of2009-1044_readme.txt

The digital data and map of this Open-File report are 
available from the following U.S. Geological Survey URL:  

http://pubs.usgs.gov/of/2009/1044/

Data Contents

The digital dataset consists of one file (cencal_mag.xyz) 
containing the approximately 2,750,000 point data that were 
gridded and contoured to produce aeromagnetic contours on 
the map.  The file contains the principal data fields of 
the aeromagnetic measurements, with header lines describing 
the flight number, flight line, and date for each 
flightline, followed by one measurement point coded per 
line.  Header lines begin with "/" to mark them as header 
information, rather than measurement information.

The format of the data is described below.  Each 
measurement has a line number, line direction, latitude, 
longitude, date and time information, radar, barometric and 
GPS altitude and various levels of magnetic field 
measurements.

Measurement Description:

Line       1Hz    *                 Line number (edited)
direction  1Hz    degrees           Flight line direction in 
                                      degrees from North

lon_nad27  1Hz    decimal degrees   DGPS longitude 
                                      (NAD-27);Transformed from 
                                      X_nad27 & Y_nad27
lat_nad27  1Hz    decimal degrees   DGPS latitude  
                                      (NAD-27);Transformed from 
                                      X_nad27 & Y_nad27
X_wgs84    1Hz    meters            DGPS UTME (WGS-84,Z10N) 
                                      Selected (WPT-DGPS)
Y_wgs84    1Hz    meters            DGPS UTMN (WGS-84,Z10N) 
                                      Selected (WPT-DGPS)
X_nad27    1Hz    meters            DGPS UTME (NAD-27 mean 
                                      CONUS,Z10N)
Y_nad27    1Hz    meters            DGPS UTMN (NAD-27 mean 
                                      CONUS,Z10N)

fid10      10Hz    sec              Geosoft fiducial
date       1Hz     *                Acquisition year and Julian 
                                      date YYYY/DDD (UTC)
tgps       1Hz     sec              UTC time (HH:MM:SS:SS)

raltlc     10Hz    meters           Radar altitude above ground 
                                      level (AGL); Edited
baltlc     1Hz     meters           Barometric altitude relative 
                                      to mean sea level (MSL); 
                                      Edited
z          1Hz     meters           DGPS altitude     (MSL); 
                                      Selected (WPT-DGPS)

baseA      1Hz     nT               Mag base station A, edited, 
                                      Base located in San Luis 
                                      Obispo, California
um3l       10Hz    nT               TMF (Total Magnetic Field), 
                                      Uncompensated TAIL, Tail 
                                      sensor, raw
mag_micro  10H     nT               Micro-levelled TMF 
magigrf    10Hz    nT               Final levelled residual 
                                      magnetic intensity

m3l        10Hz    nT               TMF, Compensated TAIL; Tail 
                                      sensor, raw
maglc      10Hz    nT               Edited TMF; De-spike & 
                                      filter applied on m3l
maglcb     10Hz    nT               diurnal corrected TMF
mag_lev    10Hz    nT               Tie line levelled TMF
igrf       1Hz     nT               IGRF (International 
                                      Geomagnetic Reference 
                                      Field) value calculated 
                                      with draped z