Comparison of methods to estimate lake-surface-water temperature using Landsat 7 ETM+ and MODIS imagery : case study of a large shallow subtropical lake in southern Brazil

Water temperature regulates many processes in lakes; therefore, evaluating it is essential to understand its ecological status and functioning, and to comprehend the impact of climate change. Although few studies assessed the accuracy of individual sensors in estimating lake-surface-water temperature (LSWT), comparative analysis considering different sensors is still needed. This study evaluated the performance of two thermal sensors, MODIS and Landsat 7 ETM+, and used Landsat methods to estimate the SWT of a large subtropical lake. MODIS products MOD11 LST and MOD28 SST were used for comparison. For the Landsat images, the radiative transfer equation (RTE), using NASA’s Atmospheric Correction Parameter Calculator (AtmCorr) parameters, was compared with the single-channel algorithm in different approaches. Our results showed that MOD11 obtained the highest accuracy (RMSE of 1.05 C), and is the recommended product for LSWT studies. For Landsat-derived SWT, AtmCorr obtained the highest accuracy (RMSE of 1.07 C) and is the recommended method for small lakes. Sensitivity analysis showed that Landsat-derived LSWT using the RTE is very sensitive to atmospheric parameters and emissivity. A discussion of the main error sources was conducted. We recommend that similar tests be applied for Landsat imagery on different lakes, further studies on algorithms to correct the cool-skin effect in inland waters, and tests of different emissivity values to verify if it can compensate for this effect, in an effort to improve the accuracy of these estimates

Long time series of Landsat images to reconstruct river surface temperature and turbidity regimes of Guadalquivir Estuary

In the last century the Guadalquivir River in Andalusia has been dramatically transformed affecting its ecological and hydrological functioning. In view of a new dredging plan to increase ship size and number arriving to Seville, a research consortium has started to study the state of the Guadalquivir Estuary. The Remote Sensing and GIS laboratory of Doñana Biological Station participates in the project with the aim to reconstruct the last 35 years regime of turbidity and river surface temperature (RST), both parameters revealing the estuarine response to natural and human-driven dynamics. Based on a long time series of Landsat images (TM and ETM+), we have developed accurate methods to systematically map RST and turbidity gradients across the last 100 km stretch of the River. We present the results of applying an empirical model for river turbidity mapping and a physical model to map RST by using optical and thermal bands of TM and ETM + sensors. Both models were validated with ground-truth data and are used to reconstruct the historical dynamics of the Guadalquivir Estuary.Peer reviewe