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Open AccessFeature PaperArticle

“Tau-Omega”- and Two-Stream Emission Models Used for Passive L-Band Retrievals: Application to Close-Range Measurements over a Forest

1
Swiss Federal Research Institute WSL, CH-8903 Birmensdorf, Switzerland
2
Gamma Remote Sensing AG, CH-3073 Gümligen, Switzerland
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(12), 1868; https://doi.org/10.3390/rs10121868
Received: 1 October 2018 / Revised: 11 November 2018 / Accepted: 14 November 2018 / Published: 22 November 2018
(This article belongs to the Special Issue Soil Moisture Remote Sensing Across Scales)
Microwave Emission Models (EM) are used in retrieval algorithms to estimate geophysical state parameters such as soil Water Content ( W C ) and vegetation optical depth ( τ ), from brightness temperatures T B p , θ measured at nadir angles θ at Horizontal and Vertical polarizations p = { H , V } . An EM adequate for implementation in a retrieval algorithm must capture the responses of T B p , θ to the retrieval parameters, and the EM parameters must be experimentally accessible and representative of the measurement footprint. The objective of this study is to explore the benefits of the multiple-scattering Two-Stream (2S) EM over the “Tau-Omega” (TO) EM considered as the “reference” to retrieve W C and τ from L-band T B p , θ . For sparse and low-scattering vegetation T B , E M p , θ simulated with E M = { TO ,   2 S } converge. This is not the case for dense and strongly scattering vegetation. Two-Parameter (2P) retrievals 2 P R C = ( W C R C , τ R C ) are computed from elevation scans T B p , θ j = T B , TO p , θ j synthesized with TO EM and from T B p , θ j measured from a tower within a deciduous forest. Retrieval Configurations ( R C ) employ either E M = TO or E M = 2 S and assume fixed scattering albedos. W C R C achieved with the 2S RC is marginally lower ( ~ 1   m 3 m 3 ) than if achieved with the “reference” TO RC, while τ R C is reduced considerably when using 2S EM instead of TO EM. Our study outlines a number of advantages of the 2S EM over the TO EM currently implemented in the operational SMOS and SMAP retrieval algorithms. View Full-Text
Keywords: passive microwave radiometry; L-band; soil moisture; vegetation optical depth; emission model; retrieval; SMOS; SMAP passive microwave radiometry; L-band; soil moisture; vegetation optical depth; emission model; retrieval; SMOS; SMAP
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MDPI and ACS Style

Schwank, M.; Naderpour, R.; Mätzler, C. “Tau-Omega”- and Two-Stream Emission Models Used for Passive L-Band Retrievals: Application to Close-Range Measurements over a Forest. Remote Sens. 2018, 10, 1868.

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