Remote Sensing of the Urban Heat Island Effect

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Remote Sensing of the Urban Heat Island Effect

• Christopher S Martin
• csmartin_at_buffalo.edu

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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

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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

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Causes contd

• 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

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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

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Data

• Thermal Infrared Band
• Actual bands vary based on the platform
• ASTER
• Bands 10-14, 8.125-11.65 µm
• Spatial Resolution of 90m x 90m
• LANDSAT
• Band 6, 10.4-12.5 µm
• Spatial Resolution of 60m x 60m

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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

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Procedure

• Calibration
• L0.0370588DN3.2
• BT Calculation
• BT K2/ln(K1/L) 1
• LST Calculation
• Ts BT/1(?BT/?)lne

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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

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Separation of Sources contd

• RnGLEH vs RnAGLEH
• 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
• Has H-Hn
• Hn is heat from radiant heat flux, i.e. natural
  causes

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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

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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)

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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

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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

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Other Methods

• Handheld Temperature Sensors
• Aerial Temperature Measurement

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Mitigation

• More Trees!
• High Albedo building materials
• External surfaces designed to reflect thermal
  radiation rather then absorb it

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Questions?
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Sources

• http//www.citeulike.org/user/csm