US20060240387A1

US20060240387A1 - Downward compatible laser transmission system

Info

Publication number: US20060240387A1
Application number: US11/111,279
Authority: US
Inventors: C. Young
Original assignee: Lockheed Martin Corp
Current assignee: Lockheed Martin Corp
Priority date: 2005-04-21
Filing date: 2005-04-21
Publication date: 2006-10-26

Abstract

A downward compatible laser transmitter of radiant energy at a 990 nm wavelength. The transmitter is usable with receivers of 905 nm radiant energy. The transmitted beam is less susceptible to humidity or temperature variations than a beam of radiant energy transmitted at 905 nm.

Description

FIELD OF THE INVENTION

The invention pertains to devices and systems for simulation of tactical engagements. More particularly, the invention pertains to such devices and systems which incorporate longer transmission wavelengths than used heretofore so as to reduce the effects of temperature and relative humidity on atmospheric transmission.

BACKGROUND OF THE INVENTION

Tactical engagement simulations can be carried out using a multiple integrated laser engagement system (MILES). MILES systems incorporate laser transmitters which are attached to participants' weapons and vehicles taking part in the simulation. They can be adjusted so as to accurately replicate weapons and lethal characteristics of the specific weapon systems. Sensors are also associated with the individuals and vehicles taking part in the simulation.
During the respective simulation, laser transmissions can be used to target opposing individuals or vehicles. Similarly, incoming laser transmissions can be sensed by the detector(s) carried by the individual or vehicle for purposes of recording hits or kills.
The standard transmission wavelength used with known MILES systems is on the order of 905 nm. This wavelength was originally chosen because it is a wavelength at which the human eye has very little response. Additionally, atmospheric transmission characteristics were acceptable, laser diodes were commercially available at the 905 nanometer wavelength and relatively inexpensive silicon sensors were also available. Such silicon sensors have a response characteristic as illustrated in FIG. 1.
Known MILES detectors incorporate sensors with characteristics, as in FIG. 1 in combination with high frequency cut off optical filters having characteristics as in FIG. 2. Such sensor-filter combinations exhibit bandwidths on the order of 810 nm-1075 nm. They are responsive to 905 nm MILES laser transmissions but they also suffer from noise due to relatively low frequency sunlight.

While known systems have been useful and effective for their intended purpose, they have and continue to exhibit deficiencies. The current 905 nanometer laser transmissions exhibit a reduced laser energy due to the effects of temperature and relative humidity. Under extreme temperature/humidity conditions, known MILES laser transmission energy can be substantially reduced at 4000 meters. The laser energy received at the detectors must be sufficient to sense a hit but not so great that hits could be scored beyond the range of the weapon being simulated. Table 1 illustrates exemplary transmission characteristics of a known MILES system under various temperature and humidity conditions.

TABLE 1


			Transmis-	Transmis-
	Temper-	Relative	sion, %,	sion, %,
Operating	ature,	Humidity,	1000	4000
Conditions	C./F.	%	meters	meters

Minimum Operating	−18/0	20	100	99.7
Temperature		(estimate)
Normal Operating	25/77	55	91	83
Temperature and
Relative Humidity
Florida Summer	35/95	100	82	48
Conditions		(estimate)
Maximum Operating	49/120	100	67	24
Temperature		(estimate)

As illustrated by Table 1, there is a substantial decline, on the order of one-third, in transmission percent at 1000 meters between minimum and maximum temperature and humidity operating conditions. At 4000 meters, there is a decline of about seventy five percent between minimum and maximum operating temperatures. The effects of atmospheric absorption are exacerbated by a decline in laser output from minimum on the order of ten percent as temperature increases from minimum to maximum.
Additionally, while the human eye has very little response to the 905 nanometer wavelength transmissions, the same cannot be said of night vision goggles. It has been recognized that effective night vision goggles can be extremely important when carrying out tactical operations at night, particularly against an opponent who is not similarly equipped. FIG. 3 illustrates representative response of known night vision goggles as a function of wavelength.
The high sensitivity of night vision goggles has produced a circumstance where the 905 nm MILES wavelength transmissions are very visible to night vision goggles which have a wavelength cutoff at about 910 nm, as illustrated in FIG. 3. The visibility of the 905 nm laser transmissions in current MILES systems to night vision goggles negatively impacts the training and simulation experience.
There thus continues to be a need for improved tactical simulation systems which would offer improved transmission characteristics under the various operating conditions. Preferably, such improved systems would also be “eye safe” at shorter ranges than in known systems.
Long range MILES laser transmitters sometimes are not “eyesafe” for individuals close to such transmitters but are “eyesafe” at some distance, the nominal ocular hazard distance (NOHD) for the transmitter. It would be desirable to be able to provide a reduced NOHD for longer range transmitters. It would also be preferable if transmissions in such systems were invisible to night vision goggles. Further, it would be preferable if a transmission wavelength could be used which is downward compatible with existing detectors. This will permit continuous use of existing equipment without any changes and thereby minimize cost increases associated with any such wavelength change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of representative response of silicon sensors of radiant energy combined with a filter as in FIG. 2 and used in detectors of known 905 nm MILES systems;
FIG. 2 is a graph of response of a filter used in known MILES detectors that incorporate sensors as in FIG. 1;
FIG. 3 is a graph illustrating low frequency band pass characteristics of representative night vision goggles;
FIG. 4 is a block diagram of a system in accordance with the invention; and
FIG. 5 illustrates details of a detector usable in the system of FIG. 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiment illustrated.
A tactical engagement simulation system in accordance with the invention incorporates a plurality of laser transmitters. The members of the plurality can be attached to small arms of a type carried by an individual, for example, rifles of various types, or can be attached to various types of vehicles. These could include armored vehicles of all types, such as tanks, personnel carriers or logistics vehicles.
In a system which embodies the invention, the members of the first plurality all transmit at a frequency on the order of 990 nm. Such transmitters exhibit improved transmission characteristics during simulations due to virtually no atmospheric absorption effects due to water vapor. The 990 nm wavelength surprisingly results in improved performance relative to both temperature and relative humidity.
Scintillation in projected laser beams which embody the invention can also be expected to be less than scintillation characteristics of 905 nm wavelength transmissions in prior art MILES tactical simulation systems. Additionally, in members of the plurality, the class 1 maximum permissible exposure (MPE) will, as in ANSIZ 136.1-2000 entitled “Safe Use of Lasers”, be on the order of 1.5 times greater than that for prior art 905 nm MILES lasers. As a result, lasers which embody the present invention have substantially reduced NOHD at 990 nm, than is the case with prior art MILES laser transmitters which transmit at 905 nm.
Interoperability and the ability to use pluralities of known MILES-type detectors, which might be carried by individual weapons or carried on vehicles of various types participating in a simulation, makes the members of the first plurality downward compatible relative to existing detector sets. As noted above, known detectors are usually implemented with silicon photo diodes operated in a photovoltaic mode. Such detectors have a response characteristic at 990 nm, which is very close to the response exhibited to incoming emissions at 905 nm as illustrated in FIG. 1. Thus existing sets of detectors can continue to be used with the members of the first plurality.
Detectors in accordance with the invention do not need to provide filtration for wavelengths beyond 1000 nm since the response characteristics of typical silicon sensors as in FIG. 1, provide a low frequency cut-off. An optical cut-off filter can be provided for use with each of the detectors consistent with 990 nm transmissions to provide a high frequency cut-off to limit the amount of sunlight which can enter the detector and contribute to noise.
A high frequency optical cut-off filter can be provided for each of the detectors to limit the high frequency end of the pass band to 900 nm or less. With this configuration, existing detectors can still be used (as is or with updated filters with lower frequency cut-offs) with 990 nm laser transmitters thereby making systems which embody the present invention much more cost effective since the existing detectors do not need to be replaced.
Further, the noise induced false alarm rate with detectors having filters with a high frequency end of the pass band on the order of 950 nm for use in all 990 nm systems should be reduced. The dominant contributor to noise can be expected to be that generated by noontime sun exposure. Since the above noted detector filters will exclude more of the broad spectrum sunlight, the threshold to noise ratio can be expected to increase. This will reduce the false alarm rate.
Further, embodiments of the present invention can be expected to produce laser transmissions which are substantially invisible to night vision goggles. Representative types of night vision goggles have a pass band as illustrated in FIG. 3. As can be seen, there is a substantial drop off in response in the vicinity of 910 nm. However, experience has shown that transmissions from known 905 nm MILES lasers are in fact very visible when using night vision goggles. A further advantage is thus obtained by using 990 nm laser transmitters which embody the present invention since night vision goggle response can be expected to decreased by several orders of magnitude. This should greatly decrease the negative training effects experienced with using night vision goggles in an environment with 905 nm laser transmitters.
FIG. 4 illustrates a tactical simulation system 10 which embodies the present invention. The system 10 incorporates a first plurality of laser transmitters 10-1, -2 . . . -n, which are mounted on various types of small arms carried by individuals I-1, -2 . . . -n participating in the simulation. Each such individual also carries one or more detectors D-1, D-2 . . . -Dn of a known type which could be implemented with silicon sensors.
FIG. 5 is a block diagram of a representative detector such as detector D-i usable in system 10. Each of the detectors, such as D-i, includes an electronics interface E-i coupled to a silicon sensor S-i. The silicon sensors, such as S-i have a pass band between 825 nm and 1075 nm as in FIG. 1.
Each of the detectors D-i also incorporates a sunlight excluding filter F-i which limits the high frequency end of the pass band of the respective detector D-i to about 900 nm to exclude broadband sunlight. One further advantage of the 990 nm lasers 10-1 of system 10 is that they can also be used with detectors from known MILES systems having cut-off filters with characteristics as in FIG. 2.
The filter F-i used in detectors of the present invention, such as D-i, of system 10 could have a cut-off in a range of 950 nm to 1075 nm. This present filter, as noted above, results in an improved detector which more effectively excludes higher frequency sunlight than do filters, as in FIG. 4, used in known detectors.
In carrying out the simulation, the various individuals who are participating, I-1, -2 . . . n, in one scenario attempt to “shoot” one another using their respective weapons W-1, W-2 . . . -n each of which has been equipped with a respective laser transmitter, such as transmitter 10-i. A hit is registered when the respective transmitted 990 nm laser beam such as L-i is incident on a respective detector, corresponding to detector D-i, and is in turn sensed by the respective silicon sensor. The sensors output can be transmitted via detector electronics to a common simulation management system.
Alternately, members of the plurality of lasers, such as lasers 16-1, -2 . . . -m could be mounted on respective vehicles such as V-1, -2 . . . -m. The nature of the respective vehicles is not a limitation of the present invention. Each of the vehicles can carry one or more sets of respective detectors, such as indicated at 20-1 . . . 20-m. The members of the sets of detectors can respond to an incoming laser beam from respective vehicular gun mounted lasers. Once again, the use of 990 nm laser transmissions from the lasers 16-1, -2 . . . -m provides improved range, greater eye protection for individuals participating in the simulation, improved noise rejection, and results in less visibility to night vision goggles than is the case with known 905 nm laser transmissions.
From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

1. A method of combat simulation comprising:

providing a first plurality of radiant energy transmitters with each transmitter having a beam wavelength with substantially zero atmospheric absorption due to water vapor;

providing a plurality of receivers having a bandwidth between 850 and 1050 nm;

moving the transmitters relative to, at least some of the receivers in a simulated combat scenario;

directing beams of various transmitters toward selected receivers,

generating electrical outputs, indicative of incident beams, from each of those receivers which are sensing an incoming beam.

2. A method as in claim 1 which includes setting the beam wavelength to a value substantially equal to 990 nm.

3. A method as in claim 1 which includes selecting the beam wavelength from a range that includes 970-1070 nm.

4. A method as in claim 2 which includes providing a second plurality of radiant energy transmitters having a beam wavelength on the order of 905 nm, and directing beams from members of the second plurality toward various of the receivers, the receivers being responsive to incident beams from both the first plurality and the second plurality of transmitters

5. A method as in claim 4 where beams from transmitters of the first plurality are transmitted with a nominal ocular hazard distance parameter that is less than a corresponding parameter for beams from transmitters of the second plurality.

6. A method as in claim 1 where the provided beam wavelength is substantially longer than a cut-off wavelength for selected night vision equipment.

7. A method as in claim 1 which includes filtering radiant energy incident on the receivers so as to exclude wavelengths less than 950 nm.

8. A transmitter/receiver combination comprising:

a transmitter of radiant energy at a wavelength in a range of 970-1070 nm;

a receiver of radiant energy, the receiver having a bandwidth between at least 900 and 1000 nm where the receiver includes an optical filter which substantially excludes wavelengths less than 900 nm.

9. A combination as in claim 8 where the transmitter emits radiant energy at a wavelength on the order of 990 nm.

10. A method comprising:

providing a plurality of radiant energy transmitters having a transmission wavelength on the order of 905 nm;

providing a plurality of receivers having a bandwidth between 850 and 1050 nm;

producing in respective receivers electrical signals in response to incident radiant energy from the transmitters;

providing a second plurality of radiant energy transmitters having a transmission wavelength on the order of 990 nm;

producing in respective receivers electrical signals in response to incident radiant energy from the members of the second plurality.

11. A method as in claim 10 which includes moving the transmitters and the receivers relative to one another, and, directing radiant energy emissions of 990 nm toward respective receivers.

12. A method as in claim 10 which includes minimizing absorption of radiant energy emitted from members of the second plurality due to atmospheric humidity.

13. A method as in claim 12 which includes minimizing temperature variation effects on radiant energy emitted from members of the second plurality.

14. A method as in claim 13 which includes reducing the numbers of the members of the plurality of transmitters thereby reducing human eye safety hazards.

15. A method as in claim 10 which includes reducing the number of 905 nm transmitters thereby reducing human eye safety hazards.

16. A method as in claim 10 which includes reducing the sensitivity of night vision equipment to the 990 nm radiant energy relative to the sensitivity of the same night vision equipment to the 905 nm radiant energy.

17. A method as in claim 10 which includes substantially excluding any radiant energy incident on the receivers that has a wavelength less than 900 nm.

18. A method as in claim 13 which includes substantially excluding any radiant energy incident on the receivers that has a wavelength less than 900 nm.

19. A method as in claim 17 which includes reducing the nominal ocular hazard distance for radiant energy transmitted at the 990 nm on the order of 15-20% below the nominal ocular hazard distance for radiant energy transmitted at 905 nm.

20. A combat simulation system comprising:

a portable transmitter of laser emitted radiant energy having a wavelength on the order of 990 nm;

a source of energy for the transmitter;

control circuits for energizing the transmitter with energy from the source;

a housing for the transmitter, the source and the control circuits;

a receiver, movable relative to the transmitter, having a reception band between 850 nm and 1050 nm;

circuitry coupled to the receiver for producing a beam incident indicium responsive to incident beams having respective wavelengths of 905 nm and 990 nm.

21. A system as in claim 20 which includes night vision goggles, the laser emitted radiant energy is substantially invisible when in a receiving range of the goggles.

22. A system as in claim 21 which includes an optional filter for the receiver with a transmission cut-off wavelength on the order of 950 nm.

23. A system comprising:

a plurality of transmitters of beams of radiant energy having about a 990 nm wavelength where the transmitters exhibit a reduced nominal ocular hazard distance when compared to a corresponding parameter of a transmitter of radiant energy at a 905 nm wavelength; and

at least one detector of the transmitted radiant energy, the detector having a predetermined frequency response, the detector including an optical filter to limit the response of the detector to incident radiant energy having a wavelength of at least 900 nm.

24. A system as in claim 23 where the detector and filter combination has a passband on the order of 900-1075 nm.

25. A system as in claim 24 which includes a plurality of night vision goggles and where the 990 nm transmissions are substantially not visible with the night vision goggles.

26. A system as in claim 23 which includes a plurality of detector and filter combinations where each detector includes a radiant energy sensor that has a predetermined bandwidth and an optical filter with a cut off wavelength on the order of 950 nm.

27. A system as in claim 25 which includes a second plurality of detectors, the members of the second plurality are responsive to at least 905 nm and 990 nm laser transmissions.

28. A system as in claim 26 which includes a plurality of night vision goggles and where the 990 nm transmissions are substantially not visible with the night vision goggles.

29. A system comprising:

a plurality of transmitters of beams of radiant energy having a first wavelength at which virtually no atmospheric absorption occurs due to water vapor and where the transmitters exhibit a reduced nominal ocular hazard distance when compared to a corresponding parameter of a transmitter of radiant energy at a 905 nm wavelength; and

30. A system as in claim 29 which includes a plurality of night vision goggles and where the goggles substantially do not respond to transmissions at the first wavelength.

31. A system as in claim 30 where the optical filter substantially blocks incoming radiant energy at wavelengths shorter than about 950 nm.