AIRBORNE HYPERSPECTRAL AND THERMAL INFORMATION FOR ASSESSING
THE HEAT ISLAND IN URBAN AREAS OF JAPAN
A.Ozawa, B. Babu Madhavan, H. Okada, K. K. Mishra, K.Tachibana and T.Sasagawa
GIS Institute, PASCO Corporation
1-1-2, Higashiyama, Meguro-ku, 153-0043, Tokyo, Japan
atsumasa ozawa(a)pasco.co.jp
KEY WORDS: **Hyperspectral, Thermal, High resolution, Urban, Aerial
ABSTRACT:
The heat island phenomenon, caused by urbanization, is one of the growing problems in Japan. In this study, we have described the
radiometric temperature of the ground surface observed by the airborne thermal sensor in the Hiroshima City. The obtained results
showed that the river and forest areas had lower temperatures whereas the roads had the highest. The temperatures of the Business
District areas were almost same as that of the bare soils. We also observed the ground surface temperature in the Fuchu City, located
near the Tokyo Metropolitan area and three kinds of hyperspectral responses of the several buildings were compared which were
selected from the high, middle and low temperature buildings. We noticed the differences in the observed DN values. Finally we
analysed the relationship between the reflectance and surface temperature of the same materials utilizing hyperspectral and thermal
data. A negative correlation of the observed temperature in the daytime data was obtained, but no correlation was seen for the
nighttime data. The study showed promising results for our current and future works to utilize the airborne thermal and hyperspectral
sensing for assessing and mitigating the heat island in Japan.
1. INTRODUCTION
The heat island phenomenon, which is caused by urbanization,
is one of the fast growing problems in Japan. However, few
studies have been performed to observe the detailed surface
temperatures by utilizing high resolution airborne remote
sensing. Airborne observation is one of effective methods for
the thermal mapping since it can cover large areas in a short
time and capture the high-resolution data as well.
High reflective materials are one of the heat island reduction
methods. They reduce temperature of the materials or sensible
heat flux because incoming solar radiation energy is reduced by
high reflection. We investigated the relationship between
reflective intensity calculated by the airborne hyperspectral
data and radiometric temperature of ground surface measured
from the airborne thermal data for the three cities, Hiroshima
(southern part), Osaka (central) and Tokyo (northern part), in
Japan. As Hiroshima City in the recent years is experiencing an
abnormal increase of the surface temperature due to the
sprawling of the City, the necessity was highly realized to
conduct the thermal mapping for the region.
Thermal properties of land-use/land-cover features were
evaluated by airborne thermal images for the Hiroshima and
Osaka Cities. We also attempted to assess the thermal
properties along with hyperspectral data obtained for the Fuchu
City in Tokyo areas.
2. URBAN HEAT ISLAND STUDY THROUGH
REMOTELY SENSED DATA
Urban heat island (UHI) is a worldwide phenomenon in which
urban areas absorb more heat than the suburban and rural areas.
The phenomenon is primarily due to the alteration of urban
landscape, which change the thermal response to solar radiation.
The urban landscapes are characterized by an inability to reflect
solar radiation. Dark-coloured objects such as buildings and
streets, and less vegetation increase the ability of an urban
landscape to store a lot of heat.
44
To appraise the effects of UHI, remotely sensed data have been
used. Different approaches were established to analyse UHI
by using the satellite derived surface temperature data.
Surface temperature patterns for cities along mid-Atlantic coast
were deduced from inferred from thermal infrared data of
TIROS (Rao, 1972). Thermal data of NOAA AVHRR
coupled with other satellite data have been used to evolve the
relation between land-use/land-cover of urban and UHI
(Carlson et al., 1977; Matson et al, 1978; Kidder and Wu,
1987; Brest, 1987; Balling and Brazel, 1988; Carnahan and
Larson, 1990; Caselles et al., 1991, Babu Madhavan and Sachio
Kubo, 1997). A good review on the utilization of satellite -
derived surface temperature data for urban climate analyses
was given in Gallo et al. (1995). The effects of UHI were
educed by many evaluation studies of satellite derived
vegetation index and radiant surface temperature (Gallo et al.,
1993a; 1993b; 1995; Gallo and Tarpley, 1996).
The effect of UHI is not restricted to large cities. The effects
have been detected in cities with populations of less than
10,000 people (Karl et al., 1988). Roth et al. (1989) estimated
surface temperature data from NOAA AVHRR thermal
infrared measurements and assessed its spatial distribution
across several cities along the West coast of North America.
In most of the UHI studies, higher surface temperatures were
correlated to industrial areas and the vegetated areas to the
cooler surface temperatures.
Albeit thermal infrared satellite data cannot directly accord the
UHI effect, they can be studied with satellite-derived
vegetation density measurements in an urban land use/land
cover. The role of vegetation in reducing the amount of heat
stored in the soil and surface structures due to transpiration, in
contrast to relatively non-vegetated urban areas was analysed
(Carlson et al., 1981;Goward, 1981; Goward et al., 1985;
Goward and Hope, 1989). To estimate the amount of leaf area
and related variables associated with agricultural crops (Gallo
and Daughtry, 1987) as well as forests (Nemani and Running,
1989) vegetation indices have been computed from LANDSAT
-TM, MSS, NOAA and SPOT data. To demonstrate the UHI
effects, vegetation indices and radiant surface temperatures
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