Emissivity of Human Skin in vivo between 2.0µ and 5.4µ measured at Normal Incidence

Abstract

THE discovery¹ that the temperature of skin overlying malignant tumours is frequently raised has led to an increasing medical interest in thermal patterns over the surface of the body. Attempts^2,3 using infrared scanning devices (‘Aga’ scanner, Bofors Thermograph, and Pyroscan) have subsequently been made to identify pathology underlying the skin in terms of temperature differences at the surface. Thermal scanners measure the energy (Q) emitted by the surface. Consequently the patterns can reflect not only variations in temperature but also changes in emissivity (ε). Unfortunately, there is conflicting evidence on the magnitude of ε. Hardy and Muschenheim⁴ concluded that dead skin should be regarded as a black body (ε = 1). While this conclusion can be justified when Q is the total energy received at all wavelengths (λ) it is not necessarily applicable in the range 2µ < λ < 5.4µ over which the detectors used in these scanners are sensitive. More recent measurements⁵ show that the emissivity of post-mortem skin samples varies rapidly with λ. It is not clear, however, whether values of ε so obtained should be compared with values measured in vivo.