Satellite
Observations Help Lessen The Effects Of Heatwaves In Urban Areas
(17 July 2008) When heatwaves strike,
it's far more difficult to cope with stifling temperatures in built-up areas
than it is out in the countryside.
An ESA campaign has just been
carried out to see if a spaceborne thermal infrared sensor could help policy
makers and town planners reduce the number of casualties when temperatures
soar.
An attempt to cool off in the hot city. (courtesy: AFP/Fred Dufour)
Over the last decade, heatwaves have claimed
an increasing number of casualties among the elderly - particularly in southern
Europe. The heatwave that hit Europe in 2003, for instance, is estimated to
have caused more than 15 000 deaths in France alone, with about 70% of the
mortalities occurring in the over 75s.
Prolonged periods of high
temperatures also put a strain on medical resources and place an additional
financial cost to society as a whole.
In densely built cities with a low percentage of vegetation and water, the temperatures in the heart of the city might, in some cases, be up to 10º C warmer than in the surrounding countryside.
High densely built-up areas trap the heat,
especially at night, causing what is called Urban Heat Islands (UHI) in which
city centres can be up to 10º C warmer than surrounding rural areas.
Another consequence of UHIs is that energy consumption rises with the increased
use of air conditioners and refrigeration appliances.
Whilst poor
insulation keeps buildings hot in the summer, it also allows heat to escape in
the winter months - another factor associated with high-energy consumption and
poor efficiency. With the social and financial costs that UHIs bring as well as
climate-change issues in mind, many city councils have already adopted a range
of energy efficiency policies to assess and monitor energy
consumption.
ESA has recently launched a set of activities to aid
decision and policy makers mitigate the effects of UHIs though appropriate
alert systems, and in terms of reducing risk - through improved urban
planning.
Within the framework of the proposed activities for the
'Reorientation of the Fuegosat Consolidation Phase', which falls under the
Earth Watch element of ESA's Living Planet Programme, a high-resolution thermal
infrared capability was recognised as necessary for Europe in the medium- to
long-term.
During the DESIREX 2008 campaign, two flight lines along the NW-SE & the N-S urban axis have been done at 3 different times of the day (around sunrise, noon and midnight) in order to characterise the warming/cooling process of the urban areas. Some of the DESIREX 2008 flights have been organised contemporarily with an ASTER pass over the city of Madrid. This image shows the two flight lines and the footprint of an AHS-observed surface temperature area overlaid on an ASTER satellite image of the city of Madrid. (courtesy: University of Valencia, INTA and Jet Propulsion Laboratory (ASTER))
In addition to the original fire-related
application areas, infrared observations have the potential to contribute to
reducing the effects of UHIs. To this end, an ESA project called Urban Heat
Islands and Urban Thermography, funded through the agency's Data User Element
(DUE), is currently the subject of an open and competitive tender, which will
be initiated in September 2008 with the participation of 10 European
cities.
In preparation for this project, ESA organised a dedicated
campaign - Desirex-2008, which involved taking airborne and ground measurements
with infrared sensors. The objective was to produce thermal datasets to support
the upcoming trade-off studies that will be made by the Urban Heat Islands and
Urban Thermography project, and to perform a preliminary mission analysis for a
dedicated satellite sensor for the provision of temperature observations over
European cities.
Madrid in Spain was chosen as the test site for the
campaign as it is one of the cities in Europe that suffers many heatwaves with
air temperatures sometimes reaching 50º C.
More than 60 researchers
from 14 different institutes gathered in Madrid to participate in the two-week
field campaign, which ended on 4 July. The intensive campaign, organised in
close co-operation with the Madrid City Council, involved multiple satellites,
airborne and field instruments.
Map of observed Airborne Hyperspectral Scanner (AHS) relative temperatures of an area of Madrid, Spain at midnight. The cooler temperatures are indicated in dark blue and the higher temperatures in red. Details: Zone: Paseo de la Castellana Image: 1 July 2008, at night Spatial resolution: 3 m/pixel (courtesy: University of Valencia)
Ana Botella, who is responsible for
Environmental Affairs at Madrid's City Council, said: "The City Council of
Madrid considers that its participation to the Desirex-2008 project will
provide results of high relevance for the future urban planning and towards a
more sustainable development of the city."
The campaign successfully
generated a representative thermal dataset that will allow the project team to
analyse the observational requirements for better assessment and monitoring of
UHIs in Madrid.
"The datasets produced during the Desirex 2008 campaign
will serve ESA's Urban Heat Island and Urban Thermography," explained Professor
José Antonio Sobrino from the University of Valencia, and the Principal
Investigator for Desirex-2008.
"The Analysis of such a comprehensive
dataset will allow us to better understand the spatial and temporal variability
of Urban Heat Islands in the city of Madrid, and should help us to define what
would be the best satellite mission for efficient monitoring of European cities
during summertime."
INTA Airborne Hyperspectral Scanner (AHS) line-scanner in operation during a night survey over Madrid carried on the CASA-212 aircraft (courtesy: INTA)
The main instrument used during the campaign
was the Airborne Hyperspectral Scanner (AHS), which is an imaging line-scanner
radiometer, installed on a CASA-212 200 series aircraft owned by Spain's
National Institute for Aerospace Technology (INTA).
The AHS has 80 spectral
channels available in the visible, shortwave infrared and thermal infrared.
Thirty acquisition flight lines (15 flights in total) were obtained over Madrid
with spatial resolutions varying from 2.5 to 6.8 metres.
Multiple field
instrumentations operated by the partners in the Desirex 2008 campaign have
provided extremely detailed ground measurements, such as radiometric
measurements used for calibration and validation of parameters extracted from
the AHS airborne sensor, measurements for characterising the UHI, such as the
air and radiometric temperatures in different building terraces.
Four
cars carrying instrumentation followed the flight paths and analysed the effect
and the evolution of the UHI during the experiment.
Many satellite
measurements were also acquired during the campaign from a range of satellite
sensors, notably the Medium Resolution Imaging Spectrometer (MERIS) and
Advanced Along Track Scanning Radiometer (AATSR) instruments aboard Envisat,
the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instrument aboard
MSG-1 (Meteosat Second Generation) and the Moderate Resolution Imaging
Spectroradiometer (MODIS) and Advanced Spaceborne Thermal Emission and
Reflection Radiometer (ASTER) onboard Terra.
An extensive analysis of
all the Desirex-2008 data collected from spaceborne, airborne and ground
observations will now take place with the first results expected in November
2008.
During the DESIREX campaign, four cars carrying instrumentation drove along the two flight lines three times a day to take meteorological and radiometric measurements. (courtesy: University of Valencia)
"The city of Madrid will benefit greatly
from the Desirex-2008 campaign. The results will allow us to have detailed
information on Urban Heat Islands for the delineation of these highly sensitive
areas and their incorporation into more effective urban planning for heat wave
mitigation," said José Manuel Romero Cuadrado, Head of the Cartographic
Department with the Madrid City Council.
"The availability of
information on urban climate should also help our city council to optimise an
intelligent use of energy at the level of the city districts but also at
building level."
The Desirex-2008 activity was funded through ESA's
Reorientation of the Fuegosat Consolidation Phase. Participants included
Spanish teams from Universities in Valencia (UVEG), Madrid (UAM, UCM) and Vigo
(UVIGO), along with national institutes (INTA, AEMET, CIEMAT, CECAF, AENA and
LABEIN), French teams from the University of Strasbourg and the City Council of
Madrid.
(source: ESA)
