Abstract
Correct specification of a target’s longwave infrared (LWIR) surface emissivity has been identified as one of the greatest sources of uncertainty in the remote sensing of land surface temperature (LST). Field and laboratory emissivity measurements are essential for improving and validating LST retrievals, but there are differing approaches to making such measurements and the conditions that they are made under can affect their performance. To better understand these impacts we made measurements of fourteen manmade and natural samples under different environmental conditions, both in situ and in the laboratory. We used Fourier transform infrared (FTIR) spectrometers to deliver spectral emissivities and an emissivity box to deliver broadband emissivities. Field- and laboratory-measured spectral emissivities were generally within 1–2% in the key 8–12 micron region of the LWIR atmospheric window for most samples, though greater variability was observed for vegetation and inhomogeneous samples. Differences between laboratory and field spectral measurements highlighted the importance of field methods for these samples, with the laboratory setup unable to capture sample structure or inhomogeneity. The emissivity box delivered broadband emissivities with a consistent negative bias compared to the FTIR-based approaches, with differences of up to 5%. The emissivities retrieved using the different approaches result in LST retrieval differences of between 1 and 4 °C, stressing the importance of correct emissivity specification.
Highlights
Emissivity is a spectrally varying property of a material, describing at any particular wavelength the efficiency at which an object emits electromagnetic radiation as a function of its temperature
We have focused on Fourier transform infrared (FTIR) spectrometer-based emissivity measurement systems since these are the most common type used to provide spectral emissivity measurements, applying to the measured spectra a variety of different post-processing approaches to derive the surface emissivity information
We conducted an inter-comparison of four different methods of longwave infrared (LWIR) surface emissivity retrieval, encompassing methods that derived full spectral emissivity data and broadband emissivities, and which operate in the field and in the laboratory
Summary
Emissivity is a spectrally varying property of a material, describing at any particular wavelength the efficiency at which an object emits electromagnetic radiation as a function of its temperature. It is important to understand their spectrally varying emissivity across the electromagnetic spectrum, including within the longwave infrared (LWIR) spectral atmospheric window (8–13 μm) where most remote sensing of land surface temperature (LST) is conducted. This is the case when estimating LST remotely, where knowledge of the target’s surface emissivity in the LWIR is essential when converting infrared brightness temperature (BT) measurements into accurate estimates of LST [3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
