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Broad Band IR Emissivity Impact on Validation of Land Surface Temperature

This study analyzes the validation of land surface temperature using broad band IR emissivity data observed over three years. The systematic errors depend on window emissivity, and adjustments for diurnal variations are made for accuracy. Results show bias decreases with emissivity increase, and seasonal adjustments reduce errors.

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Broad Band IR Emissivity Impact on Validation of Land Surface Temperature

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  1. LST Validation and Broad Band IR Emissivity δW • Three-year (2001, 2004, 2005) GOES-10 observed LSTG is considered as Ground Truth. Systematic error in LSTG depends on Window Emissivity δG . • Δ LSTG ≈ -37 * ΔδG • Time series of LSTS at SURFRAD stations are computed using different values of δW broad band IR emissivity of observational plot. • LSTS = LSTS (δW) • 3. Next slide shows dependences of systematic and standard errors in LSTS on δW • <LSTG- LSTS >, STD(LSTG- LSTS), & STD(LST’G- LST’S) • LST’G and LST’S are LSTG and LSTS adjusted for diurnal/seasonal variations in the expected value. Kostya Vinnikov. Team Meeting on October 2, 2009

  2. Mean bias decreases with Broad Band Emissivity increase. Bias is minimal at Broad Band Emissivity=1. • Mean bias ≈ 1.8 K. Δ[Bias (K)]/ Δ[Window Emissivity] ≈ -37 K; Bias=0 if Window emissivity is 0.05 smaller than it is in now (green vertical lines). • Dependence of RMS Errors on Broad Band Emissivity is rather week. We cannot use minimal RMSE because this increase a bias too much. • Seasonal/Diurnal adjustment decrease RMSE and remove bias. • There is no reason to change our current emissivities.

  3. This is basic GOES-10 ~ SURFRAD 3-year validation statistics THREE YEAR (2001, 2004 & 2005) STATISTICS OF CLEAR SKY LAND SURFACE TEMPERATURE SIMULTANEOUSELY OBSERVED AT GOES-10 SATELLITE AND AT SIX SURFRAD STATIONS Nobs– is Number of observations; a00(TG-TS) –is diurnal/seasonal cycles adjusted bias of satellite observed LST; <TG-TS> - is raw estimate of bias of satellite observed LST; SD(TG-TS) – is Standard Deviation of LST validation difference; SD(TG’-TS’) – is Standard Deviation of diurnal/seasonal cycles adjusted LST validation difference; SD(<TG-TS>) – is Standard Deviation of diurnal/seasonal component LST validation difference;

  4. Conclusion: Observed temporal variations of Clear Sky LST and SAT (Surface Air Temperature) carry the same weather related signal!

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