DOI: 10.5281/zenodo.12738285
title: Improved magnetometric airborne product - Sao Paulo-Rio de Janeiro survey (Sao Paulo)

description: The airborne data for the São Paulo - Rio de Janeiro survey (São Paulo segment) were acquired in 1978 by Encal S/A Consultoria e Aerolevantamentos, and the source files are available from the Geological Survey of Brazil repository (GEOSGB), referenced as dataset number 1039. 

Manual levelling

The manual leveling technique requires meticulous care and is time-intensive. It is an interpretative process where researchers must analyze data profiles repeatedly, iterating to identify necessary adjustments for each line, in order to minimize non-geological anomaly features. In the case of 1039 dataset, the review of magnetometric anomaly addresses linear artifacts caused by tilted and segmented lines, and minor line segments with no crossover constraints.

Beyond the line levelling improvement, I also have separated the survey in northern and southern areas fro gridding, due to the significant misfit along their boundaries. After the gridding process, I have made a grid mosaic with the Oasis Montaj Software (mosaic data version). 

A directional cossine was applied as a final processing technique, in order to remove the N-S noise.

 

Original source file head:/PROJETO AEROGEOFISICO SAO PAULO-RIO DE JANEIRO  (FASE SAO PAULO)   CODIGO NA BASE AERO = 1039/COORDENADAS UTM  ELIPSOIDE INTERNACIONAL  HAYFORD  1910  MC= -51§ E -45§/LINE-   20 A 2487 (243 PERFIS)  TIE- 9000 A 9220 (25 PERFIS)  TOTAL= 268 PERFIS/LINE- 2540 A 8120 (532 PERFIS)  TIE- 9230 A 9880 (54 PERFIS)  TOTAL= 586 PERFIS

 

If you have any issues, please contact Luizemara Szameitat at contato@lszameitat.com.

 
description: VERSION 1.0

This 1039 data version was focused on mitigating only worst levelling issues and most detailed levelling in the central part of the survey, which area was not overlaid by the 1095 (Paraná-Santa Catarina) and 4099 (Botucatu) surveys from the Brazilian repository. At first, tie lines were revised through manual inspection of general trends of crossing values. Part of the crossing ties and lines in the same flight direction were unified, while lines not crossing any tie line were removed. In the whole process, ties and lines were corrected by DC shift and tilt in most cases, and light spline correction if necessary. After the ties review, the lines were separated into two groups based on their spatial distribution: South and North groups. Lines were observed individually, according to crossing ties, the comparison with neighbor lines, and their effect in the general aspect of the gridded magnetic data. 

The final gridded data is represented by the mosaic of the two grids. ascii files are gridded data with cell dimensions of 500x500 m. In the file names, 'MA' indicates the magnetic anomaly after removing the IGRF. The gridded data (XYZ) was developed in the local coordinate system UTM23S Sirgas2000.

1039_rev10.csv:

Line: original line number

LONG,LAT,XUTM23,YUTM23: coordinates

ALT: aircraft altitude

MAoriginal: original magnetic anomaly

MArev10: reviewed magnetic anomaly levelling, prior to the grid mosaic

_Distance: distance along lines (meters)

IGRF: regional geomagnetic field

MArev10_mosaic: reviewed magnetic anomaly levelling, after the grid mosaic

MArev10_mosaic_dircos: filtered grid mosaic (directiona cossine for 0N)