@article{PAR00010735,
  title = {{V}alidation of {SMOS} {L}1{C} and {L}2 products and important parameters of the retrieval algorithm in the {S}kjern {R}iver catchment, {W}estern {D}enmark},
  author = {{B}ircher, {S}. and {S}kou, {N}. and {K}err, {Y}ann},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {S}oil {M}oisture and {O}cean {S}alinity ({SMOS}) satellite with a passive {L}-band radiometer monitors surface soil moisture. {I}n addition to soil moisture, vegetation optical thickness tau({NAD}) is retrieved ({L}2 product) from brightness temperatures ({T}-{B}, {L}1{C} product) using an algorithm based on the {L}-band {M}icrowave {E}mission of the {B}iosphere ({L}-{MEB}) model with initial guesses on the two parameters (derived from {ECMWF} products and {ECOCLIMAP} {L}eaf {A}rea {I}ndex, respectively) and other auxiliary input. {T}his paper presents the validation work carried out in the {S}kjern {R}iver {C}atchment, {D}enmark. {L}1{C}/{L}2 data and the most sensitive algorithm parameters were analyzed by network and airborne campaign data collected within one {SMOS} pixel (44 km diameter). {T}he {SMOS} retrieval is based on the prevailing low vegetation class. {F}or the {L}1{C} comparison, {T}-{B}'s were calculated from in situ soil moisture using {L}-{MEB}. {C}onsistent with worldwide findings, the initial/retrieved {SMOS} soil moisture captures the in situ dynamics well but with significant wet/dry biases and too large amplitudes in case of the latter. {W}hile the initial tau({NAD}) is in range with an in situ estimate for low agricultural vegetation, the retrieved tau({NAD}) is too high with too pronounced temporal variability. {A} filter based on {L}2 criteria removed radio frequency interference ({RFI}) and improved the {R}-2 between retrieved and network soil moisture from 0.49 to 0.61, while the bias remained (-0.092/-0.087 m(3)/m(3)). {L}ikely error sources include the following: 1) still present {RFI}; 2) potential link between high retrieved tau({NAD}) and other {L}-{MEB} parameters, e. g., low roughness parameter ({H}-{R}); 3) similar to 18% lower sand and similar to 8% higher clay fractions while similar to 0.35 g/cm(3) lower bulk density in {SMOS} algorithm than in situ; and 4) caveats in the {D}obson dielectric mixing model implemented in the {L}-{MEB} model. {A} previous study at the {D}anish validation site had revealed superior performance of the {M}ironov dielectric mixing model at the 2 x 2 km scale. {S}tudies are ongoing to address the aforementioned issues, and the role of organic surface layers will be investigated.},
  keywords = {{L}-band ; {L}-band microwave emission of the biosphere ({L}-{MEB}) ; passive ; microwaves ; soil moisture ; {S}oil {M}oisture and {O}cean {S}alinity ({SMOS}) ; validation ; {DANEMARK}},
  booktitle = {},
  journal = {{IEEE} {T}ransactions on {G}eoscience and {R}emote {S}ensing},
  volume = {51},
  numero = {5},
  pages = {2969--2985},
  ISSN = {0196-2892},
  year = {2013},
  DOI = {10.1109/tgrs.2012.2215041},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00010735},
}