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PROGRAM:

NUME

grdredpol - Compute the Continuous Reduction To the Pole, AKA differential RTP.

REZUMAT

grdredpol anom_grd rtp_grd [dec/dip] [ dec_grd/dipgrd] [ <m/n>] [ m|r] [ ] [ win_width] [
[nivel] ] [ an ] [ filtergrd ] [ [nivel] ] [ -n]

Notă: Nu este permis niciun spațiu între indicatorul opțiunii și argumentele asociate.

DESCRIERE

grdredpol will take a nc file with a magnetic anomaly and compute the reduction to the
pole (RTP) anomaly. This anomaly is the one that would have been produce if the bodies
were magnetized vertically and the anomalies were observed at the geomagnetic pole.
Standard RTP procedure assumes the direction of magnetization to be uniform throughout the
causative body, and the geomagnetic field to be uniform in direction throughout the study
region. Although these assumptions are reasonable for small areas, they do not hold for
suprafete mari.

In the method used here computations are carried out in both the frequency and the space
domains. The idea is that a large area may be decomposed in small size windows where both
the ambient field and the magnetization vector change by a very small amount. Inside each
of those windows, or bins, a set of filter coefficients are calculate and reconstruct for
each individual point the component filter using a first order Taylor series expansion.

NECESARE ARGUMENTE

anom_grd
The anomaly grid to be converted.

-Grtp_grd
is the filename for output grdfile with the RTP solution

OPTIONAL ARGUMENTE

-Cdec/dip
Use this (constant) declination and inclination angles for both field and
magnetization. This option consists in the classical RTP procedure.

-Edip_grd/dec_grd
Get magnetization DIP & DEC from these grids [default: use IGRF]. Note that these
two grids do not need to have the same resolution as the anomaly grid. They can be
mai grosolană.

-Fm/n The filter window size in terms of row/columns. The default value is 25x25.

-Mm|r Set boundary conditions. m|r stands for mirror or replicate edges (Default is zero
umplutură).

-N Do NOT use Taylor expansion.

-Rvest/est/sud/nord
defines the Region of the output points. [Default: Same as input.]

-Tan Decimal year used by the IGRF routine to compute the declination and inclination at
each point [default: 2000]

-Wlățime
The size of the moving window in degrees [5].

-Zfilter_grd
Write the filter file to disk.

-V[nivel] (Mai mult ...)
Selectați nivelul de verbozitate [c].

-n[b|c|l|n][+a][+bBC][+c][+tprag] (Mai mult ...)
Selectați modul de interpolare pentru grile.

CONSECINȚE OF GRID RESAMPLARE

Reeșantionarea sau eșantionarea grilelor va folosi diverși algoritmi (vezi -n) care poate duce la
posibile distorsiuni sau rezultate neașteptate în valorile reeșantionate. Un efect așteptat
de reeșantionare cu spline este tendința ca noile valori reeșantionate să depășească ușor
limitele globale min/max ale grilei originale. Dacă acest lucru este inacceptabil, puteți impune
tăierea valorilor reeșantionate astfel încât acestea să nu depășească valorile min/max de intrare cu
adăugare +c de dvs. -n opțiune.

EXEMPLE

Să presupunem că anom.grd is a file with the magnetic anomaly reduced to the 2010 epoch and
faptul că dec.grd și dip.grd contain the magnetization declination and inclination
respectively for an area that encloses that of the anom.grd, compute the RTP using bins of
2 degrees and a filter of 45 coefficients.

gmt grdredpol anom.grd -Grtp.grd -W2 -F45/45 -T2010 -Edec.grd/dip.grd -V

To compute the same RTP but now with the field and magnetization vectors collinear and
computed from IGRF :

gmt grdredpol anom.grd -Grtp.grd -W2 -F45/45 -T2010 -V

REFERINȚE

Luis, J.L. and Miranda, J.M. (2008), Reevaluation of magnetic chrons in the North Atlantic
between 35N and 47N: Implications for the formation of the Azores Triple Junction and
associated plateau. JGR, VOL. 113, B10105, doi:10.1029/2007JB005573

DREPTURI DE AUTOR

2015, P. Wessel, WHF Smith, R. Scharroo, J. Luis și F. Wobbe

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