This invention relates generally to systems for identifying military vehicles as friendly or hostile and, more particularly, to identification systems that rely on infrared emissions of the military vehicles.
Friend or foe identification systems used by military aircraft are generally radar-based systems, which operate in the microwave portion of the electromagnetic spectrum. Because the basic radar return from an aircraft is highly diffracted, the basic return cannot be used to positively identify the shape and, therefore, the type of aircraft. However, other portions of the radar return can be used to identify the type of aircraft. For example, a jet engine modulation (JEM) system analyzes the doppler shift of the radar return to determine the number and rotational velocities of the turbine blades in an aircraft""s jet engine. From this, the type of jet engine can be identified and, once the jet engine has been identified, it is usually a simple matter to identify the type of aircraft. However, this system is not reliable as the enemy may be operating the same type of aircraft.
Another friend or foe identification system used by military aircraft utilizes a transponder to encode the radar return with the identity of the vehicle. However, this radar system can also be jammed and, in addition, can be intercepted or mimicked by the enemy. Accordingly, there has been a need for an improved identification system providing rapid and positive friend or foe identification of land, sea and air vehicles at long ranges without the possibility of being jammed, intercepted or mimicked. The present invention clearly fulfills this need.
The present invention resides in an infrared identification system for identifying military vehicles as friendly or hostile. Briefly, and in general terms, the present invention includes a seed introduction system, in each friendly vehicle, that introduces trace quantities of a particular seed formulation into the vehicle""s exhaust. An infrared detection system, also in each friendly vehicle, detects the spectrally-discrete thermal emissions of the seed formulation to identify those vehicles having the thermal emissions as friendly.
More specifically, in a presently preferred embodiment of the invention, the seed introduction system introduces trace quantities of a particular seed formulation, which is changed preferably on a daily basis, into the vehicle""s exhaust. The seed formulation can be introduced either continuously or upon interrogation by another friendly vehicle or other friendly source, such as a ground-based radar installation. When thermally excited, the seed formulation emits infrared radiation at known spectrally-discrete wavelengths. The infrared detection system can detect the faint infrared radiation all but buried in atmospheric and exhaust background noise, but only by knowing the particular seed formulation in use for that day. Detection of the infrared radiation confirms that the vehicle is friendly.
The seed introduction system includes a pressurized tank for storing the seed formulation of the day and a control system for injecting trace quantities of the seed formulation into the vehicle""s exhaust. The control system includes a valve for releasing the seed formulation from the pressurized tank and a receiver for opening the valve when interrogated by a friendly source. Seed formulations that have been found to have suitable emissions within the infrared spectrum include the following halides:
hydrogen chloride (HCl)
hydrogen bromide (HBr)
hydrogen iodide (HI)
hydrogen fluoride (HF),
the following hydrides:
sodium hydride (NaH)
calcium hydride (CaH)
potassium hydride (KH),
and the following oxides:
beryllium oxide (BeO)
germanium oxide (GeO)
magnesium oxide (MgO)
selenium oxide (SeO)
aluminum oxide (AlO).
The infrared detection system includes a wide angle, optical lens and a standard, off-the-shelf infrared detector having a high sensitivity in the spectral region of interest. Because the infrared and visible spectrums are so close in frequency, an optical lens may be used to collect the observed radiation and concentrate it onto the sensitive infrared detector. The output of the infrared detector is filtered with a high-resolution bandpass filter that is centered at a frequency of one of the spectrally-discrete infrared emissions of the seed formulation of the day. The output of the bandpass filter is applied to a threshold trigger, which activates an indicator light when the total energy output by the bandpass filter exceeds a predetermined value, indicating that the interrogated vehicle is friendly.