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Remote Sensing the Urban Heat Island Effect
 

Remote Sensing the Urban Heat Island Effect

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An overview of methods used for remote sensing urban heat islands

An overview of methods used for remote sensing urban heat islands

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  • Great presentation of urban heat island effect!! The modelisation of that effect with remote sensing is the latest and the best analysis of urban effects on temperature.
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Remote Sensing the Urban Heat Island Effect Remote Sensing the Urban Heat Island Effect Presentation Transcript

  • Remote Sensing of the Urban Heat Island Effect Christopher S Martin [email_address]
  • Definition
    • An Urban Heat Island (UHI) is a condition in which the Land Surface and Air Temperatures around a Metropolitan area are significantly greater then the surrounding area.
    • 3 Layers
      • Surface Layer
      • Canopy Layer
      • Boundary Layer
  • Causes
    • Primary
      • Construction Materials
        • Significantly different properties then found in rural areas
      • Lack of Plants
        • Green leafy plants reflect more heat then they absorb
        • Transmission reduces the amount of thermal energy that reaches the surface
  • Causes cont’d
    • Secondary
      • “Urban Canyon”
        • Geometry of urban settlements provide multiple surfaces for refection and absorption
        • Blocks cooling via convection
      • Anthropogenic
        • Waste Heat from energy production, consumption
  •  
  • Remote Sensing Instruments
    • ASTER
      • Advanced Spaceborne Thermal Emission and Reflection Radiometer
      • Imaging device on the TERRA satellite
    • ETM+
      • Enhanced Thematic Mapper
      • Sensor platform on the LANDSAT satellite
  • Data
    • Thermal Infrared Band
    • Actual bands vary based on the platform
      • ASTER
        • Bands 10-14, 8.125-11.65 μ m
        • Spatial Resolution of 90m x 90m
      • LANDSAT
        • Band 6, 10.4-12.5 μ m
        • Spatial Resolution of 60m x 60m
  • Temperature Calculation
    • Land Surface Temperature
      • Is Not the only portion of an UHI
      • IS the only portion that can be measured via satellite
    • Procedure
      • Calibration
      • Convert to BT
      • Calculate LST
  • Procedure
    • Calibration
      • L=0.0370588·DN+3.2
    • BT Calculation
      • BT = K 2 /{ln[(K 1 /L) + 1]}
    • LST Calculation
      • T s = BT/{1+[(λ ⋅BT/ρ)⋅lnε]}
  • Separation of Sources
    • Calculated LST contains heat generated from 2 sources:
      • Radiation
      • Anthropogenic Sources
    • This is difficult
      • Kato and Yamaguchi (2005) developed a new method
  • Separation of Sources cont’d
    • R n =G+LE+H vs R n +A=G+LE+H
    • Estimate the values of each term above
      • In particular, G varies based on material
      • Lots of complex math
      • Includes meteorological data
      • Ultimately end up with H, total value of heat flux
    • H as =H−H n
      • H n is heat from radiant heat flux, i.e. “natural causes”
  • UHI - Vegetation Relationship
    • The amount of green vegetation in an area directly affects UHI
      • More green = less heat
    • How to quantify this?
      • 3 methods for measuring
  • NDVI
    • Normalized Difference Vegetation Index
    • A numerical indicator that can be used to assess whether the target being observed contains live green vegetation.
    • NDVI = (NIR - RED)/(NIR + RED)
  • Vegetation Fraction
    • vegetation fraction derived from a spectral mixture model
    • Uses LSMA to determine if a pixel contains vegetation
      • Works at the sub-pixel level
    • The jury is still out
      • Some indication that is may be more accurate then NDVI
  • LAI
    • Leaf Area Index
      • Not always a result of remote sensing
      • Two field measurement methods
        • destructive harvesting of leaves within a vertical column passing upward through the entire tree canopy
        • collection of leaf litterfall
    • Can be calculated from NDVI measurement
  • Other Methods
    • Handheld Temperature Sensors
    • Aerial Temperature Measurement
  • Mitigation
    • More Trees!
    • High Albedo building materials
      • External surfaces designed to reflect thermal radiation rather then absorb it
  • Questions?
  • Sources
    • http://www. citeulike . org/user/csm