@article{fdi:010088146,
  title = {{C}orrection for {LST} directionality impact on the estimation of surface upwelling longwave radiation over vegetated surfaces at the satellite scale},
  author = {{H}u, {T}. and {R}oujean, {J}. {L}. and {C}ao, {B}. and {M}allick, {K}. and {B}oulet, {G}illes and {L}i, {H}. and {X}u, {Z}. {H}. and {D}u, {Y}. {M}. and {L}iu, {Q}. {H}.},
  editor = {},
  language = {{ENG}},
  abstract = {{S}urface upwelling longwave radiation ({SULR}) is a major component of the {E}arth's radiation budget and directly influences the retrieval of evapotranspiration ({ET}) in the terrestrial ecosystems. {L}and surface temperature ({LST}) is an {E}ssential {C}limate {V}ariable ({ECV}) for direct estimation of {SULR}. {H}owever, accurate retrieval of {SULR} from satellite observations may be severely hindered by the anisotropic properties of land surface targets since most of them show marked angular variations in {LST}. {T}his study aims at investigating the magnitude and impact factors of the directional effects of {LST} on {SULR} estimation over vegetated surfaces given that angular variation in emissivity has a limited impact on {SULR} estimation over most land surface types. {I}t follows an attempt to correct for such effects in {SULR} estimation. {W}e further explore the possibility to find a viewing direction at which {SULR} estimated from the directional {LST} can surrogate the hemispherical integration. {T}o do so, a parametric model mimicking {LST} anisotropy with the hot spot is incorporated into the physical temperature-emissivity method. {T}wo widely used {M}oderate {R}esolution {I}maging {S}pectroradiometer ({MODIS}) {LST} products (i.e., {MYD}11_{L}2 and {MYD}21_{L}2) are analyzed. {SULR} estimates before and after correcting for {LST} directionality are compared with insitu measurements acquired at 15 sites from the {FLUXNET} and {SURFRAD} networks in different regions. {O}ur analysis reveals that {LST} directional effects on {SULR} estimation exhibit diurnal and seasonal variations, which are substantial in spring and summer for the daytime. {T}he effects are negligible (<5 {W} m  2) in autumn and winter for the daytime except for in arid and semiarid regions. {F}or the night-time, the effects are insignificant over all the biomes. {U}sing {MYD}21 {LST}, after correction, the average root-mean-square error ({RMSE}) and bias of {SULR} estimates for all sites decrease by 8 and 8.34 {W} m  2 in spring, and by 8.9 and 12.13 {W} m  2 in summer. {U}sing {MYD}11 {LST}, after correction, the average {RMSE} is between 10 and 15 {W} m  2 and the average bias is close to zero in all seasons. {T}he {RMSE} and absolute bias of {SULR} estimates for sites with low to moderate vegetation ({LAI} <3) is lowered substantially (7-14 {W} m  2) after correction. {I}nterestingly, {SULR} estimates from {LST} viewed at 54 degrees backward and hemispherically integrated are close, with differences <3 {W} m  2 at most of the sites. {T}hese findings support a strategy for {SULR} estimation in {ET} retrieval over vegetated surfaces from directional {LST}.},
  keywords = {{LST} ; {T}hermal directionality ; {P}arametric model ; {MODIS} ; {SULR}},
  booktitle = {},
  journal = {{R}emote {S}ensing of {E}nvironment},
  volume = {295},
  numero = {},
  pages = {113649 [22 p.]},
  ISSN = {0034-4257},
  year = {2023},
  DOI = {10.1016/j.rse.2023.113649},
  URL = {https://www.documentation.ird.fr/hor/fdi:010088146},
}