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US005086396A
United States Patent [19]
[11]
[45]
Waruszewski, Jr.
APPARATUS AND METHOD FOR AN
AIRCRAFT NAVIGATION SYSTEM HAVING
IMPROVED MISSION MANAGEMENT AND
SURVIVABILITY CAPABILITIES
[54]
[75] Inventor: Harry L. Waruszewski, Jr.,
Albuquerque, N. Mex.
[73] Assignee: Honeywell Inc., Minneapolis, Minn.
121] Appl. No.: 657,275
Feb. 19, 1991
[22] Filed:
Related US. Application Data
[51]
[52]
Int. Cl.5 ............................................ .. G06F 15/50
[58]
Field of Search ............. .. 364/448, 449, 443, 460,
US. Cl. .................................. .. 364/454; 364/456;
364/449; 364/460
364/454, 461; 340/990, 995
References Cited
U.S. PATENT DOCUMENTS
[56]
4,063,073
4,224,669
4,584,646
4,646,244
4,675,823
4,706,199
4,896,154
4,805,108
12/1977
9/ 1980
4/ 1986
2/1987
6/1987
11/1987
Guerin
5,086,396
Date of Patent:
Feb. 4, 1992
Author Unknown, “Electronic Pilot Passes Fight
(Flight) Tests,” Machine Design, May 21, 1987, pp. 12.
GEC Avionics (brochure), “Spartan, Terrain Refer
enced Navigation” (Date Unknown).
Kolcum, “Harris Corp. Offering Digital Map Genera
tor for Airborne Operations,” Aviation Week & Space
Technology, Mar. 16, 1987, pp. 84-87.
Dale', “Terrain Pro?le Matching for Missile Guidance”,
pp. l7-l9-Publication and date unknown.
Hostetler, “Optimal Terrain-Aided Navigation Sys
tems,” Presented at the AIAA Guidance and Control
Conference, Aug. 1978, Palo Alto, California, SAND
Continuation of Ser. No. 305,805, Feb. 2, 1989, aban
doned.
[63] .
Patent Number:
78-0874C.
'
Primary Examiner-Thomas G. Black
Attorney, Agent, or Firm-Dale E. Jepsen; Don J.
Lenkszus; Al Medved
[57]
ABSTRACT
An aircraft navigation system is disclosed for use in
missions involving unfamiliar terrain and/or terrain
having hostile forces. The navigation system includes
an inertial navigation system, a map of the terrain with
elevational information stored in a digitized format as
function of location, a typical energy managed or nar
row (radar or laser) beam altimeter, a display system,
and a central processing unit for processing data ac
............. ..
2/1989
1/ 1990 Factor
Feuerstein
et a1.et .....................
al.
.. 340/995
OTHER PUBLICATIONS
Hostetler et al., “Nonlinear Filtering Techniques for
Terrain-Aided Navigation,” IEEE Transactions on Au
tomatic Control, vol. AC-28, No. 3, Mar. 1983, pp.
315-323.
Fellerhoff, “Sitan Implementation in the Saint System,”
IEEE (CH2365-5/86/0000-0089), May 1985, pp.
89-95.
Boozer et al., “The AFTI/F-16 Terrain-Aided Navi
gation System,” Proc. IEEE 1985 National Aerospace
and Electronics Conference, May 1985, pp. 351-357
cording to preselected programs. The data processing
system includes an operational mode (software pro
gram) for relating the continuing sequence of altimeter
readings with the changing aircraft position on the digi
tized map. In, this manner, the true position of the air
craft can be determined with respect to the digitized
map and can be displayed on a plan view of the map.
When the correct position of the aircraft with respect to
the digitized map is known, a display of the map and the
aircraft can provide presentations useful to the naviga
tion of the aircraft, e.g., by displaying surface features
that can provide potential danger for the aircraft. The
correct position of the aircraft with respect to the digi
tized map can permit the aircraft to engage in terrain
following procedures using only the relatively difficult
to detect altitude range ?nding apparatus as a source of
(0547-3578/85/0000-0351).
emitted electromagnetic radiation. The navigation sys
tem, in conjunction with information regarding hostile
antiaircraft facilities, can provide a display permitting
(CH1839-0/83/00O0-0064).
an operator to determine a reduced risk ?ight path.
Baird, “Performance Analysis of Elevation Map Refer
enced Navigation Systems,” pp. 14.6.1-l4.6.7, IEEE
Bialecke et al., “A Digital Terrain Correlation System
for Tactical Aircraft,” pp. 14.1.1—14.l.5, IEEE
(CHl839-0/83/0000-0059).
.
O
20 Claims, 6 Drawing Sheets
I
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US. Patent
Feb. 4, 1992
Sheet 1 of 6
5,086,396
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US. Patent
Feb. 4, 1992
7
Sheet 2 of 6
5,086,396
I
I'DlSO FT (TERRAIN REFERENCE NAVIGATION)
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300 FT
(I00 M)
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US. Patent
Feb. 4, 1992
Sheet 3 of 6
FIG‘. 2.
5,086,396
US. Patent
Feb. 4, 1992
FIG’. 3.
Sheet 4 of 6
5,086,396
US. Patent
Feb. 4, 1992
Sheet 5 of 6
5,086,396
2200
TAELRIUDN
2000
"
I800
—
I600
'
4/
I400
42
I
I200 ‘ 220
I000
DISTANCE
(LINEAR 0R LOGARITHMIC SCALE)
FIG. 4.
5/
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FIG‘. 5.
5/
US. Patent
Feb. 4, 1992
Sheet 6 of 6
5,086,396
1
5,086,396
2
Correlation and Recognition of Terrain Elevation” and
invented by L. C. Chan and F. B. Snyder.
APPARATUS AND METHOD FOR AN AIRCRAFT
NAVIGATION SYSTEM HAVING IMPROVED
MISSION MANAGEMENT AND SURVIVABILITY
CAPABILITIES
In order to enhance the survivability of an aircraft
entering hostile air space, several techniques to protect
the aircraft and/or to minimize the risk of detection
have been developed. Because target acquisition radar
This is a continuation of copending application Ser.
No. 07/305,805, ?led Feb. 2, 1989, now abandoned.
BACKGROUND OF THE INVENTION
1. Field of the Invention
system is generally most effective for line of sight tar
gets, a typical procedure has been to keep the aircraft as
close to the ground as possible, attempting to interpose
10 terrain features between the aircraft and the radar sys
This invention relates generally to navigation systems
tem. The target acquisition radar system can not then
detect the intruding aircraft or can have difficulty sepa
used in aircraft and similar vehicles and, more particu
larly, to navigation systems that can be useful for an
permit an aircraft to ?y as close to the ground surface as
aircraft operating in hostile territory. The navigation
system of the present invention is speci?cally designed
rating the intruding aircraft from background noise. To
15
to provide an operator with requisite data for decreas
ing risk from unfriendly activity in a manner permitting
netic radiation, automatically maintain an aircraft a
preselected distance from the ground. These terrain
following systems have the disadvantage that the very
electromagnetic radiation needed to guide the aircraft
increases the detectability. A second technique used to
more attention to other aspects of the mission.
2. Description of the Related Art
In aircraft assigned missions over hostile terrain, the
demands on the ?ight deck have become increasingly
severe. The ?ight deck must monitor position and ?ight
enhance the survivability of an aircraft entering hostile
air space is to equip an aircraft with electronic counter
parameters while pursuing mission objectives. The mis
sion objectives can include penetration of air space 25
protected by hostile antiaircraft ordinance.
The aircraft position is typically monitored by an
inertial navigation system. After calibration, the objec
tive is to have the inertial navigation system provide the
global coordinates (i.e., latitude and longitude parame
ters) of the current aircraft position. In the inertial navi
gation system, small systematic errors are typically
possible, terrain following (radiation) systems have
been developed that, in response to emitted electromag
measures apparatus. Theelectronic counter measures
apparatus disrupts the signal received by the detecting
apparatus of the hostile target acquisition system so that
the aircraft is not detected, so that false targets are
detected, or so that maintaining a radiation “lock” on
30 the aircraft is not possible. The electronic counter mea
sures apparatus is expensive and is subject to rapid obso
lescence as the technological advances provided reduce
the effectiveness of currently implemented electronic
present that can cause the current designated position to
countermeasures. A similar result can be achieved by an
deviate from the actual position by an amount that in
creases with time. To remedy these errors, coordinates 35 aircraft by releasing (electromagnetic radiation) re?ect
ing chaff. The chaff typically provides a “bright” or
of known locations over which the aircraft passes are
dominant background as seen by the target acquisition
system, obscuring the image of the aircraft. The aircraft
used to provide a correction to the position designated
by the inertial navigation system.
More recently, maps of various portions of the globe
can rapidly leave the area of the chaff becoming once
have become available in which digitized terrain eleva 40 again visible to the target acquisition system. In addi
tion, signal processing of the returned electromagnetic
tions are provided as a function of a grid of (latitude and
radiation can remove the false background provided by
the chaff. The aircraft can also be provided with elec
longitude) locations. The availability of these digitized
grid elevation maps has resulted, in; systems that can,
tronic equipment that permit, when hostile antiaircraft
based on measurement of the distance between the air
craft the terrain, correlate the position of the aircraft on 45 apparatus has “acquired” or has “locked on” the intrud
ing aircraft, the aircraft to engage in defensive maneu
vers. Finally, a class of stealth aircraft are becoming
operational that are con?gured to provide a reduced
image for re?ected electromagnetic radiation (as well as
system has been described in “Optimal Terrain-Aided
Navigation Systems”, by L. D. Hostetler, AIAA Guid 50 other aircraft detection techniques). These stealth air
craft have elaborate and costly concealment mecha
ance and Control Conference. Aug. 7-9, 1978 (SAND78
nisms that are impractical for reasons of cost to all but
0874C); “Nonlinear Kalman Filtering Techniques for
a small percentage of aircraft. Non-the-less, stealth air
Terrain-Aided Navigation” by L. D. Hostetler and R.
craft can also bene?t from low level and threat avoid
D. Andreas, IEEE Trans. on Automatic Control, Vol.
the grid of the digitized map. These position locating
systems generally rely on Kalman ?lters. For example,
the SITAN (Sandia Inertial Terrain-Aided Navigation)
AC-28, No. 3, March 1983, pages 315-323; “SITAN
Implementation in the Saint System” by J. R. Fellerh
off, IEEE, 1985, (CH2365-5/86/0000—0089); and “The
55
AFTI/Fl6 Terrain-Aided Navigation System”, by D.
D. Boozer, M. K. Lau and J. R. Fellerhoff, Proc. of the
IEEE National Aerospace and Electronics Conference,
May 20-24, 1985 (0547-3578/85/0000-0351). Other
systems have been described in “Performance Analysis
of Elevation Map Referenced Navigation Systems” by
C. A. Baird, IEEE. 1983, (CH1839-0/83/0000-0064);
“A Digital Terrain Correlation System for Tactical
Aircraft” by E. P. Bialecke and R. C. Lewis, IEEE,
1983, (CI-Il839-0/83/0000-0059); and U5. Pat. No.
4,584,646, issued Apr. 22, 1986, entitled “System for
ance techniques by minimizing the opportunity for vi
sual detection of the aircraft.
A need has therefore been felt for an aircraft naviga
tion system that can not only permit guidance of the
aircraft, but can support mission objectives over hostile
terrain including support for response to known hostile
antiaircraft installations and for covert low level ?ight.
This support can take the form of displays using avail‘
able data bases which simplify the decision process in
the ?ight of the aircraft.
65
FEATURES OF THE INVENTION
It is an object of the present invention to provide an
improved aircraft navigation system.
5,086,396
3
It is a feature of the present invention to provide an
aircraft navigation system that uses known terrain fea
tures to locate a current aircraft position.
It is another feature of the present invention to pro
4
DESCRIPTION OF THE PREFERRED
EMBODIMENT
1. Detailed Description of the Figures
vide an aircraft navigation system that permits terrain
transmission of electromagnetic radiation.
Referring now to FIG. 1A, the errors arising in the
components due to the inertial navigation system of the
present invention are shown. A grid with points con
It is a further feature of the present invention to use
the digitized terrain map to assist an aircraft ?ight deck
meters for level 1 DLMS data) apart. (In the actual
following and avoidance capability without widespread
taining digitized elevation data are placed 300 ft (=100
in execution of mission responsibilities.
digitized terrain data base, the grid points are de?ned in
It is yet a further feature of the present invention to
use the terrain map to provide presentations to the ?ight
terms of degrees of arc to compensate for the earth’s
deck assisting in identifying and responding to tactical
situations.
located at position 1, but can actually be reporting a
curvature). The inertial ft. The aircraft is physically
location at position 2, 3,000 ft distance from position In
It is yet another feature of the present invention to
provide a navigation system that can provide the air
addition, even when the coordinates of position 2 are
craft with reduced detectability by the target acquisi
tion system of hostile forces,
coordinates of the digitized map have an absolute error
accurately known (i.e., for example with GPS), the
of 2425 ft. This absolute map position uncertainty is
It is still another feature of the present invention to 20 illustrated by the circle in FIG. 1A.
Referring to FIG. 1B, the errors in position when
use the digitized terrain map and aircraft altitude to
terrain aided navigation is used are illustrated. The
provide threat terrain masking, intervisibility display to
apparatus processing the (radar or laser) altimeter infor
aid in the avoidance of detected positions threatening
the aircraft.
SUMMARY OF THE INVENTION
The aforementioned and other features are attained,
according to the present invention, by providing an
aircraft navigation system with an inertial navigation
system that can control the ?ight of an aircraft through
terrain represented by a terrain map data base. The
navigation system includes an altitude determining sys
mation and providing position data is accurate to i 150
25
ft for moderately rough terrain. Therefore, the aircraft
physically located at position 1 can actually be report
ing a location at position 2 with respect to the coordi
nates of the digitized map. Even when the coordinates
of position 2 with respect to the map are accurately
known, the coordinates have a relative accuracy in
position of $100 ft. This relative uncertainty in position
of the aircraft is illustrated by the circle in FIG. 1B. By
comparing FIG. 1A and FIG. 1B, the improvement of
the accuracy is clearly illustrated. Part of the improve
tem which, once an initial location of the aircraft rela
tive to the terrain map is determined, can be used to
con?rm and correct the position of the aircraft as deter 35 ment in accuracy is a result of not using the absolute
mined by the inertial navigation system. The con?rma
tion or correction of the aircraft position is the result of
the comparison of the terrain map altitude of the chang
ing position of the aircraft as determined by the inertial
navigation system with the measured altitude. The posi
tion of the aircraft is displayed relative to the terrain
position coordinates based on latitude and longitude to
position the aircraft, but rather using position relative,
to the coordinates of the digitized map derived from
terrain reference navigation. When the presentations
described below are presented to the ?ight deck, the
errors from the inertial navigation system, i.e., 1425 ft
plus the actual inertial navigation system error (poten
tially more than 3,000 ft.) compared to errors in the
map data base. In addition, the terrain map data base can
be used to provide visual displays of terrain hazards to
terrain aided navigation system, i.e., $100, plus the
the aircraft and to provide visual presentations of
threats to the aircraft that can permit the ?ight deck to 45 actual terrain aided navigation system (i150 ft) indi
cate the substantial improvement in accuracy for deci
select a safe flight path through the terrain hazards and
sion making in the terrain aided navigation mode of
associated threat locations associated with hostile
operation.
forces.
Referring next to FIG. 2, a tactical situation in a plan
These and other features of the present invention will
view map is shown. The map illustrates the terrain
be understood upon reading of the following descrip
features 24 with contours of constant elevation. The
tion along with the drawings.
position of the aircraft 20 and alternate ?ight paths 21
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates errors in position when using only
an inertial navigation system; while FIG. 1B illustrates
the errors in position arising from terrain aided naviga
tion system.
FIG. 2 illustrates a tactical situation display plan view
of an aircraft ?ight plan.
FIG. 3 illustrates a quantized elevational situation
display.
FIG. 4 is a terrain elevation pro?le map for present
aircraft flight path.
'
and 22 are shown relative to the terrain. A antiaircraft
installation 23 is shown and the circumference 23A
illustrating the effective operational limits of the antiair
craft installation is designated. For purposes of clarity,
the terrain structure is designated by contours of con
stant elevation. For purposes of illustration, relatively
few contours are shown, however, the density of con
tours of constant elevation can be increased. In the
preferred embodiment, instead of elevation de?nition
by contours, the terrain is de?ned by sun angle shadow
ing on a color display. Indeed, a plurality of colors can
be used to assist in the recognition of terrain features.
FIG. 5 is a full perspective display of the terrain in 65 Intensity levels or region texturing can be used in lieu of
advance of the aircraft ?ight path.
colors to designate characteristics of regions.
FIG. 6 is an intervisibility or threat, display for anti
Referring to FIG. 3, a further re?nement in the tacti
aircraft weapons associated with hostile force.
cal situation display is illustrated. In this multicolor
5
5,086,396
6
In the present invention, the digitized terrain map is
used as the basis for providing displays for which inter
display (wherein the different colors are illustrated by
different patterns in separated regions), three colors are
used to alert the ?ight deck to the relationship of the
aircraft to the terrain. The color of the ?rst group of
regions 32 designates to the ?ight deck that the associ
ated terrain is safely below the aircraft and collision
pretation is relatively convenient. Because the displays
are generated in relation to the digitized terrain map
with the terrain at the present aircraft altitude is not
(and not the inertial navigation system), the accuracy of
the relative location of the terrain map features and the
aircraft is correspondingly increased. The increase in
possible. The color of the second group of regions 33 is
a visual designation that, give the errors in the terrain
maps and the margin of errors, there is a risk of collision put
with the terrain in these regions. The color of the third
group of regions 35 is visual designation to the ?ight
deck that entry of the aircraft 20 into those regions will
simple aircraft/terrain display illustrated by FIG. 2 is
provided by simply overlaying the aircraft icon on the
terrain map in a position determined by one of the posi
tion determining algorithms identified above. (Note that
the shadowing algorithms for providing a more physi
result in a terrain collision.
Referring next to FIG. 4, a display with a terrain
pro?le map, determined by the position of aircraft 20, is
illustrated. This display provides the following informa
accuracy reduces the risk to the aircraft. The relatively
cally realistic display are well known to those skilled in
the art of displays). The relational aircraft/terrain dis
plays of FIG. 3 and FIG. 4, for example, provide a
readily interpretable indication of the risks involving
terrain features. These displays are the result of process
ing the digitized terrain map and the sensors of the
tion. The aircraft icon 20 has associated therewith a
climb/dive indicator 42 which designates the current
altitude change relative to the horizontal direction. In
addition, the display shows the distance between the
aircraft 20 and the terrain directly below the aircraft.
(In the preferred embodiment, a linear scale or a loga
rithmic scale can be selected for the horizontal coordi
aircraft. The threat display of FIG. 6 permits the ?ight
deck to respond toknown hostile installations and to
pop-up threats (such as a newly positioned mobile SAM
installation). In this display, the location of the hostile
forces, antiaircraft installations can be incorporated in a
separate data base, and during signal processing, com
nate). Finally, the display provides the ?ight deck with
bined with the digitized terrain map data. The forward
display of FIG. 5 can assist the ?ight deck in maneuver
ing among terrain features and uses the information of
the digitized terrain map in combination with the pa
rameters of the aircraft determined from the aircraft
the pro?le of the terrain in the current ?ight path of the
aircraft relative to the present altitude of the aircraft 20.
Referring to FIG. 5, a display of the terrain in front of
the aircraft’s current ?ight path is shown. The display
illustrated in FIG. 5 contains only ridge lines 51. Air
sensors.
craft orientation markings are included to assist the
As will be familiar to those skilled in the art, data
?ight deck in identifying the terrain features relative to
bases are also available that provide positional informa
the aircraft. The ridge line display is particularly well
tion relative to potential aircraft obstructions, i.e., an
suited for a head’s up display (HUD) to assist the ?ight LU 5 tenna, smokestacks, buildings, etc. These data bases can
deck in correlating the terrain map with the visible
be incorporated into the display to alert the ?ight deck
terrain features. The display of FIG. 5 can, when used
of the presence of obstructions not de?ned by the ter
in a color display, be implemented with colors with
rain map. Indeed, some data bases can define seasonal
shading and with a plurality of colors to provide more
differences in the signature of the terrain altitude.
complete information of the forward terrain to the 40 The foregoing description is included to illustrate the
?ight deck.
operation of the preferred embodiment and is not meant
Referring next to FIG. 6, the terrain map of FIG. 2 is
repeated with a threat overlay. The antiaircraft installa
tion 23 can typically acquire a target and project ordi
nance at the target (within the installation range 23A) 45
for line‘of-sight targets. Therefore, intervening terrain
structures 24 can screen the aircraft from the antiair
to limit the scope of the invention. The scope of the
invention is to be limited only by the following claims.
From the foregoing description, many variations will be
apparent to those skilled in the art that would yet be
encompassed by the spirit and scope of the invention.
What is claimed is:
craft installation. The display illustrated by FIG. 6 is
1. A navigation system for use in aircraft, said naviga
provided to inform the pilot of the danger from the
tion system comprising:
antiaircraft installation if the present altitude and ?ight 50 an inertial navigation system;
path 22 is maintained. In this instance, a new route 21
can be planned, either manually or automatically, to
a data base including a terrain map with digitized
terrain elevations as a functions of global coordi
minimize detection and threats to the aircraft, thereby
reducing mission risks.
2. Operation of the Preferred Embodiment
In the missions currently assigned to aircraft, the
nates;
a directional distance apparatus measuring a distance
55
attention of the ?ight deck must be directed to a multi
between an aircraft and terrain over which said
aircraft is ?ying;
'
processor means responsive to said inertial navigation
system and to said terrain map for determining an
plicity of situational aspects of the mission. The present
position of the aircraft, the destination of the aircraft,
the ?ight path from the present position to the destina
tion, risks resulting from enemy armament, in addition
approximate position of said aircraft relative to said
to the status and operational characteristics of the air
craft, must be monitored by the ?ight deck. As will be
clear, the amount of information to which the pilot must 65
respond is so large that attempts have been made to
terrain map and to terrain pro?les measures by said
directional distance apparatus for identifying a
current position of said aircraft relative to said
provide the information in an easily comprehendible
format.
terrain map, said processor means responsive to
terrain map profiles of said terrain map in said
approximate position of said aircraft relative to said
terrain map, said processor means identifying se
lected features of said terrain map which have a
predetermined relationship with said aircraft; and
7
5,086,396
a monitor unit responsive to said processor means for
displaying said current position of an aircraft rela
tive to a portion of said terrain map, said monitor
means displaying said selected features located on
said terrain map portion.
2. The navigation system of claim 1 wherein said
processor means processes said digitized terrain map to
provide a pro?le view of terrain in a ?ight path of said
aircraft as viewed from a position of said aircraft icon
on said terrain map, said pro?le view being displayed on
said monitor unit.
3. The navigation system of claim 1 wherein said
monitor unit provides a display selected from the group
of displays consisting of a pro?le of terrain contours
visible from the flight deck of said aircraft, each display
of said group of displays being provided by said proces
sor means in response to said digitized terrain map and
a position of said aircraft relative to said digitized ter
rain map.
4. The navigation system of claim 1 wherein said
monitor unit displays threats from antiaircraft installa
tions for a current altitude of said aircraft for a position
of said aircraft relative to said digitized terrain map, a
8
and global coordinate identi?cation of said terrain map
feature positions.
11. The method of assisting navigation of claim 10
wherein said implementing step includes a step of pro
viding said presentation with a visual indication of re
gions of safety from antiaircraft armament relative to a
current position of said aircraft.
12. The method of assisting navigation of claim 10
wherein said implementing step includes a step of pro
viding said presentation with a visual indication of a
pro?le view of terrain features in a ?ight path of said
aircraft relative to a current position of said aircraft.
13. The method of assisting navigation of claim 10
wherein said implementing step includes a step of pro
viding said presentation with a visual indication of ter
rain features in front of said aircraft as viewed from a
?ight deck of said aircraft.
14. The method of assisting navigation of claim 10
wherein said implementing step includes a step of pro
viding said presentation with a visual geographical fea
tures providing a threat to said aircraft as a result of
present ?ight parameters of said aircraft.
15. A navigation system for assisting operators of an
aircraft in executing complex mission objectives in hos
display of said threats being determined by said process
tile territory, said navigation system comprising:
25
ing means.
an aircraft-to-terrain distance measuring device;
5. The navigation system of claim 4 wherein said
a terrain map storing digitized terrain elevation data
monitor unit provides an intervisibility display of
as a function of terrain map coordinates, said ter
rain map including threats to said aircraft;
threats to said aircraft from known hostile installation
relative to said aircraft icon, said intervisibility display
including terrain masking for said current altitude of
said aircraft.
6. The navigation system of claim 5 wherein a ?rst
color designates terrain structures having an altitude as
high or higher than a current altitude of said aircraft.
7. The navigation system of claim 1 wherein said
monitor unit displays threats to a ?ight path on said
terrain map relative to said aircraft icon in a plurality of
colors, each of said colors identifying a parameter of
threats relative to said aircraft.
40
8. The navigation system of claim 1 wherein said
processor means includes means for providing sum
8
terrain aided navigation system coupled to said
distance measuring device and to said terrain map
for determining a position of said aircraft relative
to said terrain map coordinates by comparing ter
rain pro?les measured by said aircraft-to-terrain
distance measuring device to terrain pro?les of said
terrain map; and
a display unit coupled to said terrain aided navigation
system and to said terrain map for displaying an
icon of said aircraft on a presentation of a region of
said terrain map, an icon location being determined
by said terrain aided navigation system, said pre
sentation including visual indications of threats to
said aircraft in a neighborhood of a ?ight path of
said aircraft.
16. The navigation system of claim 15 wherein said
angle shadowing on a terrain map displayed by said
monitor unit.
9. The method of assisting navigation of an aircraft on 45
presentation includes a location of at least one antiair
a mission, said method comprising the steps of:
craft installation, said presentation providing a visual
by means of navigational equipment, identifying an
presentation of regions wherein said antiaircraft instal
approximate position of said aircraft relative to a
lation threatens said aircraft when said aircraft is ?ying
terrain map, said terrain map having at least digi
at an altitude of said aircraft using said navigation sys
tized terrain elevations stored as a functions of 50 tern.
global coordinates;
comparing terrain pro?les determined by measure
17. The navigation system of claim 15 wherein said
presentation includes a pro?le view of terrain features
ments of a distance of said aircraft from terrain
in a ?ight path of said aircraft relative to a current
over which said aircraft is ?ying with terrain map
position of said aircraft.
.
pro?les to determine a position of said aircraft 55
18. The navigation system of claim 15 wherein said
relative to said terrain map;
presentation includes a view of terrain features in front
displaying a presentation of a local region of said
of said aircraft as viewed from a ?ight deck of said
terrain map with an icon of said aircraft positioned
aircraft.
on said presentation in said position of said aircraft
19. The navigation system of claim 15 wherein said
relative to said terrain map; and
terrain aided navigation system used with said terrain
implementing said presentation to provide a visual
map reduces an uncertainty in a position of said aircraft
indication of terrain map features which currently
relative to said threats resulting from a use of global
provide a threat to aircraft security.
coordinates to identify positions of said threats and said
10. The method of assisting navigation of claim 9
aircraft.
wherein said comparing and said displaying steps re 65 20. The navigation system of claim 15 wherein said
duce uncertainties in a position of said aircraft relative
presentation includes sun angle shadowing of terrain
to features of said digitized terrain map resulting from
features.
global coordinate identi?cation of said aircraft position
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