[gembud] NARR conversion to height coordinateâs?

List:
I'm trying to convert NARR gem files from pressure to height (agl)
coordinates using GDVINT. I've tried various combinations for VCOORD
but I always receive the same error about "required surface elevation is
absent". When I downloaded the grib files, I selected all variables.
Here is some sample output:
 GEMPAK-GDVINT>display
GDFILE Grid file 20100128_1800.gem
GDOUTF Output grid file 20100128_1800z.gem
GDATTIM Grid date/time f00
GVCORD Grid vertical coordinate pres/zagl
GLEVEL Grid level 500-10000-500
MAXGRD Maximum number of grids 999
GAREA Graphics area grid
VCOORD Vertical coordinate type pres;none
GEMPAK-GDVINT>r
PRES found.
TMPK found.
HGHT found.
SPFH found.
OMEG found.
UWND found.
VWND found.
TKE found.
CLWMR found.
ICMR found.
MCONV found.
LFTX found.
* [GDVINT 4] Warning--no surface elevation grid exists.
[GDVINT -7] Required surface elevation is absent.
* Parameters requested: GDFILE,GDOUTF,GDATTIM,GVCORD,GLEVEL,MAXGRD,GAREA,
VCOORD.
Does anyone have any experience converting NARR to height AGL coordinates?
Is there a separate surface elevation grid?
I apologize if this message posts in duplicate - it appears I wasn't
subscribed to the list the first time.

Thanks in advance!
-- 
Peter C. Banacos, Lead Forecaster
NOAA/National Weather Service
WFO Burlington, VT
weather.gov/btv
E-mail: peter.banacos@xxxxxxxx
Phone: (802) 862-2475