They were created at the end of April, begining of May 2009.  The reference half-spaces were 1000, 250 (and 250,10 for Block C), using only coplanar data.  To calculate depth of investigation I did not use alpha factor, but Burke's normalized expression only, accepthing the values:  [log(r1)-log(r2)]/[log(ref1000)-log(ref250)]/last value<0.2.  I checked - this should be close to a DOI using alpha factor. The B was fixed to 10. The channel with final solution is called res1_28_mask.
 
At the end of each database I added 2 channels - sampled DTM and difference between the Fugro's DTM and sampled DTM.
Because:
While working with Airbuckles lake data I noticed that the very ends of the 4 lines from HEM that reach the lake,  have DTM values that are not consistent with the elevation collected on the lake.  So I downloaded the newest DEM (10m) from USGS seamless site and sampled the DEM - and indeed: DTM in the HEM data are too low by 23-26 m.  I also contoured the seamless 10m grid at 266 level and it closely follows the lake boundary and 875 ft (266m) lake level  on the 24k DRG.  The HEM-derived DTM almost perfectly trace the sampled DEM - so it appears that Fugro, while processing the data assumed z channel to be helicopter elevation instead of bird elevation, maybe?