1 st EARSeL Workshop on Temporal Analysis of Satellite Images 1 Mykonos, Greece, 23 rd – 25 th May, 2012 MONITORING OF INVASIVE AQUATIC PLANTS USING MULTITEMPORAL RAPIDEYE DATA Sebastian Roessler 1 , Patrick Wolf 1 , Thomas Schneider 1 and Arnulf Melzer 1 1. Technical University of Munich, Institute of Limnology, Iffeldorf, Germany; Sebastian.roessler@mytum.de ABSTRACT Rising water temperatures due to climate change seem to favor thermopilic invasive aquatic plants. In Central Europe an increased spread of Najas marina and Elodea nuttallii can be observed. A monitoring system is required to estimate the effect of their expansion on the ecosystem. The observation of these spatiotemporal highly variable developments requires rapid on-demand information which can only be achieved by spaceborne multitemporal remote sensing data. The ability of RapidEye, which offers the desired temporal and spatial resolution, is tested. Two study sites in Bavaria (Lake Starnberg and Lake Tegernsee) were visited 2011 periodically to measure in-situ reflectance of Elodea nuttallii and Najas marina with submersible RAMSES spectroradiometers. Since measurements were performed directly above the vegetation patches, as well as beneath the water surface, information about water constituents is also available. The combination of two measurements of the downwelling irradiance in different depths allows the calculation of the vertical diffuse attenuation, which is as an apparent optical property (AOP) related to inherent optical properties (IOP) like Phytoplankton, colored dissolved organic matter (cDOM) and suspended particulate matter (SPM) content. Information about the water constituents is necessary to correct for the exponential radiation loss through the water column and to achieve bottom reflectances or water column corrected derivatives. The frequent reflectance measurements (14 days interval) allow building up a multiseasonal spectral library for both plants representing each phenological state. The in-situ derived attenuation measurements were used to calculate depth-invariant band ratios using a simple semi-empirical method based on logarithmic transformed and atmospherically corrected RapidEye data. These depth-invariant indices were also calculated for in-situ measurements. The transformed in-situ measurements were used as endmember in a subsequent linear spectral unmixing approach based on the matched filtering method. This was done to achieve sub pixel abundances of Najas marina and Elodea nuttallii. INTRODUCTION Some submersed macropyhtes, which can be used as longterm indicators for the trophic state of freshwater lakes [1], can now act as indicators for climate change profiting from increasing water temperatures [2]. In the freshwater lakes of Southern Bavaria a spread of Najas marina and Elodea nuttallii can be observed and it is assumed that both species profits from climate warming. Najas marina is indigenous to Europe while Elodea nuttallii is a neophyte, which is introduced from Northern America. However, the invasive growth of both plants causes severe ecological and economic problems. The species differ in their expansion speed with E. nuttallii expanding much faster. A regular monitoring of these plants will give important information about the ecologic development of these fragile ecosystems and would allow counter measures at an early stage. A frequent observation of aquatic habitats is often limited to diving based mapping – a very cost and time intensive method. Only hyperspectral airborne data were used successfully to identify different species of submerged macrophytes [3, 4]. This is also a very expensive method and not suitable for observations on monthly to weekly intervals. This short revisit times are necessary since aquatic ecosystems are characterized by very fast developments and fluctuations during the growing season (either limited by temperature or incoming radiation).