ALBERT

Description: Survey data from 2001 are given as 100 m ASCII grid file (ESRI format). All data are given in UTM (Zone 19H) coordinates. Laguna del Laja (Chile) is located at 36° 54' S and 71°05' W in the upper part of the Laja river basin in the Andean range at the east of Antuco volcano, at an altitude of 1360 m a.s.l. It is the largest and most important lacustrine system of the Biobío Region (Chile), with a watershed of ca. 975 km², the lake is fed by several small streams and is drained by the Laja river and two artificial tunnels for hydropower generation. The lake was surveyed in November 2001. The system used consisted of a Trimble GPS (4000 SSi, Fa. Trimble) connected by an echo sounder (EA400 Simrad). A special software was used to collect the data. About 160 cross profiles were measured within two weeks. The distance between profiles was 500 m in the main basin and 1000 m in the rest of the lake. At the beginning of measurements the water level was 1346 m above mean sea level. During the mapping campaign the water level rose 20 cm. The data were post-processed using the ARC/INFO TIN and GRID tools. A theoretical shoreline was digitized from topographic maps (scale 1:50.000) for the altitude of the dam overflow at the elevation of 1400 m a.s.l and was used as outer border line to the calculated lake depth model. The shoreline during campaign of survey was estimated from the digitized one and the end of the tracklines for the actual elevation of 1346 m a.s.l.. The resulting data were put into the GIS as xyz tripels to produce a TIN (trianguleted irregular network). With help of the TIN different raster maps were generated.

Description: Lake Geiseltal is the largest lake of Saxony-Anhalt and the largest artificial lake of Germany (max. depth 78 m; mean depth 22.8 m; volume 423 Mio. m³; surface area 1853 ha) and can be classified as oligotrophic. It was created by the excavation of lignite in several former surface mines starting at industrial scale in 1906 (formerly only small-scale mining dated back to 1698; Knochenhauer 1996). Mining stopped 1993 after 1.4*109 tons of lignite and the same mass of overburden were excavated. To stabilize the slopes of the residual mine pits and to avoid acidification from mine drainage, a planned, large scale flooding of the residual mine pits started in 2003 by pumping water from River Saale that was cleaned up by sand filtration before (Fritz et al. 2001). In 2011, the flooding of the lake was completed (LMBV 2018). Algal productivity in the lake is low and water transparency high, the littoral compartments along the shores harbor large stocks of submerged macrophytes. This publication series includes datasets collected on Lake Geiseltal during the Inland Water Remote Sensing Validation Campaign 2017 (Bumberger et al. 2023).

Description: In this measurement campaign of five water bodies (lakes and reservoirs) several German research groups organised a joint effort to collect a data set for testing, evaluating, and potentially improving the abilities of satellite-based monitoring of water quality in standing waters. The strategy of the campaign is summarised in Figure 1 (documentation "Conceptual design of Inland Water Remote Sensing Validation Campaign 2017") and consists of three independently measured categories of data: (i) satellite-based monitoring, (ii) in situ monitoring, and (iii) bio-optical characterisation. The latter aspect, in particular, was intended in order to go beyond classical comparison of satellite-based and in-situ observations and to enable a more process-oriented and physically-based assessment of the observations made during the satellite overcasts. We concentrated our work on one week in summer 2017 and organised a synoptically measurement campaign on five lakes in Central Germany (Lake Arendsee, Lake Geiseltalsee, Kelbra Reservoir, Rappbode Reservoir, Lake Süßer See, see Tab. 1 in documentation "Main physical and limnological characteristics of the five water bodies from Inland Water Remote Sensing Validation Campaign 2017") based on various field and lab methods. The synoptically approach required the equipment of five sampling teams that are able to work independently from each other. Field- instruments used during the campaign (which required to be available in five sets) had been compared with each other in a separate intercalibration day. All lab-based measurements took place at the central lab of the Helmholtz-Centre for Environmental Research in Magdeburg using methods as outlined in Friese et al. (2014). The five water bodies were intentionally chosen because they reflect a broad range of temperate standing waters with respect to size, depth, trophic state, and the occurrence of cyanobacterial blooms. In addition, also natural and artificial water bodies are reflected by this set of lakes/reservoirs. To our knowledge, this is one of the rare multiple-teams efforts in remote sensing research on water quality making the collection of data in terms of their synoptic evaluation and broad methodological basis particularly useful and valuable.

Description: Density calculations are essential to study stratification, circulation patterns, internal wave formation and other aspects of hydrodynamics in lakes and reservoirs. Currently, the most common procedure is the use of CTD (conductivity, temperature and depth) profilers and the conversion of measurements of temperature and electrical conductivity into density. In limnic waters, such approaches are of limited accuracy if they do not consider lake-specific composition of solutes, as we show. A new approach is presented to correlate density and electrical conductivity, using only two specific coefficients based on the composition of solutes. First, it is necessary to evaluate the lake-specific coefficients connecting electrical conductivity with density. Once these coefficients have been obtained, density can easily be calculated based on CTD data. The new method has been tested against measured values and the most common equations used in the calculation of density in limnic and ocean conditions. The results show that our new approach can reproduce the density contribution of solutes with a relative error of less than 10 % in lake waters from very low to very high concentrations as well as in lakes of very particular water chemistry, which is better than all commonly implemented density calculations in lakes. Finally, a web link is provided for downloading the corresponding density calculator.