Effect of surface roughness on the microwave emission from soils

Choudhury, Bhaskar J.; Schmugge, Thomas J.; Chang, A. T. C.; Newton, R. W.

doi:10.1029/jc084ic09p05699

Cited by 532 publications

(312 citation statements)

References 8 publications

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“…The dielectric constants were calculated using [20] based on the soil texture and density and an assumed salinity of 2 ppt for the soil water, which is reasonable for irrigated soils. A minimal value of 0.1 was assumed for the roughness parameter to account for the effects of surface roughness on the emission [21]. The results of the calculation are presented in Fig.…”

Section: ) Prediction Using a Radiative Transfer Modelmentioning

confidence: 95%

Soil water infiltration observation with microwave radiometers

Jackson¹,

Schmugge

O'Neill³

et al. 1998

IEEE Trans. Geosci. Remote Sensing

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Abstract-Experiments were conducted using truck-based microwave radiometers operating at 1.41-(L-band) and 2.65-GHz (S-band) horizontal polarization to observe small plots during and following sprinkler irrigation. These experiments were conducted on a sandy loam soil in 1994 and a silt loam in 1995. Sandy loam soils typically have higher infiltration capabilities than clays, and in our studies, we were not able to exceed this with the irri-

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Section: ) Prediction Using a Radiative Transfer Modelmentioning

confidence: 95%

Soil water infiltration observation with microwave radiometers

Jackson¹,

Schmugge

O'Neill³

et al. 1998

IEEE Trans. Geosci. Remote Sensing

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“…Inversion for the soil roughness parameter HR from 10 radiometer measurements above the soil-only setup (Step 2 of the layer experiment, see Figure 4) gave a value of 0.49, which corresponds to a standard deviation of the surface height σR of 0.012 m based on the formulation proposed by Choudhury et al [34] or a σR of 0.013 m if we used the formulation of Wigneron et al [12]. It should be noted that the inversion was performed in a large parameter space (0 < HR < 1), which ensured finding the global optimum.…”

Section: Soil Roughness Parametermentioning

confidence: 98%

Passive L-Band Microwave Remote Sensing of Organic Soil Surface Layers: A Tower-Based Experiment

et al. 2018

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Organic soils play a key role in global warming because they store large amount of soil carbon which might be degraded with changing soil temperatures or soil water contents. There is thus a strong need to monitor these soils and, in particular, their hydrological characteristics using, for instance, space-borne L-band brightness temperature observations. However, there are still open issues with respect to soil moisture retrieval techniques over organic soils. In view of this, organic soil blocks with their vegetation cover were collected from a heathland in the Skjern River catchment in western Denmark and then transported to a remote sensing field laboratory in Germany where their structure was reconstituted. The controlled conditions at this field laboratory made it possible to perform tower-based L-band radiometer measurements of the soils over a period of two months. Brightness temperature data were inverted using a radiative transfer (RT) model for estimating the time variations in the soil dielectric permittivity and the vegetation optical depth. In addition, the effective vegetation scattering albedo parameter of the RT model was retrieved based on a two-step inversion approach. The remote estimations of the dielectric permittivity were compared to in situ measurements. The results indicated that the radiometer-derived dielectric permittivities were significantly correlated with the in situ measurements, but their values were systematically lower compared to the in situ ones. This could be explained by the difference between the operating frequency of the L-band radiometer (1.4 GHz) and that of the in situ sensors (70 MHz). The effective vegetation scattering albedo parameter was found to be polarization dependent. While the scattering effect within the vegetation could be neglected at horizontal polarization, it was found to be important at vertical polarization. The vegetation optical depth estimated values over time oscillated between 0.10 and 0.19 with a mean value of 0.13. This study provides further insights into the characterization of the L-band brightness temperature signatures of organic soil surface layers and, in particular, into the parametrization of the RT model for these specific soils. Therefore, the results of this study are expected to improve the performance of space-borne remote sensing soil moisture products over areas dominated by organic soils.

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“…Nonetheless, several simulations were performed to evaluate the differences with other methods: Rayleigh approximation for an ideal needle ( Figure A2a), Rayleigh approximation for a needle (Figure A2b), and the GRG approximation for a needle ( Figure A2c). Additionally, the leaves-soil scattering mechanism was evaluated using the same scattering methods for the leaves, and the Choudhury method [35] to account for the electromagnetic interaction with the soil (Figures A2d-f). These simulations show that there are several differences: (a) A larger dynamic range of the co-polar reflectivity over leaves using the GRG method (~30 dB) as compared to that obtained with the Rayleigh approximation for an ideal needle (~20 dB); and (b) both the cross-and the co-polar reflectivities for leaves-soil interactions.…”

Section: Discussionmentioning

confidence: 99%

“…A much lower tree density for a biomass density of 100 t/ha (725 trees/ha instead ~2,700 trees/ha as in [32] for a tree height ~20 m) was required to make the simulations feasible. The electromagnetic models selected for the expression of the bistatic scattering matrices were the Semi-Exact solution for the branches S [33], the Generalized Rayleigh-Gans (GRG) approximation for a needle in the case of leaves S [34], and the Choudhury method for the soil S [35]. The Semi-Exact solution was selected because the radii of curvature of the branches of Northern Sweden forests is not an order of magnitude larger than the signals wavelength used in the simulations (λ = 19 cm).…”

Section: Discussionmentioning

confidence: 99%

“…Since the specular reflection point changes with time, the values of the electric fields in Equation (A2) are also a function of time.The Choudhury method [35] is used to simulate the direct scattering of the GPS signals E over the ground surface. To the first order of approximation, the scattering from every type of forest element is approximated by the superposition of the scattered field from each scatterer within the tree structure.…”

Section: Part Ii: Theoretical Electromagnetic Modelmentioning

confidence: 99%

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First Polarimetric GNSS-R Measurements from a Stratospheric Flight over Boreal Forests

et al. 2015

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Abstract:The first-ever dual-frequency multi-constellation Global Navigation Satellite Systems Reflectometry (GNSS-R) polarimetric measurements over boreal forests and lakes from the stratosphere are presented. Data were collected during the Swedish National Space Board (SNSB)/European Space Agency (ESA) sponsored Balloon Experiments for University Students (BEXUS) 19 stratospheric balloon experiment using the P(Y) and C/A ReflectOmeter (PYCARO) instrument operated in closed-loop mode. Maps of the polarimetric ratio for L1 and L2 Global Positioning System (GPS) and GLObal Navigation Satellite System (GLONASS), and for E1 Galileo signals are derived from the float phase at 27,000 m height, and the specular points are geolocalized on the Earth's surface. Polarimetric ratio (Γ /Γ ) maps over boreal forests are shown to be in the range 2-16 dB for the different GNSS codes. This result suggests that the scattering is taking place not only over the soil, but over the different forests elements as well. Additionally to the interpretation of the experimental results a theoretical investigation of the different contributions to the total reflectivity over boreal forests is performed using a bistatic scattering model. The simulated cross-(reflected Left Hand Circular Polarization LHCP) and co-polar (reflected Right Hand Circular Polarization RHCP) reflectivities are evaluated for the soil, the canopy, and the canopy-soil interactions for three different biomass densities: 725 trees/ha, 150 trees/ha and 72 trees/ha. For elevation angles larger than the Brewster angle, it is found that the cross-polar OPEN ACCESSRemote Sens. 2015, 7 13121 signal is dominant when just single reflections over the forests are evaluated, while in the case of multiple reflections the co-polar signal becomes the largest one.

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Effect of surface roughness on the microwave emission from soils

Cited by 532 publications

References 8 publications

Soil water infiltration observation with microwave radiometers

Soil water infiltration observation with microwave radiometers

Passive L-Band Microwave Remote Sensing of Organic Soil Surface Layers: A Tower-Based Experiment

First Polarimetric GNSS-R Measurements from a Stratospheric Flight over Boreal Forests

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