# A Comparison of Radiometric and Spectrometric Emissivity Evaluation Methods in Infrared Thermometry

## TL;DR

This paper compares two methods for measuring emissivity in infrared thermometry and finds that the radiometric method is simpler and more practical for real-world use.

## Contribution

The study provides a practical comparison of spectral and radiometric emissivity evaluation methods under real-world conditions.

## Key findings

- Spectral and radiometric emissivity evaluation methods produce consistent results for stable, homogeneous samples.
- The radiometric method is preferable for in situ infrared thermometry due to simplicity and lower uncertainty.
- Surface instability and inhomogeneity affect the reliability of emissivity evaluation methods.

## Abstract

What is the main finding?
Instrumental emissivity is a prerequisite in infrared thermometry and can be traceably obtained either by a spectrometric or radiometric method.

Instrumental emissivity is a prerequisite in infrared thermometry and can be traceably obtained either by a spectrometric or radiometric method.

What are the implications of the main findings?
In practical comparison, results correspond between the two methods for samples of sufficient quality.A radiometric method is practically preferable for simplicity, inexpensiveness and generally lower uncertainty of subsequent temperature measurement.

In practical comparison, results correspond between the two methods for samples of sufficient quality.

A radiometric method is practically preferable for simplicity, inexpensiveness and generally lower uncertainty of subsequent temperature measurement.

Accurate radiation thermometry of real objects critically depends on knowledge of surface emissivity, which is rarely known a priori and often varies with surface condition, temperature, and environment. Although theoretical models for spectral emissivity evaluation exist, their practical validation under application-relevant conditions remains limited. In this study, spectral and radiometric emissivity evaluation methods are compared on metallic samples up to 350 °C. The spectral method derives effective emissivity from spectroscopy-measured spectral emissivity using instrument-specific spectral sensitivity (responsivity), while the radiometric method evaluates emissivity directly from radiance measurements using a radiation thermometer and a reference contact temperature. The radiometric method is treated as an application-level reference. Stable and homogeneous chromium nitride (CrN)-coated samples show good agreement between the two methods, whereas raw metals and polysiloxane-coated samples highlight practical limitations related to sample surface instability and inhomogeneity. The results demonstrate that spectral emissivity evaluation is valid in practice when its underlying method assumptions are fulfilled, while radiometric evaluation remains preferable for in situ infrared thermometry.