Abstract
Abstract. Lake water temperature (LWT) is an important driver of lake ecosystems and it has been identified as an indicator of climate change. Consequently, the Global Climate Observing System (GCOS) lists LWT as an essential climate variable. Although for some European lakes long in situ time series of LWT do exist, many lakes are not observed or only on a non-regular basis making these observations insufficient for climate monitoring. Satellite data can provide the information needed. However, only few satellite sensors offer the possibility to analyse time series which cover 25 years or more. The Advanced Very High Resolution Radiometer (AVHRR) is among these and has been flown as a heritage instrument for almost 35 years. It will be carried on for at least ten more years, offering a unique opportunity for satellite-based climate studies. Herein we present a satellite-based lake surface water temperature (LSWT) data set for European water bodies in or near the Alps based on the extensive AVHRR 1 km data record (1989–2013) of the Remote Sensing Research Group at the University of Bern. It has been compiled out of AVHRR/2 (NOAA-07, -09, -11, -14) and AVHRR/3 (NOAA-16, -17, -18, -19 and MetOp-A) data. The high accuracy needed for climate related studies requires careful pre-processing and consideration of the atmospheric state. The LSWT retrieval is based on a simulation-based scheme making use of the Radiative Transfer for TOVS (RTTOV) Version 10 together with ERA-interim reanalysis data from the European Centre for Medium-range Weather Forecasts. The resulting LSWTs were extensively compared with in situ measurements from lakes with various sizes between 14 and 580 km2 and the resulting biases and RMSEs were found to be within the range of −0.5 to 0.6 K and 1.0 to 1.6 K, respectively. The upper limits of the reported errors could be rather attributed to uncertainties in the data comparison between in situ and satellite observations than inaccuracies of the satellite retrieval. An inter-comparison with the standard Moderate-resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature product exhibits RMSEs and biases in the range of 0.6 to 0.9 and −0.5 to 0.2 K, respectively. The cross-platform consistency of the retrieval was found to be within ~ 0.3 K. For one lake, the satellite-derived trend was compared with the trend of in situ measurements and both were found to be similar. Thus, orbital drift is not causing artificial temperature trends in the data set. A comparison with LSWT derived through global sea surface temperature (SST) algorithms shows lower RMSEs and biases for the simulation-based approach. A running project will apply the developed method to retrieve LSWT for all of Europe to derive the climate signal of the last 30 years. The data are available at doi:10.1594/PANGAEA.831007.
Highlights
The interest in lake surface water temperature (LSWT) is manifold
We performed an inter-comparison between the standard Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature and Emissivity (LST/E) 5-Minute Level 2 Swath 1 km data set (MOD_L2 and MYD_L2, Version 5; Wan and Dozier, 1996) and the Advanced Very High Resolution Radiometer (AVHRR)-based LSWT data set proposed in this study for the years between 2000 (2002 for Aqua) and 2011
EPFL and BDS1 reflect the retrievals for large lakes, whereas the station KONS is located in a fjord-like part of Lake Constance, called Lake Überlingen, which is merely 2 to 3 km wide and about 21 km long (∼ 60 km2)
Summary
The interest in lake surface water temperature (LSWT) is manifold. The temperature of lakes is an important parameter for lake ecosystems influencing the dynamics of physiochemical reactions, the concentration of dissolved gazes (e.g. oxygen), and vertical mixing (Delpla et al, 2009). With this study we want to demonstrate the potential to derive LSWT for climatological studies from satellite data for the many lakes in Europe within the size range between approximately 15 (depending on the shape) and 500 km, which is the limit used in the study of Schneider and Hook (2010) Such a data set can hardly be provided on a global scale (with ∼ 12 300 inland waters in the range of 10 to 100 km2; Reynolds, 2007), but it offers great potential for regional or even continental scale climate analyses
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