INTERPRETING THE "FNOC" MODAL HEIGHT DATA FILE

General Information:

Global elevation data at a resolution of 10 minutes were prepared 
by the Navy Fleet Numerical Oceanography Center (FNOC) at 
Monterey, CA. For each 10x10 minute area [lat x lon], the set 
includes modal elevation, minimum elevation, maximum elevation, 
orientation of ridges, terrain characteristics, and urban 
development. The FNOC began creating the original 10' terrain data 
set in the mid-1960s; work extended into the early 1970s. The main 
sources for the data were the US Department of Defense Operational 
Navigational Charts (ONC), scale 1:1,000,000. For certain regions 
the ONCs were not available; for such areas, selected charts from 
the Jet Navigation Charts and World Aeronautical Charts were used. 
The charts were hand-read out to paper forms, and then read by 
optical character reader to magnetic tape. The values were 
estimates from contour lines. Isometric graphs were made for 
quality control, such as checking terrain features. Later, other 
errors were corrected by the National Center for Atmospheric 
Research in Boulder, Colorado. 

Summaries of data distribution show a strong tendency for 
elevation values to cluster around multiples of 500 feet. This is 
probably due to the contour intervals in the original maps or to 
some characteristic in the method of reading map values.

The true resolution of the data is reduced to 20 minutes poleward 
of 70 degrees latitude, but the data values are still present for 
each 10-minute square. More information on the original data 
format, and the routines designed for the Navy to read the 
original format may still be available from FNOC.

** USING THE SOFTWARE ON THE NGDC_RELIEF CD-ROM: **

The FNOC file is translated into binary data on the CD for speed of
access, so programs have been provided to allow copying of portions
of the data. The binary data on the CD are in PC/VAX "lo-byte-first"
order, so special software is needed for Macintosh, Sun, Amiga, and
other "hi-byte-first" processors. We have provided:

DOS PC's: program FNOC.EXE will read the file and copy data onto
your hard disk. It will also echo data values to your PC screen as
the copies are made. Enter the character "@" to select the data file
on the CD-ROM, or the full pathname to your own copy on hard disk
if you have made one.


Macintosh: In the directorys of Mac files, look for
     "MACINTOSH_FILES:PUBLIC_SOFTWARE:NGDC_SOFTWARE:COPY_FNOC;1"
for copying data. Swapped integers are un-swapped for proper use.
Enter the character "@" to select the data file on the CD-ROM, or the
full pathname to your own copy on hard disk if you have made one.

Sun and others: Source code "FNOC.C" is included but must be
compiled for use. Remember to skip the swapping instructions if
your machine uses lo-byte-first ordering.

The binary data structure is:

   struct	in_record
     {
      short longitude,latitude,modal_elev,max_elev,min_elev;
      char  ridges_tot,ridges_dir,primary_sfc,secondary_sfc;
      short sfc_water,sfc_urban;
     };

The ASCII data format produced by the copy program exactly matches
the format used on previous magnetic tape copies of the FNOC data,
and is described below.

** THE ASCII FNOC FORMAT **

A few sample 40-character data records, as reformatted in 1982 by 
the National Geophysical Data Center (NOAA/NGDC) follow:

Column #  0         1        2         3         4
          1234567890123456789012345678901234567890
          ----------------------------------------
              .00 -90.00  91  92 90  0 0 2 1  0  0
              .33 -90.00  91  92 90  0 0 2 1  0  0
              .50 -90.00  91  92 90  0 0 2 1  0  0
              .67 -90.00  91  92 90  0 0 2 1  0  0
              .83 -90.00  91  92 90  0 0 2 1  0  0
             1.00 -90.00  91  92 90  0 0 2 1  0  0
             1.17 -90.00  91  92 90  0 0 2 1  0  0
             1.33 -90.00  91  92 90  0 0 2 1  0  0
             1.50 -90.00  91  92 90  0 0 2 1  0  0
        ...
          -100.00  46.17  20  20 19  0 0 1 1  1  0
           -99.83  46.17  19  23 18  0 0 1 1  1  0
           -99.67  46.17  20  25 20  0 0 1 1  0  0
           -99.50  46.17  20  20 19  0 0 1 4 10  0
           -99.33  46.17  20  20 15  0 0 1 4 10  0
           -99.17  46.17  20  20 19  0 0 1 4  6  0
           -99.00  46.17  20  24 18  0 0 1 0  3  0
           -98.83  46.17  16  18 16  0 0 1 1  0  0
           -98.67  46.17  15  15 14  0 0 1 1  1  0
           -98.50  46.17  15  15 13  0 0 1 4  2  0
        ...

The data fields are defined below:

Columns  Format    Name
------------------------------------------------------
1-7     sXXX.XX    Longitude (+/- 180 Deg, + = East)
9-14     sXX.XX    Latitude (+/- 90 Deg., + = North)
16-18       XXX    Modal height in 100's of FEET
20-22       XXX    Maximum height in 100's of feet
23-25       XXX    Minimum height in 100's of feet
27-28        XX    Number of significant ridges
29-30        XX    Direction of ridges in 10's of degrees (0-18)
31-32        XX    Primary surface code type
33-34        XX    Secondary surface type code
35-37       XXX    % of surface covered by water
38-40       XXX    % of surface covered by urban development

Note that zero values of elevation do not necessarily denote ocean 
surface -- use primary terrain characteristic to identify ocean. 
Inland water bodies are coded with the elevation of the water 
surface (except in the minimum field, where it is always zero).

"Surface Codes":

    0 - salt or lake bed
    1 - flat or relatively flat
    2 - desert (or, for high altitude, glacier or permanent ice)
    3 - marsh
    4 - lake country or atoll
    5 - major valley or river bed
    6 - isolated mountains or hills
    7 - low mountains or hills
    8 - average mountains
    9 - extremely rugged mountains
   62 - ocean (identified in primary-type field only)

"% of water":

    For ocean areas at sea level, the value is 100; for all other
    areas the range is 00 to 99 (larger lakes or inland seas will
    not be coded as 100)

"% urban development":

    "Highly subjective" (FNOC documentation)

Data Organization in the file:

The data file "FNOC.ASC" is ASCII text, with a logical record 
length of 40 characters. There are NO linefeed or carriage-return 
characters to mark the end of a record. Data points start at 0 Deg 
longitude at the South Pole, and a point is given for each 10' of 
longitude eastward for 30 values, then stepping 10' north for the 
next 30, and so on, until a 5 degree square has been filled (0D 0' 
to 4D 50' in lat and lon). The next 5 Deg square then begins, and 
so on until the full circle has been traversed (0 > 180, -180 > 
0); then the data squares step 5 degrees North. Each 5-degree 
square is composed of 900 data records, or 36,000 bytes.