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Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)

View Article: PubMed Central - PubMed

ABSTRACT

The high spatio-temporal variability of soil moisture is the result of atmospheric forcing and redistribution processes related to terrain, soil, and vegetation characteristics. Despite this high variability, many field studies have shown that in the temporal domain soil moisture measured at specific locations is correlated to the mean soil moisture content over an area. Since the measurements taken by Synthetic Aperture Radar (SAR) instruments are very sensitive to soil moisture it is hypothesized that the temporally stable soil moisture patterns are reflected in the radar backscatter measurements. To verify this hypothesis 73 Wide Swath (WS) images have been acquired by the ENVISAT Advanced Synthetic Aperture Radar (ASAR) over the REMEDHUS soil moisture network located in the Duero basin, Spain. It is found that a time-invariant linear relationship is well suited for relating local scale (pixel) and regional scale (50 km) backscatter. The observed linear model coefficients can be estimated by considering the scattering properties of the terrain and vegetation and the soil moisture scaling properties. For both linear model coefficients, the relative error between observed and modelled values is less than 5 % and the coefficient of determination (R2) is 86 %. The results are of relevance for interpreting and downscaling coarse resolution soil moisture data retrieved from active (METOP ASCAT) and passive (SMOS, AMSR-E) instruments.

No MeSH data available.


Scatterplots of observed and modelled backscatter scaling coefficients a (left) and b (right).
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f9-sensors-08-01174: Scatterplots of observed and modelled backscatter scaling coefficients a (left) and b (right).

Mentions: This can be more clearly observed in Figure 9 which shows scatter plots between observed and modelled coefficients. The smaller dynamic range is likely related to the fact that clr was set equal to zero and dlr equal to one in order to obtain the simplified models (24) and (25). Nevertheless, the high correlation between the observed and modelled coefficients (R2 = 0.86 for both a and b based on 67645 data points) and the low root mean square error (0.73 dB for a and 0.095 for b, which corresponds to a relative error of about 5 % in both cases) clearly show that the backscatter scaling model developed in section 2.2. describes the main physical phenomena very well.


Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)
Scatterplots of observed and modelled backscatter scaling coefficients a (left) and b (right).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3927501&req=5

f9-sensors-08-01174: Scatterplots of observed and modelled backscatter scaling coefficients a (left) and b (right).
Mentions: This can be more clearly observed in Figure 9 which shows scatter plots between observed and modelled coefficients. The smaller dynamic range is likely related to the fact that clr was set equal to zero and dlr equal to one in order to obtain the simplified models (24) and (25). Nevertheless, the high correlation between the observed and modelled coefficients (R2 = 0.86 for both a and b based on 67645 data points) and the low root mean square error (0.73 dB for a and 0.095 for b, which corresponds to a relative error of about 5 % in both cases) clearly show that the backscatter scaling model developed in section 2.2. describes the main physical phenomena very well.

View Article: PubMed Central - PubMed

ABSTRACT

The high spatio-temporal variability of soil moisture is the result of atmospheric forcing and redistribution processes related to terrain, soil, and vegetation characteristics. Despite this high variability, many field studies have shown that in the temporal domain soil moisture measured at specific locations is correlated to the mean soil moisture content over an area. Since the measurements taken by Synthetic Aperture Radar (SAR) instruments are very sensitive to soil moisture it is hypothesized that the temporally stable soil moisture patterns are reflected in the radar backscatter measurements. To verify this hypothesis 73 Wide Swath (WS) images have been acquired by the ENVISAT Advanced Synthetic Aperture Radar (ASAR) over the REMEDHUS soil moisture network located in the Duero basin, Spain. It is found that a time-invariant linear relationship is well suited for relating local scale (pixel) and regional scale (50 km) backscatter. The observed linear model coefficients can be estimated by considering the scattering properties of the terrain and vegetation and the soil moisture scaling properties. For both linear model coefficients, the relative error between observed and modelled values is less than 5 % and the coefficient of determination (R2) is 86 %. The results are of relevance for interpreting and downscaling coarse resolution soil moisture data retrieved from active (METOP ASCAT) and passive (SMOS, AMSR-E) instruments.

No MeSH data available.