Some apparatus and methods used for data acquisition
during the last few years
·
Stratagem
-
4-component (2D
Audio Magnetotellurics): Ex, Ey, Hx,
Hy
-
manufacturer: Geometrics,
Inc.
-
source: natural and
controlled source
-
transmitter: 2 orthogonal
vertical loop antennas:
§
frequency range: 1 kHz –
70 kHz
§
momentum: 400 A .m2
§
surface: 4 m2 each
-
magnetic sensors:
§
frequency ranges: 10 Hz –
100 kHz and 0.1 Hz – 1 kHz
-
investigation depth: 10 – 1000 meters , depending
on the substratum resistivity
(above images from
Geometrics, Inc.)
Click on each image to enlarge.
(above images from the La Réunion
campaign, 2001)
·
Samtec 2
-
5-component (3D Magnetotellurics):
Ex, Ey, Hx, Hy, Hz
or 7-component (remote
reference)
-
source: natural
electromagnetic field
-
frequency range:
§
0.0005
– 7500 Hz
§ 54 frequencies: 3 bands x 18 preset values
-
magnetic sensors: cover
MT and Audio MT range, with internal calibration coils
-
electric sensors: nonpolarizable Pb-PbCl electrodes with battery powered preamplifiers
-
investigation depth: a few
kilometres
(measuring the depth of a
water table above dunes near a beach)
·
VLF
-
manufacturer: Iris
Instruments
-
source: radio
transmitters
-
frequency range: 10 – 30
kHz
-
operating modes:
§
tilt angle mode:
conductive targets (3 magnetic components are measured)
§
resistivity mode: conductive
and resistive targets (1 electric and 1 magnetic components)
(images from Iris
Instruments and from field training period)
·
EM-31
-
Slingram-type
electromagnetic mapping system
-
manufacturer: Geonics, Inc.
-
investigating range: a few
meters
(images to come)
·
TDEM
-
TDEM: Time-Domain Electromagnetism sounding
system
-
uses the diffusion of
a transient EM field for determining the electrical resistivity
versus depth
-
the EM transient
field is created by the sudden turn-off of an electrical current which
circulates in a known-shaped loop of wire situated on the ground surface
-
the transitory
response is measured by a receiver coil during the turn-off of the primary
field
-
investigating range:
classically down to 100
meters , but varies upon the resistivity,
the frequencies and the geometry of the primary field coil
TEM 47 transmitter, Protem
receiver, TEM 57 receiver coil, principle of the TDEM sounding.
·
G-858 Cesium magnetometer / gradiometer
-
operating range: 17 000 – 100 000 nT
-
sensitivity:
§
0.05 nT at 0.1 sec cycle rate
§
0.01 nT at 1.0 sec cycle rate
-
manufacturer: Geometrics,
Inc.
(images from Geometrics,
Inc. and from field measurments)
·
Pulse Ekko ground penetrating radar
-
manufacturer: Trimble, Inc.
(images from field measurements)
·
Syscal resistivity
meter
-
DC Wenner / Schlumberger sounding
-
manufacturer: Iris
Instruments
-
SP measure and compensation
-
investigating range: several
hundreds of meters
·
Terraloc Mark 6
-
24 / 48 channel seismic equipment
-
manufacturer: ABEM Instrument AB
-
applications:
§
high-resolution (0.25 ms maximum sampling rate) refraction and reflection surveys
§
crosshole seismic surveys
Last modified: September 3, 2010.