Hi,
If the files are still in Esri GRID format, make a text file called prj.adf and place this text in it:
projection transverse
units meters
parameters 6371204 6371204
0.926
-100 00 00
00 00 00
0.0
0.0
We don't have a separate spherical transverse mercator. Instead, you set the gcs/datum to use a sphere and that triggers the correct map projection equations.
If the raster's been converted to another format, try creating a text file called DNAG.prj and put this in it (as a single line)
PROJCS["DNAG",GEOGCS["GCS_STM1987",DATUM["D_STM1987",SPHEROID["STM1987",6371204.0,0.0]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-100.0],PARAMETER["Scale_Factor",0.926],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]
Put DNAG.prj into the ArcGIS install location's Coordinate Systems, Projected Coordinate Systems folder. Now you can browse to it and set it as a raster's coordinate system in Define Projection Tool or the data's property page in ArcCatalog.
Melita