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- ItemMethoden für die präzise obstbauliche Produktion(Darmstadt : KTBL, 2012) Zude, Manuela; Peeters, Aviva; Selbeck, Jörn; Käthner, Jana; Gebbers, Robin; Bengal, Alon; Hetzroni, Amots; Jaeger-Hansen, Claes; Griepentrog, Hans-Werner; Pforte, Florian; Rozzi, Paolo; Torricelli, Alessandro; Spinelli, Lorenzo; Ünlü, Mustafa; Kanber, RizaDer Ansatz von Precision Horticulture im Obstbau lehnt sich an das aus dem Ackerbau stammende Konzept der Präzisionslandwirtschaft bzw. der teilflächenspezifischen Bewirtschaftung an. Hierbei sollen präzise an das individuelle Gehölzwachstum angepasste Pflegemaßnahmen die bislang praktizierte einheitliche Behandlung aller Bäume in einer Anlage ablösen. Voraussetzungen hierfür sind u. a. Bodenkarten und Informationen zum Pflanzenwachstum. Das Ziel ist es, den informationsgestützten Obstbau voranzutreiben und durch ein räumlich und zeitlich differenziertes Management eine effizientere und nachhaltigere Bewirtschaftung zu erreichen.
- ItemTerahertz spectroscopy for proximal soil sensing: An approach to particle size analysis(Basel : MDPI, 2017) Dworak, Volker; Mahns, Benjamin; Selbeck, Jörn; Gebbers, Robin; Weltzien, CorneliaSpatially resolved soil parameters are some of the most important pieces of information for precision agriculture. These parameters, especially the particle size distribution (texture), are costly to measure by conventional laboratory methods, and thus, in situ assessment has become the focus of a new discipline called proximal soil sensing. Terahertz (THz) radiation is a promising method for nondestructive in situ measurements. The THz frequency range from 258 gigahertz (GHz) to 350 GHz provides a good compromise between soil penetration and the interaction of the electromagnetic waves with soil compounds. In particular, soil physical parameters influence THz measurements. This paper presents investigations of the spectral transmission signals from samples of different particle size fractions relevant for soil characterization. The sample thickness ranged from 5 to 17 mm. The transmission of THz waves was affected by the main mineral particle fractions, sand, silt and clay. The resulting signal changes systematically according to particle sizes larger than half the wavelength. It can be concluded that THz spectroscopic measurements provide information about soil texture and penetrate samples with thicknesses in the cm range.
- ItemApplication of Terahertz radiation to soil measurements: Initial results(Basel : MDPI, 2011) Dworak, Volker; Augustin, Sven; Gebbers, RobinDeveloping soil sensors with the possibility of continuous online measurement is a major challenge in soil science. Terahertz (THz) electromagnetic radiation may provide the opportunity for the measurement of organic material density, water content and other soil parameters at different soil depths. Penetration depth and information content is important for a functional soil sensor. Therefore, we present initial research on the analysis of absorption coefficients of four different soil samples by means of THz transmission measurements. An optimized soil sample holder to determine absorption coefficients was used. This setup improves data acquisition because interface reflections can be neglected. Frequencies of 340 GHz to 360 GHz and 1.627 THz to 2.523 THz provided information about an existing frequency dependency. The results demonstrate the potential of this THz approach for both soil analysis and imaging of buried objects. Therefore, the THz approach allows different soil samples to be distinguished according to their different absorption properties so that relations among soil parameters may be established in future.
- ItemSoil pH mapping with an on-the-go sensor(Basel : MDPI, 2011) Schirrmann, Michael; Gebbers, Robin; Kramer, Eckart; Seidel, JanSoil pH is a key parameter for crop productivity, therefore, its spatial variation should be adequately addressed to improve precision management decisions. Recently, the Veris pH ManagerTM, a sensor for high-resolution mapping of soil pH at the field scale, has been made commercially available in the US. While driving over the field, soil pH is measured on-the-go directly within the soil by ion selective antimony electrodes. The aim of this study was to evaluate the Veris pH ManagerTM under farming conditions in Germany. Sensor readings were compared with data obtained by standard protocols of soil pH assessment. Experiments took place under different scenarios: (a) controlled tests in the lab, (b) semicontrolled test on transects in a stop-and-go mode, and (c) tests under practical conditions in the field with the sensor working in its typical on-the-go mode. Accuracy issues, problems, options, and potential benefits of the Veris pH ManagerTM were addressed. The tests demonstrated a high degree of linearity between standard laboratory values and sensor readings. Under practical conditions in the field (scenario c), the measure of fit (r2) for the regression between the on-the-go measurements and the reference data was 0.71, 0.63, and 0.84, respectively. Field-specific calibration was necessary to reduce systematic errors. Accuracy of the on-the-go maps was considerably higher compared with the pH maps obtained by following the standard protocols, and the error in calculating lime requirements was reduced by about one half. However, the system showed some weaknesses due to blockage by residual straw and weed roots. If these problems were solved, the on-the-go sensor investigated here could be an efficient alternative to standard sampling protocols as a basis for liming in Germany.
- ItemVertical soil profiling using a galvanic contact resistivity scanning approach(Basel : MDPI, 2014) Pan, Luan; Adamchuk, Viacheslav I.; Prasher, Shiv; Gebbers, Robin; Taylor, Richard S.; Dabas, MichelProximal sensing of soil electromagnetic properties is widely used to map spatial land heterogeneity. The mapping instruments use galvanic contact, capacitive coupling or electromagnetic induction. Regardless of the type of instrument, the geometrical configuration between signal transmitting and receiving elements typically defines the shape of the depth response function. To assess vertical soil profiles, many modern instruments use multiple transmitter-receiver pairs. Alternatively, vertical electrical sounding can be used to measure changes in apparent soil electrical conductivity with depth at a specific location. This paper examines the possibility for the assessment of soil profiles using a dynamic surface galvanic contact resistivity scanning approach, with transmitting and receiving electrodes configured in an equatorial dipole-dipole array. An automated scanner system was developed and tested in agricultural fields with different soil profiles. While operating in the field, the distance between current injecting and measuring pairs of rolling electrodes was varied continuously from 40 to 190 cm. The preliminary evaluation included a comparison of scan results from 20 locations to shallow (less than 1.2 m deep) soil profiles and to a two-layer soil profile model defined using an electromagnetic induction instrument.
- ItemMicro UAV based georeferenced orthophoto generation in VIS + NIR for precision agriculture(München : European Geopyhsical Union, 2013) Bachmann, Ferry; Herbst, Ruprecht; Gebbers, Robin; Hafner, Verena V.This paper presents technical details about georeferenced orthophoto generation for precision agriculture with a dedicated selfconstructed camera system and a commercial micro UAV as carrier platform. The paper describes the camera system (VIS + NIR) in detail and focusses on three issues concerning the generation and processing of the aerial images related to: (i) camera exposure time; (ii) vignetting correction; (iii) orthophoto generation.