Optimizing gamma-ray spectrometers for UAV-borne surveys with geophysical applications

Heavy duty unmanned aerial vehicles (UAVs) have made it possible to fly with large gamma-ray spectrometers that weigh several kilograms. Moreover, they can be purchased at an affordable price. These large UAV-borne gamma-ray detection systems are used to map the naturally occurring radionuclides 40K, 238U, 232Th. Such platforms have the advantage that they can be deployed over terrain that is difficult to access, while still maintaining a high spatial resolution. In contrast to UAV-borne radioactive pollution studies, the naturally occurring radionuclides have a much lower activity and therefore require longer integration time, slower flying speed or a larger detector, in order to effectively determine the spatial radionuclide distribution. Therefore, the question arises: what is the minimum practical detector size required to successfully map 40K, 238U and 232Th concentrations from UAV platforms. In this study an agricultural field has been mapped with three different scintillator-based gamma-ray spec-trometers: a 2000 ml, 1000 ml, and 350 ml detector. They were mounted together on the same UAV. At a flying height of 20 m and a speed of 5.6 m

Footprint and height corrections for UAV-borne gamma-ray spectrometry studies

Advancements in the development of gamma-ray spectrometers (GRS) have led to small and lightweight spectrometers that can be used under unmanned aerial vehicles (UAVs). Airborne GRS measurements are used to determine radionuclide concentrations in the ground, among which the natural occurring radionuclides K-40, U-238, and Th-232. For successful applications of these GRS sensors, it is important that absolute values of concentrations can be measured. To extract these absolute radionuclide concentrations, airborne gamma-ray data has to be corrected for measurement height. However, the current analysis models are only valid for the height range of 50-250 m. The purpose of this study is to develop a procedure that correctly predicts the true radionuclide concentration in the ground when measuring in the UAV operating range of 0-40 m. An analytical model is developed to predict the radiation footprint as a function of height. This model is used as a tool to properly determine a source-detector geometry to be used in Monte-Carlo simulations of detector response at various elevations between 0 and 40 m. The analytical model predicts that the smallest achievable footprint at 10 m height lies between 22 and 91 m and between 40 and 140 m at 20 m height. By using Monte-Carlo simulations it is shown that the analytical model correctly predicts the reduction in full energy peak gamma-rays, but does not predict the Compton continuum of a spectrum as a function of height. Therefore, Monte-Carlo simulations should be used to predict the shape and intensity of gamma-ray spectra as a function of height. A finite set of Monte-Carlo simulations at intervals of 5 m were used for the analysis of GRS measurements at heights up to 35 m. The resulting radionuclide concentrations at every height agree with the radionuclide concentration measured on the ground

A drone as platform for airborne gamma-ray surveys to characterize soil and monitor contaminations

Gamma-ray spectrometers are an invaluable tool in the field of geophysics where they are used for geological mapping and mineral exploration. Recent technological advances introduce the emergence of a new platform for gamma-ray surveys: Unmanned Airborne Vehicles (UAVs) otherwise known as drones. This new platform enables the fast and efficient collection of environmental radiometric data in otherwise inaccessible areas. An overview is given of the technological and data-analysis developments to realize the use of a spectrometer under a drone. As a result of weight and power optimization a spectrometer system based on a 1.0L NaI crystal can be used under a drone. The system collects gamma spectra with sufficient statistics to perform full spectrum analysis and determine variation in geophysical soil parameters. The platform can autonomously measure and process data giving real-time insight in the collected data and results. Two test cases are discussed in which the use and accuracy of this platform is validated for precision farming as well as locating and monitoring radioactive contaminations. It is concluded that a self-contained gamma-ray measurement system under a drone combines the best of two worlds by maintaining high resolution while increasing the ease of use.</p

A drone as platform for airborne gamma-ray surveys to characterize soil and monitor contaminations

Gamma-ray spectrometers are an invaluable tool in the field of geophysics where they are used for geological mapping and mineral exploration. Recent technological advances introduce the emergence of a new platform for gamma-ray surveys: Unmanned Airborne Vehicles (UAVs) otherwise known as drones. This new platform enables the fast and efficient collection of environmental radiometric data in otherwise inaccessible areas. An overview is given of the technological and data-analysis developments to realize the use of a spectrometer under a drone. As a result of weight and power optimization a spectrometer system based on a 1.0L NaI crystal can be used under a drone. The system collects gamma spectra with sufficient statistics to perform full spectrum analysis and determine variation in geophysical soil parameters. The platform can autonomously measure and process data giving real-time insight in the collected data and results. Two test cases are discussed in which the use and accuracy of this platform is validated for precision farming as well as locating and monitoring radioactive contaminations. It is concluded that a self-contained gamma-ray measurement system under a drone combines the best of two worlds by maintaining high resolution while increasing the ease of use.</p

Mapping soil texture with a gamma-ray spectrometer : comparison between UAV and proximal measurements and traditional sampling : validation study

The need for up-to-date soil information for e.g. spatial planning, infrastructure, agriculture and nature conservation has resulted in the Dutch Key Registration of the Subsurface (BRO), which also contains the 1: 50,000 soil map of the Netherlands. Classifying properties for this map are a.o. related to soil texture. Therefore, methods are needed that efficiently and effectively measure these at the right scale level and with the required accuracy. This report describes a validation study into the possibility, accuracy and costs of mapping clay and loam content of the tillage layer (0 - 30 cm) by augering, by measuring gamma radiation from a UAV (unmanned aerial vehicle or drone) or on foot. The research was carried out in an agricultural area of 40 ha in the Flevoland polder, the Netherlands. The results show that the accuracy and precision of the UAV and soil-bound measurements is largely comparable. A higher point density and smaller spatial support of the ground-bound sensor have a positive effect on capturing spatial patterns, accuracy and precision. After correction for the difference in point density, results are comparable. The difference in deployment costs is limited. The effect of the use of a national reference calibration set on costs and accuracy is a lot bigger and lowers both. However, when using national calibration scale accuracy could be increased with the inclusion of more soil geographic situations. We advise assessing similar questions by first assessing the required accuracy, measurement depth and resolution, then select possible platforms and choose calibration scale within budget limits. Gamma radiation measurements for mapping soil texture is potentially a scalable and cost-efficient technique for supporting actualisation of the Soil Map of the Netherlands and for applications with higher resolution such as precision agriculture and local spatial planning.---De behoefte aan actuele bodeminformatie voor bijv. ruimtelijke ordening, infrastructuur, landbouw en natuurbehoud heeft geresulteerd in de Basisregistratie Ondergrond (BRO) van Nederland die onder andere de 1: 50.000 Bodemkaart van Nederland bevat. Classificerende eigenschappen hiervoor zijn onder meer gerelateerd aan de bodemtextuur. Daarom zijn methoden nodig die deze op het juiste schaalniveau en met de vereiste nauwkeurigheid efficiënt en effectief inmeten. Dit rapport beschrijft een validatiestudie naar de mogelijkheid, nauwkeurigheid en kosten voor het karteren van klei en leemgehalte van de bouwvoor (0 - 30 cm) door boringen, door metingen van gammastraling vanaf een UAV (unmanned aerial vehicle of drone) of lopend. Het onderzoek is uitgevoerd op een landbouwareaal van 40 ha in de polder van Flevoland. De resultaten laten zien dat de nauwkeurigheid en precisie van de UAV-metingen grotendeels vergelijkbaar zijn met de grondgebonden metingen. Een hogere puntdichtheid en kleinere ruimtelijke ondersteuning van de lopende meting heeft een positief effect op het verklaren van de ruimtelijke patronen, nauwkeurigheid en precisie. Wanneer voor puntdichtheid wordt gecorrigeerd, zijn de resultaten vergelijkbaar. Het verschil in kosten van de inzet van de verschillende platforms is beperkt. Het effect van het gebruik van een nationale referentie kalibratieset op de kosten en nauwkeurigheid is een stuk groter, beide worden dan lager. De nauwkeurigheid met nationale kalibratieschaal kan worden verhoogd wanneer meer bodemtypen en grondsoorten zouden zijn opgenomen. We adviseren om bij een vergelijkbare vraag eerst de vereiste nauwkeurigheid, meetdiepte en resolutie te beoordelen, vervolgens mogelijke platforms te selecteren en de kalibratieschaal te kiezen binnen budgetgrenzen. Gamma-stralingsmetingen voor het karteren van bodemtextuur vormt in potentie een schaalbare en kostenefficiënte techniek om het actualiseren van de Bodemkaart van Nederland te ondersteunen en voor toepassingen met hogere resolutie zoals precisielandbouw en lokale ruimtelijke planning

Mapping soil texture with a gamma-ray spectrometer : comparison between UAV and proximal measurements and traditional sampling : validation study

The need for up-to-date soil information for e.g. spatial planning, infrastructure, agriculture and nature conservation has resulted in the Dutch Key Registration of the Subsurface (BRO), which also contains the 1: 50,000 soil map of the Netherlands. Classifying properties for this map are a.o. related to soil texture. Therefore, methods are needed that efficiently and effectively measure these at the right scale level and with the required accuracy. This report describes a validation study into the possibility, accuracy and costs of mapping clay and loam content of the tillage layer (0 - 30 cm) by augering, by measuring gamma radiation from a UAV (unmanned aerial vehicle or drone) or on foot. The research was carried out in an agricultural area of 40 ha in the Flevoland polder, the Netherlands. The results show that the accuracy and precision of the UAV and soil-bound measurements is largely comparable. A higher point density and smaller spatial support of the ground-bound sensor have a positive effect on capturing spatial patterns, accuracy and precision. After correction for the difference in point density, results are comparable. The difference in deployment costs is limited. The effect of the use of a national reference calibration set on costs and accuracy is a lot bigger and lowers both. However, when using national calibration scale accuracy could be increased with the inclusion of more soil geographic situations. We advise assessing similar questions by first assessing the required accuracy, measurement depth and resolution, then select possible platforms and choose calibration scale within budget limits. Gamma radiation measurements for mapping soil texture is potentially a scalable and cost-efficient technique for supporting actualisation of the Soil Map of the Netherlands and for applications with higher resolution such as precision agriculture and local spatial planning.---De behoefte aan actuele bodeminformatie voor bijv. ruimtelijke ordening, infrastructuur, landbouw en natuurbehoud heeft geresulteerd in de Basisregistratie Ondergrond (BRO) van Nederland die onder andere de 1: 50.000 Bodemkaart van Nederland bevat. Classificerende eigenschappen hiervoor zijn onder meer gerelateerd aan de bodemtextuur. Daarom zijn methoden nodig die deze op het juiste schaalniveau en met de vereiste nauwkeurigheid efficiënt en effectief inmeten. Dit rapport beschrijft een validatiestudie naar de mogelijkheid, nauwkeurigheid en kosten voor het karteren van klei en leemgehalte van de bouwvoor (0 - 30 cm) door boringen, door metingen van gammastraling vanaf een UAV (unmanned aerial vehicle of drone) of lopend. Het onderzoek is uitgevoerd op een landbouwareaal van 40 ha in de polder van Flevoland. De resultaten laten zien dat de nauwkeurigheid en precisie van de UAV-metingen grotendeels vergelijkbaar zijn met de grondgebonden metingen. Een hogere puntdichtheid en kleinere ruimtelijke ondersteuning van de lopende meting heeft een positief effect op het verklaren van de ruimtelijke patronen, nauwkeurigheid en precisie. Wanneer voor puntdichtheid wordt gecorrigeerd, zijn de resultaten vergelijkbaar. Het verschil in kosten van de inzet van de verschillende platforms is beperkt. Het effect van het gebruik van een nationale referentie kalibratieset op de kosten en nauwkeurigheid is een stuk groter, beide worden dan lager. De nauwkeurigheid met nationale kalibratieschaal kan worden verhoogd wanneer meer bodemtypen en grondsoorten zouden zijn opgenomen. We adviseren om bij een vergelijkbare vraag eerst de vereiste nauwkeurigheid, meetdiepte en resolutie te beoordelen, vervolgens mogelijke platforms te selecteren en de kalibratieschaal te kiezen binnen budgetgrenzen. Gamma-stralingsmetingen voor het karteren van bodemtextuur vormt in potentie een schaalbare en kostenefficiënte techniek om het actualiseren van de Bodemkaart van Nederland te ondersteunen en voor toepassingen met hogere resolutie zoals precisielandbouw en lokale ruimtelijke planning

Influence of materials' optical response on actuation dynamics by Casimir forces

The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the far-infrared range. For less conductive systems, such as phase change materials or conductive silicon carbide, the reduced force offers the advantage of increased stable operation of MEMS devices against pull-in instabilities that lead to unwanted stiction. Bifurcation analysis with phase portraits has been used to compare the sensitivity of a model actuator when the optical properties are altered