基于NDVI滇池水华特征的时空变化研究

Study on Spatio-temporal Changes of Water Bloom in Dianchi Lake Based on NDVI

相较于其他传感器,MODIS数据在水质监测方面具有明显优势。基于2000-2017年的MODIS影像16d合成250m×250m分辨率的归一化植被指数(NDVI)数据,应用ArcGIS、GetData、Grapher10等软件对数据进行处理,从逐年、逐月到逐旬详细分析了滇池地区NDVI的时空分布规律,探讨了不同等级蓝藻水华的分布面积和空间变化特征。结果表明,(1)时间变化上,2000-2017年间滇池年NDVI总体呈现减少趋势,蓝藻水华覆盖度有所降低,富营养化偏向减轻;多年平均的轻度水华面积约占滇池总面积的54.99%,中度水华和重度水华面积分别占总面积的27.42%和17.59%;11-4月滇池以无水华区域为主,5-10月以轻度水华为主,中度水华主要出现在5-10月,重度水华则集中在7-9月;蓝藻水华的暴发时间大约在7月上旬和8月下旬,其重度水华面积分别达到11.4%和14.0%。(2)空间变化上,滇池蓝藻水华的暴发格局总体呈现"北重南轻"的分布态势,水华较严重的区域集中在北部草海、断桥、晖弯和滇池边界;但从变化趋势上,NDVI减小,表征蓝藻水华覆盖度减少的地区主要分布在滇池北部的断桥和中部部分区域。该研究结论可为丰富滇池水质监测方法,建立实时预警系统,以及水资源的合理利用与有效管理提供科学依据。

Water quality monitoring is one of the important application areas of remote sensing technology. Compared with other sensors, MODIS data has obvious advantages in water quality monitoring. Based on the 16-day synthetic 250 m×250 m resolution normalized vegetation index(NDVI) data product of MODIS image form 2000 to 2017, the data were processed by Arc GIS,GetData, Grapher10 and other software, The spatio-temporal distribution of NDVI in Dianchi Lake was analyzed in detail. The distribution area and spatial variation characteristics of different levels of cyanobacterial blooms were discussed. The results showed that annual NDVI in Dianchi area showed a decreasing trend from 2000 to 2017. No blooms area accounted for 54.99% of the total area, and the moderate water blooms and heavy water blooms accounted for 27.42% and 17.59% respectively. In spring, summer and autumn, Dianchi Lake was dominated by mild water blooms. However, the area without water bloom accounted for the largest proportion in winter. From January to April, Dianchi Lake was mainly dominated by no blooms region. From May to October, it was dominated by mild water bloom. Moderate water blooms mainly occurred from May to October. Heavy water blooms were concentrated in July-September. The outbreak time was approximately early July and late August, with heavy water bloom reaching 11.4% and 14.0% respectively. The cyanobacteria bloom was heavier in north region in Dianchi Lake than that of the south region. The relatively serious areas of water bloom were concentrated in Northern Caohai, Duanqiao and Huiwan. However, the decrease of NDVI indicated that the coverage of cyanobacteria water bloom was decreasing, and the areas where the water quality was improved were mainly located in the northern part of Dianchi Lake and some areas in the middle parts. The conclusion of this study can provide a scientific basis for enriching the water quality monitoring method of Dianchi Lake, establishing a early warning system, and the rational utilization and effective management of water resources.