Staring array A staring array , staring - plane array , focal - plane array ( FPA ) , or focal - plane is an image sensing device consisting of an array ( typically rectangular ) of light - sensing pixels at the focal plane of a lens . FPAs are used most commonly for imaging purposes ( e . g . taking pictures or video imagery ) , but can also be used for non - imaging purposes such as spectrometry , LIDAR , and wave - front sensing . In radio astronomy the term " FPA " refers to an array at the focus of a radio - telescope ( see full article on Focal Plane Arrays ) . At optical and infrared wavelengths it can refer to a variety of imaging device types , but in common usage it refers to two - dimensional devices that are sensitive in the infrared spectrum . Devices sensitive in other spectra are usually referred to by other terms , such as CCD ( charge - coupled device ) and CMOS image sensor in the visible spectrum . FPAs operate by detecting photons at particular wavelengths and then generating an electrical charge , voltage , or resistance in relation to the number of photons detected at each pixel . This charge , voltage , or resistance is then measured , digitized , and used to construct an image of the object , scene , or phenomenon that emitted the photons . Applications for infrared FPAs include missile or related weapons guidance sensors , infrared astronomy , manufacturing inspection , thermal imaging for firefighting , medical imaging , and infrared phenomenology ( such as observing combustion , weapon impact , rocket motor ignition and other events that are interesting in the infrared spectrum ) . Comparison to scanning array . Staring arrays are distinct from scanning array and TDI ( time - domain integration ) imagers in that they image the desired field of view without scanning . Scanning arrays are constructed from linear arrays ( or very narrow 2 - D arrays ) that are rastered across the desired field of view using a rotating or oscillating mirror to construct a 2 - D image over time . A TDI imager operates in similar fashion to a scanning array except that it images perpendicularly to the motion of the camera . A staring array is analogous to the film in a typical camera ; it directly captures a 2 - D image projected by the lens at the image plane . A scanning array is analogous to piecing together a 2D image with photos taken through a narrow slit . A TDI imager is analogous to looking through a vertical slit out the side window of a moving car , and building a long , continuous image as the car passes the landscape . Scanning arrays were developed and used because of historical difficulties in fabricating 2 - D arrays of sufficient size and quality for direct 2 - D imaging . Modern FPAs are available with up to 2048 x 2048 pixels , and larger sizes are in development by multiple manufacturers . 320 x 256 and 640 x 480 arrays are available and affordable even for non - military , non - scientific applications . Construction and materials . The difficulty in constructing high - quality , high - resolution FPAs derives from the materials used . Whereas visible imagers such as CCD and CMOS image sensors are fabricated from silicon , using mature and well - understood processes , IR sensors must be fabricated from other , more exotic materials because silicon is sensitive only in the visible and near - IR spectra . Infrared - sensitive materials commonly used in IR detector arrays include mercury - cadmium - telluride ( HgCdTe , " MerCad " , or " MerCadTel " ) , Indium Antimonide ( InSb , pronounced " Inns - Bee " ) , Indium Gallium Arsenide ( InGaAs , pronounced " Inn - Gas " ) , and Vanadium Oxide ( VOx , pronounced " Vox " ) . A variety of lead salts can also be used , but are less common today . None of these materials can be grown into crystals anywhere near the size of modern silicon crystals , nor do the resulting wafers have nearly the uniformity of silicon . Furthermore , the materials used to construct arrays of IR - sensitive pixels cannot be used to construct the electronics needed to transport the resulting charge , voltage , or resistance of each pixel to the measurement circuitry . This set of functions is implemented on a chip called the multiplexer , or readout integrated circuits ( ROIC ) , and is typically fabricated in silicon using standard CMOS processes . The detector array is then hybridized or bonded to the ROIC , typically using indium bump - bonding , and the resulting assembly is called an FPA . Some materials ( and the FPAs fabricated from them ) operate only at cryogenic temperatures , and others ( such as resistive amorphous silicon ( a - Si ) and VOx microbolometers ) can operate at uncooled temperatures . Some devices are only practical to operate cryogenically as otherwise the thermal noise would swamp the detected signal . Devices can be cooled evaporatively , typically by liquid nitrogen ( LN2 ) or liquid helium , or by using a thermo - electric cooler . A peculiar aspect of nearly all IR FPAs is that the electrical responses of the pixels on a given device tend to be non - uniform . In a perfect device every pixel would output the same electrical signal when given the same number of photons of appropriate wavelength . In practice nearly all FPAs have both significant pixel - to - pixel offset and pixel - to - pixel photo - response non - uniformity ( PRNU ) . When un - illuminated , each pixel has a different " zero - signal " level , and when illuminated the delta in signal is also different . This non - uniformity makes the resulting images impractical for use until they have been processed to normalize the photo - response . This correction process requires a set of known characterization data , collected from the particular device under controlled conditions . The data correction can be done in software , in a DSP or FPGA in the camera electronics , or even on the ROIC in the most modern of devices . The low volumes , rarer materials , and complex processes involved in fabricating and using IR FPAs makes them far more expensive than visible imagers of comparable size and resolution . Staring plane arrays are used in modern air to air missile s and anti - tank missile s such as the AIM - 9X Sidewinder , ASRAAM