Passive ranging technique for infrared search and track (IRST) systems

Claim 1

A method for the passive determination of the range and type of a target, comprising the following steps: (a) intermittently estimate atmospheric transmittance from available meteorological data and intermittently estimate background spectral radiance from meteorological data or spectral radiance sensors; (b) at each of consecutive observation times: (i) measure the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; (ii) considering step (b)(i), indicate whether said target has a radially inbound trajectory; (iii) estimate a range for said target, as follows: select a target type from a library of target types storing signatures of the target types considering the measured contrast irradiance as well as the measure of the contrast irradiance at the previous observation time, if any; estimate the range of the target considering the selected target type, said estimated atmospheric transmittance and background spectral radiance and the measured contrast irradiance; (iv) where the target has other than a radially inbound trajectory, estimate a range for said target as follows: estimate a trajectory for said target; select a target type from said library, considering the estimated trajectory; estimate the range of said target considering the selected target type, the angular movement of the target, and the range estimate for the target made at the previous observation time; and (v) select a target type and range based on the selections and estimations from step (iii) and step (iv).

Claim 2

A method for the passive determination of the range and type of a target, comprising the following steps: (a) intermittently estimate atmospheric transmittance from available meteorological data and intermittently estimate background spectral radiance from meteorological data or spectral radiance sensors; (b) at each of consecutive observation times: (i) measure the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; (ii) considering step (b)(i), indicate whether said target has a radially inbound trajectory; (iii) estimate a range for said target, as follows: select a target type from a library of target types storing signatures of the target types considering the measured contrast irradiance as well as the measure of the contrast irradiance at the previous observation time, if any; estimate the range of the target considering the selected target type, said estimated atmospheric transmittance and background spectral radiance and the measured contrast irradiance; (iv) where the target has other than a radially inbound trajectory, estimate a range for said target as follows: estimate a trajectory for said target; select a target type from said library, considering the estimated trajectory; estimate the range of said target considering the selected target type, the angular movement of the target, and the range estimate for the target made at the previous observation time; and (v) select a target type and range based on the selections and estimations from step (iii) and step (iv).

Claim 15

A method for the passive determination of the range, speed, and type of a target, comprising the following steps: (a) intermittently estimate atmospheric transmittance from available meteorological data and intermittently estimate background spectral radiance from meteorological data or spectral radiance sensors; (b) at each of consecutive observation times: (i) measure the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; (ii) if the target is newly detected, assume said target has a trajectory which is radially inbound, otherwise determine whether the trajectory of said target is radially inbound by comparison of the measured azimuth with the azimuth of said target measured at the previous observation time; (iii) estimate a range for said target, as follows: access a library of target types storing information relating to the signature of each target type including the expected speed of each target type and, considering said library target signatures, predict the contrast irradiance which would be expected in the next observation time for each target type; where said target is newly detected, assume a target type, otherwise compare the measured contrast irradiance with the predictions for contrast irradiance resulting from the measurement of contrast irradiance at the previous observation time and select a target type considering said comparisons; estimate the range of the target considering said selected target type, said measured contrast irradiance, and said estimated atmospheric transmittance and background spectral radiance; (iv) where the target has other than a radially inbound trajectory or where, by comparison of the measured elevation with the elevation of said target measured at the previous observation time, the elevation of said target is changing; considering the range and speed estimated for the target during the last observation time, and the angular movement of the target, determine a trajectory for said target; access said library of target types and select a target type considering said estimated trajectory; estimate the current range of said target considering the selected target type, the range estimated for said target during the last observation time and the angular movement of said target.

Claim 16

A method for the passive determination of the range, speed, and type of a target, comprising the following steps: (a) intermittently estimate atmospheric transmittance from available meteorological data and intermittently estimate background spectral radiance from meteorological data or spectral radiance sensors; (b) at each of consecutive observation times: (i) measure the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; (ii) if the target is newly detected, assume said target has a trajectory which is radially inbound, otherwise determine whether the trajectory of said target is radially inbound by comparison of the measured azimuth with the azimuth of said target measured at the previous observation time; (iii) estimate a range for said target, as follows: access a library of target types storing information relating to the signature of each target type including the expected speed of each target type and, considering said library target signatures, predict the contrast irradiance which would be expected in the next observation time for each target type; where said target is newly detected, assume a target type, otherwise compare the measured contrast irradiance with the predictions for contrast irradiance resulting from the measurement of contrast irradiance at the previous observation time and select a target type considering said comparisons; estimate the range of the target considering said selected target type, said measured contrast irradiance, and said estimated atmospheric transmittance and background spectral radiance; (iv) where the target has other than a radially inbound trajectory or where, by comparison of the measured elevation with the elevation of said target measured at the previous observation time, the elevation of said target is changing; considering the range and speed estimated for the target during the last observation time, and the angular movement of the target, determine a trajectory for said target; access said library of target types and select a target type considering said estimated trajectory; estimate the current range of said target considering the selected target type, the range estimated for said target during the last observation time and the angular movement of said target.

Claim 17

A system for the passive determination of the range and type of a target, comprising the following: atmospheric estimation means to estimate atmospheric transmittance; background spectral radiance measurement means; measurement means to measure, at each of consecutive observation times, the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; storage means to store measurements made by said measurement means and determinations made by radiometric means and kinematic means; radially inbound trajectory determination means to determine whether said target has a radially inbound trajectory; library means to store a library of target types along with signatures of each target type; said radiometric means being responsive to said radially inbound trajectory determination means, said library means, said measurement means, said storage means, and said atmospheric estimation means to select a target type and range; and said kinematic means being responsive to said radially inbound trajectory determination means, said measurement means, said storage means, and said library means to estimate a trajectory, range, and target type for said target.

Claim 18

A system for the passive determination of the range and type of a target, comprising the following: atmospheric estimation means to estimate atmospheric transmittance; background spectral radiance measurement means; measurement means to measure, at each of consecutive observation times, the contrast irradiance in the direction of a target as well as the azimuth and elevation of said target; storage means to store measurements made by said measurement means and determinations made by radiometric means and kinematic means; radially inbound trajectory determination means to determine whether said target has a radially inbound trajectory; library means to store a library of target types along with signatures of each target type; said radiometric means being responsive to said radially inbound trajectory determination means, said library means, said measurement means, said storage means, and said atmospheric estimation means to select a target type and range; and said kinematic means being responsive to said radially inbound trajectory determination means, said measurement means, said storage means, and said library means to estimate a trajectory, range, and target type for said target.