David Hann

Wavelet estimation of plant spatial patterns in multitemporal aerial photography

Wavelet analysis represents a powerful set of image processing techniques that have considerable potential to quantify ecologically relevant patterns at multiple scales. This paper provides a preliminary assessment of whether two‐dimensional wavelets convolved with 1 m panchromatic aerial photography can be used to detect automatically the location and crown diameters of western juniper (Juniperus occidentalis) plants as they encroach upon a sagebrush (Artemisia spp.) steppe landscape. The juniper crown diameters derived from wavelet analysis produced a strong correlation with crown diameters measured via comparable hand‐digitizing in a geographic information system (r = 0.96, n = 69) with a 5% commission and an 8% omission error. Through comparison with historical photography, we found that juniper plant cover increased 2.7 fold (from 2.7% to 7.3% total cover) during the period from 1939 to 1998 within the 15 ha study area. This approach has considerable potential for the long‐term monitoring of vegetation change via aerial photograph and other remotely sensed imagery.

The measurement of flow velocity and acoustic particle velocity using particle-image velocimetry

This paper outlines the method by which the flow velocity and acoustic particle velocity can be measured instantaneously over an area using particle-image velocimetry techniques. Theoretical expressions for the power spectrum and autocorrelation function of the intensity distribution in the plane of the interrogation area when a flow and sound field is present are derived and it is shown that the flow velocity and the acoustic particle velocity can be measured. The technique is used to measure the velocities in a standing wave tube with a monotonic sound field of sufficient strength such that acoustic streaming is set up. The limitations of this technique are also discussed.

A simple methodology for predicting laser-weld properties from material and laser parameters

In laser material processing, understanding the laser interaction and the effect of processing parameters on this interaction is fundamental to any process if the system is to be optimized. Expanding this to different materials or other laser systems with different beam characteristics makes this interaction more complex and difficult to resolve. This work presents a relatively simple physical model to understand these interactions in terms of mean surface enthalpy values derived from both material parameters and laser parameters. From these fundamental properties the melt depth and width for any material can be predicted using a simple theory. By considering the mean enthalpy of the surface, the transition from conduction limited melting to keyholing can also be accurately predicted. The theory is compared to experimental results and the predicted and observed data are shown to correspond well for these experimental results as well as for published results for stainless steel and for a range of metals. The results suggest that it is important to keep the Fourier number of the weld much smaller than one to make it efficient. It is also discussed that the surface enthalpy could be used to prodict other effects in the weld such as porosity and material expulsion.

Production of vegetation spatial-structure maps by per-object analysis of juniper encroachment in multitemporal aerial photographs

The remote sensing of vegetation, which has predominantly applied methods that analyze each image pixel as independent observations, has recently seen the development of several methods that identify groups of pixels that share similar spectral or structural properties as objects. The outputs of “per-object” rather than “per-pixel” methods represent characteristics of vegetation objects, such as location, size, and volume, in a spatially explicit manner. Before decisions can be influenced by data products derived from per-object remote sensing methods, it is first necessary to adopt methodologies that can quantify the spatial and temporal trends in vegetation structure in a quantitative manner. In this study, we present one such methodological framework where (i) marked point patterns of vegetation structure are produced from two per-object methods, (ii) new spatial-structural data layers are developed via moving-window statistics applied to the point patterns, (iii) the layers are differenced to highlight spatial-structural change over a 60 year period, and (iv) the resulting difference layers are evaluated within an ecological context to describe landscape-scale changes in vegetation structure. Results show that this framework potentially provides information on the population, growth, size association (nonspatial distribution of large and small objects), and dispersion. We present an objective methodological comparison of two common per-object approaches, namely image segmentation and classification using Definiens software and two-dimensional wavelet transformations.

Automatic detection of shrub location, crown area, and cover using spatial wavelet analysis and aerial photography

Characterizing shrub-steppe rangeland condition often requires fine-scale measurement of individual plants across broad areas. Advances in remote sensing to develop improved algorithms to census and monitor individual rangeland plants using image data are important for improving the efficiency with which these critical areas are monitored. Here, we performed and evaluated the first test of spatial wavelet analysis (SWA) to automatically detect the location and crown diameter of individuals of two species of shrubs (Artemisia tridentata and Purshia tridentata). Additionally, we quantified the aggregated cover of these shrubs at the plot scale. High spatial resolution (0.25 and 1 m) multispectral aerial imagery and field-based vegetation measurements were collected in both spring and fall 2005. We found that image- and field-based measures of individual shrubs and their crown areas were highly correlated in the fall imagery (r = 0.89). Image-based SWA prediction of shrub cover at the plot level correlated better with field-based measures (r = 0.91) than did a traditional, image texture-based measure (r = 0.71). Analyses of imagery acquired in spring resulted in poorer relationships due to the decreased phenological contrast between shrubs and understory grasses in spring relative to fall. Statistical equivalence tests demonstrated that individual shrub crown areas derived from field data and SWA were statistically equivalent and not biased, but the SWA- and field-based assessments of plot-level cover were not statistically equivalent. These results represent progress towards developing automatic methods to analyze shrubs at the landscape scale using remotely sensed imagery.

Particle image velocimetry for the measurement of mean and acoustic particle velocities

A novel method is outlined which allows measurement of the amplitude of oscillation of a sinusoidal sound field and the mean flow using particle image velocimetry. The method involves simplifying the interrogation area in such a way that the autocorrelation function contains four significant peaks. The accuracy is of the order of half pixel resolution, once a constant offset related to the non-continuous nature of the probability function of a sine wave is taken into account. This constant, which originates from the pixelation of the image, is shown to be 0.85 pixels.

Acoustic measurements in flows using photon correlation spectroscopy

Laser Doppler anemometry using the photon correlation method of signal processing has been used to measure a velocity field in which sinusoidal fluctuations generated acoustically are superimposed on a steady flow. A stochastic model has been developed for the form of the correlation function, and it is shown to be consistent with previous models for a steady flow and for sinusoidal fluctuations in an acoustic field. Measurements have been made of the velocity field associated with steady flow in a tube with a superimposed acoustic field, the results were shown to be consistent with the theoretical predictions.

Piezoelectric Fan Cooling: A Novel High Reliability Electric Machine Thermal Management Solution

Electric machine thermal management is critical for the correct operation of high power density electrical machines. This is, however, challenging to achieve in safety-critical applications where the reliability of the cooling system needs to be significantly higher than conventional solutions. Piezoelectric fans are presented here as a novel fault-tolerant forced cooling convective system for electric machines. Particle image velocimetry techniques in conjunction with infrared thermal measurements were implemented to map and quantify the flow fields generated by such a cooling arrangement as well as to determine the effective cooling enhancement. This paper also outlines the main design variables for such a system and highlights the main considerations to be accounted for to optimize the cooling potential. For the specific machine presented in this paper, the optimal fin/fan geometry resulted in mean flows in excess of 2.41 m/s and turbulence values in excess of 2.38 m/s, which resulted in an average convective heat transfer coefficient enhancement of 364.8% on the fin base and a further enhancement of 53.6% on each of the fin side walls. This, in turn, led to a 61.8% reduction in the electric machine heat sink cooling mass.

Design and development of a low-cost, electricity-generating cooking Score-Stove™

A design of the thermo-acoustic engine to combustion interface of an electrically generating clean cookstove is presented. Social surveys carried out by the SCORE project have indicated that adding electrical generation to a clean cookstove should increase their uptake considerably above the current 8% level (outside China) as electricity is perceived as high value and so wanted by the communities. This work discusses the development process, using elements of the formal design methodology BS 7000 to design a mass-producible, easy-to-manufacture, low-cost cooking stove that uses a thermo-acoustic engine to produce electricity whilst cooking. The iterative design process is discussed with analyses made of predicted cost and performance at each iteration and compared with the targets set from social surveys. With currently available technology and suitable investment in tooling and production facilities, estimated production costs are £100. An independent audit by engineers and cost estimators from a large international blue chip company made a prediction of £150. At this stage of the design, this is considered a quite good correlation. Proposals for bringing this cost down to £60 are made. To obtain lower costs would require more research. SCORE market evaluations indicate that at the upper-cost target of £60 (2007 prices), 60 million people would afford the stove. A wood-burning Score-Stove™2 prototype successfully developed 22.7 W of electricity based on the presented planar thermo-acoustic engine design, indicating that the new Score-Stove™2 design may have the potential, when manufactured in volume, to meet the social and cooking requirements of rural people in developing countries.

Development of Thermoacoustic Engine Operating by Waste Heat from Cooking Stove

There are about 1.5 billion people worldwide use biomass as their primary form of energy in household cooking[1]. They do not have access to electricity, and are too remote to benefit from grid electrical supply. In many rural communities, stoves are made without technical advancements, mostly using open fires cooking stoves which have been proven to be extremely low efficiency, and about 93% of the energy generated is lost during cooking. The cooking is done inside a dwelling and creates significant health hazard to the family members and pollution to environment. SCORE (www.score.uk.com) is an international collaboration research project to design and build a low-cost, high efficiency woodstove that uses about half amount of the wood of an open wood fire, and uses the waste heat of the stove to power a thermoacoustic engine (TAE) to produce electricity for applications such as LED lighting, charging mobile phones or charging a 12V battery. This paper reviews on the development of two types of the thermoacoustic engine powered by waste heat from cooking stove which is either using Propane gas or burning of wood as a cooking energy to produce an acceptable amount of electricity for the use of rural communities.There are about 1.5 billion people worldwide use biomass as their primary form of energy in household cooking[1]. They do not have access to electricity, and are too remote to benefit from grid electrical supply. In many rural communities, stoves are made without technical advancements, mostly using open fires cooking stoves which have been proven to be extremely low efficiency, and about 93% of the energy generated is lost during cooking. The cooking is done inside a dwelling and creates significant health hazard to the family members and pollution to environment. SCORE (www.score.uk.com) is an international collaboration research project to design and build a low-cost, high efficiency woodstove that uses about half amount of the wood of an open wood fire, and uses the waste heat of the stove to power a thermoacoustic engine (TAE) to produce electricity for applications such as LED lighting, charging mobile phones or charging a 12V battery. This paper reviews on the development of two types of the thermo...