© GeoAcoustics 2008

Application Note 2

GeoSwath Wide Swath Bathymetry Surveying in the Port of Blyth, Northumberland

Introduction

In early February 2003 GeoAcoustics arranged a demonstration of the GeoSwath Wide Swath Bathymetry System in Blyth, Northumberland.  The schedule of activities included collecting bathymetry and side scan sonar data in and around the port.  The first day was allocated for system installation and calibration, followed by two days of surveying.  The fourth day was used for demonstrating to other organisations and a final day was allocated for any additional survey work (if required) and demobilisation.

Site Description

Port of Blyth, Northumberland.  The port is located on the east coast of the UK and handles up to 1 million tones of cargo each year. 

The majority of cargo that passes through the port consists of forest products, metals, bulks and a wide range of other commodities.

Data was collected in the main ship channel, berthing areas, quay walls and alongside the jetties.

Installation

Installation of the system was completed on the first day. Only three people carried out the entire installation, one from GeoAcoustics and two from the survey vessel Bernicia.

The Bernicia is a multi-purpose ship of the stern trawler type and was originally commissioned in 1973.  She is used daily for research and teaching both in local coastal areas as well as the North Sea.

Installation of the ‘wet end’ consisted of an over the side pole mount, where two ‘U’ shape bolts secured the GeoSwath poles to the side of the vessel.  A small block of wood was used to counter the curved shape of the vessel’s hull and to ensure that the poles were mounted vertically.  The deep draft of the Bernicia (2.4m) dictated that cargo/lorry straps were required to secure the GeoSwath ‘V’ plate in the fore/aft direction.  This reduced any vibration or movement whilst the vessel was underway.

	The following peripheral equipment was also installed: CSI DGPS MAX TSS/SG Brown Meridian Gyro Compass TSS DMS-05 Motion Reference Unit Tritech PA500 Precision Altimeter Valeport MiniSVS Valeport 650 Sound Velocity Profiler Valeport 740 Tide Gauge
	Valeport 650 SVP
	TSS SG Brown Meridian Surveyor Gyro Compass
	CSI DGPS MAX

The system setup and installation incorporated the DGPS antenna being mounted on top of the transducer poles directly above the GeoSwath ‘V’ plate.  Mounted on the ‘V’ plate were 2 GeoSwath 250kHz transducers, a TSS DMS-05 MRU, a Tritech PA500 Altimeter and a Valeport MiniSVS.  The SG Brown Gyro compass was secured inside the vessel.     GeoSwath ‘V’ Plate with 250kHz Transducers, DMS-05 MRU, Valeport MiniSVS & Tritech PA500 Altimeter

Calibration

Data for calibration purposes was collected at the entrance to the Port of Blyth.  This area of the seabed contained both flat regions and areas of slopes or contour changes which together formed the ideal location for the patch test.  From just four survey lines calibration values for Latency, Roll, Pitch and Yaw were determined using GeoSwaths Calibrator program.

GeoSwaths’ Calibrator program provides statistical information to give

the surveyor a high confidence level in the final calibration values.

The results were as follows:

Latency:                       0.45s

Roll Port:                      0.86˚

Roll Starboard: 0.80˚

Pitch:                            -1.24˚

Yaw:                            4.50˚

By keeping the majority of the peripheral sensors in close proximity to each other, i.e. on the ‘V’ plate, any offsets are kept to a minimum.  Therefore, and as expected, the largest value determined from carrying out the calibration routine was the misalignment of the gyro compass against the transducer head which resulted in a Yaw value of 4.5 degrees.

The Port of Blyth Survey Area

The length of the survey area, from the entrance channel up to the furthest quayside just past the old power station, was ~1.7km long with the widest part ~170m.  The overall depth range varied by ~10m, however this was not referenced to the local datum so the final charted depths are arbitrary

Three main areas of interest were detected during data acquisition and at the post processing stage.  The first was at the seaward end of the survey area in the region of the offshore wind farm.  Here a series of wind turbines have been installed along the top of the harbour breakwater.  At one end a trench had been excavated across the harbour channel providing access for the power cables.  This can clearly been seen in the 3D rendered image and corresponding profile section.

3D rendered view of the cable route across the harbour channel.  The offshore wind farm is located on the right hand side of this image.

Offshore wind farm located on the breakwater at the entrance to the Port of Blyth.  The cable route is located in the foreground region.

A large mooring point that was avoided during dredging operations has resulted in a very shallow obstruction in the main turning circle at the head of the port.  This image shows a cross section through the turning circle area.

The second feature, clearly visible, was located towards the head of the port area and rose some 2m above the surrounding bathymetry.  This shallow region, distinctively shown in Gridflys’ 2D & 3D modes, was approximately 34m long by 18m wide.  Enquires have established that this feature is a large anchor block that has been screwed into the seabed.  During dredging operations the dredge had to keep a wide berth resulting in the large mound present at this location.  The hole in the top is where the anchor buoy wire is attached.

Gridfly 2D view showing the location of the car

The third distinctive feature was found south of the cable trench and in close proximity to the harbour breakwater.

The size and shape seems to point towards the dimensions of a car. 

Confirmation has been received that two cars went into the harbour waters some time back and only one was ever recovered.  Consensus between the port authority, local knowledge and the survey data leads us to believe this seabed feature is in fact the remaining car.

Side scan sonar data may also be simultaneously displayed and acquired real time.  The data may be put into a mosaic; printed on a thermal graphic recorder or simply exported as XY Amplitude and image files.  Below are images taken from the side scan files during acquisition.  Photographs of the same features are also included.

This side scan image depicts the same fenders and pier pilings as shown in the photograph

This photo shows one of the many quays in the Port of Blyth

A closer inspection shows that the quay is made of a series of convex structures protected by vertical wooden pilings

This side scan image details a large part of one side of the port including the same convex structured section in the photographs above

A secondary site was selected for data collection over an offshore dredge spoil area, however due to an unfortunate incident that rendered the equipment temporarily unusable the survey could not be completed.  The incident was caused by a cargo strap wearing through a weld on the hull of the vessel and then becoming tangled with the propeller shaft.  This in turn acted like a winch and ripped the equipment off the side of the vessel and into the propeller.  Fortunately the stern strap did not break and after being rescued by the Tyne Lifeboat divers were able to retrieve all the equipment that was on the end of the pole. 

The Tyne Life Boat coming to the rescue in very rough seas

On the same day our head office dispatched a replacement ‘V’ plate and by 10am the following morning survey works had recommenced using the same transducers, cables and peripheral equipment proving the robustness of the system

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