1. Field of the Invention
This invention relates to an operational verification system for testing the operational capability of a missile approach warning system, such as is deployed on military aircraft, and methods for using that system. In particular this invention relates to an active coupler that creates and emits a test signal and which can be connected directly to electro-optical sensors deployed on aircraft to detect electro-optical signals emitted from missiles.
2. Description of the Related Art
Today's armed forces face increasing worldwide proliferation of missiles, including advanced infrared (IR) guided missiles, surface-to-air missiles, and air-to-air missiles. Political entities that once were confined to arms used in hand-to-hand combat have developed surface-to-air missiles. Missiles often attack without being visually observed, and can strike in a matter of seconds. Reliance upon and installation of missile warning systems is therefore increasing. Such systems are useful in multiple types of aircraft, and even in tanks to detect anti-tank missiles.
As a missile is essentially a variation on a rocket, each missile, as it travels towards its target, generates a plume, or exhaust trail, unique to that missile. Accurate plume analysis permits accurate identification of missiles and engagement in appropriate countermeasures. In analyzing the plume, the sensor counts photons in a sub-spectrum of interest of the ultraviolet or near-infrared spectrum. The sensor integrates the photon counts over small time intervals, which results in an optical power versus time signature, in watts over time, for each missile. This signature is compared to templates and the presence or absence of a match determined. The sensors reject man-made and natural clutter sources, and can detect missile plumes from a substantial distance.
The AAR-47 and 57 Missile Warning System/Missile Avoidance Warning System (“MAWS”), and other missile warning systems known in the art, are frequently used optical-based sensor systems deployed on fixed and rotary winged aircraft to detect short range missile launches. They consist of multiple electro-optical sensors, which read the signature and convey that data to an internal electronics control unit. The control unit processes the data, categorizes the missile, provides direction-of-arrival and elevation information, provides a warning, and directs countermeasures such as flares or jamming.
Such missile warning systems must be accurate; both early detection and a low rate of false alarms are required to protect pilots and their cargo without the stress of false alarms. The sensors must be very sensitive to the presence of plumes at a substantial distance, particularly when the aircraft is at a high altitude. Unfortunately, these missile warning systems rely on electronic and optical components that deteriorate with age and exposure to extreme environmental conditions such as those present at high altitudes and combat conditions (e.g., sand and salt water, in the case of aircraft launched from aircraft carriers). Sensitivity and accuracy of signature matching must be tested routinely in order to maintain optimal sensor performance. In addition, as new missiles with previously unknown signatures are developed, the sensors' accuracy in detecting those new signatures must be tested and evaluated.
One way of testing missile warning systems is by providing them with a signal in the same wavelength as a missile signature and evaluating the system's response. Such missile signature testing emits a signal in the appropriate wavelength, varying intensity (watts) and duration (time) of light presented to the sensor within the duration of the signal and between signals. This type of testing can be performed in the UV and infrared parts of the spectrum. Such a signal may be called a “waveform.” The sensor's response to the simulated signature is then analyzed for its ability to detect the waveform and direct appropriate countermeasures. More details about current waveform emission and sensor testing will be set forth below as its disadvantages are discussed in turn.
Current testing systems present many problems. One concern is the level of extraneous light in many test situations, which weakens the test's accuracy. This is because the sensor counts both the photons in the environment, which are present in an uncontrolled and inconsistent amount, and the photons emitted by the tester. Welding, street lamps, and other sources can create environmental light in the spectrum generated by missile plumes and detected by missile warning systems. If light from these sources is detected by the sensor during a test, it will make the test less accurate because it is no longer based solely on the tester's calibrated emission. It is therefore desirable for a tester to be coupled to the sensor in a manner that excludes environmental light input and provides an isolated test environment. Herein, the term “coupler” refers to any mechanical enclosure that provides an isolated testing environment similar to that of a laboratory environment by preventing any undesired environmental effects.
Some current testers have a coupler designed to block such ambient light. Such couplers are separate entities from the tester itself. They are generally tube-shaped and are held in place by the technician while he/she is simultaneously operating the sensor. This handheld manner of use introduces a great deal of human error, as the technician may easily inadvertently move the coupler, especially when tired or in harsh conditions as is probably the case in the context of an armed conflict or extended training exercise. Such movement may expose the sensor to ambient light while the tester is emitting its signal, thereby destroying the accuracy of that test and any grounds for comparison with other tests. In addition, the technician cannot walk away from the aircraft to attend to other tasks in testing the sensor, because the technician must hold the coupler.
Current couplers also do not allow for accurate or repeatable positioning of the emitter and coupler. This may result in varying input angles that in turn adversely affect sensitivity testing data. That is, because the light shields of current testers are handheld and subject to inconsistent placement, the tester's signal is inconsistent in its intensity and directional approach relative to the sensor. Such inconsistency is unacceptable, as it is desirable to test the accuracy of a sensor's review of intensity and directional approach. It therefore remains desirable for a sensor to include a self-attaching coupler that completely and consistently blocks ambient light without relying on human positioning, and that standardizes the direction and intensity of the tester's signal.
Substantively, current tests are also far from comprehensive. Standard signature tests, called “Built-In-Tests” (“BITs”), are performed by a relatively small emitter that is part of the sensor itself as opposed to any exterior, more complex tester. BITs simply test whether the sensor does or does not detect any signal at all. Because the BITs do not generate a simulated signature or waveform, but rather a very simple “on/off” emission, they do not evaluate the sensor's accuracy in discerning between signatures. As such, BITs do not test a sensor's accuracy for different missile arsenals. This is particularly important as the field of missile technology advances and different countries generate different missiles. BITs also do not test the sensor's ability to accurately read the missile's angle of approach. Neither do they test the sensor's sensitivity, which is important as it reflects the sensor's ability to detect a plume at a substantial distance. BIT testing also does not test all quadrants of the sensor's field of view, leaving room for undetected inaccuracy. It is therefore desirable to expand standard sensor testing to test signature identification, all sensor quadrants, sensor sensitivity, and angle of approach.
A more sophisticated current test is called Flight Line Test Set, or FLTS. FLTS uses low pressure mercury vapor lamps to generate a non-signature waveform: that is, the signal simply vacillates between low and high intensity, in the form of a light simply blinking on and off, rather than generating a signal that resembles an actual signature in its complexity. The sensor being tested thus receives not a simulation of a missile signature, but a relatively simpler “on-off” signal with no relation to any missile. This non-signature waveform does not adequately test the sensor's ability to read a complex signature. It also does not test the system's capability to detect and correctly recognize a specific missile threat, or to discern between different missiles. While the manufacturer of FLTS has limited FLTS to simple non-signature waveforms in the belief that actual signature testing is not necessary, such testing is believed important as the field of missile technology advances and different countries generate different missile arsenals.
One current improvement on FLTS, the Baringa, has a more accurate sensitivity test and can produce actual signatures. This system, too, is limited in its ability to simulate actual signatures, as its signals do not accurately represent missiles approaching from different directions. The generation of signatures representing approaches from different directions is performed by simply walking around the aircraft while transmitting a missile signature. This method is very inaccurate in representing a missile approaching from a specific direction. Sensors should be able to discern the direction from which a missile approaches, in order to provide the most useful information in the context of evasive or countermeasures (i.e., in which direction the plane should fly to avoid the missile, or in which direction antimissile projectiles should be launched).
It is therefore desirable for waveform testing to generate a simulated signature that can test the system's ability to discern between missiles and the direction from which those missiles approach. It is especially desirable for a tester to be equipped with software to produce signature simulations in accordance with set parameters, such as the actual signatures of missiles in an arsenal an aircraft may actually encounter in an upcoming mission. In this way, a fleet of planes or other vehicles headed for a conflict or warzone may be tested for their ability to detect the missiles prevalently used by enemy combatants in that area. In addition, it is desirable for these parameters to be reprogrammable, to adapt the tests to changing arsenals. In this way, planes or vehicles that move among or between conflicts or warzones over time may be tested for their ability to detect the most relevant arsenal.
Current testers also do not provide any means for storing actual or simulated signature parameters, for reference in evaluating past tests or in creating and customizing future tests. Current testers cannot accomplish such storage of any information about the performed test. Testers with the capacity to internally generate waveforms and store test parameters and results are thus both self-sufficient and fully customizable. The customization according to stored parameters permits development and improvement of a threat library with signatures that simulate the plumes of the arsenal the aircraft may likely encounter. Another desirable use of memory is in the event of a sensor failure, to retroactively review what signatures were used in past tests of that sensor that permitted its failure to occur undetected.
One current tester, the Baringa, permits signature storage and generation of signatures according to stored parameters, but requires access to and exchange of information with a laboratory. Given the often remote locations in which aircraft sensors are tested, including aircraft carriers and deployments, this requirement of access to a laboratory hampers the ability to store signatures often when it is needed most, in battle or deployment. In addition, heightened security in those contexts often prohibits the exchange of data between a laboratory and the tester. It therefore remains desirable for a tester to be able to store signature data without requiring an external laboratory, in a simplified and portable theater.
Regarding portability, it is particularly desirable for the generator and emitter to constitute one self-contained entity capable of enduring rugged conditions. It is also desirable that the tester not require calibration upon delivery to a test site. Portability is also enhanced by having a replaceable battery power source.
Current testers only provide a very poor level of sensitivity testing. This is due in part to the inaccuracy inherent in the use of the handheld coupler, explained above, which lets in ambient light that the sensor may detect instead of or in addition to the faint sensitivity test signal. It is therefore desirable for a missile testing system to accurately test sensitivity. Sensors with good sensitivity are especially important as missiles become faster and it becomes more necessary to detect the missiles from a further distance in order to respond defensively.
Another disadvantage of FLTS is that each tester must be placed around three meters from the aircraft, with one operator per tester. Testing from a further distance requires another, separate set of long range testers; these multiple tester sets are expensive and tedious to transport and set up. It is therefore desirable for a missile tester to be able to test from any distance.
FLTS emits its signal using low pressure mercury vapor lamps without a fluorescent coating. Such lamps present many problems. They use a great deal of power, which shortens the life of any associated battery power source. They are extremely heavy, which decreases the tester's portability and manipulability. In addition, such lamps require a high voltage, which creates a great deal of inefficiency in the form of heat when the lamps are turned on. Such lamps also waste operator time in that they require at least five minutes to “warm up” and stabilize before they can be used.
More specifically, mercury vapor lamps are not well suited to the specific task at hand of creating a variety of test signatures. It is not easy to change the intensity of a mercury vapor lamp's output, which stymies the instant purpose of creating different signatures based on varying intensity. These bulbs must be outfitted with bandpass filtering in order to produce definite wavelengths. This is problematic, as bandpass filtering does not in fact completely filter all undesired wavelengths, but simply attenuates those at the margins of desirability. Thus, testing with bulbs relying on bandpass filtering is not completely accurate. It is therefore desirable to use a sensor testing system that generates certain wavelengths without reliance upon bandpass filtering.
Another problem inherent in using mercury vapor lamps is that, in order to achieve different wavelengths, different specially designed bulbs must be built, purchased, and interchanged. This is costly, tedious, inefficient, and requires the risky manipulation of fragile tester components. It is therefore desirable for a sensor to be able to generate different wavelengths without bulb replacement.
The output between different sets of mercury vapor lamps is quite variable, as much as 30% between units; this detracts from the uniformity and ease of comparability between test results. It is desirable for a simulating tester to utilize bulbs other than low pressure mercury vapor lamps, in order to increase uniformity across testers.
An additional difficulty with current testers is that their filters are external and thereby prone to being damaged. Testers require filters in order to filter the signal from the strength at which it is generated to the strength appropriate for processing by the sensor. Some tests are unfiltered, while others are not; this depends in part on the tester's distance from the aircraft. Filters on current testers are external to the tester, such that they are easily scratched or shattered. The filter's external position is particularly risky due to the often harsh environments in which it is employed; aircraft are often in harsh environments wherein the filter may be damaged by sand, salt water, ice, or any other windblown particulate. In switching between filtered and unfiltered tests, current operators must manually remove the filter from the tester and stow it; this also introduces risk of damage to or loss of the filter. It is therefore desirable to have a filter internal to the tester which can be selectively engaged without separation from the tester.