You can simply use Bentley's MicroStation / Point cloud tool and import.
DTED is a format Typically used by USACE and Consultants for the DOD.
Because MicroStation allows the user to set a coordinate system,files such as Point clouds or other spatial data becomes relavent at the earliest planning and design stages without the need for additional software add ons. This interoperability seperates Bentleys software from Autodesk.
These cloud files can later be consumed by either civil- Open Roads Technology or Geospatial app such as Descartes.
The other thing to consider is speed. Typically C3D will choke on clouds 1/3 the size of those easily handled by the MicroStation point cloud engine.
The low cost MapWorks Surfaces add-on (running inside Civil3D) will read NGA Digital Terrain Elev Data Level 0-2 (*.dt#) files or convert them to more acceptable formats. Use the free 21-day full working demo to process the file at your location.
Reading this link it looks like AutoCAD Map can use this data, although I'm not sure that the surface it creates would be usable in Civil3D.
A layer in Display Manager containing a raster-based surface such as a Digital Elevation Model (DEM), an ESRI Grid file, or Digital Terrain Elevation Data (DTED). A surface layer is brought in using. See also feature layer.
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Using Autodesk Infrastructure Modeler, I was able to add the DTED files to a model, and then export just the portion I needed to a .imx file and then bring that into Civil 3D.
If you have Civil 3D 2013 on subscription, you will be able to migrate to the Infrastructure Desgin Suite at no addtional cost (other then the additional subscription cost) and that will include Infrastructure Modeler.
I didn't even need to assign a coordinate system to AIM to get this to work, just in Civil 3D.
You can see how long it took to do HERE.
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