Mapping soil moisture across the Tibetan Plateau plains using Aquarius active and passive L-band microwave observations

Qiang Wang* (Corresponding Author), R. van der Velde, Paolo Ferrazzoli, Xuelong Chen, Xiaojing Bai, Zhongbo Su

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

An algorithm is developed for retrieving soil moisture at plateau scale by combined usage of Aquarius active and passive L-band observations. In this algorithm, Look-Up-Tables (LUTs) are established for bare soil and vegetated areas by using the physical based Tor Vergata discrete electromagnetic model (hereafter, TV-DEM). In the case of vegetated area, the LUT is built based on simulations with varying soil moisture and Leaf Area Index (LAI). Only soil moisture is variable for the bare soil case, and values calibrated in previous works are adopted for the other TV-DEM parameters. Soil moisture is then retrieved by minimizing a squared difference object function based on the emissivity and backscatter coefficient observed by Aquarius and the corresponding TV-DEM simulations included in the LUT. The soil moisture retrievals are assessed at Aquarius footprint scale using in-situ measurements collected at three regional scale networks spread across the Tibetan Plateau. The unbiased root mean squared differences (ubRMSDs) from the three networks vary from 0.016 to 0.050 m 3 m −3 and coefficients of determination (R 2 ) are from 0.274 to 0.499 (-). This ubRMSD and R 2 is in the same order of the passive-only official Aquarius product, Metop-A Advanced SCATterometer (ASCAT) L2 soil moisture product (hereafter ASCAT) as well as reanalysis data generated by European Centre for Medium-Range Weather Forecasts (hereafter, ERA-Interim). At Plateau-scale, all four soil moisture products capture the seasonal trend, whereby the dynamic range during the monsoon season captured by the ERA-Interim product is relatively small. Further, the northwest-southeast dry-wet gradient due to precipitation and evapotranspiration is well captured by the soil moisture spatial distributions produced by TV-DEM Aquarius, official Aquarius and ASCAT products, but less pronounced in the ERA-Interim product. This study demonstrates that the TV-DEM based algorithm can be used to retrieve soil moisture over a Plateau scale with robust results in terms of error statistics (e.g. bias, R 2 and ubRMSD) and can generate realistic spatial patterns for soil moisture at Plateau-scale.

Original languageEnglish
Pages (from-to)108-118
Number of pages11
JournalInternational Journal of Applied Earth Observation and Geoinformation
Volume77
Early online date11 Jan 2019
DOIs
Publication statusPublished - 1 May 2019

Fingerprint

Soil moisture
soil moisture
Microwaves
plateau
digital elevation model
ASCAT
bare soil
microwave
plain
Error statistics
MetOp
Soils
Evapotranspiration
emissivity
footprint
leaf area index
backscatter
in situ measurement
Spatial distribution
simulation

Keywords

  • Aquarius
  • Combined active/passive microwave remote sensing
  • Discrete electromagnetic model
  • Soil moisture
  • ITC-ISI-JOURNAL-ARTICLE

Cite this

@article{99eddde9822e43acbd336112498e1829,
title = "Mapping soil moisture across the Tibetan Plateau plains using Aquarius active and passive L-band microwave observations",
abstract = "An algorithm is developed for retrieving soil moisture at plateau scale by combined usage of Aquarius active and passive L-band observations. In this algorithm, Look-Up-Tables (LUTs) are established for bare soil and vegetated areas by using the physical based Tor Vergata discrete electromagnetic model (hereafter, TV-DEM). In the case of vegetated area, the LUT is built based on simulations with varying soil moisture and Leaf Area Index (LAI). Only soil moisture is variable for the bare soil case, and values calibrated in previous works are adopted for the other TV-DEM parameters. Soil moisture is then retrieved by minimizing a squared difference object function based on the emissivity and backscatter coefficient observed by Aquarius and the corresponding TV-DEM simulations included in the LUT. The soil moisture retrievals are assessed at Aquarius footprint scale using in-situ measurements collected at three regional scale networks spread across the Tibetan Plateau. The unbiased root mean squared differences (ubRMSDs) from the three networks vary from 0.016 to 0.050 m 3 m −3 and coefficients of determination (R 2 ) are from 0.274 to 0.499 (-). This ubRMSD and R 2 is in the same order of the passive-only official Aquarius product, Metop-A Advanced SCATterometer (ASCAT) L2 soil moisture product (hereafter ASCAT) as well as reanalysis data generated by European Centre for Medium-Range Weather Forecasts (hereafter, ERA-Interim). At Plateau-scale, all four soil moisture products capture the seasonal trend, whereby the dynamic range during the monsoon season captured by the ERA-Interim product is relatively small. Further, the northwest-southeast dry-wet gradient due to precipitation and evapotranspiration is well captured by the soil moisture spatial distributions produced by TV-DEM Aquarius, official Aquarius and ASCAT products, but less pronounced in the ERA-Interim product. This study demonstrates that the TV-DEM based algorithm can be used to retrieve soil moisture over a Plateau scale with robust results in terms of error statistics (e.g. bias, R 2 and ubRMSD) and can generate realistic spatial patterns for soil moisture at Plateau-scale.",
keywords = "Aquarius, Combined active/passive microwave remote sensing, Discrete electromagnetic model, Soil moisture, ITC-ISI-JOURNAL-ARTICLE",
author = "Qiang Wang and {van der Velde}, R. and Paolo Ferrazzoli and Xuelong Chen and Xiaojing Bai and Zhongbo Su",
year = "2019",
month = "5",
day = "1",
doi = "10.1016/j.jag.2019.01.005",
language = "English",
volume = "77",
pages = "108--118",
journal = "International Journal of Applied Earth Observation and Geoinformation (JAG)",
issn = "1569-8432",
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Mapping soil moisture across the Tibetan Plateau plains using Aquarius active and passive L-band microwave observations. / Wang, Qiang (Corresponding Author); van der Velde, R.; Ferrazzoli, Paolo; Chen, Xuelong; Bai, Xiaojing; Su, Zhongbo.

In: International Journal of Applied Earth Observation and Geoinformation, Vol. 77, 01.05.2019, p. 108-118.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Mapping soil moisture across the Tibetan Plateau plains using Aquarius active and passive L-band microwave observations

AU - Wang, Qiang

AU - van der Velde, R.

AU - Ferrazzoli, Paolo

AU - Chen, Xuelong

AU - Bai, Xiaojing

AU - Su, Zhongbo

PY - 2019/5/1

Y1 - 2019/5/1

N2 - An algorithm is developed for retrieving soil moisture at plateau scale by combined usage of Aquarius active and passive L-band observations. In this algorithm, Look-Up-Tables (LUTs) are established for bare soil and vegetated areas by using the physical based Tor Vergata discrete electromagnetic model (hereafter, TV-DEM). In the case of vegetated area, the LUT is built based on simulations with varying soil moisture and Leaf Area Index (LAI). Only soil moisture is variable for the bare soil case, and values calibrated in previous works are adopted for the other TV-DEM parameters. Soil moisture is then retrieved by minimizing a squared difference object function based on the emissivity and backscatter coefficient observed by Aquarius and the corresponding TV-DEM simulations included in the LUT. The soil moisture retrievals are assessed at Aquarius footprint scale using in-situ measurements collected at three regional scale networks spread across the Tibetan Plateau. The unbiased root mean squared differences (ubRMSDs) from the three networks vary from 0.016 to 0.050 m 3 m −3 and coefficients of determination (R 2 ) are from 0.274 to 0.499 (-). This ubRMSD and R 2 is in the same order of the passive-only official Aquarius product, Metop-A Advanced SCATterometer (ASCAT) L2 soil moisture product (hereafter ASCAT) as well as reanalysis data generated by European Centre for Medium-Range Weather Forecasts (hereafter, ERA-Interim). At Plateau-scale, all four soil moisture products capture the seasonal trend, whereby the dynamic range during the monsoon season captured by the ERA-Interim product is relatively small. Further, the northwest-southeast dry-wet gradient due to precipitation and evapotranspiration is well captured by the soil moisture spatial distributions produced by TV-DEM Aquarius, official Aquarius and ASCAT products, but less pronounced in the ERA-Interim product. This study demonstrates that the TV-DEM based algorithm can be used to retrieve soil moisture over a Plateau scale with robust results in terms of error statistics (e.g. bias, R 2 and ubRMSD) and can generate realistic spatial patterns for soil moisture at Plateau-scale.

AB - An algorithm is developed for retrieving soil moisture at plateau scale by combined usage of Aquarius active and passive L-band observations. In this algorithm, Look-Up-Tables (LUTs) are established for bare soil and vegetated areas by using the physical based Tor Vergata discrete electromagnetic model (hereafter, TV-DEM). In the case of vegetated area, the LUT is built based on simulations with varying soil moisture and Leaf Area Index (LAI). Only soil moisture is variable for the bare soil case, and values calibrated in previous works are adopted for the other TV-DEM parameters. Soil moisture is then retrieved by minimizing a squared difference object function based on the emissivity and backscatter coefficient observed by Aquarius and the corresponding TV-DEM simulations included in the LUT. The soil moisture retrievals are assessed at Aquarius footprint scale using in-situ measurements collected at three regional scale networks spread across the Tibetan Plateau. The unbiased root mean squared differences (ubRMSDs) from the three networks vary from 0.016 to 0.050 m 3 m −3 and coefficients of determination (R 2 ) are from 0.274 to 0.499 (-). This ubRMSD and R 2 is in the same order of the passive-only official Aquarius product, Metop-A Advanced SCATterometer (ASCAT) L2 soil moisture product (hereafter ASCAT) as well as reanalysis data generated by European Centre for Medium-Range Weather Forecasts (hereafter, ERA-Interim). At Plateau-scale, all four soil moisture products capture the seasonal trend, whereby the dynamic range during the monsoon season captured by the ERA-Interim product is relatively small. Further, the northwest-southeast dry-wet gradient due to precipitation and evapotranspiration is well captured by the soil moisture spatial distributions produced by TV-DEM Aquarius, official Aquarius and ASCAT products, but less pronounced in the ERA-Interim product. This study demonstrates that the TV-DEM based algorithm can be used to retrieve soil moisture over a Plateau scale with robust results in terms of error statistics (e.g. bias, R 2 and ubRMSD) and can generate realistic spatial patterns for soil moisture at Plateau-scale.

KW - Aquarius

KW - Combined active/passive microwave remote sensing

KW - Discrete electromagnetic model

KW - Soil moisture

KW - ITC-ISI-JOURNAL-ARTICLE

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JO - International Journal of Applied Earth Observation and Geoinformation (JAG)

JF - International Journal of Applied Earth Observation and Geoinformation (JAG)

SN - 1569-8432

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