Non-Contact Measurement of the Spectral Emissivity through Active/Passive Synergy of CO₂ Laser at 10.6 µm and 102F FTIR (Fourier Transform Infrared) Spectrometer.

Ren-Hua Zhang,Su-Juan Mi,Jing Tian,Hong-Bo Su,Zhao-Liang Li

doi:10.3390/s16070970

Abstract

In the inversion of land surface temperature (LST) from satellite data, obtaining the information on land surface emissivity is most challenging. How to solve both the emissivity and the LST from the underdetermined equations for thermal infrared radiation is a hot research topic related to quantitative thermal infrared remote sensing. The academic research and practical applications based on the temperature-emissivity retrieval algorithms show that directly measuring the emissivity of objects at a fixed thermal infrared waveband is an important way to close the underdetermined equations for thermal infrared radiation. Based on the prior research results of both the authors and others, this paper proposes a new approach of obtaining the spectral emissivity of the object at 8–14 µm with a single-band CO2 laser at 10.6 µm and a 102F FTIR spectrometer. Through experiments, the spectral emissivity of several key samples, including aluminum plate, iron plate, copper plate, marble plate, rubber sheet, and paper board, at 8–14 µm is obtained, and the measured data are basically consistent with the hemispherical emissivity measurement by a Nicolet iS10 FTIR spectrometer for the same objects. For the rough surface of materials, such as marble and rusty iron, the RMSE of emissivity is below 0.05. The differences in the field of view angle and in the measuring direction between the Nicolet FTIR method and the method proposed in the paper, and the heterogeneity in the degree of oxidation, polishing and composition of the samples, are the main reasons for the differences of the emissivities between the two methods.

Highlights

Large-scale information on land surface temperature (LST) is of great importance to global changes, water circulation and balance, crop production forecast, agricultural drought monitoring, urban heat islands, and some other fields
Krishnan et al compared in situ, aircraft, and satellite land surface temperatures and the results showed that the standard deviation of the brightness temperature during the flight periods were
The irradiance of the CO2 laser is measured with the multi-point steady-temperature gilded plate and the 102F FTIR

Summary

Introduction

Large-scale information on land surface temperature (LST) is of great importance to global changes, water circulation and balance, crop production forecast, agricultural drought monitoring, urban heat islands, and some other fields. In the inversion of land surface temperature with airborne and satellite data, gaining information on land surface emissivity is most challenging. Humans can only roughly obtain satellite pixel scale emissivity through temperature-emissivity retrieval algorithms, which are related to atmospheric radiation and transmission, rather than directly measuring land surface emissivity using the airborne or satellite platforms. Temperature-emissivity retrieval is challenging because both the true land surface temperature and the emissivity contained in the thermal infrared radiation signal measured at a certain waveband are unknown, which makes the radiative transfer equations not closed. As only the infrared radiation information (radiation temperature) measured by the sensor is available, the number of equations increases with that of the wavebands, leading to n + 1 unknowns in n equations. Either removing one of the unknowns, or inverting both emissivity and temperature, is the goal of separating temperature and emissivity

Methods

Discussion

Conclusion