URUANA DE MINAS — PROJECT 1009 CGBA HISTORICAL MAGNETIC AUDIT
Generated 2026-08-14
Frozen city center: -16.0593, -46.2585
Frozen target radius: 8 km

SOURCE / PROVENANCE
- Archive: 1009_XYZ.zip
- PGW combined file: CGBA_LAT_LONG_PGW.XYZ
- WMC combined file: CGBA_LAT_LONG_WMC.XYZ
- README states CGBA acquisition occurred in 1971–1972.
- README states PGW data are IGRF-reduced; WMC data contain an unknown arbitrary value added to MAG.
- Uruana is covered by PGW, not WMC, within the frozen 8-km target.
- PGW target: 73 digitized points across 8 line IDs; nearest point 0.402 km.
- WMC target: 0 points.

TEST A — 2011 RAW-GRADIENT RULE ADAPTED TO 1009 GEOMETRY
Limitation: 1009 local main lines are approximately E-W, so the exact within-line N-S slope used in 2011 cannot be repeated.
Geometry-adapted test: line medians in fixed longitude corridors, estimate N-S between-line slope.
PGW MAG is an IGRF-reduced residual; approximate historical total field reconstructed as residual + IGRF13 F at point/date/altitude.
Across dates 1971.0, 1971.5, 1972.0 and corridor half-widths 1–4 km:
- IGRF N-S slope: 1.356 to 1.373 nT/km (positive)
- PGW residual N-S slope: -0.356 to -0.233 nT/km (negative)
- reconstructed total N-S slope: 1.000 to 1.144 nT/km (positive)
Verdict: FAIL as direct historical replication of the 2011 total-field meridional-gradient sign inversion.
Secondary observation: the historical crustal residual trend opposes the main-field gradient, but is too small to reverse the reconstructed total field.

TEST B — NUMERIC 1DV RECONSTRUCTION FROM PGW RESIDUAL
Robustness family:
- interpolation: linear, cubic
- grid spacing: 0.5, 1.0, 1.5 km
- polynomial detrend: degrees 1, 2, 3
- upward continuation: 0, 1, 2, 4, 6 km
- local interpolation windows: 25, 30, 35, 40, 50 km
Total: 450 reconstructions.
Nearest 1DV=0 distance from frozen city center:
- minimum: 0.005 km
- median: 2.375 km
- maximum: 6.864 km
- reconstructions with nearest zero <=8 km: 450/450
Verdict: ROBUST HISTORICAL CORROBORATION of a local vertical-derivative sign boundary within the frozen 8-km target.
This is not a raw-flight test; the 1009 source is digitized/reprocessed historical map data.

TEST C — PRE-EXISTING SAO DOMINGOS FAULT-SIDE WINDOW APPLIED TO 1009
Fault geometry fixed independently from SGB GIS.
Same side windows as prior 2008 audit: medians 0.5–3 km west vs 0.5–3 km east.
Nearest historical crossing (line 15.21, ~7.834 km from city):
- PGW residual step east-west: 13.750 nT
- local slope: 3.619 nT/km
Four largest |steps| among the 23 available near-region crossings occur at:
 line  cross_city_km  step_nT
 1.56       8.459541   15.000
 2.55      10.237743   15.000
 3.53      11.910770   13.905
15.21       7.833959   13.750
Status: CORROBORATIVE / EXPLORATORY historical fault response. Do not claim monotonic along-fault decay: the 1009 data do not reproduce the strong monotonic decay seen in 2008.

CURRENT DEFENSIBLE TEMPORAL SYNTHESIS
- 1971–72 CGBA/1009: numeric 1DV sign boundary robustly within 8 km; crustal residual N-S trend opposes IGRF; reconstructed total-field N-S inversion FAILS; São Domingos residual step is present in the near-Uruana sector.
- 2008 ANP 0032: independent 1DV boundary and strong localized São Domingos response.
- 2011 SGB 3087: raw total-field meridional gradient sign inversion relative to IGRF in 14/14 target lines.
- Direct vector Z/inclination remains unresolved pending raw fZ.