International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
A STUDY ON EXTRACTING THIN SEA ICE AREA FROM SPACE
*Kohei Cho* , Yusuke Mochizuki*, Yuuta Yoshida? , Haruhisa Shimoda and Chi-Farn CHEN?
* Tokai University, 2-28-4 Tomigaya. Shibuya -ku, Tokyo 151-0063 Japan
Tel: (81)-3-3481-0611, E-mail: cho@yoyogi.ycc.u-tokai.ac.jp
®Center for Space and Remote Sensing Research (CSRSR)
National Central University, E-mail: cfchen@csrsr.ncu.edu.tw
Commission VIII, WG VIII/10
KEY WORDS: Sea of Okhotsk, MODIS, FORMOSAT-2, AMSR-E, optical sensor, passive microwave sensor
ABSTRACT:
Global warming is one of the most serious problems the earth is facing in the 21* Century. In order to detect the sign of global
warming, the importance of sea ice monitoring is increasing. Especially, sea ice thickness is an key parameter for understanding the
heat flux of sea ice area. However, estimation of sea ice thickness with satellite remote sensing is not easy. In this study authors have
examined the possibility of extracting thin sea ice area from remotely sensed data from space. The study was performed in the Sea of
Okhotsk. Firstly, the possibility of estimating thin ice thickness with high resolution optical sensor RSI(IFOV=8m) on FORMOSAT-
2 satellite was examined. The comparison of RSI data with in situ measurement of ice thickness suggested the possibility of
estimating sea ice thickness with RSI data for less than 20 cm under the cloudless and snow free condition. The correlation between
RSI data and MODIS data(IFOV=250m) was also examined for the thin ice area. The result also suggested the possibility of
extracting thin sea ice area from MODIS data. Based on these results, the authors have examined possibility of extracting thin sea ice
area with passive microwave sensor AMSR-E by using thin ice area estimated with MODIS data as truth data. Since the horizontal
polarization of 19GHz are more sensitive to water than the vertical polarization of 19GHz, the authors have utilized the polarization
difference of 19GHz for extracting thin sea ice area from AMSR-E data. The detailed study result will be presented in this paper.
1. INTRODUCTION
Sea ice has an important role of reflecting the solar radiation
back into space. However, the reduction of ice cover due to the
global warming decreases the earth albedo, and increases the
amount of solar energy absorption leading to more global
warming. This means that the trend of global warming is likely
to be enhanced in sea ice area. Sea ice also has a role of
preventing heat exchange between sea and air. Especially, since
the heat flux of thin ice is strongly affected by the ice thickness
difference (Maykut, 1978), ice thickness estimation and thin ice
area extraction ice are quite important.
Under the cloud free condition, high resolution optical
sensors are quite useful for monitoring the detailed condition of
sea ice. Various studies on estimating ice thickness with optical
sensor AVHRR onboard NOAA satellites have been performed
in the past (some examples are Allison, 1993, Perovich et al.,
1982, and Grenfell, 1983). Basically, the albedo increases as
the ice thickness increases. However, detailed comparison of
thin ice thickness with high resolution satellite data were not
much done in the past. In this study, firstly, authors have
evaluated the possibility of estimating thin sea ice thickness
with high resolution optical sensor RSI data observed from
satellite FORMOSAT-2. Then, the RSI data were compared
with moderate resolution optical sensor MODIS data acquired
from Aqua satellite to evaluate the possibility of extracting thin
sea ice area from MODIS images. Finally, the method for
extracting thin ice area from passive microwave sensor AMSR-
E data acquired from Aqua satellite was proposed and the result
was evaluated using simultaneously collected MODIS data.
2. TEST SITE
In this study, the Sea of Okhotsk was selected as the test site
for the detailed evaluation of thin ice area extraction from
remotely sensed data from space. Figure 1 show the maps of the
test site. The Sea of Okhotsk is located in the north side of
Japan, and is one of the most southern seasonal sea ice zones in
the northern hemisphere. Since many thin ice area can be found
in the Sea of Okhotsk, the sea is suitable for this study. The in
situ measurements of ice thickness were performed at the
Monbetsu Bay and Saroma Lake along the coast of Hokkaido,
Japan.
m
x i
M
d ©
RM lut
Tegre
\ / (b) Monbetsu bay
Saroma
Lake
Sea of
Okhotsk
I
ES
i210 Googie 160m 7 ©2010 RIN
T :
SS S m Vl 4 |
(a) Sea of Okhotsk (c) Saroma Lake
Figure 1. Location of test sites
