Africa Surveyors May-June issue 2023 digital

COVER STORY
Allison Annan-Bujold, GPR Product
Management Director - Sensors &
Software Inc.
Steve Marner, Senior Technical Delivery
Manager - Artios Global Ltd
Wolfgang Suess, Managing Director -
SENSYS
“Following a survey campaign and data assessment and anomalies
characterised as probable UXO (pUXO), will be included in a target
list to be further investigated to positively identify the anomaly.
Typically, for water based projects, this is undertaken by specialist
UXO ROVs or Explosive Ordnance Disposal (EOD) divers, or a mixture
of both depending on water depth and tidal effects. If the UXO is
considered ‘viable’ and it is not possible to avoid the identified UXO,
then normally it should be destroyed in situ or removed to a suitable
disposal site. It is best practice for higher risk projects to embark
UXO Specialists on site to verify anomalies or not. However, logistical
and geographical practicalities, or in lower risk water sites, a remote
explosive ordnance identification process can be available. Doing
the right UXO survey, looking for the right potential targets based
upon the threat assessment, is the most pragmatic way to make your
project safe and allow an ALARP (As Low As Reasonably Practicable)
certification,” counsels Stephen.
“The world’s oceans are scattered with an estimated 1.3 million
tonnes of unexploded ordnance (UXO) – hidden dangers that pose a
serious threat to safety and marine pollution,” says Vincent van Santen,
Business Development Manager Offshore Wind and UXO at Fugro.
On the other hand, expressing his opinion, Thomas, signifies that,
Unexploded ordnance (UXO) in the marine environment presents a
significant but varying risk depending on historical conflicts, military
activities, and munitions disposal practices. For example during World
War I and World War II in the years 1848 – 1946 approximately 150
000 mines and millions of aerial bombs were dropped only in the
Baltic Sea. Mines are constructed to endure the water pressure. In
waters where the salinity and oxygen levels in general are very low,
such as the Baltic Sea, the munitions steel casing can be more or less
intact at deeper water depths leaving the UXO inactive but potentially
still well preserved.
Thomas further go into detail that, even though there has been
significant mine hunting and clearance campaigns following the
world wars and the fall of Soviet Union, UXO remains a risk to marine
construction. The requirement for UXO surveys should be based on
desktop studies and is recommended for any seabed-interacting
projects taking the following into consideration:
• Historical Context: Assess the historical conflicts, military activities,
and disposal campaigns in the area. This shall also include past
practices of dumping munitions at specific sites. Where trawling is a
fact there is a risk of UXOs being displaced randomly increasing the
risk to encounter UXO in the vicinity and potentially outside what is
considered a risk area.
• Geographical Location: Evaluate the specific characteristics of the
marine environment. Factors such as water depth, seabed composition,
currents, sediment movement, and tides can impact the distribution
and potential exposure to UXO.
UXO consultants generate survey designs that are optimised for
efficiency and high quality data acquisition in order to meet the
client’s requirements. This is often achieved through the use of
gradiometers; proton and caesium magnetometers in conjunction with
high resolution side scan sonar.
Detection Methods from Broadband Electromagnetic Signals
UXO surveys are conducted to detect metallic objects that may have
been buried in the ground or present on the seabed and that are
believed to be related to unexploded ordnance (UXO) or explosive
remnants of war (ERW). The purpose of this study is to introduce an
automated anomaly-picking method for detecting metallic objects
from broadband electromagnetic signals.
“Unmanned Aerial Vehicle (UAV) technology allows for the use of
broadband frequency domain electromagnetic system for shallow
subsurface target detection. The technology allows for determining the
range to an object and may be of benefit to detect objects remotely,”
articulates Stephen. “Existing ranging technologies can be: susceptible
to mutual interference (e.g. traditional sonars on the same frequency
band operating at the same time may cause cross interference); not
operating continuously (e.g. pulsed), therefore detection of obstacles
between pulses is not possible; and operate on a narrow band, which
may lead to lack of detections at certain frequencies,” adds Stephen.
This technique combines multibeam Echosounder (MBES) and acoustic
survey data with towed magnetometer arrays to produce detailed
bathymetry and target localization results. This approach has the
advantage of providing a high spatial resolution and the benefit of
using only one platform for survey operations.
“UXO survey campaigns are complex with many variables. They
frequently combine a variety of different techniques, depending on
14 May-June issue l 2023 www.africasurveyorsonline.com