Aircraft Signature Studies Using Infrared Cross Section and Infrared Solid Angle

Abstract

Aircraft infrared (IR) signature studies are complex, due to their dependence on several parameters, e.g., line of sight ($\mathrm{LOS}$ ) and viewing aspect ($\widehat{\mathrm{LOS}}$ ). There is no equivalent counterpart of the well-known radar cross section (RCS) that can be easily used for obtaining IR lock-on range, $R_{\mathrm{LO},\lambda 1-\lambda 2}$ . This study introduces the concept of IR cross section $(\mathrm{IRCS}{)}_{\lambda 1-\lambda 2}$ of complete aircraft as seen by seeker in ${\lambda }_1–{\lambda }_2$ band in $\widehat{\mathrm{LOS}}$ and of aircraft part in an orthogonal view. The IR solid angle (${\omega }_{\mathrm{IR},\lambda 1-\lambda 2}$ ) subtended by $(\mathrm{IRCS}{)}_{\lambda 1-\lambda 2}$ of complete aircraft and of an aircraft part is also introduced, which is the basis for redefined general criterion for lock-on by IR-guided missile. Equality based on ${\omega }_{\mathrm{IR},\lambda 1-\lambda 2}$ at aircraft part level and at complete aircraft level is the basis for obtaining $R_{\mathrm{LO},\lambda 1-\lambda 2}$ of complete aircraft in terms of its $(\mathrm{IRCS}{)}_{\lambda 1-\lambda 2}$ . Dimensionless scalar factor, ${\mathrm{\Pi }}_{\mathrm{IRCS},\lambda 1-\lambda 2}$ , converting visual area to $(\mathrm{IRCS}{)}_{\lambda 1-\lambda 2}$ is studied, for temperatures ranging from close to ambient to maximum afterburning (reheat) mode of aeroengine. The ${\mathrm{\Pi }}_{\mathrm{IRCS},\lambda 1-\lambda 2}$ enables assessment of effectiveness of IR seekers with single or dual bands, for all-aspect engagement and for rear-view only.