AS-polRI: Analysis of apparent spectral polarization radiant intensity in the midwave infrared band for man-made object detection

Detecting remote man-made objects in mid-infrared band is an important problem in aerial surveillance. Spectral polarization in the midwave infrared (MWIR) hyperspectral band can be a feasible solution but it has been studied less than the visible light band. The conventional degree of linear polarization (DoLP) metric cannot provide physical spectral polarization information because it is defined as a energy-normalized ratio, which leads to incorrect polarization degree in low signal-to-noise ratio in MWIR band. This paper presents a novel physical metric called apparent spectral polarization radiant intensity (AS-polRI) for MWIR spectral polarization in man-made object detection. AS-polRI, measured in Watts per steradian (W/sr), is obtained by integrating the difference between parallel spectral radiance and perpendicular spectral radiance assuming a 1 m2 object area. The proposed AS-polRI is compared with the degree of linear polarization (DoLP) in terms of man-made object detection. Experimental results for various outdoor scenarios and materials validate the usefulness of the proposed AS-polRI. •AS-polRI is a physical metric desgined for for man-made object detection.•AS-polRI is compared with conventional DoLP to check the pros and cons.•AS-polRI is calculated and analyzed for various types of materials.•AS-polRI can find a band that separates the dominant spectrum of reflectance and emittance.•The usefulness of AS-polRI is validated through outdoor experiments.