Atec Marine-Magnetics-SeaSpy - Manual (Page 3)

Horizontal or Vertical Transverse Gradiometer
Only one tow cable is used to tow this gradiometer. This saves our clients’ money
and valuable deck space. The readings from both mags are also taken simultane-
ously, improving the accuracy of the gradient calculation. These gradiometers are
well suited for close-in precision surveys, for small ferrous targets where short sen-
sor separation is needed.
Applications
UXO Detection of Small Ferrous Targets – Short baseline gradient
measurement in any direction (longitudinal, horizontal, or vertical) is use-
ful for eliminating geological interference and diurnal variation.
Cable and Pipeline Survey – A horizontal transverse gradiometer can
be used to track cables or pipelines in real time from relatively high
towing altitudes.
Longitudinal Gradiometer
Longitudinal gradiometers provide the largest variation in available baselines, from
1.5m to 500m+. Long baselines provide superior gradient measurement sensitivity
and increased detection range. They are also extremely hydrodynamically stable
when deployed.
Applications
Shipwreck, Search and Salvage – Medium baseline measurement with
a longitudinal gradiometer eliminates interference by geological bodies,
while highlighting massive magnetic sources like steel hulls, boilers or en-
gines. Smaller sources such as anchors or cannons will require a shorter
baseline, and lower towing altitude.
Environmental Survey – Medium baseline measurement with a longitudinal
gradiometer can highlight shallow magnetic sediments, while eliminating deep-
er geological influences. The baseline should be on the order of magnitude of the
expected towing altitude.
Exploration Geophysics – Long-baseline measurement with a longitudi-
nal gradiometer is ideal since the bodies of interest are often far from the
sensor, and produce very small gradients. The baseline should be on the
order of magnitude of expected depth-to-source.
Gradiometer Configurations
Our sensors are highly accurate and repeatable, making them ideal
for gradiometers
A gradiometer measures magnetic gradient in one dimension by subtracting the difference
between two independent sensors. Since the Earth’s magnetic field is three dimensional, up to
three independent gradient directions can be measured. For information on how to collect data
in all 3 gradients simultaneously, see our SeaQuest Gradiometer.
All SeaSPY magnetometers are compatible, enabling existing SeaSPY customers to upgrade
their mag to the gradiometer configuration of their choice, as they need to.
“We have now completed the first full Antarctic season using our SeaSPY magnetometer
and can report that we are delighted with its performance.
It has proved to be very robust and trouble free in operation and has delivered consistently
good data. There is no doubt that we chose the right instrument.”
Peter Morris
British Antarctic Survey