U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Description of digital aeromagnetic data collected north and west of Albuquerque, New Mexico by U. S. Geological Survey (MS 964, Federal Center, Denver, CO 80225), with an Appendix by SIAL Geosciences, Inc. (1400 boul. Gouin Ouest, Montreal, Quebec, Canada H3M 3B1) Open-File Report 97-286 This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U. S. Geological Survey These data have been approved for release and publication by the Director of the USGS. Although these data have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, they are released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Digital files of the data (constructed for display purposes only) can be downloaded via 'anonymous ftp' from a USGS system named greenwood.cr.usgs.gov (136.177.21.122). The files are located in a directory named /pub/open-file-reports/ofr-97-0286 and are described in an ASCII file named readme.txt. A web browser can access these files at http://rmmcweb.cr.usgs.gov/public/mrgb/mrgbhome.html. The original digital geophysical data (flight-line data and grids constructed by the contractor) can be obtained from the National Geophysical Data Center, Boulder, Colorado (http://www.ngdc.noaa.gov/seg/potfld/ad_sys.html). The data contact is: V. J. S. ("Tien") Grauch 303-236-1393 tien@usgs.gov U. S. Geological Survey Box 25046, MS 964 Federal Center Denver, CO 80225 ABSTRACT This report describes aeromagnetic data collected by SIAL Geosciences, Inc. for the U. S. Geological Survey north and west of Albuquerque, New Mexico. Aeromagnetic surveys were conducted in November and December, 1996 over two areas within the Middle Rio Grande Basin: (1) north and west of Albuquerque covering Rio Rancho and (2) west of Albuquerque. Digital files of the data (constructed for display purposes only) can be downloaded via 'anonymous ftp' from a USGS system named greenwood.cr.usgs.gov (136.177.21.122). The files are located in a directory named /pub/open-file-reports/ofr-97-0286 and are described in an ASCII file named readme.txt. A web browser can access these files at http://rmmcweb.cr.usgs.gov/public/mrgb/mrgbhome.html. The original digital geophysical data (flight-line data and grids constructed by the contractor) can be obtained from the National Geophysical Data Center, Boulder, Colorado (http://www.ngdc.noaa.gov/seg/potfld/ad_sys.html). DESCRIPTION OF DATA This report describes aeromagnetic data collected by SIAL Geosciences, Inc. who were contracted by the U. S. Geological Survey to fly two areas within the Albuquerque Basin, which is contained within the Middle Rio Grande Basin: (1) north and west of Albuquerque, covering Rio Rancho (area A, fig. 1), and (2) west of Albuquerque (area B, fig. 1). Data acquisition for the surveys was completed in December, 1996; data were delivered April, 1997. The overall objective of these surveys, in conjunction with airborne electromagnetic surveys flown in March, 1997, is to improve the understanding of the geologic and hydrogeologic framework of the Middle Rio Grande Basin. This improved understanding will lead to refinements in the hydrologic model of the Basin. The survey over the Rio Rancho area (area A, fig. 1) was flown along east-west lines spaced 100 m apart and at a nominal altitude of 100 m above ground level (AGL) except over urban areas, where altitudes increased to 150 m AGL. The survey over Albuquerque west (area B, fig. 1) was flown with lower resolution than the Rio Rancho survey, with 150- m spacing and heights 150 m AGL (300 m over urban areas). Further details of the flight surveys are included in Appendix A. The flight-line data were projected from latitude/longitude coordinates to Universal Transverse Mercator coordinates (Zone 13; central meridian 105oW). The contractor leveled the flight-line data using four north-south tie lines spaced from 7 to 13 km apart (Appendix A). The leveled data were then gridded independently by the contractor and by the USGS using two somewhat different methods: the contractor used a bi- directional akima gridding algorithm and filtered the grid to reduce anomalies due to manmade structures (Appendix A), whereas the USGS used a minimum curvature algorithm (Webring, 1981) with no further filtering. All grids were constructed using a 50-m grid interval except for the contractor's grid for the Rio Rancho survey, which was constructed at 25-m interval. Color shaded-relief images of the USGS grids were generated by the computer program ERMapper at both page size and at 1:100,000 scale. A sun angle of 90o (east) and sun elevation of 35o above the horizon were used in the shaded-relief algorithm. USGS grid files in Arc interchange format, digital images (constructed for display purposes only), and brief ASCII text (readme.txt) can be downloaded via 'anonymous ftp' from a USGS system named greenwood.cr.usgs.gov (136.177.21.122). The files are located in a directory named /pub/open-file-reports/ofr-97-0286 and are described in an ASCII file named readme.txt. A web browser can access these files at http://rmmcweb.cr.usgs.gov/public/mrgb/mrgbhome.html. The original digital geophysical data (flight-line data and grids constructed by the contractor) can be obtained from the National Geophysical Data Center, Boulder, Colorado (http://www.ngdc.noaa.gov/seg/potfld/ad_sys.html). DESCRIPTIONS OF FILES CONTAINED IN THE ANONYMOUS FTP AREA FILE NAME FILE TYPE DESCRIPTION -----grid files----- rrsmag.e00 Arc interchange ArcGrid of the Rio Rancho data file (50-m grid interval) in interchange format for import to ArcInfo systems. awsmag.e00 Arc interchange ArcGrid of the Albuquerque west data file (50-m grid interval) in interchange format for import to ArcInfo systems. ---image files---- rrsmag.tif tagged image file Page size color shaded-relief image format of the USGS Rio Rancho magnetic grid. awsmag.tif tagged image file Page size color shaded-relief image format of the USGS Albuquerque West magnetic grid. rrsmag.eps encapsulated 1:100,000 scale color shaded- postscript file relief image of the USGS Rio Rancho magnetic grid. awsmag.eps encapsulated 1:100,000 scale color shaded- postscript file relief image of the USGS Albuquerque west magnetic grid. rrsmag.pdf portable document Color shaded-relief image of the file (PDF) format USGS Rio Rancho magnetic grid at 100 dpi resolution. awsmag.pdf portable document Color shaded-relief image of the file (PDF) format USGS Albuquerque west magnetic grid at 100 dpi resolution. figure1.eps encapsulated Black and white image of figure 1 postscript file of the report (survey index map). figure1.pdf portable document Black and white image of figure 1 file (PDF) format of the report (survey index map).. -----text-------- readme.txt ASCII text Text describing files in the anonymous ftp area. text.txt ASCII text Text (this file) that contains text of the report without figure or Appendix A. Appendix A is only available as a paper copy through Open-File Services, USGS, Denver, CO ACKNOWLEDGEMENTS We are very grateful to Sandia Pueblo for their permission to acquire data over their land and to Laguna Pueblo who allowed the plane to fly turns over their land. We are also thankful to the people of Albuquerque and surrounding communities for their tolerance during the low-level flying over their homes and businesses. REFERENCES CITED Webring, Michael, 1981, MINC: A gridding program based on minimum curvature: U. S. Geological Survey Open-File Report 81-1224, 41 p.