Estimation Of Mangrove Biomass In Shenzhen Bay Based On Multi-source Remote Sensing Data

Mangrove forest is an important part of carbon cycle because of its good carbon sequestration ability.But it's also very fragile and vulnerable to destruction by human activities.Based on Landsat remote sensing data from 1973 to 2017,and using multilevel classification based on object oriented to extraction of mangrove area in Shenzhen Bay.And build the regression relationship between biomass and variables using neural network method in order to calculation the change of mangrove biomass in 44 years.Based on Worldview-2 and Radarsat-2,a variety of methods are used to classify the tree species of mangroves in Shenzhen Bay in 2015.Each species was constructed with a biomass regression equation and calculated the biomass of each tree species in 2015.It is expected to provide data support for the carbon sequestration study of mangroves in Shenzhen Bay,and to provide experience for other mangrove biomass studies.The main achievements of this study are as follows:?1?Comparison of different data sources and regression method,using spectral data and radar data combined with texture data can get better classification results using only the spectral data.Using the random forest method based on object oriented species classification result is better than the decision tree,support vector machine and K-nearest neighbor.?2?When using different data sources to estimate the total biomass,the results are different.The regression models with radar and texture features are higher than those that only use spectral data.The main reason is that when only using spectral data the saturation of vegetation index restricts the expression of biomass,while using radar and texture data will not be restricted.?3?Mangrove species in Shenzhen Bay are mainly Kandelia candel?KC?,Avicennia marina?AM?and Aegiceras corniculatum?AC?and Sonneratia apetala?SA?.In 2015,the mangrove area of Shenzhen Bay was 489.01 hm²,of which the mangrove area of Futian was 92.70 hm²,and the mangrove area of Mai Po was 396.31 hm².The dominant species proportion is from big to small in turn KC,AM,AC,SA;the amount of biomass from large to small is KC,AM,AC,SA;the average biomass density is in turn from large to small be KC,AC,AM,SA in turn.In 2015,the total biomass of mangrove forest in Shenzhen Bay was about 1.35×10⁵t,and the average biomass density was 276.06 t·hm^-2.The biomass of Futian was 2.051×10⁴t,and the biomass of Mai Po mangrove forest was 1.14×10⁵t.KC is densely distributed in two areas.AC mainly concentrated in the front of mangrovenear near bare beach in north Mai Po,there are also a small amount of distribution in Shazui,Futian.AM is mainly distributed between the back end of the AC and the front end of the KC in north Mai Po,and distributed in middle tidal flat in middle Mai Po.There are also banded areas on the east side of bird watching Pavilion and the long narrow middle tidal flat near Che Kung Temple in Futian.SA is mainly distributed in the northwest of the bird watching Pavilion,and the beaches on the front of the reserve,and the north shore of the Shenzhen River in Futian.And it is scattered in the Mai Po,mainly near the edge of the mangrove area.?4?The area and biomass of mangroves in Shenzhen Bay experienced a trend of decreasing at first and increasing after from 1973 to 2017.In 1973,the mangrove forest in Shenzhen Bay had 522.26hm²,biomass of 1.21×10⁵t.The area and biomass in 1988 were the smallest,with an area of 290.34hm² and biomass of 7.11×10⁴t.In 2017,the area reached 715.41 hm² and biomass reached 1.76×10⁵t.The area of the Futian mangrove disappearance is now near Futian Free Trade Zone and the area beside the coastline.Due to the artificial planting of SA and the widen of the mangrove width along the coastline,the mangrove area of Futian was increased after 1988.The area of the Mai Po mangrove disappearance is now near Hongkong Wetland Park and the beach between Jianbizui and Jintian River.The mangrove area of Mai Po was increased too after 1988,because of the mangroves on the beach between the Jintian River and the Shenzhen River was increased and the mangroves near the Hongkong Wetland Park began to recover.Analysis of the types of land use before and after the mangrove region changes,large-scale reclamation,urbanization and pond culture caused the mangrove region changed into woodland,impervious surface and ponds.,most of the mangrove area at present was existed as ponds in the year 1973.?5?Compared with Mai Po mangrove in Hongkong,Futian mangrove in Shenzhen is smaller,the average biomass density is lower,total biomass is lesser.The area of Futian mangrove decreased rapidly before 1988,and then the area recovered slowly.