Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Parameterization of Vegetation Scattering Albedo in the Tau-Omega Model for Soil Moisture Retrieval on Croplands

Chang-Hwan Park
* ,
Thomas Jagdhuber
ORCID logo ,
Andreas Colliander
,
Johan Lee
,
Aaron Berg
ORCID logo ,
Michael Cosh
ORCID logo ,
Sung-bum Kim
,
Yoonjae Kim
,
Volker Wulfmeyer
Version 1 : Received: 28 July 2020 / Approved: 30 July 2020 / Online: 30 July 2020 (10:58:24 CEST)

A peer-reviewed article of this Preprint also exists.

Park, C.-H.; Jagdhuber, T.; Colliander, A.; Lee, J.; Berg, A.; Cosh, M.; Kim, S.-B.; Kim, Y.; Wulfmeyer, V. Parameterization of Vegetation Scattering Albedo in the Tau-Omega Model for Soil Moisture Retrieval on Croplands. Remote Sens. 2020, 12, 2939. Park, C.-H.; Jagdhuber, T.; Colliander, A.; Lee, J.; Berg, A.; Cosh, M.; Kim, S.-B.; Kim, Y.; Wulfmeyer, V. Parameterization of Vegetation Scattering Albedo in the Tau-Omega Model for Soil Moisture Retrieval on Croplands. Remote Sens. 2020, 12, 2939.

Abstract

An accurate radiative transfer model (RTM) is essential for the retrieval of soil moisture (SM) from microwave remote sensing data, such as the passive microwave measurements from the Soil Moisture Active Passive (SMAP) mission. This mission delivers soil moisture products based upon L-band brightness temperature data, via retrieval algorithms for surface and root-zone soil moisture, the latter is retrieved using data assimilation and model support. We found that the RTM based on the tau-omega (?-ω) model, can suffer from significant errors over croplands (in average between -9.4K and + 12.0K for Single Channel Algorithm SCA; -8K and + 9.7K for Dual-Channel Algorithm DCA) if the vegetation scattering albedo (omega) is treated as a constant and the temporal variations are not accounted. In order to reduce this uncertainty, we propose a time-varying parameterization of omega for the widely established zeroth order radiative transfer ?-ω model. The main assumption is that omega can be expressed by a functional relationship between vegetation optical depth (tau) and the Green Vegetation Fraction (GVF). The validation was performed from 14 May to 13 December 2015 over 61 Climate Reference Network sites (SCRN) classified as croplands. The application of the proposed time-varying vegetation scattering albedo results in a consistent improvement for the unbiased root mean square error of 16% for SCA and 15% for DCA. The reduction for positive and negative biases was 45% and 5% for SCA and 26% and 12% for DCA, respectively. This indicates that vegetation dynamics on croplands are better represented by a time-dynamic single scattering albedo.

Keywords

soil moisture; scattering albedo; tau-omega model; allometry; vegetation fraction; vegetation water content; passive microwave remote sensing; SMOS; SMAP; AMSR-E

Subject

Environmental and Earth Sciences, Environmental Science

Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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