Improvement of microwave emissivity parameterization of frozen Arctic soils using roughness measurements derived from photogrammetry

ABSTRACT

Soil emissivity of Arctic regions is a key parameter for assessing surface properties from microwave brightness temperature (Tb) measurements. Particularly in winter, frozen soil permittivity and roughness are two poorly characterized unknowns that must be considered. Here, we show that after removing snow, the 3D soil roughness can be accurately inferred from in-situ photogrammetry using Structure from Motion (SfM). We focus on using SfM techniques to provide accurate roughness measurements and improve emissivity models parametrization of frozen arctic soil for microwave applications. Validation was performed from ground-based radiometric measurements at 19 and 37 GHz using three different soil emission models: the Wegmüller and Mätzler [1999, TGRS] model (Weg99), the Wang and Choudhury [1981, JGR] model (QNH), and a geometrical optics model (Geo Optics). Measured and simulated brightness temperatures over different tundra and rock sites in the Canadian High Arctic show that Weg99, parametrized with SfM-based roughness and optimized permittivity $(\epsilon )$, yielded an RMSE of 3.1 K ($R^2=0.71$) for all frequencies and polarizations. Our SfM based approach allowed us to measure roughness with 0.1 mm accuracy at 55 locations of different land cover type using a digital camera and metal plates of know dimensions.

KEYWORDS:

• Surface roughness
• microwave remote sensing
• frozen Arctic soil
• SfM photogrammetry

Acknowledgements

The authors would like to thank Benoît Montpetit and Alex Mavrovic for their contribution and helpful comments on this work. We thank Donald McLennan, Johann Wagner and Serguei Ponomarenko for the ecosystem map and their help in Cambridge Bay. We also thank Daniel Kramer, Simon Levasseur, Coralie Gautier, Guillaume Couture and Patrick Cliche from Université de Sherbrooke and Ludovic Brucker from the NASA Cryospheric Sciences Laboratory for field work assistance, instrument maintenance and overall guidance.

Data availability statement

All brightness temperatures and emissivity values will be available on request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

Note: Permittivity from Montpetit et al. (2018) was used for calculation.

Note: VMC stands for volumetric moisture content.

Additional information

Funding

This research was made possible thanks to the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC), Polar Knowledge Canada, Canada Foundation for Innovation (CFI), Fonds québécois de la recherche sur la nature et les technologies (FRQNT-Québec), Northern Scientific Training Program (NSTP), Environment and Climate Change Canada Grant and Contribution program and research funding from Northumbria University, UK.