Defence of space-based assets

Space-based assets (satellites and the terrestrial ground stations that communicate with them) provide critical support to military and civilian operations. They are vulnerable to unintentional damage and disruption, and to deliberate attack. This POSTnote outlines how the UK uses and accesses satellites, potential risks to satellites, and approaches to mitigation

Mapping and living in marine habitats - Sonars, seismics and ambient sounds

Thorough mapping of the marine environments has started close to 70 years ago, and it makes use of increasingly sophisticated instruments mostly relying on acoustics. These instruments either create their own sounds and listen to their echoes, or rely exclusively on sounds produced naturally or by a variety of physical processes. We are using these tools to harvest resources like fish and hydrocarbons, to monitor the increases in commercial and recreational shipping, their sustainability and their impacts, and to de-risk the development of marine renewable energies. This creates challenges for data storage, long-term data access, reliable standardisation and interpretation, and for comparison between regions and between times. These challenges, and the different ways forward, will be illustrated with examples from Arctic waters to temperate coastal environments. The quantitative results afforded by acoustic measurements can then be meaningfully used to solve controversies, or add a useful evidence base to on-going activities and debates

Acoustic Signatures of Shipping, Weather and Marine Life: Comparison of NE Pacific and Arctic Soundscapes

Acoustic signatures of shipping, weather and marine life are relatively well constrained, but there are strong variations with their oceanographic context and human activities. We investigate two contrasted settings, for timescales up to a year and frequencies up to 2 kHz. Arctic data from NOAA Noise Reference Station(NRS) NRS01, 500 m deep in the Arctic Chukchi Sea and away from major shipping areas is compared with measurements from Folger Deep, part of the Ocean Networks Canada network, 95 m deep and close to shipping lanes. PAMGuide is used to quantify broadband Sound Pressure Levels (SPLs), Third-Octave band Levels (TOLs), Power Spectral Densities (PSDs) and percentile contributions. The Acoustic Complexity Index (ACI) is an emerging metric to measure the apparent acoustic biodiversity, and we use its Seewaveimplementation. We compare the third-octave bands centred on 63 Hz and 125 Hz (“shipping” bands of the European Marine Strategy Framework Directive) in each environment and assess their use in the presence of heavy ice and little to no shipping. Metrics designed for open waters are not directly applicable to icyenvironments, or at least not on their own. They must be supplemented with multivariate analyses of context-specific third-octave bands

Imaging large fields of small targets with shaped EM fields, adaptive beam steering and dynamic constellation antennas

Space debris is an increasing problem, with ca. 18,000 objects large enough to be tracked from the ground and conservative estimates of 670,000 small (1 – 10 cm) debris. Collisions have become a key issue in operation and decommissioning of spacecraft, adding costs and risks to space missions in all orbits, with the added threat of collisional cascading if some debris fields become dense enough. Their accurate mapping in 3-D, and their evolutionwith time, therefore become paramount, but in-flight approaches are constrained by limited fields of view and limited spatial resolutions. The shapes of debris are of interest as it might affect long-term movements, and thelarger ones will be of interest for retrieval missions and in the emerging field of debris exploitation. Leveraging on developments in acoustic imaging of complex subsea targets (e.g. Guigné, 1986; Blondel and Caiti, 2006; Guignéand Blondel, 2017), we propose an approach based on a collection of transducers acting as both EM transmitters and EM receivers, imaging debris fields in 4 dimensions (space and time) and using techniques such as beam steering and waveform inversion to retrieve as much information as possible on their shape and size distributions. Accurately located nanosatellites (as a constellation or in very small swarms) are positioned dynamically to image a particular volume in space. Individual sources are repeatedly actuated, with the other nanosatellites in the swarm acting as receivers. This gives access to a potentially large series of multistatic scattering measurements of any target. These are processed in real-time within each node, reducing the overall computation burden. The first result is a volumetric image of debris within the field of view aggregated from all nodes. Beam steering focuses on diffractions, creating virtual pencil beams from which high-resolution imagery can be formed, yielding information on sizes of individual targets and on shapes (via multi-angle diffraction patterns). This requires accurate positioning of the individual transducer nodes (nanosatellites), achievable using global positioning networks and EM time-of-flight checks between nodes. By varying the relative positions of nodes in the swarm, it is also possible to adapt the focusing toregions of particular interest. By using several nodes as transmitters, positive/destructive interference between sources can also be used to induce high signals in places of interest and null signals in other places (for example toavoid interference with or detection by instruments within the field of view). This enabling technology is adaptive, as the number of individual nodes can be adapted to suit operational requirements, from small groups to largerconstellations of nanosatellites. It is also dynamic as the virtual antenna they create can be changed very fast, either by repositioning them or only activating particular transmitters/receivers, making for responsive space missions. Onboard data processing allows fast, distributed processing, making individual nodes more affordable, and the modular aspect allow growing constellations or re-deploying subsets as mission profiles evolve. Beyond Earth orbit, thisapproach can also be used to map planetary environments and assist future asteroid mining operations

Arctic Acoustic Environments – Federating observations and analyses with the International Quiet Ocean Experiment

Arctic waters are experiencing rapid changes due to global warming, affecting ecosystems and leading to increasing economic activities. Many of these changes can be measured directly or indirectly with underwater acoustics. The Working Group on the Arctic Acoustic Environment (AAE) of the International Quiet Ocean Experiment (IQOE) aims to stimulate observations of sound (levels and distribution) in the Arctic Ocean and its impacts. We organised a virtual conference in November 2020 to share recent results from the international community and discuss common issues and possible solutions. The COVID-19 pandemic amplified the challenges of Arctic deployments and recoveries, curtailing access to ships at very short notice, but also opening the way for more direct collaboration. The post-COVID task will be to establish more resilient international back-up mechanisms for Arctic operations to support acoustic (and other) observations. The increasing length of the measurements, spanning several decades now, with sampling rates often close to 100,000 samples/second, results in “big data” challenges of storage, sharing, data retrieval and long-term archiving. Discussions also addressed the emerging trends in acoustic propagation models across complex terrains and machine learning (with the need for accessibility and traceability). Finally, the embedding of local and traditional knowledge must be accomplished through dialogue and co-ownership of the science and results

Mapping and living in marine habitats - Sonars, seismics and ambient sounds

Thorough mapping of the marine environments has started close to 70 years ago, and it makes use of increasingly sophisticated instruments mostly relying on acoustics. These instruments either create their own sounds and listen to their echoes, or rely exclusively on sounds produced naturally or by a variety of physical processes. We are using these tools to harvest resources like fish and hydrocarbons, to monitor the increases in commercial and recreational shipping, their sustainability and their impacts, and to de-risk the development of marine renewable energies. This creates challenges for data storage, long-term data access, reliable standardisation and interpretation, and for comparison between regions and between times. These challenges, and the different ways forward, will be illustrated with examples from Arctic waters to temperate coastal environments. The quantitative results afforded by acoustic measurements can then be meaningfully used to solve controversies, or add a useful evidence base to on-going activities and debates