联合哨兵卫星系列雷达与光学影像的洞庭湖水域面积变化高时空分辨率监测

High spatial and temporal resolution monitoring of water area changes of Dongting Lake by joint Sentinel satellite series of radar and optical images

洞庭湖是中国第二大淡水湖,干湿季节水体波动幅度大、频率高。卫星高频观测洞庭湖水体变化对及时、准确地监测其水文动态变化具有重要意义。本研究利用Sentinel-1和Sentinel-2影像(10 m),在兼具高时频与空间分辨率条件下重建和分析2017年—2020年洞庭湖水域面积的精细时序信息。此外,本研究拟创建一种基于湖区部分清晰影像来重建全湖水域面积的方法。该方法利用湖区某个区块面积与Sentinel-1全幅影像提取的湖泊面积构建的统计拟合关系建立经验模型,从而得到更密集的洞庭湖水域面积时间序列。拟合结果显示,每个区块的面积与总面积呈显著正相关,平均R2值为0.94。将2017年—2020年获取的119景Sentinel-1影像和38景Sentinel-2影像用于提取洞庭湖区块水体淹没范围,以重建整个湖区面积。结合Sentinel-1和Sentinel-2影像,平均每个月可获取的观测影像为6景,某些月内监测次数可达10次,时间间隔为3—6 d。此外,本研究重建的水域面积时间序列可以精确地刻画显著的季节波动和年际变化,水域面积在7月达到峰值,11—2月达到谷值。研究发现一个月内最大面积与最小面积的平均比率为1.36;地表水域最剧烈的波动发生在11月,比率为1.52。整合Sentinel-1/2影像确定,2017年—2020年洞庭湖的平均水域面积约为1147.13 km2。与基于Sentinel-1/2影像构建的洞庭湖水域面积时间序列相比,结合Landsat 8影像的水体面积时间序列能够在某些月将水体观测的时间分辨率提高,但是对于水域面积的月均值和年均值影响较小。综上,本研究联合高时空分辨率的哨兵系列雷达与光学影像发展高时频水域面积序列的精细提取方法,可为提升洞庭湖及长江中下游高动态湖泊水域遥感监测和水资源精细管理提供科技支撑。

Dongting Lake is the second largest freshwater lake in China,and the water body fluctuates greatly and frequently in dry and wet seasons.The high-frequency observation of water body changes in Dongting Lake by satellite is important for timely and accurate monitoring of its hydrological dynamic changes.This study aims to reconstruct and analyze the elaborate time series information of Dongting Lake water area from 2017 to 2020 by using Sentinel-1 and Sentinel-2 images(10 m)under the condition of high time-frequency and high spatial resolution.In addition,this study develops a method to reconstruct the whole lake water area and encrypt the time series of lake area based on the partially cloudless image of the lake area.This method uses the statistical fitting relationship between the block area and total area extracted from Sentinel-1 full image to establish an empirical model for obtaining a dense time series of Dongting Lake water area.Fitting results show that the area of each block is significantly positively correlated with the lake total area,and the average R2 value is 0.94.From 2017 to 2020,119 Sentinel-1 images and 38 Sentinel-2 images were obtained to extract the block inundation range of Dongting Lake for reconstructing the whole lake area.After all Sentinel-1 and Sentinel-2 images were combined,the average observation images available in each month are 6.In some months,the monitoring times can reach 10 times,and the time interval is 3—6 days.It can conduct fine monitoring of the water area change of Dongting Lake.Besides,the time series of water area reconstructed in this study can accurately describe the significant seasonal fluctuations and interannual changes.The water area reaches the peak in July and the valley from November to February.The average ratio of maximum area to minimum area in a month is 1.36.The most violent fluctuation in surface waters occurred in November,with a ratio of 1.52.After Sentinel-1/2 image observation time series were integrated,the average water area of Dongting Lake from 2017 to 2020 is about 1147.13 km2.Compared with the water area time series of Dongting Lake constructed based on Sentinel-1/2 images,the water area time series combined with landsat-8 image can improve the time resolution of water observation.However,it has little effect on the monthly and annual averages of water area.This study combines sentinel series radar and optical images of high temporal and spatial resolution to develop a fine extraction method of high time-frequency water area series.In summary,this study can provide scientific and technological support for improving remote sensing monitoring and fine management of water resources in Dongting Lake and high dynamic lakes in the middle and lower reaches of the Yangtze River.