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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.


Same as Figure 1 but for the Twente region.
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f2-sensors-12-09965: Same as Figure 1 but for the Twente region.

Mentions: The Twente soil moisture monitoring network is located in the eastern part of the Overijssel province in The Netherlands, mainly covering the region called Twente, but also part of the Salland region and the Gelderland province (52°05′–52°27′N, 6°05′–7°00′E). The region is flat, with an elevation ranging between 3 m to 50 m a.s.l. The most extensively occurring land cover is grassland for pasture which is harvested and fertilized several times a year. However, the land use of this region also includes a mosaic of agricultural fields, forest patches and several urban areas. A Landsat 5TM image collected in June 2010 of the Twente region is shown in Figure 2, with the locations of the monitored sites highlighted as white rectangles. The main crop is corn, which is planted in April and harvested in September. In this region, the soil texture of the surface layer is mainly sand and loamy sand. Soil moisture and soil temperature have been continuously monitored since July 2009 at 20 sites, spread across an area of approximately 50 km × 40 km at a depth of 5 cm every 15 min. The sites were selected in order to monitor the area extensively for a variety of soil types and land covers. However, one of the main factors affecting the spatial variability of soil moisture in this area, besides land cover, is the ground water table. Due to groundwater management occurring in this region, the groundwater table may rise to 25 cm below the soil surface as well as drop to below 160 cm. EC-TM ECH2O probes (Decagon Devices, Inc., USA) are used to measure the soil moisture and temperature at 5 cm depth, as well as in deeper layers. A detailed description of the network and the dataset is reported in Dente et al., [9].


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

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

Same as Figure 1 but for the Twente region.
© Copyright Policy
Related In: Results  -  Collection

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

f2-sensors-12-09965: Same as Figure 1 but for the Twente region.
Mentions: The Twente soil moisture monitoring network is located in the eastern part of the Overijssel province in The Netherlands, mainly covering the region called Twente, but also part of the Salland region and the Gelderland province (52°05′–52°27′N, 6°05′–7°00′E). The region is flat, with an elevation ranging between 3 m to 50 m a.s.l. The most extensively occurring land cover is grassland for pasture which is harvested and fertilized several times a year. However, the land use of this region also includes a mosaic of agricultural fields, forest patches and several urban areas. A Landsat 5TM image collected in June 2010 of the Twente region is shown in Figure 2, with the locations of the monitored sites highlighted as white rectangles. The main crop is corn, which is planted in April and harvested in September. In this region, the soil texture of the surface layer is mainly sand and loamy sand. Soil moisture and soil temperature have been continuously monitored since July 2009 at 20 sites, spread across an area of approximately 50 km × 40 km at a depth of 5 cm every 15 min. The sites were selected in order to monitor the area extensively for a variety of soil types and land covers. However, one of the main factors affecting the spatial variability of soil moisture in this area, besides land cover, is the ground water table. Due to groundwater management occurring in this region, the groundwater table may rise to 25 cm below the soil surface as well as drop to below 160 cm. EC-TM ECH2O probes (Decagon Devices, Inc., USA) are used to measure the soil moisture and temperature at 5 cm depth, as well as in deeper layers. A detailed description of the network and the dataset is reported in Dente et al., [9].

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.