Limits...
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.


Relative soil moisture measured at 5 cm depth at 20 time domain reflectometry (TDR) stations within the REMEDHUS network and their mean (bold black diamonds) in the period 2003-2005.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3927501&req=5

f2-sensors-08-01174: Relative soil moisture measured at 5 cm depth at 20 time domain reflectometry (TDR) stations within the REMEDHUS network and their mean (bold black diamonds) in the period 2003-2005.

Mentions: Soil moisture data from the 20 soil probes installed at 5 cm of the REMEDHUS network are plotted in time together with the spatial mean in Figure 2. It can be seen that the temporal variation of the soil moisture values at individual stations to a large extent follows that of the mean soil moisture. However, the absolute values and dynamic ranges differ from station to station. These observations are confirmed by Figure 3 which shows scatter plots of point scale soil moisture, θp, versus regional scale soil moisture, θr, for three selected stations of the REMEDHUS network. One can see that a linear downscaling model as given by Equation (5) is quite appropriate for describing the soil moisture scaling properties. The results for all TDR stations are summarized in Table 1. It is found that the coefficient of determination is in general relatively high with a mean value of 0.75. The standard error of estimate is on average only 5 % relative soil moisture. Therefore it can be concluded that the linear downscaling model (5) is well suited for connecting the point scale to the regional scale ℛ. By mathematical deduction it is also possible to confirm the suitability of Equation (13) to connect the local (ℒ) and regional (ℛ) scale (section 2.2.).


Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)
Relative soil moisture measured at 5 cm depth at 20 time domain reflectometry (TDR) stations within the REMEDHUS network and their mean (bold black diamonds) in the period 2003-2005.
© Copyright Policy
Related In: Results  -  Collection

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

f2-sensors-08-01174: Relative soil moisture measured at 5 cm depth at 20 time domain reflectometry (TDR) stations within the REMEDHUS network and their mean (bold black diamonds) in the period 2003-2005.
Mentions: Soil moisture data from the 20 soil probes installed at 5 cm of the REMEDHUS network are plotted in time together with the spatial mean in Figure 2. It can be seen that the temporal variation of the soil moisture values at individual stations to a large extent follows that of the mean soil moisture. However, the absolute values and dynamic ranges differ from station to station. These observations are confirmed by Figure 3 which shows scatter plots of point scale soil moisture, θp, versus regional scale soil moisture, θr, for three selected stations of the REMEDHUS network. One can see that a linear downscaling model as given by Equation (5) is quite appropriate for describing the soil moisture scaling properties. The results for all TDR stations are summarized in Table 1. It is found that the coefficient of determination is in general relatively high with a mean value of 0.75. The standard error of estimate is on average only 5 % relative soil moisture. Therefore it can be concluded that the linear downscaling model (5) is well suited for connecting the point scale to the regional scale ℛ. By mathematical deduction it is also possible to confirm the suitability of Equation (13) to connect the local (ℒ) and regional (ℛ) scale (section 2.2.).

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.