Browse Prior Art Database

Terrain Exposure Factor

IP.com Disclosure Number: IPCOM000110989D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 188K

Publishing Venue

IBM

Related People

Stiles, P: AUTHOR

Abstract

Terrain Exposure Factor - Military pilots and aircrews often need to locate and avoid hostile air defense systems. IBM Federal Systems Company, along with other companies and universities, uses this location information in various automated mission planning and situation assessment applications.

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This is the abbreviated version, containing approximately 47% of the total text.

Terrain Exposure Factor

      Terrain Exposure Factor - Military pilots and aircrews often
need to locate and avoid hostile air defense systems.  IBM Federal
Systems Company, along with other companies and universities, uses
this location information in various automated mission planning and
situation assessment applications.

      One example is onboard aircraft route planning.  To avoid a
dangerous flight path when the air defense positions are precisely
known, it is common practice to use digital map elevation data and
compute the air defense system's intervisibility - that is, which
parts of the map can be seen by its sensors and are therefore more
dangerous.  In general, however, the air defense locations are not
precisely known.  There are shoulder launched surface-to-air missiles
as well as other mobile threats.  Since they don't necessarily emit
electromagnetic signals, there is often no indication as to their
presence until it is too late.  In this case it's common to select
flight paths over lower elevation terrain on the premise that the
aircraft is less exposed to unknown air defense systems when flying
down a valley as opposed to along a ridgeline or over the top of a
mountain.

      A terrain exposure factor (TEF) database that significantly
helps solve problems related to air defense location and avoidance
can be computed.  The map area of interest is quantized by breaking
it up into small square cells of terrain - perhaps 100 meters on a
side.  The TEF is a number assigned to each map cell which reflects
the fraction of surrounding terrain from which this map cell can be
seen.  For instance, a completely exposed mountain peak that can be
seen from any position within 10 km would be assigned a TEF value of
1.0 (100%).  A map cell in a fairly well hidden narrow valley might
be assigned a value of 0.1 (only 10% of surrounding terrain can see
it).  The TEF database is the composite array which is comprised of
such a value for every map cell.

      TEF is computed by applying an intervisibility algorithm, such
as the IBM algorithm cited below, to every map cell.  The parameters
necessary, and the settings currently used, are:

o   Maximum radius to be treated as surrounding terrain (10 km)

o   Nominal ownship altitude: assumed flight altitude,
    above-ground-level (AGL), (AGL), of the aircraft (100 ft)

o   Nominal threat height: assumed AGL height of a typical air
    defense antenna or sensor (10 ft)

These settings are not unique; the same algorithm applies for
different ranges and altitudes, and could also be computed for
multiple altitudes, if desired.  The results are relatively
insensitive to small variations (10-20% at least) of these
parameters.

      The algorithm computes the terrain exposure factor for each map
cell by keeping a count of all surrounding map cells that can see
that cell, and also a count of the total number of surrounding map
cells.  (Since some cells are...