Analysis of Effects of Environmental Factors on Spatio-Temporal Distribution of Ice in Liaodong Bay with Envisat ASAR and MODIS Imagery

1
Analysis of Effects of Environmental Factors on
Spatio-Temporal Distribution of Ice in Liaodong
Bay with Envisat ASAR and MODIS Imagery
esa
SEASAR 2008
Haibo YUE (1) , Yonggang JI (2) and Xi ZHANG
(2) (1) Ocean University of China, NO.5 Yushan
Road, Qingdao 266071, China (2) First Institute
of Oceanography, SOA, NO.6 Xianxialing Road,
Hi-Tech Industry Park, Qingdao 266061, China
Introduction
The ice in Liaodong bay is seasonal first-year
ice. Every year, Liaodong bay begins to freeze
during early winter, then the cold temperature
and severe storms enlarge the coverage area of
sea ice and thicken the thickness. During the
spring, the sea ice melts. The melt and freeze
cycles of sea ice responds quickly to
meteorogically, such as temperature, wind,
topography, tide, salinity, and other factors.
And the spatial distribution and temporal
evolution of sea ice is dominated by many
environmental factors. So the relationship
between the ice and the environmental factors in
the Liaodong Bay should be studied. Those
researches are very useful to the prevention and
reduction of sea ice disaster, and they are also
useful to the exploiture of the fresh water
resources.
Data Description

Topographty

ENVISATWe acquire 58 ENVISAT ASAR images during
2005-2006 and 2006-2007.
2006.12.19
2006.12.31
2006.12.25
2007.1.3
2006.1.29
topography isobath of Liaodong Bay (Gu,2003)
MODIS image of Dec 24, 2005 to Jan 6, 2006
MODISASAR EOS/MODIS can provide multi-waveband
data whose resolution is 250m compared with
NOAA/AVHRR MODIS. We collect all the MODIS images
during 2006-2007.
In generally, the shallow water freeze
firstly, then expand to deep water. Here shows
the topography of the Liaodong bay.
In initial ice period, the ice edge parallel with
isobath in the north of Liaodong bay. But in
serious period, there is little influence to ice
edge. That can be seen from the MODIS image of
Dec 24, 2005 to Jan 6, 2006.
Tide
marine coastal weather stations data
Environmental Factors Effect
The sea ice in Liaodong bay may be dragged by
tide, and the motion of sea ice presents in
Figure 12 and Figure 13. The two figures show
that the ice area isnt change a lot. The tide
can drag sea ice raft at very short time (within
2 hours) and the displacement is 3.5km at
Bayuquan ocean station (speed is 0.6m/s). Near
the sea ice edge, the sea ice move faster, and
the speed can reach 1.2m/s.Therefore when the ice
has bigger thickness, the motion of sea ice will
be danger to the oil platform.
Temperature
we establish the mathematic model between
change of areas and that of temperature. Firstly
we assume that there is a critical temperature T0
(corresponding to the air temperature), when the
air temperature Tgt T0,the areas S decrease vice
versa the areas S increase when the air
temperature Tlt T0. Here we assume the increase of
ice areas is proportional to the decrease of air
temperature and critical temperature (T- T0). The
formula is Si S0a?TjaiT0
(1) Where, S0 is the area of sea ice at
the first day,Tj is the in situ measurement air
temperature,T0 is the critical temperature,a is
fit curve coefficient. Fig.4 presents the result
of simulation of sea ice areas. At different ice
period, the critical temperature T0 and
coefficient a are different.
Salinity
The sea ice of the west of Liaodong bay melt
firstly, then does the east of Liaodong bay, and
the north of Liaodong bay is latest. This
phenomenon depends upon salinity. The injection
of fresh water can reduce the salinity of the
ocean water. The salinity reduction of ocean
water will elevate the freezing point and melting
point. Then the southeast parts of Liaodong Bay
froze earlier and melt later, which make the ice
last for a longer time.
Conclusion
Wind
1) The change of ice area in Liaodong bay mostly
depends on the change of temperature. When the
air temperature is higher than the critical
temperature, the area will minish and it expands
when the air temperature is lower than the
critical temperature. 2) The topography can make
a deeply influence on the ice edge at initial ice
period. Especially in initial ice period, the ice
edge parallel with the isobath in the north of
Liaodong bay. 3) In initial ice period and
melting ice period, wind can affect the speed of
ice growing and melting. In the serious ice
period, the winds have little effect on the ice
area, but it can influence ice surface
feature. 4) The tide can change the ice area a
lot, but it can make the floe ice zone raft in a
short time, and the displacement maybe several
kilometers, the speed is about 0.5m/s. 5) The
injection of fresh water can reduce the salinity
and make the ice of lower salinity last longer.
The wind can influence the shape of ice edge.
When winds blow from the pack ice to open water,
a diffuse edge forms and the zones composed of
both ice and open water, and can be spread over a
very wide area making delineation of an open
water and ice boundary very difficult. When an
on-ice wind event occurs (e.g., when the wind
blows toward the ice), the ice edge will then be
compact. During these events, locating the edge
on SAR imagery is quite easy. In initial ice
period and melting ice period, wind plays an
important role in the growing and melting of the
ice. In the serious ice period, the wind has a
little effect on the area of ice, but that can
impact on the ice surface feature.
From February 8, 2006 to February 10, 2006, the
air temperature increase sharply, that makes the
sea ice melt quickly into rotten ice which
exhibits rapid dynamic and thermodynamic
responses. The Figure 8 shows that the surface of
ice reveals a succession of cloud bands under the
wind effect.
ACKNOWLEDGEMENT Supported by fundamental
scientific research special funds of operating
expenses (2007B06) and state oceanic
administration youth marine science foundation.
ADVANCES IN SAR OCEANOGRAPHY FROM ENVISAT AND ERS
MISSIONS 21-25 January 2008
ESA ESRIN Frascati Rome Italy