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Remote sensing event campaign with various optical and thermal sensors for soil moisture and evapotranspiration derivation in Central Germany investigating possible effects of different spatial scales

The heat waves and droughts of 2018 / 2019 and in 2020 have had a devastating impact on the functioning of ecosystems and have led to an increasing vulnerability beyond the duration of heat waves (e.g. degradation and increased erosion, reduced carbon uptake by vegetation, modulated energy balance). Such impacts also include loss of agricultural production. A better understanding of the progression and the consequences of heatwaves and droughts is essential for the development and improvement of adaptation and protection measures. The airborne remote sensing event campaign performed in the agricultural area of the 'Magdeburger Boerde' in Central Germany aimed at providing remote sensing data sets from different platforms to derive high quality data for improving the understanding of influences and lag effects on hydrologic, biological/biogeochemical and atmospheric processes induced by the summer drought 2020. Multiple recurrences of drought periods in previous years may have led to irreversible changes in structure, composition and functioning of terrestrial ecosystems reducing ecosystem services and resilience. A second goal of the campaign with different available sensors in terms of an inter-calibration is to provide comprehensive and reliable data to ensure future campaign inter-comparability. The acquired data set includes airborne remote sensing data covering variable land cover types obtained by optical, thermal and multispectral sensors (see supplementary material: Schulz et al. (2020), Milewski et al. (2021) ). Furthermore, extensive data from various ground-truthing activities are available such as field spectrometer measurements, soil temperature mapping and soil moisture mapping via Cosmic Ray rovering and TDR-measurements. To complete the data set, micrometeorological time series, soil samples and vegetation characteristics were also taken.

Soil moisture distribution at the Hordorf (Central Germany) groundtruthing site determined by mobile Cosmic Ray Neutron Sensing

Cosmic Ray neutron sensing (CRNS) is an emerging technology which is used to close the scaling gap between point measurements, such as TDR or soil samples, and the airborne remote sensing data. CRNS estimates the area-average soil water content by the detection of soil-reflected cosmic-ray neutrons in air. This method is characterized by an non-linearly shaped horizontal footprint of hundreds of meters and a vertical footprint of tens of centimetres (Köhli et al. 2015). During the campaign, a portable sensor (the so-called CRNS Rover) was used to study the spatial soil moisture variability in the target area in Hordorf. The rover was equipped with a CRNS-RV unit from Hydroinnova LLC (HI-RC01 detector) and a polyethylene shield below the detector to better reduce local effects of the field track. Neutron count data were processed including several physical, soil, and terrain corrections (see Schrön 2020, cfg file and the software <https://git.ufz.de/CRNS/cornish_pasdy>) to obtain the spatial soil moisture distribution at the Hordorf ground truthing site.

Reflectance spectra measured with ASD field spectrometer and ground truthing of vegetation heights and phenology for different crops and bare soil at the Hordorf (Central Germany) ground truthing sites

The data were taken to obtain information on soil and vegetation information at ground surface. That included (1) measurements of soil moisture, soil temperature and surface temperature of a 40 m x 40 m stubble field west of the flux tower station Hordorf (Central Germany); (2) the measurements of soil moisture, soil temperature and surface temperature as well as spectra taken with an Analytical Spectral Devices (ASD) field spectrometer of a bare soil reference area close to flux tower station: (3) measurements of soil moisture, soil temperature, field spectra with ASD field spectrometer, height of plant height, chlorophyll content and pheno-code on crop fields (sugar beet, potatoes) close to flux tower station and (4) the available ASD data files. Alle data points are merged with its GPS coordinates.The time base is CET, except of the ASD field spectra, where CEST was used.

Soil properties considering pH-values, total nitrogen and carbon content of soil samples, and soil type determination based on sand, silt, clay composition at the Hordorf (Central Germany) groundtruthing sites

The data set contains the results of laboratory examination of 13 soil samples taken at the ground truthing reference sites during the flight campaign.

Spektralbibliotheken zur Interpretation fernerkundlich erfasster Hyperspektraldaten SKYPER

Die neue technische Qualität moderner Fernerkundungssysteme, die zunehmend auch genaue quantitative Aussagen zulässt, verlangt entsprechend optimierte Auswerteverfahren. Dazu zählt die exakte Kalibrierung der hyperspektralen Daten ebenso wie die umfassende Verifizierung von Spektralkurven am Boden. Die im Rahmen des Projektes geplante Verfahrensentwicklung besteht darin, die zeitgleich zur Flugkampagne stattfindenden Arbeiten am Boden (Gro und Truthing) den besonderen Anforderungen der hyperspektralen Datenaufnahme anzupassen und ein mobiles GIS zu entwickeln, das die relevanten Geländeinformationen digital, in Echtzeit und hochgenau verortet aufzeichnet. Außerdem sollen die von verschiedenen Testflächen im Ground Truthing gewonnenen spezifischen Spektralkurven in einer Spektralbibliothek zusammengeführt und für die Generierung und Optimierung von aussagestarken Auswertealgorithmen hyperspektraler Fernerkundungsdaten eingesetzt werden. Die Testflächen sind so ausgewählt, dass sie charakteristische Einsatzgebiete für die Fernerkundung u.a. in der Landwirtschaft und im Obstanbau abdecken. Die Forschungsarbeiten dienen der Vorbereitung einer erweiterten kommerziellen Nutzung satellitengestützter Hochtechnologie am Standort Bremen.

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