NTM-derived digital ortho quads ?

Good Afternoon,

I'm interested to know if anyone can tell me what NTM-derived digital data
is and if there is a web site available that may have such data that
can be downloaded.

Also coes anyone know of sites that archive time frames of land use and
cover data for the years 40's through 90's ?

One last thing concerning the NTM data, can it be read by Grass ? , GrassLand ?

Thank you

Jeremy