AVIRIS aerosol retrievals for fires observed during the 2019 FIREX-AQ campaign

Abstract:

Aerosols are an important component of the Earth system that contribute to global radiative forcing, interact with clouds and radiation, and substantially affect air quality on local, regional, and global scales. Smoke emissions from wild and agricultural fires are composed of a variety of aerosol particles. There is a critical need to investigate the potential contribution of the latest generation remote sensing techniques for high-resolution, large-scale aerosol emissions and smoke plume development characterization in order to provide observational constraints on the dispersion of smoke from landscape fires.

The joint NASA/NOAA Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign took in the summer of 2019 to improve understanding of wildfire and agricultural fire impacts on air quality, weather, and climate. As part of this effort, the NASA high-altitude ER-2 research aircraft flew 11 flights over targets in Washington, Oregon, California, Utah, and Arizona. The remote sensing package on the ER-2 consisted of seven instruments including the Airborne Visible / Infrared Imaging Spectrometer (AVIRIS-C).

In this study, we analyze AVIRIS-C datasets collected during the FIREX-AQ campaign in order to assess the capacity of an optimal-estimation based retrieval to simultaneously calculate aerosol optical depth (AOD) and surface reflectance from Visible Shortwave Infrared (VSWIR) imaging spectroscopy. We demonstrate that the surface information provided by the VSWIR spectral interval enables continuous maps of aerosols at high spatial resolution across heterogeneous terrain. In a case study, we examine retrievals made from multiple data acquisitions over the Williams Flat fire in Washington. In particular, we calculate ~15m ground level resolution maps of AOD, surface reflectance, and the associated uncertainties over a variety of aerosol and terrain conditions. We demonstrate that these estimates compare favorably with in direct AOD measurements from mobile and stationary AERONET platforms. We further demonstrate the capacity to distinguish between sulfate and smoke models, and demonstrate sensitivity to the aerosol size distribution. Finally, we present an investigation into the stability of surface reflectance retrievals under high AOD conditions.