The use of electromagnetic (EM) soil moisture probes is proliferating rapidly, in two broad domains: in field and laboratory research; and in strongly practical applications such as irrigation scheduling in farms or horticultural enterprises, and hydrological monitoring. Numerous commercial EM probes are available for measurement of volumetric water content (θ v ), spanning a range of measurement principles, and of probe dimensions and sensing volumes. However probe calibration (i.e. the relationship of actual θ v to probe electrical output) can shift, often substantially, with variations in parameters such as soil texture, organic matter content, wetness range, electrical conductivity and temperature. Hence a single-valued, manufacturer-supplied calibration function is often inadequate, forcing the user to seek an application-specific calibration. The purpose of this paper is to describe systematic procedures which probe users can use to check or re-determine the calibration of their selected probe(s). Given the wide diversity of operating principles and designs of commercially-available EM probes, we illustrate these procedures with results from our own calibrations of five different short probes (length of 5 to 20 cm). Users are strongly recommended to undertake such calibration checks, which provide both a) pre-use experience, and b) more reliable in-use data. Používanie elektromagnetických (EM) snímačov vlhkosti pôdy sa rýchlo rozširuje tak v terénnom výskume, ako aj v laboratóriu. Sú používané v praktických aplikáciách ako je riadenie závlah na farmách a záhradách, ako aj v hydrologickom monitoringu. Pre meranie vlhkosti pôdy (θ v ) sú dostupné početné typy komerčných EM snímačov, založených na viacerých princípoch merania a snímače majú rozdielnu veľkosť snímaných objemov pôdy. Kalibračné krivky takýchto snímačov (t.j. závislosti medzi reálnou vlhkosťou pôdy θ v a elektrickým výstupom snímača) sa môžu posúvať -niekedy podstatne -a to v závislosti od rozdielnych parametrov pôdy, ako je jej textúra, obsah organických látok, rozsah vlhkostí, elektrická vodivosť a teplota. Z toho vyplýva, že jednoznačná kalibračná krivka, dodávaná výrobcom je často neadekvátna, čo núti užívateľa snímač kalibrovať v špecifických podmienkach. Cieľom tohto príspevku je opísať procedúry, ktoré môžu byť použité užívateľmi pri rekalibrácii vybraných typov snímačov. Berúc do úvahy širokú paletu princípov EM snímačov, ilustrujeme tieto procedúry výsledkami vlastných kalibračných testov na piatich typoch krátkych snímačov (dĺžka od 5 do 20 cm). Užívateľom odporúčame rekalibráciu komerčných snímačov, ktorými získajú predbežné skúsenosti a spoľahlivejšie výsledky pri meraní vlhkosti pôdy.KĽÚČOVÉ SLOVÁ: snímače vlhkosti pôdy, elektromagnetické snímače, TDR, kalibrácia.
For many water management issues of shallow lakes with non-consolidated sediments hydrographic surveys of the open water area and reed belt areas are required. In the frame of water management strategy for the steppe lake Neusiedler See, located between Austria and Hungary, a hydrographic survey was conducted. In the open water area (water depth ≥1 m) a sediment echosounder was used. To validate these measurements and to distinguish between water, mud, and sediment layers in the shallow lake and reed belt area additional measurements were needed. As no common standard methods are available yet, we developed a measurement system based on two commonly applied soil physical measurement techniques providing reproducible physical values: a capacitive sensor and a cone penetrometer combined with GNSS-positioning enable dynamic measurements of georeferenced vertical water-mud-bedsediments profiles. The system bases on site-specific calibrated sensors and allows instantaneous, in situ measurements. The measurements manifest a sharp water-mud interface by a sudden decline to smaller water content which is a function of the dielectric permittivity. A second decline indicates the transition to compacted mud. That is concurrently the density where the penetrometer starts registering significant penetration resistance. The penetrometer detects shallow lakebed-sediment layers. Within the lake survey this measurement system was successfully tested.
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