Atmospheric Tomography as a Tool for Quantification of CO2 Emissions from Potential Surface Leaks: Signal Processing Workflow for a Low Accuracy Sensor Array

AbstractAtmospheric tomography is a monitoring technique that uses an array of sampling sites and a Bayesian inversion technique to simultaneously solve for the location and magnitude of a gaseous emission. Application of the technique to date has relied on air samples being pumped over short distances to a high precision FTIR Spectrometer, which is impractical at larger scales. We have deployed a network of cheaper, less precise sensors during three recent large scale controlled CO2 release experiments; one at the CO2CRC Ginninderra site, one at the CO2CRC Otway Site and another at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility in Horsham, Victoria. The purpose of these deployments was to assess whether an array of independently powered, less precise, less accurate sensors could collect data of sufficient quality to enable application of the atmospheric tomography technique. With careful data manipulation a signal suitable for an inversion study can be seen. A signal processing workflow based on results obtained from the atmospheric array deployed at the CO2CRC Otway experiment is presented

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

We propose three nontraditional dielectric geometries and present an experimental and theoretical analysis and comparison of time domain reflectometry (TDR) performances for them. The traditional geometry (the probes inserted in material of essentially infinite extent) is compared to three nontraditional geometries where the probes are affixed outside of a core sample, inside of a bore, or flat on the surface of a semi‐infinite solid. Our derivation relates the velocity of electromagnetic wave propagation to the complex permittivities and permeabilities of the media and the geometry for the three nontraditional configurations. Experimental results for air, styrofoam, dry sand, wet sand of varying water content, nylon, dry wood, and ferromagnetic steel are obtained for the three proposed configurations and are in fair agreement with the literature within the experimental uncertainties. Through experiments and theoretical analysis, the TDR performance is found to be the same within the experimental uncertainties for the three nontraditional geometries. The proposed geometries yield slightly lower sensitivities compared to the traditional geometry. Advantages and disadvantages of the geometries compared to the traditional geometry are also discussed

Measurement of advection and surface-atmosphere exchange in complex terrain.

grant NER/S/J/2004/13118Accurate observations of the carbon cycle are essential as inputs to global climate models. Observations made by the micrometeorological technique of eddy covariance, whist widespread, may be incorrect if air is advected away from below the sensor system. This is potentially a serious issue for FLUXNET, a global network of eddy flux sites. The approach in this thesis to investigate this problem was twofold: A full micrometeorological mass balance using an instrumented 50 m long by 50 m wide by 6 m high Cartesian control volume (CV) covering the understorey vegetation of a 40 m high Eucalyptus forest was carried out; situated adjacent to the Tumbaruma eddy covariance site in Australia. At night positive (into the atmosphere) advection fluxes caused by down-slope katabatic drainage within the forest trunk space, dominated the CO2 flux budget of the CV, with both vertical and horizontal advection terms having predominantly positive values. The nighttime estimates of advection were subject to large systematic errors that were of the same order of magnitude as the advection signal. Nevertheless, the nocturnal respiration flux of the understorey vegetation was clearly resolved by the diurnal full mass balance flux curve that resulted from the experiment, having a typical value of 5 μmol m-2 s-1. A second experiment carried out at the Griffin forest in Scotland demonstrated the presence of sub-canopy katabatic/gravity flows at night that would be likely to cause scalar advection resulting in underestimation of the nocturnal respiration flux of CO2. Finally, it is recommended that the micrometeorological mass balance technique should not be deployed across FLUXNET because of financial cost and issues of systematic error

Short, Multineedle Frequency Domain Reflectometry Sensor Suitable for Measuring Soil Water Content

Time domain reflectometry (TDR) is a well-established electromagnetic technique used to measure soil water content. Time domain reflectometry sensors have been combined with heat pulse sensors to produce thermo-TDR sensors. Thermo-TDR sensors are restricted to having relatively short needles to accurately measure soil thermal properties. Short needle lengths, however, can limit the accuracy of the TDR measurement of soil water content. Frequency domain reflectometry (FDR) sensors are an alternative to TDR sensors that can provide an inexpensive measurement of soil water content. The objective of this study was to determine whether short FDR sensors can accurately measure soil water content. We designed and constructed a short FDR sensor. For four soil types across a range of water contents, temperatures, and salt contents, we measured soil dielectric spectra with the short FDR sensor. A vector network analyzer was used to obtain soil dielectric spectra in the 1-MHz to 3-GHz frequency range. The ideal frequency of a short FDR sensor is the frequency at which the permittivity is not altered by changing temperature or salt content. The 47- to 200-MHz range was an ideal frequency range for measuring soil water content, and 70 MHz was the frequency least influenced by temperature and salt content. The short FDR sensor provided quick, continuous, stable, and cheap measurements of soil water content. Because of the promising performance of the short thermo-FDR sensor in laboratory studies, sensors should be evaluated in future field studies

Bayesian atmospheric tomography for detection and quantification of methane emissions : application to data from the 2015 Ginninderra release experiment

Detection and quantification of greenhouse-gas emissions is important for both compliance and environment conservation. However, despite several decades of active research, it remains predominantly an open problem, largely due to model errors and assumptions that appear at each stage of the inversion processing chain. In 2015, a controlled-release experiment headed by Geoscience Australia was carried out at the Ginninderra Controlled Release Facility, and a variety of instruments and methods were employed for quantifying the release rates of methane and carbon dioxide from a point source. This paper proposes a fully Bayesian approach to atmospheric tomography for inferring the methane emission rate of this point source using data collected during the experiment from both point-and path-sampling instruments. The Bayesian framework is designed to account for uncertainty in the parameterisations of measurements, the meteorological data, and the atmospheric model itself when performing inversion using Markov chain Monte Carlo (MCMC). We apply our framework to all instrument groups using measurements from two release-rate periods. We show that the inversion framework is robust to instrument type and meteorological conditions. From all the inversions we conducted across the different instrument groups and release-rate periods, our worst-case median emission rate estimate was within 36% of the true emission rate. Further, in the worst case, the closest limit of the 95% credible interval to the true emission rate was within 11% of this true value

Formation and characteristics of ions and charged aerosol particles in a native Australian Eucalypt forest

International audienceBiogenic aerosol formation is likely to contribute significantly to the global aerosol load. In recent years, new-particle formation has been observed in various ecosystems around the world but hardly any measurements have taken place in the terrestrial Southern Hemisphere. Here, we report the first results of atmospheric ion and charged particle concentrations as well as of new-particle formation in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measurements were carried out with an Air Ion Spectrometer (AIS) with a size range from 0.34 to 40 nm. The Eucalypt forest was a very strong source of new aerosol particles. Daytime aerosol formation took place on 52% of days with acceptable data, which is 2?3 times as often as in the Nordic boreal zone. Average growth rates for negative/positive 1.5?3 nm particles during these formation events were 2.89/2.68 nmh?1, respectively; for 3-7 nm particles 4.26/4.03, and for 7?20 nm particles 8.90/7.58 nmh?1, respectively. The growth rates for large ions were highest when the air was coming from the native forest which suggests that the Eucalypts were a strong source of condensable vapours. Average concentrations of cluster ions (0.34?1.8 nm) were 2400/1700 cm?3 for negative/positive ions, very high compared to most other measurements around the world. One reason behind these high concentrations could be the strong radon efflux from the soils around the Tumbarumba field site. Furthermore, comparison between night-time and daytime concentrations supported the view that cluster ions are produced close to the surface within the boundary layer also at night but that large ions are mostly produced in daytime. Finally, a previously unreported phenomenon, nocturnal aerosol formation, appeared in 32% of the analysed nights but was clustered almost entirely within six months from summer to autumn in 2006. From January to May, nocturnal formation was 2.5 times as frequent as daytime formation. Therefore, it appears that in summer and autumn, nocturnal production was the major mechanism for aerosol formation in Tumbarumba

New insights into nocturnal nucleation

Formation of new aerosol particles by nucleation and growth is a significant source of aerosols in the atmosphere. New particle formation events usually take place during daytime, but in some locations they have been observed also at night. In the present study we have combined chamber experiments, quantum chemical calculations and aerosol dynamics models to study nocturnal new particle formation. All our approaches demonstrate, in a consistent manner, that the oxidation products of monoterpenes play an important role in nocturnal nucleation events. By varying the conditions in our chamber experiments, we were able to reproduce the very different types of nocturnal events observed earlier in the atmosphere. The exact strength, duration and shape of the events appears to be sensitive to the type and concentration of reacting monoterpenes, as well as the extent to which the monoterpenes are exposed to ozone and potentially other atmospheric oxidants

Studying feasibility and effects of a two-stage nursing staff training in residential geriatric care using a 30 month mixed-methods design [ISRCTN24344776]

<p>Abstract</p> <p>Background</p> <p>Transfer techniques and lifting weights often cause back pain and disorders for nurses in geriatric care. The Kinaesthetics care conception claims to be an alternative, yielding benefits for nurses as well as for clients.</p> <p>Starting a multi-step research program on the effects of Kinaesthetics, we assess the feasibility of a two-stage nursing staff training and a pre-post research design. Using quantitative and qualitative success criteria, we address mobilisation from the bed to a chair and backwards, walking with aid and positioning in bed on the staff level as well as on the resident level. In addition, effect estimates should help to decide on and to prepare a controlled trial.</p> <p>Methods/Design</p> <p>Standard basic and advanced Kinaesthetics courses (each comprising four subsequent days and an additional counselling day during the following four months) are offered to n = 36 out of 60 nurses in a residential geriatric care home, who are in charge of 76 residents. N = 22 residents needing movement support are participating to this study.</p> <p>On the staff level, measurements include focus group discussions, questionnaires, physical strain self-assessment (Borg scale), video recordings and external observation of patient assistance skills using a specialised instrument (SOPMAS). Questionnaires used on the resident level include safety, comfort, pain, and level of own participation during mobilisation. A functional mobility profile is assessed using a specialised test procedure (MOTPA).</p> <p>Measurements will take place at baseline (T0), after basic training (T1), and after the advanced course (T2). Follow-up focus groups will be offered at T1 and 10 months later (T3).</p> <p>Discussion</p> <p>Ten criteria for feasibility success are established before the trial, assigned to resources (missing data), processes (drop-out of nurses and residents) and science (minimum effects) criteria. This will help to make rational decision on entering the next stage of the research program.</p> <p>Trial Registration</p> <p>Current Controlled Trials <a href="http://www.controlled-trials.com/ISRCTN24344776">ISRCTN24344776</a>.</p

The Ginninderra CH4 and CO2 release experiment: An evaluation of gas detection and quantification techniques

A methane (CH4) and carbon dioxide (CO2) release experiment was held from April to June 2015 at the Ginninderra Controlled Release Facility in Canberra, Australia. The experiment provided an opportunity to compare different emission quantification techniques against a simulated CH4 and CO2 point source release, where the actual release rates were unknown to the participants. Eight quantification techniques were assessed: three tracer ratio techniques (two mobile); backwards Lagrangian stochastic modelling; forwards Lagrangian stochastic modelling; Lagrangian stochastic (LS) footprint modelling; atmospheric tomography using point and using integrated line sensors. The majority of CH4 estimates were within 20% of the actual CH4 release rate (5.8 g/min), with the tracer ratio technique providing the closest estimate to both the CH4 and CO2 release rates (100 g/min). Once the release rate was known, the majority of revised estimates were within 10% of the actual release rate. The study illustrates the power of measuring the emission rate using multiple simultaneous methods and obtaining an ensemble median or mean. An ensemble approach to estimating the CH4 emission rate proved successful with the ensemble median estimate within 16% for the actual release rate for the blind release experiment and within 2% once the release rate was known. The release also provided an opportunity to assess the effectiveness of stationary and mobile ground and aerial CH4 detection technologies. Sensor detection limits and sampling rates were found to be significant limitations for CH4 and CO2 detection. A hyperspectral imager’s capacity to image the CH4 release from 100 m, and a Boreal CH4 laser sensor’s ability to track moving targets suggest the future possibility to map gas plumes using a single laser and mobile aerial reflector