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

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

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

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

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

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

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]}

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

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”

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

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)

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

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

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

Handheld Temperature Sensors

Aerial Temperature Measurement

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

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

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