低盐湖泊水体盐度光学遥感反演研究——以博斯腾湖为例

Measuring salinity of low salinity lake by optical remote sensing:A case study of Bosten Lake

利用光学遥感反演盐度,可以充分利用遥感数据的空间代表性,以及目前高分率遥感数据的高时空精度。本文利用MERIS(Medium Resolution Imaging Spectrometer)300 m数据,以干旱区的博斯腾湖(博湖)为例,探讨了光学遥感数据反演低盐湖泊水体盐度的可行性。结果显示:在开都河入流影响的博湖西南角,存在光学遥感反演盐度利用的黄色物质(CDOM)与盐度的反比关系,但相关性不高,而且在博湖区域不同时间、不同区域CDOM与盐度的关系都不同。博湖盐度低于3 g·L-1,而遥感数据计算盐度的精度约为1.1 psu,因而用光学遥感数据计算博湖盐度的误差太大。博湖本身CDOM与盐度关系的时空异质性以及相关性不高,目前光学遥感反演精度有限,因此,在博湖用光学遥感数据反演整个湖区的盐度有困难。用光学数据反演水体盐度要求盐度足够高,盐度和CDOM存在梯度,并满足CDOM扩散守恒,因此用光学遥感反演低盐湖泊水体盐度较为困难。

Salinity is a basic property of natural water. Therefore, assessing this property is relevant. Measuring salinity by using optical remote sensing data provides the advantages of spatial coverage and high spatiotemporal precision of currently available high-resolution satellite data. Full-resolution images from a medium-resolution imaging spectrometer were used to explore the feasibility of measuring the low salinity of a lake based on ocean color data. Bosten Lake was selected as the study area for this research. The study was carried out by establishing the empirical relationship between salinity and Colored Dissolved Organic Material （CDOM） absorption coefficients. We focused on different areas of the lake on April 27, 2011 and in the whole lake for an entire year from June 2010 to June 2011, in which the day of April 27, 2011 is the flood day of the Kaidu River. Salinity data were acquired by using YSI-6600 and in situ sampling and combining the data gathered by the researcher. CDOM absorption coefficients were obtained by using BEAM 4.10.3 software. The salinity of southwestern Bosten Lake, which is dominated by the Kaidu River, exhibits an inverse relationship with CDOM absorption coefficients; however, no significant correlation is observed. The relationships between CDOM absorption coefficients and salinity vary in space and time in Bosten Lake, which is similar to other study areas. The salinity of Bosten Lake is lower than 3 g · L^-1, and the root mean square error of measuring salinity from a satellite in space is approximately 1.1 practical salinity units. The errors are nearly close to the salinity value of the lake, thus denoting that they are too large for estimating the salinity of Bosten Lake by using optical remote sensing data. Thus, measuring the salinity of Bosten Lake by using optical remote sensing data is difficult. Because the considerable heterogeneities observed from the relation- ships between CDOM absorption coefficients and salinity at different times and areas have no significant correlation, and the error of the salinity calculated by optical remote sensing data is too large. Measuring water salinity by using optical data requires that water must possess sufficient salinity and has both salinity and CDOM gradients. Moreover, CDOM conservative mixing must also be satisfied. These conditions make monitoring the low salinity of a lake difficult.