Edge Detection and Depth Estimates – Application to
Pseudogravity and Reduced to Pole Results: Part I
•Edge detection on an oversampled synthetic anomaly with no
additional noise
•Comparing Horizontal Gradient, Total Gradient (Analytic Signal),
and Local Wavenumber
Magnetic anomaly calculated
for 1.5 meters above the
ground surface. Dimensions
are kilometers, sampling
interval is 400 meters,
contour interval is 10 nT,
inclination = 68o.
Subsurface model:
• Minimum depth is 250
meters, maximum is 3.35
kilometers
•Magnetic susceptibility is
constant and positive with no
remanent magnetization
The Model from Different Perspectives
•East-west faults get deeper and have less throw along strike from the center as
they traverse from edge to edge of the model area
•The north-south fault gets deeper to the south but the throw is constant
•The long wavelength shape is that of a truncated dome.
Total field anomaly;
inclination = 68o
Reduced to pole anomaly
Reduced to pole anomaly (RTP)
Horizontal Gradient of the RTP
anomaly
Maxima of the Horizontal
Gradient of the RTP anomaly
Maxima of the Horizontal
Gradient of the RTP anomaly
overlain on the source model
Reduced to pole anomaly (RTP)
Total Gradient (Analytic Signal)
of the RTP anomaly
Maxima of the Total Gradient of
the RTP anomaly
Maxima of the Total Gradient of the RTP
anomaly overlain on the source model
Reduced to pole anomaly (RTP)
Local Wavenumber of the RTP
anomaly
Maxima of the Local Wavenumber
of the RTP anomaly
Maxima of the Local Wavenumber of the
RTP anomaly overlain on the source model
Total field anomaly (inc = 68o)
Pseudogravity (Vertical Integral of RTP)
Pseudogravity
Horizontal Gradient of the Pseudogravity
Maxima of the Horizontal Gradient
of the Pseudogravity
Maxima of the Horizontal Gradient of the
Pseudogravity overlain on the source model
Pseudogravity
Total Gradient (Analytic Signal) of
the Pseudogravity
Maxima of the Total Gradient of the
Pseudogravity
Maxima of the Total Gradient of the
Pseudogravity overlain on the source
model
Pseudogravity
Local Wavenumber of the Pseudogravity
Maxima of the Local Wavenumber
of the Pseudogravity
Maxima of the Local Wavenumber of
the Pseudogravity overlain on the
source model
The Model from Different Perspectives
•East-west faults get deeper and have less throw along strike from the center
but go from edge to edge of the model area
•The north-south fault gets deeper to the south but the throw is constant
•The long wavelength shape is that of a truncated dome.
All Maxima; Analysis on Pseudogravity
All Maxima; Analysis on RTP
Maxima from the methods: Blue = HGM; Green = AS; Magenta = LWN
•For each case, operating on the pseudogravity (vertical integration of RTP) results in fewer
spurious results; vertical integration is a low-pass operator.
•East-west faults run edge to edge and get deeper away from the center; only the LWN
maxima trace faults continuously to the edges on both PSG and RTP.
•Only HGM on PSG gives insight into the curved nature of the main dome.
Top Four Quintiles of Gradient Maxima From the Pseudogravity
Classed post map of the four upper quintiles of the combined results of HGM,
AS, and LWN analysis of the pseudogravity (purple, blue, green, and red in
order of increasing significance).