A method of characterizing the emissivity of a sample, comprising: a) placing a low-e mirror behind the sample, said sample and said low-e mirror positioned to overfill a field of view, FOV, of a radiometer; b) controlling a heat source to heat the sample through thermal conduction, wherein the heat source comprises an annular heating element having a central void therethrough, and wherein the sample is placed on the surface of the annular heating element over the central void, wherein the low-e mirror is placed behind and spaced apart from the annular heating element, and wherein a portion of the sample and the low-e mirror within the central void overfill the FOV of the radiometer; c) measuring a sample radiance in the FOV over a spectral band with the sample in-situ, wherein the spectral band spans at least one of the MWIR and LWIR bands; d) measuring the temperature of the sample; e) computing an ideal radiance over the spectral band at the measured temperature; f) extracting a calculated sample radiance over the spectral band from the measured sample radiance; g) computing the sample emissivity as the ratio of the calculated sample radiance to the ideal radiance over the spectral band; and h) repeating steps b through g at increments over a temperature range, wherein said low-e mirror exhibits a reflectance of at least 90% and an emissivity of at most 7.5% over the spectral band for sample temperatures over the temperature range, wherein the method further comprises: characterizing the reflectance of the low-e mirror and the transmission of the sample over the spectral range; measuring an ambient radiance emitted from an ambient source; measuring a low-e mirror radiance emitted from the low-e mirror without the sample; subtracting the ambient radiance from the low-e mirror radiance and the measured sample radiance; and extracting the calculated sample radiance over the spectral band as a scaled difference between the adjusted low-e mirror radiance and adjusted measured sample radiance. a) placing a low-e mirror behind the sample, said sample and said low-e mirror positioned to overfill a field of view, FOV, of a radiometer; b) controlling a heat source to heat the sample through thermal conduction, wherein the heat source comprises an annular heating element having a central void therethrough, and wherein the sample is placed on the surface of the annular heating element over the central void, wherein the low-e mirror is placed behind and spaced apart from the annular heating element, and wherein a portion of the sample and the low-e mirror within the central void overfill the FOV of the radiometer; c) measuring a sample radiance in the FOV over a spectral band with the sample in-situ, wherein the spectral band spans at least one of the MWIR and LWIR bands; d) measuring the temperature of the sample; e) computing an ideal radiance over the spectral band at the measured temperature; f) extracting a calculated sample radiance over the spectral band from the measured sample radiance; g) computing the sample emissivity as the ratio of the calculated sample radiance to the ideal radiance over the spectral band; and h) repeating steps b through g at increments over a temperature range, wherein said low-e mirror exhibits a reflectance of at least 90% and an emissivity of at most 7.5% over the spectral band for sample temperatures over the temperature range, wherein the method further comprises: characterizing the reflectance of the low-e mirror and the transmission of the sample over the spectral range; measuring an ambient radiance emitted from an ambient source; measuring a low-e mirror radiance emitted from the low-e mirror without the sample; subtracting the ambient radiance from the low-e mirror radiance and the measured sample radiance; and extracting the calculated sample radiance over the spectral band as a scaled difference between the adjusted low-e mirror radiance and adjusted measured sample radiance. characterizing the reflectance of the low-e mirror and the transmission of the sample over the spectral range; measuring an ambient radiance emitted from an ambient source; measuring a low-e mirror radiance emitted from the low-e mirror without the sample; subtracting the ambient radiance from the low-e mirror radiance and the measured sample radiance; and extracting the calculated sample radiance over the spectral band as a scaled difference between the adjusted low-e mirror radiance and adjusted measured sample radiance.