L-band radiometer measurements of soil water under growing clover grass

Schwank, Mike; Mätzler, Christian; Guglielmetti, Massimo; Flühler, H.

doi:10.1109/tgrs.2005.855135

Cited by 44 publications

(37 citation statements)

References 27 publications

(46 reference statements)

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“…This indicates that the measures taken to avoid drying the leaves during storage were effective. However, compared with fresh green leaves (with typically m d = 0.15 kg · kg −1 [22]), the water contained in the dead leaves of a litter layer is considerably lower.…”

Section: Litter Preparationmentioning

confidence: 99%

Testing a New Model for the L-Band Radiation of Moist Leaf Litter

Schwank

Guglielmetti²,

Mätzler

et al. 2008

IEEE Trans. Geosci. Remote Sensing

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Abstract-The crown vegetation of a deciduous forest is known to be semitransparent at low microwave frequencies, and leaf litter covering the forest soil has been recognized to have a significant impact on ground emission. The proposed approach for modeling the L-band radiative transfer through leaf litter consists of an isotropic effective medium approach for the litter permittivities, a coherent radiative transfer model for computing the coherent reflectivities from dielectric depth profiles, and an averaging procedure for computing the reflectivities determining the field-scale brightness temperatures. Evaluations were performed for the case of leaf litter on top of a conducting wire grid (litter-grid formation) and for litter on underlying soil (litter-soil formation). A model sensitivity analysis was performed with respect to parameters characterizing litter thickness variations and boundary roughness. For the litter-soil formation, the model was rather sensitive to local irregularities at the air-to-litter boundary. Modeled microwave signatures reproduced the major features of the measurements performed on a site comprising a litter-grid formation. Under dry conditions, the investigated litter layer was nearly "invisible." When the same litter layer was wetted, it acted as an important radiation source to be taken into account for the quantitative remote soil moisture detection of forested areas. Under certain conditions, the simulations revealed an increasing brightness when the litter is wetted prior to the underlying soil. Further wetting of the litter-soil system then resulted in a decreasing brightness as expected for increased moisture. Such effects are important to know to avoid misleading interpretations of L-band signatures.

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Section: Litter Preparationmentioning

confidence: 99%

Testing a New Model for the L-Band Radiation of Moist Leaf Litter

Schwank

Guglielmetti²,

Mätzler

et al. 2008

IEEE Trans. Geosci. Remote Sensing

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“…At field sites, the effect of the vegetation cover on the microwave observations has been studied intensively. Saleh et al (2006) discovered a strong contribution of litter and wet canopy on the microwave emission and Schwank et al (2005) demonstrated the effects of vegetation structure change by studying microwave observations of clover grass prior and after a hail storm. However, these studies are all based on L-band microwave observations at field sites and the validity of these findings at global scale has yet to be shown.…”

Section: Introductionmentioning

confidence: 99%

Global Soil Moisture Patterns Observed by Space Borne Microwave Radiometers and Scatterometers

et al. 2008

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Within the scope of the upcoming launch of a new water related satellite mission (SMOS) a global evaluation study was performed on two available global soil moisture products. ERS scatterometer surface wetness data was compared to AMSR-E soil moisture data. This study pointed out a strong similarity between both products in sparse to moderate vegetated regions with an average correlation coefficient of 0.83. Low correlations were found in densely vegetated areas and deserts. The low values in the vegetated regions can be explained by the limited soil moisture retrieval capabilities over dense vegetation covers. Soil emission is attenuated by the canopy and tends to saturate the microwave signal with increasing vegetation density, resulting in a decreased sensor sensitivity to soil moisture variations. It is expected that the new low frequency satellite mission (SMOS) will obtain soil moisture products with a higher quality in these regions. The low correlations in the desert regions are likely due to volume scattering or to the dielectric dynamics within the soil. The volume scattering in dry soils causes a higher backscatter under very dry conditions than under conditions when the sub-surface soil layers are somewhat wet. In addition, at low moisture levels the dielectric constant has a reduced sensitivity in response to changes in the soil moisture content. At a global scale the spatial correspondence of both products is high and both products clearly distinguish similar regions with high seasonal and inter annual variations. Based on the global analyses we concluded that the quality of both products was comparable and in the sparse to

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“…Section 3 deals with the evaluation methods. Section 4 presents the results, which are discussed in Section 5, in particular the potential of L-VOD to 20 estimate AGB at large scale. Finally, Section 6 summarizes the results and presents the conclusions of this study.…”

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confidence: 99%

The high sensitivity of SMOS L-Band vegetation optical depth to biomass

Rodriguez‐fernandez¹,

Mialon²,

Mermoz³

et al. 2018

Preprint

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Abstract. The vegetation optical depth (VOD) measured at microwave frequencies is related to the vegetation water content and provides information complementary to visible/infra-red vegetation indices. This study is devoted to the characterisation of a new VOD data set obtained from SMOS (Soil Moisture and Ocean Salinity) satellite observations at L-band (1.4 GHz).Three different SMOS L-band VOD (L-VOD) data sets (SMOS Level 2, Level 3 and SMOS-IC) were compared with data sets on tree height, visible/infra-red indexes (NDVI, EVI), cumulated precipitation, and above ground biomass (AGB) for the 5 African continent. For all relationships, SMOS-IC showed the lowest dispersion and highest correlation. Overall, we found a strong (R > 0.85) correlation with no clear sign of saturation between L-VOD and four AGB data sets. The relationship linking L-VOD to tree height (R = 0.87) and Baccini's AGB (R = 0.94) was strong and linear. The relationships between L-VOD and three other AGB data sets were linear per land cover class, but with a changing slope depending on the land cover type. For low vegetation classes, the annual mean of L-VOD spans a range from 0 to 0.7 and it is linearly correlation with the amount of 10 the average annual precipitations. SMOS L-VOD showed a higher sensitivity to AGB as compared to NDVI and K/X/C-VOD (VOD measured, respectively, at 19, 10.7, and 6.9 GHz). The results showed that although the spatial resolution of L-VOD is coarse (∼ 40 km), the high temporal frequency and sensitivity to AGB makes SMOS L-VOD a very promising index for large scale monitoring of the vegetation status, in particular biomass.

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L-band radiometer measurements of soil water under growing clover grass

Cited by 44 publications

References 27 publications

Testing a New Model for the L-Band Radiation of Moist Leaf Litter

Testing a New Model for the L-Band Radiation of Moist Leaf Litter

Global Soil Moisture Patterns Observed by Space Borne Microwave Radiometers and Scatterometers

The high sensitivity of SMOS L-Band vegetation optical depth to biomass

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