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Validation of SMOS soil moisture products over the Maqu and Twente regions.

Dente L, Su Z, Wen J - Sensors (Basel) (2012)

Bottom Line: However, the validation analysis resulted in determination coefficients of 0.55 and 0.51 over the Maqu and Twente region, respectively, for the ascending pass data, and of 0.24 and 0.41, respectively, for the descending pass data.Moreover, a systematic dry bias of the SMOS soil moisture was found of approximately 0.13 m(3)/m(3) for the Maqu region and 0.17 m(3)/m(3) for the Twente region for ascending pass data.Several factors might have affected the retrieval accuracy, such as the presence of Radio Frequency Interference (RFI), the use of inaccurate land cover information and the presence of frozen soils not correctly detected in winter.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Hengelosestraat 99, 7514AE Enschede, The Netherlands. dente@itc.nl

ABSTRACT
The validation of Soil Moisture and Ocean Salinity (SMOS) soil moisture products is a crucial step in the investigation of their inaccuracies and limitations, before planning further refinements of the retrieval algorithm. Therefore, this study intended to contribute to the validation of the SMOS soil moisture products, by comparing them with the data collected in situ in the Maqu (China) and Twente (The Netherlands) regions in 2010. The seasonal behavior of the SMOS soil moisture products is generally in agreement with the in situ measurements for both regions. However, the validation analysis resulted in determination coefficients of 0.55 and 0.51 over the Maqu and Twente region, respectively, for the ascending pass data, and of 0.24 and 0.41, respectively, for the descending pass data. Moreover, a systematic dry bias of the SMOS soil moisture was found of approximately 0.13 m(3)/m(3) for the Maqu region and 0.17 m(3)/m(3) for the Twente region for ascending pass data. Several factors might have affected the retrieval accuracy, such as the presence of Radio Frequency Interference (RFI), the use of inaccurate land cover information and the presence of frozen soils not correctly detected in winter. Improving the RFI filtering method and the quality of the retrieval algorithm inputs, such as land surface temperature and land cover, would certainly improve the accuracy of the retrieved soil moisture.

No MeSH data available.


Related in: MedlinePlus

Color composite (R: band 4—G: band 5—B: band 1) of a Landsat 5TM image over the Maqu region (short vegetation in green, light brown and orange; forested areas in shades of reds and dark browns; urbanized areas in cyan; water bodies in dark blue). The location of the monitored sites is indicated by a white rectangle and the centre of the SMOS nodes by a white cross.
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f1-sensors-12-09965: Color composite (R: band 4—G: band 5—B: band 1) of a Landsat 5TM image over the Maqu region (short vegetation in green, light brown and orange; forested areas in shades of reds and dark browns; urbanized areas in cyan; water bodies in dark blue). The location of the monitored sites is indicated by a white rectangle and the centre of the SMOS nodes by a white cross.

Mentions: The Maqu soil moisture monitoring network was set up in July 2008 on the north-eastern fringe of the Tibetan Plateau (33°30′–34°15′N, 101°38′–102°45′E), located in the southern part of Maqu county, on the border between Gansu and Sichuan provinces in China. A detailed description of the network is reported in Dente et al., [6] and in Su et al., [7]. The network is located at the first major bend in the Yellow River, where the landscape is characterised by the large river valley and surrounding hills with an elevation ranging from 3,200 m to 4,200 m a.s.l. The Maqu region is shown in Figure 1 by a Landsat 5TM image collected in September 2007, with the locations of the monitored sites highlighted as white rectangles. The land cover consists of uniform short grassland with silt loam soils and the wetlands cover a large part of the valley. The climate is characterised by dry and cold winters (November–March) and by a rainy and relatively warmer monsoon season (April–October). Soil moisture and soil temperature are continuously measured by means of EC-TM ECH2O probes (Decagon Devices, Inc., USA) at a depth of 5 cm (and in deeper layers) at 20 sites every 15 min. The monitoring sites are distributed over an area of approximately 40 km × 80 km and are characterised by a variety of altitudes and slopes and differing soil characteristics. The network set up ensures that the soil moisture spatial variability of the Maqu region is well monitored, and the spatial average of the measurements collected at each site can be considered an accurate indicator of the soil moisture dynamics at the network scale, as shown in [6].


Validation of SMOS soil moisture products over the Maqu and Twente regions.

Dente L, Su Z, Wen J - Sensors (Basel) (2012)

Color composite (R: band 4—G: band 5—B: band 1) of a Landsat 5TM image over the Maqu region (short vegetation in green, light brown and orange; forested areas in shades of reds and dark browns; urbanized areas in cyan; water bodies in dark blue). The location of the monitored sites is indicated by a white rectangle and the centre of the SMOS nodes by a white cross.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472810&req=5

f1-sensors-12-09965: Color composite (R: band 4—G: band 5—B: band 1) of a Landsat 5TM image over the Maqu region (short vegetation in green, light brown and orange; forested areas in shades of reds and dark browns; urbanized areas in cyan; water bodies in dark blue). The location of the monitored sites is indicated by a white rectangle and the centre of the SMOS nodes by a white cross.
Mentions: The Maqu soil moisture monitoring network was set up in July 2008 on the north-eastern fringe of the Tibetan Plateau (33°30′–34°15′N, 101°38′–102°45′E), located in the southern part of Maqu county, on the border between Gansu and Sichuan provinces in China. A detailed description of the network is reported in Dente et al., [6] and in Su et al., [7]. The network is located at the first major bend in the Yellow River, where the landscape is characterised by the large river valley and surrounding hills with an elevation ranging from 3,200 m to 4,200 m a.s.l. The Maqu region is shown in Figure 1 by a Landsat 5TM image collected in September 2007, with the locations of the monitored sites highlighted as white rectangles. The land cover consists of uniform short grassland with silt loam soils and the wetlands cover a large part of the valley. The climate is characterised by dry and cold winters (November–March) and by a rainy and relatively warmer monsoon season (April–October). Soil moisture and soil temperature are continuously measured by means of EC-TM ECH2O probes (Decagon Devices, Inc., USA) at a depth of 5 cm (and in deeper layers) at 20 sites every 15 min. The monitoring sites are distributed over an area of approximately 40 km × 80 km and are characterised by a variety of altitudes and slopes and differing soil characteristics. The network set up ensures that the soil moisture spatial variability of the Maqu region is well monitored, and the spatial average of the measurements collected at each site can be considered an accurate indicator of the soil moisture dynamics at the network scale, as shown in [6].

Bottom Line: However, the validation analysis resulted in determination coefficients of 0.55 and 0.51 over the Maqu and Twente region, respectively, for the ascending pass data, and of 0.24 and 0.41, respectively, for the descending pass data.Moreover, a systematic dry bias of the SMOS soil moisture was found of approximately 0.13 m(3)/m(3) for the Maqu region and 0.17 m(3)/m(3) for the Twente region for ascending pass data.Several factors might have affected the retrieval accuracy, such as the presence of Radio Frequency Interference (RFI), the use of inaccurate land cover information and the presence of frozen soils not correctly detected in winter.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Hengelosestraat 99, 7514AE Enschede, The Netherlands. dente@itc.nl

ABSTRACT
The validation of Soil Moisture and Ocean Salinity (SMOS) soil moisture products is a crucial step in the investigation of their inaccuracies and limitations, before planning further refinements of the retrieval algorithm. Therefore, this study intended to contribute to the validation of the SMOS soil moisture products, by comparing them with the data collected in situ in the Maqu (China) and Twente (The Netherlands) regions in 2010. The seasonal behavior of the SMOS soil moisture products is generally in agreement with the in situ measurements for both regions. However, the validation analysis resulted in determination coefficients of 0.55 and 0.51 over the Maqu and Twente region, respectively, for the ascending pass data, and of 0.24 and 0.41, respectively, for the descending pass data. Moreover, a systematic dry bias of the SMOS soil moisture was found of approximately 0.13 m(3)/m(3) for the Maqu region and 0.17 m(3)/m(3) for the Twente region for ascending pass data. Several factors might have affected the retrieval accuracy, such as the presence of Radio Frequency Interference (RFI), the use of inaccurate land cover information and the presence of frozen soils not correctly detected in winter. Improving the RFI filtering method and the quality of the retrieval algorithm inputs, such as land surface temperature and land cover, would certainly improve the accuracy of the retrieved soil moisture.

No MeSH data available.


Related in: MedlinePlus