Discussion Question #1:
Find an article about a current event that discusses a change in the supply or demand of a product. For example, has there been a weather event that has affected certain food crops or the availablility of energy? Has a new consumer product been introduced? Or has a government regulation affected the production of a product? Provide a brief description of the article’s content and explain how economics can be used to analyze the situation and predict changes in equilibrium prices and quantities. Will the change likely persist over time, or is it temporary?
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ie., the SLFIi > 0 identify positively or directly correlative (X-peak)-to-(Y-peak) associations
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ie., the SLFIi < 0 identify positively or directly correlative (X-valley)-to-(Y-valley) associations
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to fruther simplify the positively correlated feature associations in the X- and Y-datasets, replot the SLFIi as=>
- map-A for all SLFIi > 0, and
- map-B for all SLFIi < 0, where the
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to fruther simplify the negaitively correlated feature associations in the X- and Y-datasets, replot the DLFIi as=>
- map-C for all DLFIi > 0, and
- map-D for all DLFIi < 0, where the
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ie., the DLFIi > 0 identify negatively or inversely correlative (X-peak)-to-(Y-valley) associations
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ie., the DLFIi < 0 identify negatively or inversely correlative (X-valley)-to-(Y-peak) associations
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To illustrate WCA, consider the signals T1 and T2 plotted in Fig. 4-below with their respective amplitude means (AM) removed.
- the signals' other statistical attributes also are highly disparate, including the
- amplitude standard deviations (ASD) and
- amplitude ranges of (min, max)-values (AR)
- the signals also have a negligible correlation coefficient (CC) that seems to be supported graphically by an apparent lack of feature associations
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- the 128-point signal T1 is the superposition of the regional background signal (B1) and the higher frequency residual signal (R1), and
- the 128-point signal T2 is the superposition of the regional background signal (B2) and the higher frequency residual signal (R2), where
- CC(B1, B2) = 0, and
- the first half of R1 is positively correlated with the first half of R2, and
- the other two halves are negatively correlated so that
- CC(R1, R2) = 0.
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- this example is from von Frese et al. (1997) and
- also is summarized in Chap. 7.3 [p. (135-138)/153] of the GeomathBook.pdf
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- to facilitate graphical correlation analysis of apples (eg., T1) to oranges (eg., T2), the signals were normalized as described on the next page-below=>
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Accordingly, in Fig. 5, the normalized T1 (ie., NT1) and T2 (ie., NT2) signals have dimensionless
- ASD(NT1) = ASD(NT2) = 2.0, and
- normalization factors (NF) so that
T1 = [NF(T1) x NT1] and T2 = [NF(T2) x NT2]
a.
Discussion Question #1Find an article about a current event tha.docx
1. Discussion Question #1:
Find an article about a current event that discusses a change in
the supply or demand of a product. For example, has there been
a weather event that has affected certain food crops or
the availablility of energy? Has a new consumer product been
introduced? Or has a government regulation affected the
production of a product? Provide a brief description of the
article’s content and explain how economics can be used to
analyze the situation and predict changes in equilibrium prices
and quantities. Will the change likely persist over time, or is it
temporary?
admin
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ie., the SLFIi > 0 identify positively or directly correlative (X-
peak)-to-(Y-peak) associations
admin
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ie., the SLFIi < 0 identify positively or directly correlative (X-
valley)-to-(Y-valley) associations
admin
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to fruther simplify the positively correlated feature associations
in the X- and Y-datasets, replot the SLFIi as=>
- map-A for all SLFIi > 0, and
- map-B for all SLFIi < 0, where the
2. admin
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to fruther simplify the negaitively correlated feature
associations in the X- and Y-datasets, replot the DLFIi as=>
- map-C for all DLFIi > 0, and
- map-D for all DLFIi < 0, where the
admin
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ie., the DLFIi > 0 identify negatively or inversely correlative
(X-peak)-to-(Y-valley) associations
admin
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ie., the DLFIi < 0 identify negatively or inversely correlative
(X-valley)-to-(Y-peak) associations
admin
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To illustrate WCA, consider the signals T1 and T2 plotted in
Fig. 4-below with their respective amplitude means (AM)
removed.
- the signals' other statistical attributes also are highly
disparate, including the
- amplitude standard deviations (ASD) and
3. - amplitude ranges of (min, max)-values (AR)
- the signals also have a negligible correlation coefficient (CC)
that seems to be supported graphically by an apparent lack of
feature associations
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- the 128-point signal T1 is the superposition of the regional
background signal (B1) and the higher frequency residual signal
(R1), and
- the 128-point signal T2 is the superposition of the regional
background signal (B2) and the higher frequency residual signal
(R2), where
- CC(B1, B2) = 0, and
- the first half of R1 is positively correlated with the first half
of R2, and
- the other two halves are negatively correlated so that
- CC(R1, R2) = 0.
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- this example is from von Frese et al. (1997) and
- also is summarized in Chap. 7.3 [p. (135-138)/153] of the
GeomathBook.pdf
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- to facilitate graphical correlation analysis of apples (eg., T1)
to oranges (eg., T2), the signals were normalized as described
4. on the next page-below=>
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Accordingly, in Fig. 5, the normalized T1 (ie., NT1) and T2
(ie., NT2) signals have dimensionless
- ASD(NT1) = ASD(NT2) = 2.0, and
- normalization factors (NF) so that
T1 = [NF(T1) x NT1] and T2 = [NF(T2) x NT2]
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- Note that normalization does not affect CC(T1, T2).
- However, this plot of the normalized signals suggests a
possible regional phase shift for WCA investigation
- Thus. wavenumber correlation filters (WCF) were developed
and applied to NT1 & NT2 to extract the minimally correlated
wavenumber components output respectively in Fig.s 6- & 7-
below
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- or set σz = σx and μz = μx to normalize Y to X, so that zi(Y) =
NY can be plotted on the same axes or contour intervals, etc. as
those of X
- or normalize both X and Y to common σz and μz so that zi(X)
and zi(Y) may be plotted with common graphical parameters,
etc.
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RMSE is the root-mean-squared error
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- an even better estimate of B1 (ie., EB1) is possible with (-0.1
< CC(k) < 0.1)
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- subtracting EB1 from T1, and EB2 from T2 yields pretty good
estimated residuals ER1 and ER2, respectively
- however=> CC(ER1, ER2) = 0
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ER1 is signal A(x) in figure on next page
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ER2 is signal B(x) in figure on next page
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=> ER1
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=> ER2
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(ER1-valley)-to-(ER2-valley) associations
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(ER1-peak)-to-(ER2-peak) associations
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(ER1-peak)-to-(ER2-valley) associations
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(ER1-valley)-to-(ER2-peak) associations
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As another example of WCF from von Frese et al. (1997),
consider the satellite magnetic observations in nT from the two
Magsat mission orbital tracks across the arctic to northern
Finnland in Fig. 14.A-below
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- these orbital track segments of lithospheric magnetic anomaly
data at 400 km altitude are within about 10 km or so of each
other
- thus the lithospheric anomaly estimates should be highly
correlated,
7. - but the CC = 0.705, which suggests an initial noise
contribution of roughly=>
no = √[(1/CC2) – 1] ≈ 0.6468 or about 65%
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- to estimate the more correlative wavenumber components in
the data tracks, a WCF for CC(k) > 0.6 was applied with output
shown in Fig. 14.B-below
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- these positively correlated signals reflect ocean-continent
boundaries and other lithospheric features
- also, the improved CC suggests a noise contribution of only=>
n1 ≈ 0.0707 or about 7.1%, or
- a noise reduction of [(no - n1)/no]100 ≈ 89%
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- however, to avoid throwing out the baby with the bath water,
it is always prudent to check out the rejected signal components
as shown in Fig. 14.C-below
- the positive residual correlation was checked by WCF for
CC(k) > 0.3,
- which output the regionally correlated components in Fig.
14.D-below
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- these regionally correlated signals seem to ignore continent-
ocean boundaries and other lithospheric features,
- thus, they were attributed mostly to external geomagnetic field
effects and
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- the residual signals of Fig. 14.C shown here also lack
prominent lithospheric affinities, and
- their amplitudes are marginal relative to the amplitudes of the
presumed lithospheric magnetic anomalies in Fig. 14.B-above
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- thus, pair-averages of the strong, positively correlated
anomalies in Fig. 14.B-above were taken as least squares
estimates of the lithospheric anomalies that the two Magsat
tracks observed
- here, the pair-averaged magnetic anomalies of the lithosphere
are mapped by the solid-line profile, whereas
- the dotted-line profile gives the pair-wise RMS-differences as
error estimates on the corresponding lithospheric magnetic
anomaly estimates
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A further WCF example from von Frese et al. (1997) considers
9. five track-pairs of geoidal undulations from ascending orbits of
the US Navy's Geosat-GM altimetry mission over a region east
of the Gunerus Ridge which extends offshore of East
Antarctica's
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- the marine altimetry estimates geoidal undulations in cm-
amplitude units (AU)
- vertical differentiation of the geoidal undulations can yield
gravity anomalies for constraints on modeling the subjacent
lithosphere
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- the tracks in these 5 pairs are separated by mean distances of
about 2 to 5 km over a mean sea floor depth of about 4 km
- so that geological features at these scales and larger should
yield strong, positively correlated features between the
altimetry tracks
- but the mean CC between the track-pairs is
CCM = 0.832, which implies a noise level of about=>
no = √[(1/CC2) – 1] ≈ 44.93%
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- to reduce the noise level, the track-pairs were WCF for CC(k)
> 0.80 for the output in Fig. 16-below
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- the WCF-output suggests an reduced noise level of about
=> n1 ≈ 29.1%, which is in a noise reduction of roughly
=> [(0.4493 - 0.2909)/0.4493]100 ≈ 35%
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- here, the rejected, broadband non-correlative features
presumably include=>
- crustal signals that are smaller than the track spacing, and
- dynamic signals from temporal and spatial variations of the
- orbit errors,
- ocean currents,
- waves and ice,
- measurement and data reduction errors, and
- other non-lithospheric effects
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Basement
- not Bedrock...which refers to the overlying Phanerozoic
sedimentary rocks
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WCA of the gravity and magnetic anomaly maps of Ohio
- adapted from von Frese et al., 1997, Spectral correlation of
magnetic and gravity anomalies of Ohio, Geophysics, v. 62,
365-380.
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compositional constraints on the basement rocks from 149
basement-penetrating boreholes
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interpretation of the anomaly maps is based on modeling of
statewide profiles A-thru-E
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interpretation examples for profiles A and B are shown below
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A-profile
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Correlative features between the two datasets=>
- reduce interpretational ambiguity
12. - and improve interpretational reliability
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CC < 0
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CC < 0
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CC > 0
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CC < 0
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B-profile
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CC > 0
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CC < 0
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CC > 0
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CC > 0
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CC > 0
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Basement geology inferred from the magnetic and gravity
anomaly data
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physical basis for correlating magnetic and gravity anomalies
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where there is
- a correlation spectrum CC(k), there also is
- an intercept spectrum A(k), and
- slope spectrum S(k) involving the ratio Δj/Δσ of physical
property contrasts
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14. A(k)
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S(k)
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pseudo-anomalies
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raw (ie., unnormalized) pseudo-anomalies derived from the
Bouguer gravity and total magnetic anomalies
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here the normalization factor NF = SF
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normalized pseudo anomalies for enhance visual-spatial
correlation analysis
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normalized FVD gravity and RTP magnetic anomalies WCF for
(+1 ≤ k ≤ 0) to emphasize positive anomaly correlations
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SLFI > 0 emphasizes peak-to-peak gravity and magnetic
features
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SLFI > 0 emphasizes peak-to-peak gravity and magnetic feature
associations
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SLFI < 0 emphasizes valley-to-valley gravity and magnetic
feature associations
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SLFI < 0 emphasizes valley-to-valley gravity and magnetic
feature associations
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SLFI > 1 standard deviation (SD) emphasizes the strongest
peak-to-peak gravity and magnetic feature associations
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SLFI < -1 standard deviation (SD) emphasizes the strongest
valley-to-valley gravity and magnetic feature associations
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normalized FVD gravity and RTP magnetic anomalies WCF for
(-1 ≤ k ≤ 0) to emphasize negative anomaly correlations
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comparison of WCF normalized FVD gravity anomalies with
DLFI based on the LFI difference=>
LFI(FVDG) - LFI(RTP)
to hi-lite inverse feature associations in the FVD gravity
anomalies
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comparison of WCF normalized RTP magnetic anomalies with
DLFI based on the LFI difference=>
LFI(FVDG) - LFI(RTP)
to hi-lite inverse feature associations in the RTP magnetic
anomalies
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comparison of normalized FVD gravity anomalies with DLFI >
0 to hi-lite=>
FVDG-peak to RTPM-valley associations
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comparison of normalized RTP magnetic anomalies with DLFI >
0 to hi-lite=>
FVDG-peak to RTPM-valley associations
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comparison of normalized FVD gravity anomalies with DLFI <
0 to hi-lite=>
FVDG-valley to RTPM-peak associations
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comparison of normalized RTP magnetic anomalies with DLFI <
0 to hi-lite=>
19. FVDG-valley to RTPM-peak associations
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DLFI > 1 standard deviation (SD) emphasizes the strongest
FVDG-peak to RTPM-valley anomaly associations
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DLFI < -1 standard deviation (SD) emphasizes the strongest
FVDG-valley to RTPM-peak anomaly associations
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normalized FVD gravity and RTP magnetic anomalies WCF for
(-0.3 ≤ k ≤ +0.3) to emphasize the null-correlated anomaly
features
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#4
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#4
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#4
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#4
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#4
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#4
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- regions of the basement rocks where the WCA emphasizes
possible occurrences of 4 physical property combinations
- the edges of these regions were mapped from the zero contours
of the SVD(g) and SVD(RTPm) anomalies
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negative=> [Δm(-), Δσ(+)]
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negative=> [Δm(+), Δσ(-)]
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22. from=>
= √[(jωl)p + (jωk)p]
- in particular, for p = 2 the horizontal curvature may be
obtained with zero contours that estimate feature edges, and
thus provide edge detection
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- this is an elementary linear differential equation of order p
with constant coefficients
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- typically found in Chap. 2 of common textbooks on ordinary
differential equations
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=> iff A = 0
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ideal SVD-response
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ideal VD-response for p = 4
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23. lousy (ie., crude) SVD-response
- perhaps derived from the data domain convolution of a
simplified first derivative operator=> (-1, 0, 1),
- where the SVD(1D)=> (-1, 0, 1(۞)-1, 0, 1) and ۞ denotes
convolution
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- much improved response of a SVD-operator such as developed
in Fig. 1-below on next page
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- derivative filters generally behave like high-pass/low-cut
filters
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Elkins 7-by-7 point SVD-grid or -mask operator
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zero row
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zero column
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- the weights at radii ri=>
r1 = Δx,
24. r2 = Δx√2,
r3 = Δx2,
etc.
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real
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imaginary with=>
i = j = √(-1)
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imaginary with=>
i = j = √(-1)
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- note that the order 'p' previously used is now 'n'
- ie., p-order => n-order
helpful for assignment 5.3
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regional gravity effect
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total gravity effect of 5-cylinders + regional
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individual gravity effects of the 5 cylinders
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- or estimate the 5 cylinder densities and regional slope and
intercept values from the total signal by inversion
- and modify the A-coefficients for coefficients that obain the
desired integral/derivative properties
- by forward modeling of the modified system assuming the
other cylinder parameters are known
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- or simply take the FFT of the total signal,
- filter it using the appropriate integral/derivative transfer
function coefficients
- and IFFT the modified spectrum to obtain the data domain
estimates of the desired integral/derivative properties
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The FFT is the superior approach in terms of numerical
efficiency, accuracy, and the minimum assumptions needed
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To evaluate the integral/derivative properties of the total signal,
we could=>
- perform graphical operations with significant computational
labor
- or equivalent convolutions with significant computational
effort and error
Ralph
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cylinder #1
Ralph
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cylinder #2
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cylinder #3
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cylinder #4
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cylinder #5
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27. plus regional
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mgal
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rind applied at both ends to minimze Gibbs' error
Ralph
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- if the investigator correctly assumes that these anomaly peaks
are all due to the gravity effects of horizontal cylinder mass
variations,
- then at the anomaly peaks or maximum amplitudes (MA), the
depths to the central axes (zc) of the sources may be estimated
from the ratios of the anomalies to their respective FVD
anomalies
- ie.,
zc = [g#1(MA)] / [∂g#1(MA)/∂z]
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mgal/km
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where the analytic FVD for the i-th cylinder is=>
28. ∂[gz(x)]i/∂z = K(Δρi)Ri2(x2 – zi2)/(x2 + zi2)2
so that for all i = 1-thru-5 cylinders and the regional, the total
analytic FHD (= ftn) is=>
∂[gz(x)]/∂z = 1∑5 ∂[gz(x)]i/∂z +
[∂gz(regional)/∂z = ???]
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first vertical derivative (FVD) of the gravity effects of the 5-
cylinders plus regional
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- the peak FVD gravity anomaly [∂g#1(MA)/∂z] so that
zc = [g#1(MA)] / [∂g#1(MA)/∂z] = -2 km
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where the Analytic Ftn=>
SVD = ∂{1∑5 ∂[gz(x)]i/∂z}/∂z +
[∂{∂gz(regional)/∂z}/∂z = ???]
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mgal/km2
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second vertical derivative (SVD) of the gravity effects of the 5-
29. cylinders plus regional
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in addition, the maximum amplitudes (MA)
- locate the x-coordinates of the central axes of the cylinders,
- of p-order may be compared against their (p±1)-order
components for the depths zi of the central axes, and
- the zero crossings of the SVD about the MAs estimate the
diameters (= 2Ri) of the related cylinders
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- thus from the FFT of the gravity anomalies, we may determine
for each cylinder the=>
- x-coordinate of its central axis,
- z-coordinate or depth of its central axis, and
- diameter of the source (eg., D#1 = 4 km)
- the above results effectively constrain the A-coefficients so
that least-squares estimates of the density contrasts (∆ρ) may be
obtained
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- integration of the FFT-SVD completely recovers the total
30. gravity signal on page 47/59
- compared to differentiation, integration is a very stable
process
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analytic ftn=>
∫∫∂/∂z[(∂gz/∂z) ∂z] ∂z = gz
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what would you get if you integrated gz one more time?
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Assignment #11=> complete exercise 5.3=>
EARTHSC_5642_Ex5-3_17Mar15
John
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note that the teacher integrated twice
John
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to produce geoid anylation or the sense of the gravity potencial.
31. admin
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-3 km
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+3 km
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- 'downward' continuation amplifies the high-frequency
components
- thus, it essentially behaves like a high-pass/low-cut filter
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- 'upward' continuation attenuates the high-frequency
components
- thus, it behaves essentially like a high-cut/low-pass filter,
whereas
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the Nyquist limit of coefficient values
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- nowadays, however, multiple altitude grids of potential field
data are becoming increasingly available from surface, airborne,
and satellite surveys,
- for which 'interval' continuation operators can be developed to
evaluate data values at the intermediate altitudes between the
grids
32. - that also honor the boundary grid values
- the 'interval' grid continuation operator is described on pages
(117-119)/153 of the GeomathBook.pdf
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- the inverse operations of 'upward' and 'downward'
continuation are most reliable only over elevations within a few
grid intervals of the observations
- due to measurement errors and the non-uniquess of
continuation
- thus, to be certain of data behavior at more distant elevations,
there is no recourse but to survey
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- array size=> 480 x 220 = 115,200 anomaly values
- station interval = 2 km
- from NRC (Keller et al., 1980)
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- note prominent edge effects
- better window carpentry can reduce these edge effects
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- upward continuation substantially reduces and smooths the
anomaly gradients with increasing altitude
Exercise 5.3 Fast Fourier Transform (FFT)
A) Show that the gravity effect of the horizontal cylinder=>
gz = [41.93 Δρ(R2/z)]/[(d2/z2) + 1]
satisfies Laplace’s equation=> ∂2gz/∂d2 + ∂2gz/∂z2 = 0.
For the gravity effects of the 5 buried horizontal cylinders
B) Compute, list, and plot the related amplitude and phase
spectra.
C) Inverse transform the Fourier coefficients and compare the
synthesized signal with the original. What are the sources of
the mismatches?
D) Compute, list and plot the first horizontal derivative ∂gz/∂d
from the FFT of (gz).
E) How do the results in D-above compare with the analytical
horizontal first derivative gravity effects of the buried
34. horizontal cylinders?
F) Compute, list, and plot the second horizontal derivative
∂2gz/∂d2 from the FFT of (gz).
G) How do the results in F-above compare with the analytical
horizontal second derivative gravity effects of the buried
horizontal cylinders?
H) Compute, list and plot the first vertical derivative ∂gz/∂z
from the FFT of (gz).
I) How do the results in H-above compare with the analytical
vertical first derivative gravity effects of the buried
horizontal cylinders?
J) Compute, list, and plot the second vertical derivative
∂2gz/∂z2 from the FFT of (gz).
K) How do the results in J-above compare with the analytical
vertical second derivative gravity effects of the buried
horizontal cylinders?
L) Compute, list, and plot (gz) from the FFT of the analytical
(∂2gz/∂z2) in K-above.
M) How do the FFT estimates from L-above compare with the
gravity effects of the 5 buried horizontal cylinders obtained in
Exercise 2.1?
Assignment TIP to consider: Just take an fft of the data and use
the MATLAB "angle" command on the output. This will
calculate the phase spectra. The "abs" command calculates the
magnitude.
35. Look page 51/59 in pdf note
%% Ex2-1 A)
% Compute the 5 gravity profiles
d=[-34 -20 0 20 35]; % in km
z=[2 3 5 10 10]; % in km
R=[2 1 3 4 3.5]; % in km
dro=[3.0 5.0 1.0 2.0 1.5]; % in gm/cm^3
gz = (41.93*dro.*R.^2./z)./(d.^2./z.^2+1);
d_itv=-100:1:100;
gz1=(41.93*dro(1)*R(1)^2/z(1))./(d_itv.^2./z(1)^2+1);
gz2=(41.93*dro(2)*R(2)^2/z(2))./(d_itv.^2./z(2)^2+1);
gz3=(41.93*dro(3)*R(3)^2/z(3))./(d_itv.^2./z(3)^2+1);
gz4=(41.93*dro(4)*R(4)^2/z(4))./(d_itv.^2./z(4)^2+1);
gz5=(41.93*dro(5)*R(5)^2/z(5))./(d_itv.^2./z(5)^2+1);
d1=d_itv+d(1);
d2=d_itv+d(2);
d3=d_itv+d(3);
d4=d_itv+d(4);
d5=d_itv+d(5);
index1=find(abs(d1)<=64);
index2=find(abs(d2)<=64);
index3=find(abs(d3)<=64);
index4=find(abs(d4)<=64);
index5=find(abs(d5)<=64);
% Plot the 5 gravity superimposed
figure(1)
plot(d1(index1), gz1(index1),'green');
hold on;
plot(d2(index2), gz2(index2),'red');
hold on;
plot(d3(index3), gz3(index3),'blue');
hold on;
plot(d4(index4), gz4(index4),'yellow');
hold on;
plot(d5(index5), gz5(index5),'black');
36. hold off
title('Gravity Profiles', 'FontSize', 20);
xlabel('Distance (km)', 'FontSize', 15);
ylabel('Gravity (mgal)', 'FontSize', 15);
legend('Caylinder 1','Cylinder 2','Cylinder 3','Cylinder
4','Cylinder 5');
%% Ex2-1 B)
% Compute the total gravity effect of the 5 cylinders by
summing their
% effects at each observation point on the profile
g=gz1(index1)+gz2(index2)+gz3(index3)+gz4(index4)+gz5(inde
x5);
% mean value
average = sum(g)/length(g);
% standard deviation
std=sqrt(sum((g-average).^2)/length(g));
% Plot the total gravity effect
figure(2);
plot(d1(index1),g);
hold on;
plot(d1(index1),repmat(average,length(index1),1));
title('Total Gravity From Five Cylinders', 'FontSize', 20);
xlabel('Distance (km)', 'FontSize', 15);
ylabel('Gravity (mgal)', 'FontSize', 15);
%% Ex2-1 C)
A1=((41.93*R(1)^2/z(1))./(d_itv.^2./z(1)^2+1))'
B1=gz1'
dro1=(inv(A1'*A1))*A1'*B1;
A2=((41.93*R(2)^2/z(2))./(d_itv.^2./z(2)^2+1))';
B2=gz2';
dro2=(inv(A2'*A2))*A2'*B2;