Hydrological Applications of LST Derived from AVHRR
Transcript of Hydrological Applications of LST Derived from AVHRR
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April 11, 2001 Presentation at BRC, Temple, TX.
Hydrological Applications of LST Derived from AVHRR
ByBalaji NarasimhanResearch Assistant
Department of Agricultural EngineeringTexas A&M University
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April 11, 2001 Presentation at BRC, Temple, TX.
Outline
� Introduction� All about LST� Model Development (Ta Vs LST)� Applications
� Potential Evapo-Transpiration� Soil Moisture Monitoring/ Hydrologic Modeling� Drought Indices (KBDI, PDSI)
� Conclusion
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April 11, 2001 Presentation at BRC, Temple, TX.
Introduction
� AVHRR - Advanced Very High Resolution Radiometer
� It is a sensor aboard NOAA - POES.� AVHRR has one visible, one near infrared
and three thermal infrared channels� Currently NOAA 12, 14, 15, 16 are
operational.� Research focus on thermal channels
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April 11, 2001 Presentation at BRC, Temple, TX.
All about LST
� Land Surface Temperature (LST), Ts is the temperature just above the land surface
� LST is different from air temperature, Ta
Air massTa
Ts
Ts
Ts
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April 11, 2001 Presentation at BRC, Temple, TX.
LST from AVHRR
� Split-window Algorithm to extract LST � to account for absorption in measured signal due to
CO2, water vapor etc.. present in the atmosphere
� Ulivieri et al. (1994):LST = T4 + 1.8(T4 - T5) + 48(1-ε) - 75∆ε
Where:T4 - Channel 4 temperature (ºK)T5 - Channel 5 temperature (ºK)ε - Average emissivity (ε4+ ε5)/2 ∆ε - ε4 - ε5.
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April 11, 2001 Presentation at BRC, Temple, TX.
LST and air temperature
� Maximum and Minimum air temperatures� Ta (max) from afternoon overpass
� Ta(min) from morning overpass
� Ts and Ta (max) are linearly related� However, this relationship varies with
location� Hence, long term monthly mean air
temperature is included in the model
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
Model Development
� Multiple Linear Regression Model� Ta = m1Ts + m2 Tlm
� Ta (max) from 27 weather stations was used for model development
� Ta (max) from 30 weather stations was used for model validation (independent dataset)
� Ts Vs Ta (max) relationships has been established for each of the10 climatic zones of Texas
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
Regression Coefficients
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
Model Validation
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
Applications
� Potential Evapo-Transpiration� Soil Moisture Monitoring/ Hydrologic
Modeling � Drought Indices
� KBDI� PDSI
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April 11, 2001 Presentation at BRC, Temple, TX.
Potential Evapo-Transpiration
� Energy Balance Model
Rn = λE + H + GWhere:Rn = net radiation flux (kJ.m-2.s-1),λE = latent heat flux,H = sensible heat flux to the air,G = sensible heat flux to the soil.
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April 11, 2001 Presentation at BRC, Temple, TX.
Potential Evapo-Transpiration (Contd..)
� Sensible Heat FluxH = -ρa.Cp.hh.(Ta - Ts)Where:H = sensible heat flux (kJ.m-2.s-1),ρa = density of air (kg.m-3),Cp = specific heat of air (kJ.kg-1.ºC-1),hh = transport coefficient (s.m-1),
= u2/208 (Grass Reference),u2 = wind velocity(m.s-1),Ta = air temperature (ºC),Ts = land surface temperature (ºC).
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April 11, 2001 Presentation at BRC, Temple, TX.
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April 11, 2001 Presentation at BRC, Temple, TX.
Soil Moisture Monitoring
� Using a water balance model� SWCt = SWCt-1+ ( Precipitation - ET - Runoff )
� Precipitation from NEXRAD� ET from AVHRR� Runoff using SCS curve number technique� Useful to calculate:
� irrigation requirements� irrigation scheduling� water allocation from reservoir
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April 11, 2001 Presentation at BRC, Temple, TX.
Drought Indices
� KBDI (Keetch-Byram Drought Index)� An index of Forest Fire Potential� Uses maximum air temperature and precipitation to
indicate fire potential in a scale of 0 to 800� Current scale - county level� Max. air temperature from AVHRR� Precipitation from NEXRAD� with GIS and remote sensing technique the spatial
accuracy could be improved to 4km X 4km
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April 11, 2001 Presentation at BRC, Temple, TX.
Drought Indices (contd�)
� PDSI (Palmer Drought Severity Index)� An index of Meteorological / Hydrological /
Agricultural Drought� Uses a simple water balance model to indicate
drought in a scale of -4 to 4.� Current scale - climatic division� improved water balance model using distributed
parameters obtained from GIS and remote sensing data
� spatial accuracy of 4km X 4km
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April 11, 2001 Presentation at BRC, Temple, TX.
Conclusion� Energy fluxes between the land surface and
the atmosphere� Daily coverage� Improved spatial accuracy� Good tool for regional scale monitoring � Drought monitoring and information system � MODIS - Moderate Resolution Imaging
Spectroradiometer
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April 11, 2001 Presentation at BRC, Temple, TX.
Questions?