A field experiment on microwave forest radiometry: L-band signal behaviour for varying conditions of surface wetness

Grant, Jennifer; Wigneron, Jean‐Pierre; Griend, Adriaan A. Van de; Kruszewski, Alain; Søbjærg, Sten Schmidl; Skou, N.

doi:10.1016/j.rse.2006.12.001

Cited by 89 publications

(62 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We found that clear spatial patterns could be distinguished in the global maps and could be associated with the main cover types (Table 2). It is important to note that the parameter is a complex synthetic parameter which accounts for many effects, such as surface roughness, soil moisture heterogeneities [18,67], vegetation litter in prairies and forests [41,60,67,68], topography [69], etc. These different effects occur over a large domain of spatial scales.…”

Section: Discussionmentioning

confidence: 99%

Global-Scale Evaluation of Roughness Effects on C-Band AMSR-E Observations

Wang

Wigneron²,

Jiang

et al. 2015

Remote Sensing

View full text Add to dashboard Cite

Quantifying roughness effects on ground surface emissivity is an important step in obtaining high-quality soil moisture products from large-scale passive microwave sensors. In this study, we used a semi-empirical method to evaluate roughness effects (parameterized here by the parameter) on a global scale from AMSR-E (Advanced Microwave Scanning Radiometer for EOS) observations. AMSR-E brightness temperatures at 6.9 GHz obtained from January 2009 to September 2011, together with estimations of soil moisture from the SMOS (Soil Moisture and Ocean Salinity) L3 products and of soil temperature from ECMWF's (European Centre for Medium-range Weather Forecasting) were used as inputs in a retrieval process. In the first step, we retrieved a parameter (referred to as the * parameter) accounting for the combined effects of roughness and vegetation. Then, global MODIS NDVI

show abstract

Section: Discussionmentioning

confidence: 99%

Global-Scale Evaluation of Roughness Effects on C-Band AMSR-E Observations

Wang

Wigneron²,

Jiang

et al. 2015

Remote Sensing

View full text Add to dashboard Cite

show abstract

“…In particular, under wet conditions, litter acts as an absorber and as a significant source of radiation in addition to the underlying soil. The "Bray 2004" L-band radiometry campaign [15], which was conducted in the coniferous forest of Les Landes near Bordeaux, France, corroborated the semitransparency of the forest canopy. Although the horizontally polarized brightness was predominantly affected by the physical temperature, a marginal correlation with simultaneously measured soil and litter moisture was identified.…”

Section: Introductionmentioning

confidence: 87%

“…However, this assumption might be false for other types of litter, leading to significantly slower drying, as observed for the litter present on the ground of coniferous forests [15].…”

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

View full text Add to dashboard Cite

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.

show abstract

“…The land cover specific L-MEB parameters used for the modelling are summarised in Table 1, they are in line with the parameters used by Wigneron et al (2007), and Grant et al (2007) and have been taken from a compilation of parameterisations of L-MEB based on experimental studies (J.-P. Wigneron, personal communication, 2007) that forms the basis of the SMOS L2 processor parameterisation. These parameters agree mostly with the default parameters that are being used in the operational version of the SMOS L2 processor for Central European Crops .…”

Section: Radiative Transfer Model L-mebmentioning

confidence: 99%

Analysis of SMOS brightness temperature and vegetation optical depth data with coupled land surface and radiative transfer models in Southern Germany

Schlenz¹,

Dall'Amico²,

Mauser³

et al. 2012

Hydrol. Earth Syst. Sci.

View full text Add to dashboard Cite

Abstract. Soil Moisture and Ocean Salinity (SMOS) L1c brightness temperature and L2 optical depth data are analysed with a coupled land surface (PROMET) and radiative transfer model (L-MEB). The coupled models are validated with ground and airborne measurements under contrasting soil moisture, vegetation and land surface temperature conditions during the SMOS Validation Campaign in May and June 2010 in the SMOS test site Upper Danube Catchment in southern Germany. The brightness temperature root-meansquared errors are between 6 K and 9 K. The L-MEB parameterisation is considered appropriate under local conditions even though it might possibly be further optimised. SMOS L1c brightness temperature data are processed and analysed in the Upper Danube Catchment using the coupled models in 2011 and during the SMOS Validation Campaign 2010 together with airborne L-band brightness temperature data. Only low to fair correlations are found for this comparison (R between 0.1-0.41). SMOS L1c brightness temperature data do not show the expected seasonal behaviour and are positively biased. It is concluded that RFI is responsible for a considerable part of the observed problems in the SMOS data products in the Upper Danube Catchment. This is consistent with the observed dry bias in the SMOS L2 soil moisture products which can also be related to RFI. It is confirmed that the brightness temperature data from the lower SMOS look angles and the horizontal polarisation are less reliable. This information could be used to improve the brightness temperature data filtering before the soil moisture retrieval. SMOS L2 optical depth values have been compared to modelled data and are not considered a reliable source of information about vegetation due to missing seasonal behaviour and a very high mean value. A fairly strong correlation between SMOS L2 soil moisture and optical depth was found (R = 0.65) even though the two variables are considered independent in the study area. The value of coupled models as a tool for the analysis of passive microwave remote-sensing data is demonstrated by extending this SMOS data analysis from a few days during a field campaign to a longer term comparison.

show abstract

A field experiment on microwave forest radiometry: L-band signal behaviour for varying conditions of surface wetness

Cited by 89 publications

References 22 publications

Global-Scale Evaluation of Roughness Effects on C-Band AMSR-E Observations

Global-Scale Evaluation of Roughness Effects on C-Band AMSR-E Observations

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

Analysis of SMOS brightness temperature and vegetation optical depth data with coupled land surface and radiative transfer models in Southern Germany

Contact Info

Product

Resources

About