Investigation of minimum resolvable temperature difference formulation for polarized thermal imaging range prediction

Abstract

Previous measurements have demonstrated that a polarization filter can increase ship-background temperature contrast in the infrared, while decreasing the received radiance. Application of this technique to increasing range for detection or recognition of ship targets is being investigated through detection range modeling for a generic FLIR sensor. Laboratory measurements have been made of effective Minimum Resolvable Temperature Difference (MRTD) of a serial-scan 8-12 micrometers sensor for polarized and unpolarized radiation. A variety of standard four-bar target boards of varied spatial frequency and controlled bar-background temperature difference were used to construct MRTD vs. spatial frequency. Results were compared with model predictions using known or measured component parameters for the AGA-780 imager, showing close agreement for observations made by a "trained observer." A modified form of MRTD was developed for a polarized target using a reformulation of the thermal derivative of Planck's law. Modeled and measured values agreed closely for the unpolarized case, and also for both vertically and horizontally polarized cases when the appropriate parameters of the polarization filters were included. Mathematical analysis and measurement agreed in displaying an increase in MRTD with polarization. Predictions of maximum detection and recognition ranges using estimates of polarized effective target-background temperature difference indicated probable range improvement for sea surface degree of polarization in excess of 20%.