Austin #6031

The totmag has questionable data on many of the lines and needs significant leveling.

Eleven lines did not have residual mag calculated so it was decided to recalculate it.  
First an elevation channel was created by sampling the topographic grid for Texas and adding 
it to the radar altitude.

The 1965 IGRF model was originally used for this quad.  An IGRF65 channel was calculated using 
the elevation channel and a median date of April 8, 1977.  A new resmag channel was then calculated. 
 All values were rounded to one decimal.  

There is a difference between the original resmag that was given for some of the lines and
the new resmag.  Therefore, it was decided to keep the new resmag for all the lines rather than 
only the lines where the resmag was missing.

Because both totmag and resmag have questionable data, totmag was chosen for the jpeg.

The Austin_rad (radiometrics) file contains the original, uncorrected residual magnetics.  It is 
recommended the resmag in the Austin_mag file be used.