Abstract
Lakes in arid regions play an important role in regional water cycles and are a vital economic resource, but can fluctuate widely in area and volume. This study demonstrates the use of a multisensor satellite remote sensing method for the comprehensive monitoring of lake surface areas, water levels, and volume for the Toshka Lakes in southern Egypt, from lake formation in 1998 to mid-2017. Two spectral water indices were used to construct a daily time-series of surface area from the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), validated by higher-resolution Landsat images. Water levels were obtained from analysis of digital elevation models from the Shuttle Radar Topography Mission (SRTM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), validated with ICESat Geoscience Laser Altimeter System (GLAS) laser altimetry. Total lake volume peaked at 26.54 × 109 m3 in December 2001, and declined to 0.76 × 109 m3 by August 2017. Evaporation accounted for approximately 86% of the loss, and groundwater recharge accounted for 14%. Without additional inflows, the last remaining lake will likely disappear between 2020 and 2022. The Enhanced Lake Index, a water index equivalent to the Enhanced Vegetation Index, was found to have lower noise levels than the Normalized Difference Lake Index. The results show that multi-platform satellite remote sensing provides an efficient method for monitoring the hydrology of lakes.
Highlights
The primary source was the complete time series of Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) 16-day composites (2000–2017), with Advanced Very High Resolution Radiometer (AVHRR) images from 1998–2000, and higher resolution Landsat-5, -7, and -8 images and SPOT-5 images used for validation (Landsat) and threshold selection (SPOT)
Like its equivalent vegetation index enhanced vegetation index (EVI), enhanced lake index (ELI) does require the presence of a blue spectral band, in addition to the red and near-infrared bands used in normalized difference lake index (NDLI)
Water-level measurements and trends can be derived from satellite laser altimetry or from analysis of digital elevation models (DEMs) using two different methods
Summary
Lakes in arid regions are sensitive to changes in local to regional hydrology [6–8], which is a troubling fact, given their disproportionate importance in the ecology and economic systems of these water-limited areas. Issues of sensor calibration and radiometric quality, atmospheric correction, and data distribution hindered the development of fully automated, high-temporal resolution systems for lake monitoring using these optical remote sensing platforms. Since 2000, the launch of operational, global monitoring systems, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Sentinel satellite constellation, including products and/or tools for deriving surface reflectance from the raw top-of-atmosphere spectral radiance measurements, has enabled the development of automated algorithms for frequent monitoring of lake surface areas from space
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