@article{fdi:010049159,
  title = {{T}he use of scintillometry for validating aggregation schemes over heterogeneous grids},
  author = {{E}zzahar, {J}. and {C}hehbouni, {A}bdelghani},
  editor = {},
  language = {{ENG}},
  abstract = {{A} number of studies have been devoted to derive the diurnal course of regional evapotranspiration ({ET}) especially in semi-arid areas where the assessment of this term is of crucial importance for water resources management. {O}ne approach to derive regional evapotranspiration is based on the use of aggregation schemes in conjunction with energy-balance or land-surface models. {H}owever, the effectiveness of this approach cannot be fully assessed without a comparison between the model's flux simulations and the ground truth observations. {I}n the present study, the issue of using scintillometry for validating spatial and temporal aggregation schemes over heterogeneous grids has been investigated. {D}ata collected within the {SUDMED} project over the oliveyard of {A}gdal which was located near the city of {M}arrakech, {M}orocco, have been used to test the aggregation schemes. {T}he {A}gdal oliveyard was made up of two contrasted fields, or patches. {E}ven though the two sites appear relatively homogeneous, they differ strongly in terms of soil moisture status and vegetation percent cover. {T}he higher soil moisture in the northern site creates heterogeneity at the scale of the entire olive yard (i.e. at grid-scale). {F}irstly, the diurnal course of the grid-scale evapotranspiration (< {ET}sim >({SA})) estimated from spatial aggregation scheme is compared to that derived from scintillometry (< {ETLAS} >). < {ET}sim >({SA}) is obtained as the residual term of the energy balance providing the estimates of the available energy ({AE} = {R}-n - {G}), where {R}-n and {G} are the net radiation and the soil heat flux, respectively, and sensible heat flux. {T}he latter is estimated by using a simple two-layer model developed by {L}homme et al. (1994). {T}he root mean square difference ({RMSD}) and the correlation coefficient ({R}-2) between < {ET}sim >({SA}) and < {ETLAS} > were about 46 {W} m(-2) and 0.78, respectively. {S}econdly, we compared the diurnal course of grid-scale evapotranspiration (< {ET}sim >({TA})) estimated from the temporal aggregation scheme with the < {ETLAS} >. < {ET}sim >({TA}) is obtained by extrapolating the instantaneous values of the available energy and the evaporative fraction ({EF} = {ET}/{AE}) estimated at the satellite overpass to daily ones. {T}he instantaneous values of {AE} and {EF} have been derived using remotely sensed surface temperature measured using a ground-based infrared thermometer combined with ancillary micrometeorological data such as wind speed, incoming and outgoing solar radiation, and temperature and humidity of the air. {T}he {RMSD} and the {R} 2 were about 43 {W} m(-2) and 0.7, respectively. {D}espite the complexity of the site induced by the strong heterogeneity in the soil moisture which is related to the employed irrigation method (flood irrigation), and the consequences in terms of the footprint of the instruments. the obtained statistical results showed that both aggregation schemes performed successfully with regard to estimates of the evapotranspiration over heterogeneous grids. {F}inally, to further assess the performance of the developed approach, a second dataset collected in northern {M}exico has been also used. {T}he result shows that the approach provides acceptable values of aggregated evapotranspiration. {C}onsequently, scintillometry can potentially be used in the development and the validation of aggregation approaches to improve the representation of surface heterogeneity land-surface-atmosphere models operating at large scales.},
  keywords = {{S}cintillometry ; {A}ggregation scheme ; {E}vapotranspiration ; {H}eterogeneous grid ; {S}emi-arid regions},
  booktitle = {},
  journal = {{A}gricultural and {F}orest {M}eteorology},
  volume = {149},
  numero = {12},
  pages = {2098--2109},
  ISSN = {0168-1923},
  year = {2009},
  DOI = {10.1016/j.agrformet.2009.09.004},
  URL = {https://www.documentation.ird.fr/hor/fdi:010049159},
}