Abstract
Knowing the exact sampling depth of microwave radiometry is essential for quantifying the performance and appreciation of the applicability of satellite soil moisture products. We investigate in this study the sampling depth (δ SM ) of the L-band microwave emission under frozen and thawed soil conditions on the Tibetan Plateau. Two years of diurnal brightness temperature (T B p ) measurements at a time interval of 30 min are collected by the ELBARA-III radiometer deployed at a Tibetan meadow site. Vertical profiles of soil temperature and volumetric liquid water content (θ liq ) are measured simultaneously at soil depths up to 1 m below the surface. The impact of the θ liq measured at different depths on the microwave emission simulations is assessed using the τ-ω emission model, whereby the permittivity of frozen and thawed soil is estimated by the four-phase dielectric mixing model. It is found that: 1) the sampling depth for the effective temperature depends on the magnitude of θ liq , and is estimated to be, on average, about 50 and 15 cm for the cold dry and wet warm period, respectively, because of the seasonality in θ liq ; 2) the δ SM is determined at 2.5 cm for both frozen and thawed soil conditions during both cold and warm periods, which is shallower than the commonly used θ liq measurement depth (i.e. 5 cm) adopted for the in-situ monitoring networks across the globe; 3) the T B p simulations performed with the θ liq measurements taken at the estimated δ SM of 2.5 cm result in lower unbiased root mean squared errors, about 14% (3.16 K) and 22% (3.36 K) for the horizontal and vertical polarizations respectively, in comparison to the simulations with the θ liq measurements taken from 5 cm soil depth; and 4) the θ liq retrieved with the single channel algorithm from the ELBARA-III measured vertically polarized T B p are in better agreement with the θ liq measured at 2.5 cm than the one measured at 5 cm. These findings are crucial for developing strategies for the calibration/validation as well as the application of satellite based soil moisture products relying on the L-band radiometry.
| Original language | English |
|---|---|
| Pages (from-to) | 16-25 |
| Number of pages | 10 |
| Journal | Remote sensing of environment |
| Volume | 226 |
| Early online date | 1 Apr 2019 |
| DOIs | |
| Publication status | Published - 1 Jun 2019 |
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Keywords
- Diurnal variations
- Grassland
- L-band radiometry
- Sampling depth
- Soil Moisture Active Passive (SMAP)
- Soil Moisture and Ocean Salinity (SMOS)
- ITC-ISI-JOURNAL-ARTICLE
Cite this
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Sampling depth of L-band radiometer measurements of soil moisture and freeze-thaw dynamics on the Tibetan Plateau. / Zheng, Donghai (Corresponding Author); Li, Xin; Wang, Xin; Wang, Zuoliang; Wen, Jun; van der Velde, R.; Schwank, Mike; Su, Zhongbo.
In: Remote sensing of environment, Vol. 226, 01.06.2019, p. 16-25.Research output: Contribution to journal › Article › Academic › peer-review
TY - JOUR
T1 - Sampling depth of L-band radiometer measurements of soil moisture and freeze-thaw dynamics on the Tibetan Plateau
AU - Zheng, Donghai
AU - Li, Xin
AU - Wang, Xin
AU - Wang, Zuoliang
AU - Wen, Jun
AU - van der Velde, R.
AU - Schwank, Mike
AU - Su, Zhongbo
PY - 2019/6/1
Y1 - 2019/6/1
N2 - Knowing the exact sampling depth of microwave radiometry is essential for quantifying the performance and appreciation of the applicability of satellite soil moisture products. We investigate in this study the sampling depth (δ SM ) of the L-band microwave emission under frozen and thawed soil conditions on the Tibetan Plateau. Two years of diurnal brightness temperature (T B p ) measurements at a time interval of 30 min are collected by the ELBARA-III radiometer deployed at a Tibetan meadow site. Vertical profiles of soil temperature and volumetric liquid water content (θ liq ) are measured simultaneously at soil depths up to 1 m below the surface. The impact of the θ liq measured at different depths on the microwave emission simulations is assessed using the τ-ω emission model, whereby the permittivity of frozen and thawed soil is estimated by the four-phase dielectric mixing model. It is found that: 1) the sampling depth for the effective temperature depends on the magnitude of θ liq , and is estimated to be, on average, about 50 and 15 cm for the cold dry and wet warm period, respectively, because of the seasonality in θ liq ; 2) the δ SM is determined at 2.5 cm for both frozen and thawed soil conditions during both cold and warm periods, which is shallower than the commonly used θ liq measurement depth (i.e. 5 cm) adopted for the in-situ monitoring networks across the globe; 3) the T B p simulations performed with the θ liq measurements taken at the estimated δ SM of 2.5 cm result in lower unbiased root mean squared errors, about 14% (3.16 K) and 22% (3.36 K) for the horizontal and vertical polarizations respectively, in comparison to the simulations with the θ liq measurements taken from 5 cm soil depth; and 4) the θ liq retrieved with the single channel algorithm from the ELBARA-III measured vertically polarized T B p are in better agreement with the θ liq measured at 2.5 cm than the one measured at 5 cm. These findings are crucial for developing strategies for the calibration/validation as well as the application of satellite based soil moisture products relying on the L-band radiometry.
AB - Knowing the exact sampling depth of microwave radiometry is essential for quantifying the performance and appreciation of the applicability of satellite soil moisture products. We investigate in this study the sampling depth (δ SM ) of the L-band microwave emission under frozen and thawed soil conditions on the Tibetan Plateau. Two years of diurnal brightness temperature (T B p ) measurements at a time interval of 30 min are collected by the ELBARA-III radiometer deployed at a Tibetan meadow site. Vertical profiles of soil temperature and volumetric liquid water content (θ liq ) are measured simultaneously at soil depths up to 1 m below the surface. The impact of the θ liq measured at different depths on the microwave emission simulations is assessed using the τ-ω emission model, whereby the permittivity of frozen and thawed soil is estimated by the four-phase dielectric mixing model. It is found that: 1) the sampling depth for the effective temperature depends on the magnitude of θ liq , and is estimated to be, on average, about 50 and 15 cm for the cold dry and wet warm period, respectively, because of the seasonality in θ liq ; 2) the δ SM is determined at 2.5 cm for both frozen and thawed soil conditions during both cold and warm periods, which is shallower than the commonly used θ liq measurement depth (i.e. 5 cm) adopted for the in-situ monitoring networks across the globe; 3) the T B p simulations performed with the θ liq measurements taken at the estimated δ SM of 2.5 cm result in lower unbiased root mean squared errors, about 14% (3.16 K) and 22% (3.36 K) for the horizontal and vertical polarizations respectively, in comparison to the simulations with the θ liq measurements taken from 5 cm soil depth; and 4) the θ liq retrieved with the single channel algorithm from the ELBARA-III measured vertically polarized T B p are in better agreement with the θ liq measured at 2.5 cm than the one measured at 5 cm. These findings are crucial for developing strategies for the calibration/validation as well as the application of satellite based soil moisture products relying on the L-band radiometry.
KW - Diurnal variations
KW - Grassland
KW - L-band radiometry
KW - Sampling depth
KW - Soil Moisture Active Passive (SMAP)
KW - Soil Moisture and Ocean Salinity (SMOS)
KW - ITC-ISI-JOURNAL-ARTICLE
UR - https://ezproxy2.utwente.nl/login?url=https://library.itc.utwente.nl/login/2019/isi/vandervelde_sam.pdf
UR - https://ezproxy2.utwente.nl/login?url=https://doi.org/10.1016/j.rse.2019.03.029
U2 - 10.1016/j.rse.2019.03.029
DO - 10.1016/j.rse.2019.03.029
M3 - Article
AN - SCOPUS:85063607073
VL - 226
SP - 16
EP - 25
JO - Remote sensing of environment
JF - Remote sensing of environment
SN - 0034-4257
ER -