alik, sabdikan,
.edu.tr
e primary importance for
ortant information and are
by extracting the coastline
liscussed in detail. In this
| Aperture Radar) satellite
rized data has been used.
re acquired in ascending
city, lies on the northwest
raction from SAR images.
^ALSAR images gathered
images were compared to
1. The average differences
, followed to refine the
matic coastline extraction
re from ALOS/PALSAR
y applied on optical data
indsat in previous study
EA
ind Bartin cities which are
Sea in the north-west part
f the study are located as
d Bolu at the south and
lere are two main streams
Bartin stream is drains at
drain in Caycuma city of
pport is underground coal
d coal mining in Turkey.
1 as limestone, marble,
study area.
ninant in Zonguldak, and
ly during the whole year.
470. Along the coastline
t. The area has a rough
BLACK SEA
EAR
NO d
; do Ls
IRA
Figure 1. Study area
3. STUDY AREA
Materials
We used Advanced Land Observing Satellite (ALOS) Phased
Array type L-band Synthetic Aperture Radar (PALSAR) data
for the coastline detection. SAR data gathered in raw format and
first converted to a Single Look Complex (SLC) data then
converted to a 4 multi-look data. Fine Beam Dual (FBD) mode
HH and HV polarized ALOS data has a 14 MHz bandwidth and
343 degrees look angle. PALSAR which uses L-band to
illuminate the Earth surface is acquired in ascending geometry,
and the ground resolution of the amplitude images are
resampled to 15 m.
In the process to indicate the effect of polarization HH and HV
polarized images processed with the algorithm separately and
compared. To verify the results two dated 2007 and 2010
PALSAR images are acquired and the algorithm was applied on
four images in total.
Swath Trac | Frame
Sensor Km Pass KNo No Pol Date
Alos- 05-09-
70 Asc. 604 820 HH
Palsar 2007
Alos- 13-06-
70 Asc. 604 820 HV
Palsar 2010
Table 1. Specifications of ALOS data
4. METHODOLOGY
In this study, the radiometric resolution of both SAR images is
32 bit As the image histogram describes the statistical
distribution of the image pixels in terms of the number of pixel
at each DN, both image scenes of the study area have bimodel
histogram which indicates two dominant materials as water and
land in the area. In the process of land (i.e. coast) and water
separation, the radiometric resolution of the images was reduced
to 8 bit in order to decouple noise from image as well as to
increase the processing speed (Figure 2). In the last step of the
process the final images were converted to binary images.
Figure 2 Part of the image scene which was reduced to 8-bit
radiometric resolution
For the purpose of making more apparent the sharp radiometric
difference between the coast (land) and sea, histogram
equalization process was applied on the images (Figure 3).
Figure 3. Histogram equalization applied image part.
Two types of images came out after the histogram equalization
process. These two types were described as "too noisy" and
"less noisy" image. Since the amount of the noise affect the
extraction of coastline, various algorithms needed to be applied.
In order to describe image as too noisy or less noisy, land and
water parts of the images were separated as the first step. For
this purpose, a 100 x 100 search window was applied on the
entire image scenes to split the completely land and completely
water portion of the images. In this process 128 was selected as
the threshold value for the windows of 10000 pixels. If the
number of pixels with 0 (black) values was %200 greater than
the number of pixels with 255 (white) values, then the pixel
group was assigned as water (Figure 4). The percentage value
(% 200) was defined empirically.
In all images a large portion of all the noise was found to have
the same gray value. One more check was done on each window
assigned as water. A check was carried out on the histograms of
the every 100x100 search window, and the gray values with
maximum number of pixel except for zeros were assigned as
noise (Figure 4).
