Field measurements can become prohibitively expensive over a
large area. Remote sensing can collect data in an unbiased and
cost-effectiveness way. Moreover, remote sensing can measure
energy at wavelengths which are beyond the range of human
vision: from ultraviolet to microwave portion of the
electromagnetic spectrum can help automatically derive
quantitative spectral features that serve the input information for
detailed mapping of urban area at subpixel level and provides
area-wide information about the fractional coverage of surface
materials of each pixel. (Xiaojung, 2011)
2.2 Research site
Bucharest, the capital of Romania, is the biggest city of the
country. It is also one of the most developed industrial and
commercial hub. The city is located in the south-east of the
country, on the Dambovita River, which is a tributary river to
Arges River, itself a tributary to the Danube River. The area
around the capital is called Bucharest Plain. This area has
various land forms with heights varying from 100-115 m in the
north-western side to 50-60 m in the south-eastern side. The
city's surface is 228 sq km and the ground elevation varies from
60 to 90 m. The metropolitan area of the city has a population
of 2.4 million inhabitans (unofficially is estimated to 3.4
millions). According to the local development projects the
metropolitan area will be expanded in the near future to include
94 regional districts of a total of 5,000 sq km.
Figure 1. Study area delimited on Bucharest map (red rectangle)
The road traffic system's infrastructure is based on a network of
avenues which form a radial layout, starting in the downtown
and expanding towards the city suburbs where they connect
with roads to other major cities in the area.
There is also a layout of important avenues which cross the city
from one end to another (north to south, east to west, north-west
to south-east) and two bypass roads around it (an inner and an
outer road belt) which greatly improve the traffic flow in and
around the city.
Lately, the road system started to become more and more
obsolete as its development for the past 30-40 years did not
account for the rapidly increasing number of registered cars.
This translates into large traffic jams during the rush hours.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Along Colentina River (a river which flows through the city) a
couple of artificial lakes were developed to regulate the water
flow — Baneasa, Floreasca, Tei, Plumbuita, Fundeni and
Pantelimon. Another lake is on the Dambovita River. Over the
time, the shores of these lakes were developed as parks and
recreational areas, highly appreciated by the local residents.
Moreover, there are also a couple of other parks like the
Botanical Garden, Tineretului Park and Alexandru Ioan Cuza
Park.
2.3 Data sources
For this study have been used space panchromatic and
multispectral images taken over Bucharest, as well as other
complementary products:
e space images: a Corona (16/09/1964) panchromatic image-
3 m resolution; a SPOT-3-HRV (09/07/1994)
panchromatic image - 10 m and multispectral image — 20 m
resolution; an IKONOS (25/06/2007) multispectral image
— 4 m resolution;
e aerial photographs at 1:5,000 scale, acquired in 1994;
e complementary products: topographic and thematic maps
at 1:2,000 and 1:5,000 scales.
A representative area of the city with dynamic and significant
changes in the past decades in: residential and commercial
areas, street network, parks and green spaces. It includes Carol
Park and Tineretului Park. The site has a rectangle form of 2.55
km x 2.32 km and is placed in south central area of Bucharest
city. Sub-images (windows) with variable size have been
created from initial space images focused the test area. The 43
year study period (1964 - 2007), includes two intervals with
different characteristics: 25 years before 1989 and 18 years after
the collapse of communist regime.
3. MATERIALS AND METHODS
3.1 Preliminary processing
One of the most important prerequisite for change-detection
applications is acquiring imagery in the same month in a year.
Images acquired during periods with powerful sun light, present
a very good contrast between various details. For example, in
this case, the contrast between covered with vegetation soil and
uncovered soil or construction areas is very high. Using the
scene acquired in the same period of the year is suggested to
change-detection with the purpose of reducing the problems
which appear because of sun-angle differences, vegetation-
phenology changes and differences in soil-moisture.
IKONOS image was used as a reference image to ensure
compatibility of multitemporal and multispectral data (SPOT
HRV). Due to the lack of information regarding atmosphere
characteristics, radiometric calibration has been realized for
every site based on 10 time-invariant or quasi-invariant objects:
darker zones (lakes surface), or brighter zones (uncovered soil
area). Radiometric transformation which tie the two values of
two images is a nonlinear regression equation which has the
form y(i) = a(i) + b(i) * x (i), where y (i) is pixel’s radiometric
value from reference image and x(i) is the corresponding
radiometric value in the corrected image.
3.2 IKONOS image processing
After the radiometric correction, images have been
geometrically rectified, so that the same pixel at one date
overlaps the same pixel for the other date. The accuracy of
