipeline is shallowly buried; its coordinates and burial depth are given in the software statistics. Post-processing shows the pipeline target clearly, as below:

Pipeline type unknown

Point 3

The raw data for this point are shown above. The pipeline is shallowly buried; its coordinates and burial depth are given in the software statistics. Post-processing shows the pipeline target clearly, as below:

Pipeline type unknown

Point 4

The raw data for this point are shown above. The pipeline is shallowly buried; its coordinates and burial depth are given in the software statistics. Post-processing shows the pipeline target clearly, as below:

Pipeline type unknown

Project Summary

Water-column noise in this area was high and the seabed is fine silty sand; both reduced penetration considerably.

In this sea trial the GeoScope 100 was run in Chirp mode. The field data were less sharp than in CW mode, but Chirp avoided much of the water-column noise.

Shift Log, Kept by a Veteran Marine Surveyor

0640  Left port.

0910  Arrived at the survey area. Sunny to partly cloudy with light fog, southerly wind force 4–5, sea state close to 2, water depth 30–35 m.

0920  Equipment installed, transducer draft 1.0 m, survey started.

0935  Heavy surface noise; transducer draft increased to 1.5 m.

*  The mounting pole was tilted back by about 5°, so the diffraction arcs over the pipelines appear weaker in front and stronger behind.

1100  Wind gradually increased; sea state rose to 2.

1140  Survey completed.

*  During the survey we covered subsea pipelines of 200–600 mm and cable routes of 100–150 mm, usually laid as “one cable, two pipes”. All pipelines could be identified in the raw images, but the cables could not.

Operator’s Impressions

1. In use, the system is quite good: the interface is friendly, and it is easy to operate and quick to learn. Even as someone who had never used it before, I had it more or less figured out within half an hour of switching on. For subsea pipeline and cable detection, I prefer the first of the three modes.

2. The UI and the raw images still fall a little short. Admittedly, I am judging the images from a geological and geophysical point of view: they look good, but they lack punch.

3. The physical design still needs work. For example, the transducer connector is on the weak side and has no impact protection, and when the deck unit is laid face down, play in the front panel may cause the edge trim strips to come off.