Presentation on theme: "Analysis of Effects of Environmental Factors on Spatio-Temporal Distribution of Ice in Liaodong Bay with Envisat ASAR and MODIS Imagery Analysis of Effects."— Presentation transcript:
Analysis of Effects of Environmental Factors on Spatio-Temporal Distribution of Ice in Liaodong Bay with Envisat ASAR and MODIS Imagery Analysis of Effects of Environmental Factors on Spatio-Temporal Distribution of Ice in Liaodong Bay with Envisat ASAR and MODIS Imagery Haibo YUE (1), Yonggang JI (2) and Xi ZHANG (2) (1) Ocean University of China, NO.5 Yushan Road, Qingdao , China (1) Ocean University of China, NO.5 Yushan Road, Qingdao , China (2) First Institute of Oceanography, SOA, NO.6 Xianxialing Road, Hi-Tech Industry Park, Qingdao , China 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. ADVANCES IN SAR OCEANOGRAPHY FROM ENVISAT AND ERS MISSIONS January 2008· ESA ESRIN · Frascati · Rome · Italy SEASAR 2008 esa ENVISAT ： We acquire 58 ENVISAT ASAR images during and Introduction Introduction Data Description Data Description Environmental Factors Effect Conclusion Conclusion ACKNOWLEDGEMENT Supported by fundamental scientific research special funds of operating expenses (2007B06) and state oceanic administration youth marine science foundation. MODIS:ASAR: EOS/MODIS can provide multi-waveband data whose resolution is 250m compared with NOAA/AVHRR MODIS. We collect all the MODIS images during marine coastal weather stations data 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. Temperature Wind 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. Topographty Tide 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 isn’t 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. Salinity we establish the mathematic model between change of areas and that of temperature. Firstly we assume that there is a critical temperature T 0 (corresponding to the air temperature), when the air temperature T> T 0 ， the areas S decrease; vice versa the areas S increase when the air temperature T< T0. Here we assume the increase of ice areas is proportional to the decrease of air temperature and critical temperature (T- T 0 ). The formula is S i = S 0 +a∑T j –a×i×T 0 (1) Where, S 0 is the area of sea ice at the first day ， T j is the in situ measurement air temperature ， T 0 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 T 0 and coefficient a are different. In generally, the shallow water freeze firstly, then expand to deep water. Here shows the topography of the Liaodong bay. topography isobath of Liaodong Bay (Gu ， 2003) 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, MODIS image of Dec 24, 2005 to Jan 6, 2006 Ocean station Feb 3, 2006Feb 4, 2006 displacementvelocitydisplacementvelocity Bayuquan3.5km0.6m/s5.3km0.4m/s ice edge7.1km1.2m/s9.6km0.8m/s 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. simulated area sea ice area simulated area sea ice area 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.