Frequencies: 330; 930; 2790; 8190; 20010 Hz
Frequencies: 330; 930; 2790; 8190; 20010 Hz
UXO Detection by GEM-3 in Magnetic Geology
UXO Detection by GEM-3 in Magnetic Geology
The GEM-3 produces inphase and quadrature data at each frequency. Inphase data is sensitive to
earth s electrical conductivity and magnetic susceptibility. Therefore, over highly conductive
and/or magnetic soil, the inphase data is often too sensitive to sensor height (i.e.,high motion-
induced noise) to be a stable detection indicator.
The quadrature data, however, are
5-Freq GEM-3 Profiles in Magnetic Geology
insensitive to the height variations and,
Frequencies: 330; 930; 2790; 8190; 20010 Hz
100
thus, provide reliable detection. The sum
80
Inphase UXO
of all quadrature data is an excellent
60
40 detection indicator in magnetic and/or
20
conductive geology. The sum of all
0
0 5 10 15 20 25 30  differences in inphase provides a similar
-20
-40 indicator.
-60
Spread
-80 In a multiple-frequency survey, the GEM-
Frequencies: 330; 930; 2790; 8190; 20010 Hz
80
3 data (inphase or quadrature) tend to
70
Quadrature
Sum
60  bunch together over background and
50
 spread out over a metallic UXO target.
40
30 The EMIS technology attempts to identify
20
a target by quantifying the spread vs.
10
0 frequency.
0 5 10 15 20 25 30
-10
GEM-3 with GPS Attachment
Distance (Feet)
64-cm Sensor with GPS 96-cm Sensor with GPS
Two Underwater GEM-3 and GPS
GPS
GEM-3 has been used at many magnetic
and conductive sites:
" Kahoolawe, Hawaii, Sep 2001
" Adak, Alaska, Sep 2000
" JPG Tech Demo, Sep 2000
GPS
" Ford Ord, CA, Summer 2000
" Kaho olawe, Hawaii, June 2000
Sensors lowered
" Mare Island, San Francisco Bay, Sep 1999 Marine UXO Survey
40-cm GEM-3 Sensor
Conductivity and Susceptibility Maps Derived from GEM-3 Data in a Magnetic Geology
Isolated conductivity anomalies are caused by buried metals.
Conductivity Map Susceptibility Map
Geophex, Ltd.