Murray Clarke

Bio: Murray Clarke is an academic researcher. The author has contributed to research in topics: Sea ice & Echo sounding. The author has an hindex of 3, co-authored 7 publications receiving 27 citations.

Instrument for detecting freeze-up, mid-winter and break-up ice processes in rivers

Abstract: A new underwater acoustic instrument for river ice studies has been designed, developed, and deployed in the Peace River in Northern Alberta, which is hydraulically regulated by upstream hydroelectric projects. The data is being collected to support studies related to ice jam occurrences and hydropower operations during the winter. An upward looking sonar instrument was deployed for the 2004-2005 ice season. From the acoustic backscatter returns of the transmitted acoustic pulses, the sonar instrument measured the distance to the water surface or the underside of floating ice at the surface. The instrument also had the capability to record the profile of acoustic backscatter returns through the river water column. The instrument provided valuable insights into numerous freeze-up, midwinter and spring ice processes difficult or impossible to obtain by other methods. These processes included formation of frazil in suspension, development of frazil ice pans, anchor ice formation/detection, formation of the river ice cover including highly dynamic freeze-up events, changes in the river ice cover over the winter, undercover ice transport and, finally, thermal break-up. 1.0 Introduction The Peace River in northern British Columbia and Alberta is regulated by the WAC Bennett and Peace Canyon dams (Figure 1.1.1). During the winter, flow releases have to be managed to reduce the potential for ice jamming and subsequent flooding that can occur under a variety of environmental conditions. At particular risk is the Town of Peace River, Alberta about 375 km downstream from the hydroelectric facilities. These management efforts require better understandings of river ice processes, including calibration of computer ice models. The collection of field data is useful for meeting these management requirements as well as for providing baseline data for ongoing evaluations and for assessing potential development of the Dunvegan Hydroelectric Project about 100 km upstream of the Town of Peace River. The Shallow Water Ice Profiling Sonar (SWIPS) unit, which was central to 2004-2005 field measurement campaign, was deployed near the Town of Peace River (Figure 1.1.1) to investigate ice processes at a location where such processes could have near-maximal impact on overall Peace River management. The chosen site was also logistically convenient, as close proximity to the town site allowed for both frequent site visits and use of other data being collected in surrounding areas. 1.1 Measurement Objectives Measurements of ice processes occurring in the water layer and/or below the uppermost ice surface have been rarely reported upon in the …

Inverted Echo Sounder on a Cabled Observatory

Abstract: High-frequency acoustic backscatter measurements have long been used as a method to detect zooplankton populations in the ocean. Ship-borne echo-sounders can map distributions over relatively large areas, but are not practical for following developments over long periods of time. Self-contained echo-sounders, either moored at depth looking upward, or mounted on surface buoys looking downward produce time series of acoustic backscatter which are a means for monitoring long-term behaviour of zooplankton populations. Combining these instruments with a cabled observatory allows this information to be acquired and monitored in near real-time, and thus to contribute to understanding and monitoring the state of one of the key components of coastal marine ecosystems. In this paper, we will discuss what we believe is the first operational example of an inverted echo sounder as part of a cabled seafloor observatory. The first component of the VENUS seafloor observatory, in Saanich Inlet, British Columbia, began operation in February, 2006. The instrument platform is located 3 km from the Institute of Ocean Sciences dock, at 96 m depth. A 200 kHz upward looking echo sounder (Acoustic Water Column ProfilerTM, also known as the ZAP, for Zooplankton Acoustic Profiler) is located on the platform. The instrument collects a profile of acoustic backscatter strength throughout the water column once per second and transmits the data over the cable to the VENUS shore station. Power and control communications are also supplied over the cable. The techniques for command and control of the instrument over the VENUS VPN are described, as are the means for real-time display of the data using TCP/IP protocols. Continuous data retrieval and image posting to the VENUS website are performed automatically using the observatory's DMAS (Data Management and Archiving System). Echograms of acoustic backscattering strength as a function of depth and time are available on the web at hourly intervals, and as daily summaries. These plots, and the data files from which they are constructed, may be used for the detection if zooplankton, fish, near-surface bubbles and internal waves. Their evolution and development can be monitored in real time, and the archived data now provide a year-long record at the Saanich Inlet site. At least two more of these instruments will be deployed at sites in Georgia Strait, when the next phase of the Venus observatory system is installed in October 2007. It is anticipated that the data from these locations will provide a valuable tool to further the understanding of the state of this coastal sea. A new generation of the AWCP is currently under development, which will provide greater A/D resolution and greater data storage for self-contained operation.

A configurable multi-sensor tripod for the study of near-bottom ocean processes

Abstract: A cost effective and highly configurable scientific platform, dubbed Norton, has been developed for the scientific study of near-bottom ocean processes. The basic platform is a collapsible lightweight aluminum tripod that can be transported in the back of a pick-up truck, and is easily accommodated on most vessels. Ballast is supplied in the form of large ship anodes bolted to the base of each leg. The desired sensors are attached to the tripod legs and bracing. A typical deployment might utilize the following sensors: Acoustic Doppler Current Profiler for current profiles and directional wave data. Marsh McBirney electromagnetic flow sensor for measurements close to the bottom, supporting both wave orbital burst sampling and average current measurements. Optical Backscatter Sensors (OBS) for sediment concentration. Sector-scanning sonar to supply bed-form images; an Imagenex variable frequency scanning head has been integrated into a self-contained housing containing a control module, data logger and power supply. Other sensors can be added as desired. Norton is usually deployed by lowering with a line from the ship. An acoustic release is used to let go of the tripod once it is on bottom. A customized 'tilt-pinger' provides confirmation to the crew that the tripod is upright. Recovery can be via a pop-up buoy and/or a ground-line.

Advances in moored upward looking sonar systems for long term measurement of arctic ice and oceanography

Abstract: A major impetus for scientific studies of climate change in the Arctic Ocean has been the reduction in the areal extent and thickness of its sea ice cover which has been experienced at accelerated rates in the past decade. These dramatic changes resulted in major climate science studies being conducted in the Arctic Ocean as well as opening the way for increased shipping and offshore oil and gas activities. An extended measurement record of the horizontal dimensions of this ice cover is available for the full Arctic Ocean Basin based upon a record compiled from nearly 40 years of relatively continuous satellite based measurements. Unfortunately, data accumulations for the ice cover's vertical dimension, i.e. sea ice thickness, as well as full temporal resolution ice velocity and under-ice ocean current profiles tend to be limited to a small number of year-long mooring data sets with durations that are only a few to several years, reflecting underlying greater measurement challenges. Moreover, the longest duration ice thickness data collection efforts, spanning more than 10 years, have been confined only to two specific portions of the Basin, namely, Fram Strait and the Canadian sector of the Beaufort Sea. However, in the past ten years, the available year-long ice and oceanographic mooring data sets have greatly increased in total number and in the number of sites. Advanced upward-looking sonar (ULS) instruments operated from subsurface moorings has been and continues to be the primary source of data with volumes and accuracy sufficient for meaningfully monitoring ice thickness, ice velocities, ocean current profiles and other in-situ water properties. The ice thickness, or more properly ice draft (underwater ice thickness) data is measured continuously with temporal resolution of 1 -2 seconds. Technological advances, since ULS instruments were first developed in the 1980's have led to new generations of iceprofiling sonar (IPS), incorporating much expanded on-board data storage capacities (up to 16 Gigabytes) and powerful realtime firmware which now allow unprecedented temporal (ping rates of up to 1 Hz). When combined with ULS Acoustic Doppler Current Profiler (ADCP) instrumentation using a special ice tracking mode (with a temporal resolution of a few minutes), details of the ice topography can be realized to resolutions of better than 0.1 m in the vertical and 1 m in the horizontal. These very high resolution ice draft measurements fully resolve individual ice features including undeformed level ice, brash ice, individual large ice keels including multi-year ice, hummocky ice rubble fields, glacial ice including icebergs and ice islands, and open water interruptions of the ice cover including leads between ice floes. Such continuous highly detailed ice measurements, along with concurrent measurements of ice velocities and ocean current profiles, are essential to understandings of mechanical and thermodynamical aspects of sea ice processes which govern ocean-atmosphere exchanges in polar waters, thereby determining ice extent and thickness parameters. The ice profiler ULS instrument can sample at higher sampling frequencies to measure non-directional ocean wave spectra and parameters (significant and individual maximum wave heights and peak periods) both during the period of mostly open water, often from mid-summer to mid-autumn, and also when ocean waves propagate into the periphery of the Arctic Ocean pack ice. Ocean wave interactions with pack ice are important in understanding the fracturing of sea ice floes and hastening the deterioration and melt of sea ice. The ULS data provide the first detailed measurements of such ocean wave - ice processes. A major challenge in moored ULS measurement systems is the inaccessibility of the measurement sites to ship logistics due to the very remote areas in the Arctic Ocean and its peripheral seas and the difficulty, resulting in very high logistic costs, of deployment and servicing the moorings due to the sea ice itself. This challenge is being addressed through the development of expanded capacity and more efficient internal power capability and increased onboard data storage, along with very high instrument reliability. With expanded alkaline battery packs, continuous operation for 2 to 3 years is now possible; lithium battery packs are being developed that will extend the in-situ ULS instrument operation to approximately five years. To provide access to the ULS data between mooring servicing intervals, two different approaches are being developed. In some areas cabled underwater observatory technology can be installed to provide real-time access to the ULS ice measurements in support of navigation and oil and gas exploration activities as previously described in Fissel et al. (2009) for sub-Arctic applications. The first such ocean observatory involving a ULS ice instrument was commissioned at Cambridge Bay in the Canadian Arctic in September 2012. At locations far from shorelines, the challenges become even greater. For offshore oil and gas drilling applications, an array of subsurface ULS moorings spanning distances of tens of kilometers, interconnected via bottom mounted fiber optics cable systems interfaced to the moored ULS instruments and to vessel platforms using acoustic modems, have been designed to provide tactical support for ice management operations in support of drilling activities. An alternative approach to provide yearly access to the multi-year moored ULS data sets is the development of small expendable buoyant “datapods” which store the ULS data on flash cards; during times of open water or very thin ice, the datapods are released from the mooring to float to the surface and the ULS data is then transmitted via satellite to provide remote access to the scientific users. There are variations on this approach involving aircraft landing on sea ice in the vicinity of the subsurface ULS moorings to access the data via on-command acoustic modem transmission of the data to acoustic receivers operated through ice holes.

Development of ice profiler sonar (IPS) target sonar with a logarithmic detector

Abstract: Upward-looking sonar (ULS) instruments have become the primary source of data for high resolution and long duration measurements of sea ice drafts to support engineering requirements for oil and gas exploration projects in Arctic and other ice-infested areas. ULS instruments, in the form of ASL's Ice Profiler Sonar (IPS), provide accurate measurements for ice draft on a continuous year-long basis and allow detailed characterization of keel shapes and other ice features. The IPS instrument was originally developed in the 1990's and it was last upgraded by ASL Environmental Sciences Inc. in 2007-2008 through improved instrument design based on more capable microprocessors and more advanced on-board firmware. Another upgrade of the IPS instrument platform is presently underway with the design, testing and implementation of a logarithmic detector module in place of the previously used linear detector module which has been used for the past decade in the instrument. The linear detector module involves the use of an echo sounder detector which generates an analog voltage output from the raw transducer input supplied which is constant, i.e. independent of the time elapsed since the acoustic pulse was originally emitted. While this approach has proven reasonably serviceable, it has the disadvantage that the dynamic range of the instrument is curtailed from the alternative approach of using a logarithmic detector module which has previously been implemented in other ASL upward looking sonar instruments. The larger dynamic range of the log detector avoids using approximate TVG compensation. With the logarithmic sonar detector, the use of discrete threshold values for target detection is avoided and the resulting target detection capability is more robust. The project involved three principal components: (a) construction of a prototype 420 kHz log sonar card; (b) simulations of the response of the IPS log sonar instrument from previous IPS data sets which guided the development of operating firmware; and (c) assembly and field testing of a prototype IPS log sonar unit operated simultaneously with a standard IPS5. The simulations of the IPS5 log sonar outputs derived from previous standard IPS5 data indicate that there are occasional differences in the target detection for borderline cases, but they will not be significant. After iterations to improve the robustness of the target detection algorithm, development of the remaining functions of the IPS5 operating firmware was then carried out and further tested. Finally the prototype IPS5 log sonar instrument unit, along with a standard IPS5 instrument, was field tested in a deep open water environment (to 200 m water depth) in order to test the accuracy of the acoustic range of the sonar targets.

Changing coasts: marine aliens and artificial structures

Abstract: Marine aliens are non-native species that have been transported across major geographical barriers by human activities, involving vectors that move propagules along pathways. Species may also be newly observed in a geographical area due to range shifts, generally in association with climate change. Artificial structures are considered to be either man-made materials or natural materials shaped or displaced to serve a specific function for human activities. All types of artificial structures are currently increasing dramatically in coastal zones due to increasing human populations on coastlines. Most of the significant marine vectors and pathways involve mobile artificial structures and are reviewed here. These include shipping (ballast water and hull fouling) and aquaculture, including stock transfer and unintentional introductions, all of which can move species into new biogeographical provinces. Some types of structures frequently move long distances but have low fouling loads (e.g., commercial shipping), whereas others (e.g., barges and pontoons) can be hyperfouled due to long stationary periods such that when moved they transport mature fouling communities. We also examine the presence of alien marine species on static (immobile) artificial structures, which support different communities from those on natural hard substrata. We consider the role of these structures, such as coastal defences, artificial reefs, and offshore platforms, in the dispersal and abundance of alien species. Marinas include both mobile and immobile structures and are apparently particularly favourable habitats for many aliens. For example, in coastal North America approximately 90% of the alien species inhabiting hard substrata have been reported from docks and marinas. Detailed case studies of alien marine species (two seaweeds and four invertebrates) are provided, with an analysis of their origin, vectors of transport, habitat in the introduced range, and potential impact. Although there are exceptions, a large majority of marine alien species seem to be associated, at least for some of the time, with artificial structures. It is clear that artificial structures can pave the way and act as stepping stones or even corridors for some marine aliens, as do urban areas, roads and riparian environments in terrestrial ecosystems. The observed acceleration of spread rates for marine invasions over the course of the last two centuries may partly be a result of the increase of artificial structures in coastal environments coupled with greater activity of vectors.

Scanners, targets, and methods for surveying

Abstract: Apparatus and methods useful in surveying to provide information rich models. In particular, information not readily or possibly provided by conventional survey techniques can be provided. In some versions targets provide reference for baseline positioning or improving position information otherwise acquired. Scanning may be carried out in multiple locations and merged to form a single image. Machine mounted and hand mounted scanning apparatus is disclosed.