Retrievals of High‐Latitude Surface Emissivity Across the Infrared From High‐Altitude Aircraft Flights

Abstract

We present retrievals of infrared spectral surface emissivities spanning the far infrared and mid-infrared from aircraft observations over Greenland, taken at an altitude of 9.2 km above sea level. We describe the flight campaign, available measurements, and the retrieval method. The principal barriers to reducing uncertainty in the emissivity retrievals are found to be instrumental noise and our ability to simultaneously retrieve the underlying surface temperature. However, our results indicate that using the instrumentation available to us it is possible to retrieve emissivities from altitude with an uncertainty of~0.02 or better across much of the infrared. They confirm that the far-infrared emissivity of snow and ice surfaces can depart substantially from unity, reaching values as low as 0.9 between 400 and 450 cm −1. They also show good consistency with retrievals from the same flight made from near-surface observations giving confidence in the methodology used and the results obtained for this more challenging viewing configuration. To the best of our knowledge, this is the first time that far-infrared surface emissivity has been retrieved from altitude and demonstrates that the methodology has the potential to be extended to planned satellite far-infrared missions.

Retrieval of Surface Spectral Emissivity in Polar Regions Based on the Optimal Estimation Method

“…Furthermore, Murray et al. (2020) also confirmed the theoretical calculations in Chen et al. (2014) and Huang et al.…”

“…While there have been a couple of field campaigns to measure the far-IR surface spectral emissivities over Greenland and Mt. Zugspitze in the German Alps (Bellisario et al, 2017;Murray et al, 2020;Palchetti et al, 2021), we hope that our findings here can further motivate more in-situ or laboratory measurements of such quantities, especially over the far-IR dirty window where few actual measurements currently exist.…”

“…They retrieved far-IR surface spectral emissivity from 18.7 to 125 μm and highlighted the need for further research on the simultaneous retrievals of mid-IR and far-IR surface emissivities. Murray et al (2020) adopted the retrieval framework in Bellisario et al (2017) and validated the feasibility of retrieving mid-IR and far-IR surface emissivity from the TAFTS spectra measured at a higher altitude than those in Bellisario et al (2017). Furthermore, Murray et al (2020) also confirmed the theoretical calculations in Chen et al (2014) and Huang et al (2016) by demonstrating that the far-IR emissivities of snow and ice surfaces can be significantly less than unity, especially over the so-called far-IR dirty window (16.7-25 μm;Rathke et al, 2002).…”

“…Murray et al. (2020) adopted the retrieval framework in Bellisario et al. (2017) and validated the feasibility of retrieving mid‐IR and far‐IR surface emissivity from the TAFTS spectra measured at a higher altitude than those in Bellisario et al.…”

“…Murray et al (2020) adopted the retrieval framework in Bellisario et al (2017) and validated the feasibility of retrieving mid-IR and far-IR surface emissivity from the TAFTS spectra measured at a higher altitude than those in Bellisario et al (2017). Furthermore, Murray et al (2020) also confirmed the theoretical calculations in Chen et al (2014) and Huang et al (2016) by demonstrating that the far-IR emissivities of snow and ice surfaces can be significantly less than unity, especially over the so-called far-IR dirty window (16.7-25 μm;Rathke et al, 2002). These two studies were restricted to observations in March 2015 over a limited region in the Greenland Plateau.…”