| This paper takes Chongming Dongtan of the Yangtze River estuary as the main research object.In October 2014 and September 2016,the Terreatrial Laser Scanner(TLS)was used to obtain the high-precision point cloud data of the Dongtan tidal flat geomorphology,for the high-coverage salt marsh vegetation,the vegetation information in TLS point cloud data was removed is target,and the relationship between vegetation properties and laser point cloud properties was constructed,filtering algorithm was constructed,TLS recover of different salt marsh vegetation precision,laser point cloud penetration depth with distance relationship and vegetation error removal,discussed the applicability of TLS in high-coverage salt marsh area,etc.And the 3D elevation of the tidal flat geomorphology was constructed.Combined with the resource IKONOS high-resolution satellite imagery,ZY-1 02 C satellite imagery and the SPOT 7 high-resolution satellite imagery,the temporal and spatial variation of the annual erosion and deposition of the Dongtan bare flat,the seasonal succession of the salt marsh vegetation population and the response pattern of the tidal flat surface morphology to the Spartina alterniflora ecological management project are analyzed.The influencing factors of dynamic sedimentary geomorphology in Chongming Dongtan were discussed.The following main results have been achieved through research:(1)Vegetation density is highly linearly related to the returning property of laser pulses,but the relationship between plant height,biomass and light return properties is not obvious;the higher the coverage of salt marsh vegetation,the lower the accuracy of terrain recover,and the two are negatively correlated.In the existing quadrats analysis,plant height,biomass and point cloud amplitude are not significantly linear;density(number of plants)has a significant linear relationship with point cloud amplitude properties,and the correlation is strong.Higher vegetation coverage leads to lower accuracy of TLS topography retrieval,they have a negative correlation.The ability of TLS laser penetrate different vegetation is not the same,when coverage greater than 50%,the laser cannot penetrate Imperata cylindrica community,Spartina alterniflora community and Scirpus mariqueter community,the original coverage corresponds to 70%,65%,65%,RMSE were 22.0,22.0,8.6 cm.when coverage equal to 50%,RMSE of topography retrieval: Imperata cylindrica community is 16 cm,Scirpus mariqueter community is 6.6 cm,Phragmites australis community and Spartina alterniflora community corresponds to 4.5,5.7 cm.when coverage less than 50%,with the decrease of the coverage,the accuracy of topography retrieval of Phragmites australis community,Spartina alterniflora community and Scirpus mariqueter community small increasing,and the accuracy of topography retrieval of Imperata cylindrica community was improved more obvious.(2)The high-coverage salt marsh vegetation,the laser penetration ability as a whole gradually decreases with the increase of the distance;the low-tidal flat low coverage of the Scirpus mariqueter region,TLS recover topographic effect is better,the accuracy is less than 2 cm.For the laser "blind zone",using the penetration depth variable and the correction factor try to remove the vegetation error is less accurate.In the high-coverage salt marsh vegetation area,the laser penetration ability generally decreases with the increase of the distance.Although the height of the instrument is helpful to improve the accuracy of the recover topography,the overall average penetration depth of the two quadrats lines is only increased by 4.68 cm and 3.83 cm,which is small.For the low tidal flats low-coverage Scirpus mariquete region,the TLS recover topography is better,with an accuracy of less than 2 cm.The RMSE of the two quadrats lines using the penetration depth recover is as high as 1.58 m and 2.22 m.The RMSE of the modified factor method in the recover of the Phragmites australi and the Imperata cylindrical white grass community is 0.2998 cm,0.2427 cm;0.1500 cm,0.1426 cm respectively.Active laser remote sensing has the incomparable advantages of other remote sensing methods in forest and vegetation height measurement.However,for high-coverage vegetation areas,the method and accuracy of recover of the terrain need further study.(3)Two years after the construction of the Spartina alterniflora ecological project(2014-2016),the response of the northern,central and southern tidal flats of Chongming Dongtan to the project was obvious difference.Horizontal change: Before the project,the north and south 2 m contour lines pushed to the sea at 26.0 m/a and 9.0 m/a respectively,after the project,the north and south 2.5 m contour lines pushed to the sea at a rate of 32.5 m/a and 8.1 m/a respectively,the northern 2 m contour line has slightly increased the rate of propulsion to the sea,which may be affected by the project,and the south is still in a natural state of development.Before the project,the north,central and southern 2.5 m contour lines pushed to the sea at rates of 16.7 m/a,60.0 m/a and 30.0 m/a respectively.After the project,the north,central and southern 2.5 m contour lines pushed to the sea at a rate of 68.5 m/a,98.0 m/a,25.2 m/a respectively.the north 2.5 m contour line has a significantly improved propulsion rate,the central 2.5 m contour line has a slightly higher propulsion rate,and the southern 2.5 m contour line has a slightly lower propulsion rate.In 2014-2016 years,the overall level of horizontal change in the level: Central > South > North.Vertical change: Whether in the south,middle and north,the intertidal zone zoning rate is higher than the sedimentation rate at the sea,and the overall siltation rate: middle > north > south.Before the project,the overall level of horizontal change in the level: Central > South > North.The Spartina alterniflora ecological management cofferdam project has changed the erosion and deposition rate of Dongtan.Profile morphology: the southern sections N1,N2,and N3 curvature from south to north gradually decreases from south to north,and the slope decreases continuously.The shape of the Z1 section in the middle section is relatively complex,the curvature of the section increases in 2014-2016 years,and the slo pe decreases steeply.Overall,2016 near-shore siltation More,the slope is large r,and after the cofferdam,the existing sediment accumulation peak will migra te,and on this basis,it will develop into a new tidal flat section.(4)Two years after the construction of Spartina alterniflora ecological management cofferdam project,the seasonal succession of the salt marshes population in the central and southern parts changed significantly.After the implementation of the Spartina alterniflora ecological management cofferdam project in 2013,due to artificial removal and control measures,the area of Spartina alterniflora in the central salt marsh tidal flat decreased significantly,reducing 204.87 ha in 2014-2016;the area of reeds increased by 115.87 ha,the increased area is mainly in the central part of Dongtan;the Scirpus mariqueter/ Scirpus triqueter community has slightly increased from 246.08 ha in 2014 to 259.93 ha in 2016.Overall,the area of salt marshes in the central and southern regions has slightly decreased.The seaward advancing rate of the vegetation-beach boundary line in 2014-2016 is 41.69 m/a,which is similar to the 30-50 m/a in 2005-2011 before the project,and is significantly lower than the 250 m/a propulsion speed in 1982-1990.In the tidal flat area of the salt marsh,near the 98 cofferdam,there is basically no abnormality of “deposition” and “erosion”.The area is more stable and the “deposition” increases in the area near the sea.In the central region,there is a large area of "erosion" phenomenon.(5)The northern tidal creek was intercepted by the cofferdam,although the central and southern tidal creeks are still developing slowly,the average growth rate of the tidal flats has decreased to varying degrees in 2014-2016(after the project)is compared to 2013-2014(before the project);The gravity of the tidal creek in the central and southern regions has not oscillated in 2013-2014.The center of gravity in 2016 is a large distance from the southeast in 2013 and 2014;There is no large offset between the central axes of the two large tidal creeks in the south of Dongtan.After the implementation of the Dongtan Ecological Management Cofferdam Project in 2013-2014,the tidal creeks in the north were seriously damaged.Although the increase of the plane parameters of the tidal creek indicates that 2014-2016(after the project)the central and southern tidal creeks continue to develop slowly,the tidal channel length,catchment area,density,tillering rate and fractal dimension are in 2014-2016(after the project).The average growth rate has been reduced to varying degrees compared to the growth rate of 2013-2014(before the project),which may be affected by the reclamation project.The implementation of the ecological management of the Spartina alterniflora ecological management project,the interannual growth rate of the plane parameters of the central and southern tidal flats of Dongtan was different from that before the project;the center of gravity of the central and southern tidal trenches shifts to the southeast after the project.The 1# and 2# tidal creek in the south of Dongtan have a stable overall performance,the 2# tidal mouth has a large offset. |
PDF Full Text Request