Polarimetric imaging for air accident investigation

We report a trial wherein a simple 4 CCD visible-band Polarimetric Imaging (PI) camera was fielded against aircraft debris distributed across an arid terrain, a littoral region and a small number of maritime debris targets A debris field realistically simulating an aircrash and a debris grid of aircraft remains were observed from an air platform flying in dry and sunny conditions. We report PI utility in support of air accident investigation by an enhanced ability to successfully locate small targets within the scene via the use of colour enhanced and decorrelated intensity PI products. Our results indicate that handheld PI capability may represent an effective low cost, upgrade and augmentation option for existing and future imaging systems that would support air accident investigators and assist in the cueing of more sophisticated assets and/or analyst attention

Fourier Transform Spectroscopy of the submillimetre continuum emission from hot molecular cores

We have used a Fourier Transform Spectrometer on the James Clerk Maxwell Telescope to study the submillimetre continuum emission from dust in three hot molecular cores (HMC). The spectral index beta of the dust emission for these sources has been determined solely within the 30 GHz wide 350 GHz (850 micron) passband to an accuracy comparable to those determined through multi-wavelength observations. We find an average beta = 1.6, in agreement with spectral indices determined from previous submillimetre observations of these sources and with those determined for HMC in general. The largest single source of uncertainty in these results is the variability of the atmosphere at 350 GHz, and with better sky subtraction techniques we show that the dust spectral index can clearly be determined within one passband to high accuracy with a submillimetre FTS. Using an imaging FTS on SCUBA-2, the next generation wide-field submillimetre camera currently under development to replace SCUBA at the JCMT in 2006, we calculate that at 350 GHz it will be possible to determine beta to +/- 0.1 for sources as faint as 400 mJy/beam and to +/- 0.3 for sources as faint as 140 mJy/beam.Comment: 11 pages, 5 figures, accepted for publication in MNRA

Stochastic Species Turnover and Stable Coexistence in a Species-Rich, Fire-Prone Plant Community

Understanding the mechanisms that maintain diversity is important for managing ecosystems for species persistence. Here we used a long-term data set to understand mechanisms of coexistence at the local and regional scales in the Cape Floristic Region, a global hotspot of plant diversity. We used a dataset comprising 81 monitoring sites, sampled in 1966 and again in 1996, and containing 422 species for which growth form, regeneration mode, dispersal distance and abundances at both the local (site) and meta-community scales are known. We found that species presence and abundance were stable at the meta-community scale over the 30 year period but highly unstable at the local scale, and were not influenced by species' biological attributes. Moreover, rare species were no more likely to go extinct at the local scale than common species, and that alpha diversity in local communities was strongly influenced by habitat. We conclude that stochastic environmental fluctuations associated with recurrent fire buffer populations from extinction, thereby ensuring stable coexistence at the meta-community scale by creating a “neutral-like” pattern maintained by niche-differentiation

Characterisation of the Physical Composition and Microbial Community Structure of Biofilms within a Model Full-Scale Drinking Water Distribution System

Within drinking water distribution systems (DWDS), microorganisms form multi-species biofilms on internal pipe surfaces. A matrix of extracellular polymeric substances (EPS) is produced by the attached community and provides structure and stability for the biofilm. If the EPS adhesive strength deteriorates or is overcome by external shear forces, biofilm ismobilised into the water potentially leading to degradation of water quality. However, little is known about the EPS within DWDS biofilms or how this is influenced by community composition or environmental parameters, because of the complications in obtaining biofilm samples and the difficulties in analysing EPS. Additionally, although biofilms may contain various microbial groups, research commonly focuses solely upon bacteria. This research applies an EPS analysis method based upon fluorescent confocal laser scanning microscopy (CLSM) in combination with digital image analysis (DIA), to concurrently characterize cells and EPS (carbohydrates and proteins) within drinking water biofilms from a full-scale DWDS experimental pipe loop facility with representative hydraulic conditions. Application of the EPS analysismethod, alongside DNA fingerprinting of bacterial, archaeal and fungal communities, was demonstrated for biofilms sampled from different positions around the pipeline, after 28 days growth within the DWDS experimental facility. The volume of EPS was 4.9 times greater than that of the cells within biofilms, with carbohydrates present as the dominant component. Additionally, the greatest proportion of EPS was located above that of the cells. Fungi and archaea were established as important components of the biofilm community, although bacteria were more diverse.Moreover, biofilms from different positions were similar with respect to community structure and the quantity, composition and three-dimensional distribution of cells and EPS, indicating that active colonisation of the pipe wall is an important driver inmaterial accumulation within the DWDS

Exploring SDA sensor architectures for the surveillance of geosynchronous spacecraft

Significant changes have taken place in the space domain over the past decade, with a growing number of emerging space-faring nations and commercial actors gaining access to the operational environment. The consequential diversification of space activities has brought about a need for a reassessment of space domain awareness (SDA) capabilities. Numerous states are developing their operational capability to undertake space-based activities, with potentially widespread ramifications for the safety of spacecraft. Rendezvous and proximity operations are becoming more prevalent in the geosynchronous (GSO) region for mission lifetime extension, active removal of debris, and satellite inspection, in all cases giving rise to novel challenges for SDA systems. What's more, there remains a largely uncharacterised population of small debris in the vicinity of the GSO region, uncovered by bespoke surveys with large aperture telescopes, and posing a significant risk to active satellites. In 2022, the UK Space Agency commissioned a study into the requirements and opportunities for SDA in the UK, carried out by CGI with support from the Global Network On Sustainability In Space (GNOSIS) and UKspace. The study highlighted research and development of sovereign sensors as one of its key recommendations, both to improve the UK's sensing capability and to contribute to closing gaps in global SDA capability. To this end, we explore the key requirements for future SDA sensor architectures, with a focus on ground-based electro-optical systems for the surveillance of spacecraft in the GSO region. Archival two-line element sets are used to simulate catalogued resident space objects (RSOs) passing through a grid of surveillance regions, tasked with monitoring the neighbourhoods of high-value assets in the vicinity of the geostationary belt, while the derived population from ESA's Meteoroid and Space Debris Terrestrial Environment Reference (MASTER) model is used as a basis for simulating the GSO debris field. We assess the observability of transiting RSOs from the vantage point of La Palma, Canary Islands, taking a variety of observational constraints into account, including the Earth's shadow, lunation, and the galactic plane. We examine the performance of the simulated surveillance regions in the context of comprehensive, yet cost-effective SDA provision. Estimated costs are weighed against important metrics for essential SDA tasks (e.g., catalogue maintenance , change detection, and conjunction analysis), such as the total traffic observed per night, the cadence of the observations, and the temporal coverage of registered RSOs. The results of the simulation are used to inform a discussion of key sensor architecture requirements for effective SDA of GSO assets, taking into consideration a combination of sensor characteristics (e.g., sensitivity, resolution, and wavelength band) and other factors (e.g., geographical placement, site quality, and observational strategy) influencing SDA capabilities. We provide a commentary on the advantages and limitations of the different architectures considered and conclude with a list of recommendations for the designs of future SDA systems for the protection of GSO spacecraft