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2. Background in Infrared
Infrared (IR) is invisible radiant energy, electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometers (frequency 430 THz) to 1 mm (300 GHz) (although people can see infrared up to at least 1050 nm in experiments). Most of the thermal radiation emitted by objects near room temperature is infrared.
Infrared radiation was discovered in 1800 by astronomer Sir William Herschel, who discovered a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect upon a thermometer. Slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has a critical effect on Earth's climate. Infrared energy is emitted or absorbed by molecules when they change their rotational-vibration movements. Infrared energy excites vibration modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared energy range.
3. Target position extraction based on instantaneous frequency
To extract a precise target position in the presence of infrared countermeasures and significant noise we propose a new algorism based on the instantaneous frequency estimation on the sinusoidal frequency modulation signal for a fixed-reticle seeker. Reticle seeker have many advantages, such as their inherent simplicity and low cost due to use of a single-element detector. The biggest disadvantage of the reticle seeker systems has proven to be their vulnerability against infrared countermeasures such as flares and jammers. In this section we propose a Infrared counter-Countermeasure technique using instantaneous frequency estimation for a fixed-reticle seeker.
3.1Modulation by a Fixed Reticle
A reticle seeker with a single Infrared detector usually generates its tracking information by a scanning process induced by the relative motion between an optically formed target image and a reticle located in the image plane. A reticle usually has transparent and opaque areas to produce an appropriate encoded signal, which makes it possible to extract the target position by the scanning of the target image on the reticle. In a fixed-reticle seeker, the reticle is stationary and the target image is scanned on the reticle by a rotating wedge or canted mirror,