基于卫星测高数据的2002~2018年太湖水位变化监测

Monitoring of water level variation in Tai Lake from 2002~2018 based on satellite altimeter data

针对传统水位监测方法的弊端以及太湖水位变化监测的现实需求,基于Envisat和Cryosat-2测高数据,采用Morlet小波分析、Mann-Kendall检验法研究2002年6月~2018年12月近20a的水位以及周期变化,并应用实测数据进行精度验证,从气象因素和人为影响两方面分析其不同时间尺度的变化趋势以及原因.结果表明:Evnisat/RA2L2GDR数据和Cryosat-2/SIRAL L2GDR数据测量精度较高,与实测水位的季、年尺度相关系数分别为0.559和0.845,可以进行长时间序列水位变化的监测;多年来太湖平均水位1.379m,最高水位为2016年6月的2.252m,最低水位为2011年10月的0.832m,每年1~4月水位逐渐上涨,在6月前后达到峰值,此后开始下降,在年末出现轻微抬升,且太湖春季水位最高,夏季最低,极差0.041m;在太湖近20a的水位变化中存在10~20个月、15~30个月以及40~60个月3类尺度的周期变化规律,且40~60个月时间尺度的周期变化最为强烈;以2015年4月份为分界点,在此之前水位呈显著下降趋势,此后水位呈上升趋势,并且在2003年3月与2004年12月水位发生显著突变;21世纪前10a太湖水位主要受控于气象因素,此后人为干预的影响逐渐加剧,使其与自然状态呈现出不一样的规律.

Due to the shortcomings of traditional water level monitoring methods and the actual needs of monitoring water level change in Tai Lake, based on Envisat and Cryosat-2 altimeter data, Morlet wavelet analysis and Mann-Kendall test were used to analyze the changes in water level and its periodicity from June 2002 to December 2018. The altimeter-derived water levels were compared with in-situ data to estimate the accuracy. Afterwards, we analyzed the change trends of water level at different time scales and discussed the causes of the changes from aspects of climatic factors and anthropogenic influences. Results indicated that the water level derived from Envisat/RA2 L2 GDR data and Cryosat-2/SIRAL L2 GDR data had high accuracies. The correlation coefficients between altimeter-derived water levels and in situ water levels were 0.559 and 0.845, respectively, at seasonal and annual scales. Therefore, altimeter data can be used monitor the change of water level in a long time series. From 2002 to 2018, the average water level of Tai Lake was 1.379 m, the highest water level was 2.252 m in June 2016, and the lowest water level was 0.832 m in October 2011. Besides, the water level gradually increased from January to April every year, reached the peak around June, and then began to decline, and slightly increased again at the end of the year. Tai Lake had the highest water level in spring, the lowest in summer, with a difference of 0.041 m. In the recent 20 years, there were three kinds of periodic changes in the water level of Tai Lake:10~20 months, 15~30 months and 40~60 months, in which the changes in the 40~60 months scale were the strongest. Before April 2015, the water level had a significant downward trend, and experienced significant mutations in March 2003 and December 2004,respectively, while after that, water level had an upward trend. In the first decade of the 21 st century, the water level of Tai Lake was mainly controlled by climatic factors. After that, the influence of human interventions gradually increased, causing the water level to show a different change pattern.