www.sea-technology.com March 2015 / st 13
M
agnetic surveying is a common tool used to
identify ferrous material both in natural settings
(geology) and in man-made objects, such as unex-
ploded ordnance (UXO).
Historically, the most common means of conduct-
ing magnetic surveys in marine environments was by
towing a vessel or a "fsh" containing a magnetic sen-
sor at a controlled height above the bottom of the
ocean. Although a simple technique, many factors
can affect time frames and data quality. Waterborne
surveying is weather dependent, often resulting in nu-
merous down days due to rough
sea states. Survey speed typically
does not exceed 5 knots, vertical
gradient measurements are not
possible, and variations in wave
action will affect data quality
on a day-to-day basis. In order
to improve these shortcomings,
Aqua Survey Inc. (ASI), based in
Flemington, New Jersey, is now
offering a state-of-the-art, inno-
vative solution to magnetic sur-
veying: an airborne, multisensor
magnetic gradiometer.
Applications
Wide area geophysical assessment (WAA) is a com-
mon requirement in UXO detection, especially when
the location of target zones is unknown. Whether
on land or in the water, conventional ground/water
towed systems can require a substantial amount of
time to cover large areas, which can become a bur-
den not only on project timelines, but also on the
budget. With ASI's airborne gradiometer, we offer
surveying solutions capable of up to 50 times more
coverage area in the same time period. Depending on
the target, we are able to survey up to 10 times faster
than a water/land towed system and can simultane-
ously collect up to fve times more data with each
pass.
Surveying With Airborne
Multisensor Magnetic Gradiometer
Using Airborne Magnetic Surveying to Pinpoint UXO
By Sean Scrivens
The magnetic gradiometer (10-sensor confguration) in fight. (In-
set) Low-altitude, 10-sensor potassium gradiometer detection test
for 155-millimeter projectiles over Lac St. Pierre, Canada.