Patent ID: 9234796
Filing Date: 2016-01-12
CPC Classification: G01J

Claim Text:
1. An infrared imaging, and calibration method, comprising: providing a laboratory-generated calibration curve for a staring focal plane imager, wherein said staring focal plane imager includes a lens and detector array having a plurality of counts, wherein said laboratory-generated calibration curve relates a value of each of said plurality of counts to a radiance value for said staring focal plane imager; disposing said detector array in a liquid nitrogen Dewar in a housing having an exterior aperture and associated window, wherein an optical axis of said detector array passes through said window; positioning a mirror outside of said housing a pre-determined distance away from said lens in an orientation perpendicular to said optical axis of said detector array when said housing is in a first position; orienting said housing in said first position during a flight; determining a first temperature, said first temperature corresponding to a temperature of said lens at a first point in time during said flight with said housing in said first position said lens associated with a lens transmission coefficient at said first temperature; determining a second temperature, said second temperature corresponding to a temperature of said window at said first point in time during said flight with said housing in said first position, said window associated with a window transmission coefficient at said second temperature; determining a third temperature, said third temperature corresponding to a temperature of said mirror at said first point in time during said flight with said housing in said first position, said mirror associated with a mirror reflectance coefficient at said third temperature; irradiating said detector array with radiation, wherein said radiation comprises radiation emitted from said lens, said window, said detector array, and said mirror; recording a count value representing said response of said detector array to said radiation over the spectral response of said detector at said first point in time; orienting said housing to a second position during said flight; recording digital imagery using said detector array in said second position during said flight, wherein said digital imagery is of natural sky background; calculating an in-band radiance value of said detector array due to said radiation at said first point in time as the sum of; calculating an offset of said focal plane imager at said first point in time, where said offset is mathematically defined as follows, where m is equal to slope of said laboratory-generated calibration curve, x is an average of said count value, and y is equal to said in-band radiance value: offset=y−mx; generating an adjusted calibration curve by adjusting said laboratory-generated calibration curve an amount equal to said offset; and assigning radiance values to count values of said digital imagery according to said adjusted calibration curve.