Remote sensing of water surface temperature and heat flux over a tropical hydroelectric reservoir

Water temperature plays an important role in ecological functioning and in controlling the biogeochemical processes of a water body. Conventional water quality monitoring is expensive and time consuming. It is particularly problematic if the water bodies to be examined are large. Conventional techniques also bring about a high probability of undersampling. Conversely, remote sensing is a powerful tool to assess aquatic systems. The objective of this study was to map the surface water temperature and improve understanding of spatiotemporal variations in a hydroelectric reservoir. In this work, MODIS land-surface temperature (LST) level 2, 1-km nominal resolution data (MOD11L2, version 5) were used. All available clear-sky MODIS/Terra images from 2003 to 2008 were used, resulting in a total of 786 daytime and 473 nighttime images. Descriptive statistics (mean, maximum and minimum) were computed for the historical images to build a time series of daytime and nighttime monthly mean temperatures. The thermal amplitude and anomaly were also computed. In-situ meteorological variables were used from 2003 to 2008 to help understand the spatiotemporal variability of the surface water temperature. The surface energy budget and the depth at which the wind can distribute the heat input of a given surface were also measured. A correlation between daytime and nighttime surface water temperatures and the computed heat fluxes were made. These relationships and the causes of the water surface temperature variability are discussed.