Remote Sensing the Urban Heat Island Effect


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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

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