STUDY ON THE COASTLINE CHANGE OF JIAOZHOU BAY BASED ON HIGH RESOLUTION REMOTE SENSING IMAGE

In recent years, with the rapid development of the Jiaozhou Bay area of Qingdao, the influence of human activities on the coastline of Jiaozhou Bay is becoming more and more serious. Based on the high resolution remote sensing image data of 10 periods from 2001 to 2017 in the Jiaozhou Bay area, and combined with the data of on-the-spot survey and expert knowledge, this paper have completed the interpretation and extraction of coastline data of each year, and analyzed the distribution, size, rate of change, and trend of the increase and decrease of the coastal area of Jiaozhou Bay in different time periods, combined with the economic construction and the marine hydrodynamic environment of the region to analyze the reasons for the change of the coastline of Jiaozhou Bay. The results show that the increase and reduction of the coastal area of Jiaozhou Bay was mainly affected by human activities such as sea reclamation and marine aquaculture, resulting in a gradual change in the rate of increase and decrease with human development. For coastal advance part,2001-2013, the average increase rate on the coastal area of Jiaozhou Bay was 2.30 km2/a, showing a trend of rapid growth, 20132017 the average increase rate of 0.53 km/a, and the growth rate slowed down. For coastal retreat part, 2001-2013, the average decrease rate was 2.58×10 km/a. 2013-2014, the decrease rate reached a peak value of 1.11 km/a. 2014-2017, the average decrease rate was 0.14 km/a. The decrease rate shows a trend of increasing first and then slowing down.


INTRODUCTION
With the country's increasing emphasis on the ocean, Qingdao has developed rapidly as a coastal city in recent years.Jiaozhou Bay is the largest bay in Qingdao, and the development of the Jiaozhou Bay area is of crucial to Qingdao.Therefore, it is highly valued by the Qingdao Municipal Government.At present, the new pattern of building the 'three bays and three cities' proposed by the Qingdao Municipal Government is still centered on Jiaozhou Bay.In recent years, the rapid economic development of Jiaozhou Bay area, the sea reclamation activities such as the construction of urban areas have greatly changed the contour and area of the coastal zone and the bay.The impact of marine aquaculture and other activities surrounding the sea on the  Corresponding author changes in the sea area of the Jiaozhou Bay have also gradually increased.Meanwhile, with a total area of Jiaozhou Bay is shrinking, gradually decrease in tidal influx, the flow rate decreases, the bay water exchange capacity weaker.These changes in turn affect the coastline of Jiaozhou Bay.

The Study Range and Data
This paper collected 10 high-resolution remote sensing images covering the Jiaozhou Bay area.The imaging time was 2001-2017, and the coverage was 120 ° 05 '~ 120 ° 25' E, 35 ° 55 '~ 36 ° 20' N (Figure 1, Figure 2).These 10 remote sensing images have been precisely corrected and the WGS84 coordinate system and the UTM-51N projection have been adopted.Data sources include Landsat-7, SPOT-5, GF-1, GF-2 and Airborne Remote Sensing.Detailed information is shown in Table 1.The principle of determining the coastline at the estuary is to take the intersection of the shoreline on both sides of the estuary and the banks of the estuary entrance to the sea, and then connect them as the estuary coastline.There are many dikes in Jiaozhou Bay, and some of the dikes extend into the sea for a long distance.

Coastline Extraction
Since this paper mainly studies the change of increase and decrease area in coastal areas, the dam body is also extracted as it is.The line between Tuandaotou and Xuejiadao-Jiaozishi is the dividing line of Jiaozhou Bay sea area.

Coastal Increase and Decrease Area Extraction Method:
ArcGIS is used as a platform to extract the coast increase and decrease areas using human-computer interaction method.The between the obtained polygon elements, the area of increase and decrease changes between any two years can be obtained.

Sea Area Extraction Principle:
The area of sea area in this paper refers to the area covered by seawater, excluding the islands and mariculture facilities in Jiaozhou Bay.From 2001 to 2017, the sea area of the Jiaozhou Bay showed a decreasing trend (Figure 8).From 2001 to 2013, the decrease rate was rapid.The area decreased from 362.9 km 2 to 337.3 km 2 , and the annual average decrease rate reached 2.13 km 2 /a.However, in recent years, the decreasing trend of the area gradually slowed down.From 2013 to 2017, the rate of area reduction was only 0.042 km 2 /a.2013-2014, 2014-2015 and 2016-2017, there even been a slight increase in sea area.These changes are closely related to the economic development model of the Jiaozhou Bay area.Before 2013, in order to pursue economic benefits and urban expansion, the development of marine aquaculture and continuous sea reclamation has led to a rapid reduction in the sea area of Jiaozhou Bay.Since 2014, with the increasing control over sea reclamation and the increasing emphasis on marine environmental protection, there has been only a slight increase in the area of sea reclamation and marine aquaculture has been strictly regulated, especially the sea cages in the bay have all been cleaned up.Only a small increase in mariculture area in certain areas along the coast.

CONCLUSION
The results of the study indicate that the changes in the shoreline in Jiaozhou Bay in recent years have obvious phase: (1)2001-2013, the average increase rate of Jiaozhou Bay was 2.13 km 2 /a, showed a rapid increase;2001-2013, the average decrease rate was 2.58×10 -3 km 2 /a, showed a slow decreasing trend.During this period, the economic development of Jiaozhou Bay was in a stage of rapid development.In order to supply land for human activities such as building houses, oil depots, and port, a large-scale sea reclamation project was carried out.At the same time, the development of marine aquaculture also takes up a large number of sea areas.These factors weaken the flow field velocity and water exchange capacity in Jiaozhou Bay, thereby weakening the natural erosion ability of seawater.
(2) 2013-2017, the average increase rate of Jiaozhou Bay is 0.53 km 2 /a, showed a slow increasing trend.2013-2014, the decrease rate reaches a peak of 1.11 km 2 /a, while the average decrease rate in 2014-2017 falls to 0.14 km 2 /a, the decrease rate showed a downward trend.In 2013, the Qingdao Municipal Government issued the 'Notice on Cleaning Aquatic Facilities in the Jiaozhou Bay Sea Area' , and a large number of mariculture facilities were cleared.The increase of this period mainly comes from sea reclamation, while decrease is mainly due to the cleaning of aquaculture facilities.
(3) The area of the sea is constantly changing with the change of increase and decrease area.2001-2013, the area of coastal area increased rapidly, resulting in a rapid reduction in sea area.2013-2017, the area of eroded areas continued to increase, the growth Figure1The study range and its coastline of Jiaozhou Bay

Figure 2
Figure 2 Remote sensing images of Jiaozhou Bay from 2001 to 2013 Principle: The Jiaozhou Bay coastline consists of bedrock shoreline, sandy shoreline, silt shoreline and artificial shoreline.The sea cliffs on the bedrock coast are steep, covered with vegetation, with clear boundaries between sea and land, and with twisting coastlines.Sandy coasts are generally flat.In remote sensing images, the location of sandy coastlines should be taken in the upper limit of the beach ridge footprint.The silt shoreline is located on the silt shore and has a wide beach.In remote sensing images, the place where the lush vegetation and sparseness are significantly different is the location of the silt shoreline.The artificial coastline formed by sea reclamation, dam, port, and salt fields and aquaculture ponds has obvious interpretation signs.In remote sensing images, the outer edge of the outline is the coastline location.
Method: ArcGIS is used as a platform to extract information of coastlines in different periods using human-computer interaction method.The detailed technical route is as follows: (1) With reference to 2001 remote sensing images, the 2001 coastline was extracted.(2) When the 2007 coastline was extracted, the 2001 coastline was first loaded onto the 2007 remote sensing image, and only the changed parts were modified to obtain the 2007 coastline.(3) Extract the coastline from 2010 to 2017 in the same way.A total of 10 coastlines were obtained.The advantage of this method is to ensure that the unchanging coastline segment has the same geographical location at different times, and the coastline position error will not be caused by the deviation of the image itself.In this way, the coastline is only the waterside line, and it is necessary to calibrate the waterside line according to on-thespot survey and expert knowledge, to obtain the coastline of 10 periods of Jiaozhou Bay.Figure 3.

Figure
Figure 3 Jiaozhou Bay Coastline 2001-2017 Method: ArcGIS is used as a platform to extract sea area using human-computer interaction method.The detailed technical route is as follows: (1) Connect the two ends of the coastline, close it and calculate its area.(2) Using the extracted increase and decrease areas, calculate the area occupied by islands and mariculture facilities in Jiaozhou Bay.(3) The total area of sea area minus the area occupied by islands and marine aquaculture facilities can obtain the actual sea area.the increase area was 13.336 km 2 , the average annual increase area was 2.223 km 2 /a, the decrease area was 0.035 km 2 , and the average annual decrease area was only 5.8×10 -3 km 2 /a.Increase areas are mainly concentrated on the eastern side of Cangkou waterway on the east bank of Jiaozhou Bay and the Huangdaoqian Bay and Haixi Bay on the south bank, and a small amount on the west bank.The visual interpretation of remote sensing images shows that the sea reclamation in the east coast is mainly used for real estate development, and the reclamation in the south bank is mainly used for the construction of port terminals and Huangdao oil depot.A small amount of aquaculture ponds added to the west bank.Decrease areas are distributed on the north and west bank, including two shorelines that are eroded by seawater, and the cleanup of a small number of mariculture facilities.

Figure 5
Figure 5 Increase and decrease in Jiaozhou Bay 2007-2013

Figure 7 Figure 8
Figure 7 Jiaozhou Bay flow field diagram of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-3, 2018 ISPRS TC III Mid-term Symposium "Developments, Technologies and Applications in Remote Sensing", 7-10 May, Beijing, China rate of silted areas slowed down, and the area of sea areas showed an alternating phenomenon of increase and decrease.In summary, human activities and policy regulation in recent years have played a decisive role in the change of coastline in Jiaozhou Bay.The hydrodynamic environment also has an important impact on human activities, indirectly affecting the changes of the coastline.At the same time, the changes in the coastline are constantly changing the hydrodynamic environment.Timely understanding of the changes in the coastline, strengthening monitoring and protection of the marine environment, formulating systematic plans, rationalizing the use of marine resources, and exploring the sustainable development of the Jiaozhou Bay area should be the focus of attention in the future.
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-3, 2018 ISPRS TC III Mid-term Symposium "Developments, Technologies and Applications in Remote Sensing", 7-10 May, Beijing, China technical route is as follows: (1) Establish an auxiliary line outside the Jiaozhou Bay coastline and form a closed line element with the extracted 2001 coastline.(2) Convert all closed