Urban heat islands occur when land and air temperatures are significantly higher in urban areas compared to surrounding rural areas. This is due to factors like construction materials that absorb more heat, lack of vegetation, and waste heat from energy use. Remote sensing using instruments like ASTER and Landsat can measure land surface temperatures to analyze urban heat islands. More advanced methods can separate natural from anthropogenic heat sources. The amount of vegetation, measured by metrics like NDVI, vegetation fraction, and LAI, directly affects the intensity of urban heat islands. Mitigation strategies include increasing urban greenery and using reflective building materials.

1. Remote Sensing of the Urban Heat Island Effect Christopher S Martin [email_address]

2. 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

3. 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

4. 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

6. 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

7. 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

8. 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

9. 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]}

10. 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

11. 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”

12. 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

13. 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)

14. 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

15. 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

16. Other Methods Handheld Temperature Sensors Aerial Temperature Measurement

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

18. Questions?

19. Sources http://www. citeulike . org/user/csm