These are examples of the ‘composite front map’ technique developed at PML, showing ocean fronts during a 7-day period. The darkness of each line indicates the significance of that front, in terms of its thermal gradient and persistence (allowing for some advection or tidal movement). The detection does NOT use the simple image gradient, but a regional statistical approach based on histogram analysis and spatial homogeneity; this is much more specific to fronts. Long-time series analysis and real-time operations have been undertaken. This capability has not yet been exploited by the fisheries management industry.
This figure indicates the most frequent front locations around the southwest UK, derived from 30,000 satellite images 1999-2008. This is the percentage of time for which a strong front was observed at each location. For the UK department of environment (Defra) we are applying these maps as a surrogate for identifying biodiversity hotspots (e.g. zooplankton, fish and basking sharks) and assist in the designation of potential Marine Protected Areas (MPAs). Cetacean and basking sharks are commonly sighted around the Isle of Man, Hebrides and SW Cornwall. The frequent front zones may improve understanding of the seasonal and inter-annual variability in their distribution.
This map was provided by one of the UK regional groups involved in deciding marine protected areas (MPAs), and shows how the frequent front data provided by PML are being used practically to guide the protection of important hotspots of pelagic biodiversity. [Click] shows potential MPAs decided primarily on the basis of oceanic fronts.
These ocean front maps are very useful to improve visualisation of features of interest, but they are difficult to analyse quantitatively due to the clusters of observations of each front over time, and scattered unimportant lines. [Click] We have developed a new line clustering algorithm to simplify the ‘spaghetti’ maps to show just the main fronts, coloured to indicate the warm and cold side (and the width indicates the strength of the front). This is analogous to the synoptic chart used for weather fronts, and this has not been previously possible for ocean fronts. Applications: naval, fisheries research, model validation.
Peter Miller & David Sims
Frequent locations of oceanic fronts as an indicator of pelagic diversity: Application to renewables Peter Miller and David Sims 1 PRIMaRE Annual Research Conference Plymouth, 06 Apr. 2011 1 MBA
Oceanic fronts for offshore renewables <ul><li>Detecting ocean fronts using EO data </li></ul><ul><li>UK project on Marine Protected Areas </li></ul><ul><li>Simplifying ocean front maps </li></ul><ul><li>Towards a global ocean front map </li></ul><ul><li>Applications for offshore renewables </li></ul>
Composite front maps: revealing strong fronts Figure 3. Schematic diagram of generation of composite front map for 21-27 Jun. 2009. More… Miller, P.I., (2009) Composite front maps for improved visibility of dynamic oceanic fronts on cloudy AVHRR and SeaWiFS data, Journal of Marine Systems . Mean gradient Persistence Advection / proximity F mean F comp X F persist X P front F prox
Advantages of front detection <ul><li>Does not blur dynamic features. </li></ul><ul><li>Highlights persistent or strong gradient fronts. </li></ul>Miller, P.I., (2009) Composite front maps for improved visibility of dynamic oceanic fronts on cloudy AVHRR and SeaWiFS data, Journal of Marine Systems . SST F comp
Ocean fronts: applications <ul><li>PML has developed novel tools to automatically detect fronts on EO data </li></ul><ul><li>Many pelagic fish distributions are related to oceanic fronts </li></ul>Sherwin, T.J., et al. (2008) Wind-driven monthly variations in transport and the flow field in the Faroe-Shetland Channel. Polar Research, 27(1), 7-22. Priede, I.G. & Miller, P.I. (2009) A basking shark tracked by satellite with simultaneous remote sensing: reveals orientation to a thermal front. Fisheries Research , 95(2-3), 370-372. Miller, P.I., (2009) Composite front maps for improved visibility of dynamic oceanic fronts on cloudy AVHRR and SeaWiFS data, Journal of Marine Systems . 5.5 ° W 5.0°W 55.5°N 55.0°N Firth of Clyde, Scotland Basking shark track Front Faroe Shetland ° W
Seasonal frequent front maps <ul><li>Percentage of time for which a strong front was observed, over 10 years </li></ul><ul><li>Fronts may be used as a proxy for pelagic biodiversity </li></ul><ul><li>Technology used by Defra to help define Marine Protected Areas </li></ul><ul><li>Techniques can be applied worldwide </li></ul>Summer 1999-2008 %
Seasonal frequent front maps Percentage of time a strong front was observed at each location Strong seasonal variability % Winter Spring Summer Autumn
Front data layers are now used for MPAs Potential MPAs located on the basis of oceanic front data
Ocean fronts: from spaghetti to synoptic chart May 2008 Miller, P.I., (in preparation), A line clustering algorithm with application to simplifying ocean front maps derived from satellite data, Remote Sensing of Environment . Warm Strong Weak Cold Key May 2008
Fronts applied to offshore renewables <ul><li>Defra are using oceanic fronts as a proxy for pelagic biodiversity, to guide the siting of some MPAs. </li></ul><ul><li>The same techniques could be applied to characterise the proposed sites of marine renewable installations. </li></ul><ul><li>This information could enable a cost-effective initial comparison of alternative sites in terms of potential impact on marine megafauna. Investigating higher resolution colour fronts. </li></ul><ul><li>Contribute to the environmental impact assessment, by estimating the likely abundance and distribution of key species known to inhabit the area. </li></ul><ul><li>During construction of a MREI, use near-real time EO data to advise on operation times to minimise acoustic impacts on marine mammals. </li></ul><ul><li>PML is gathering further evidence on the importance of fronts to basking sharks, marine mammals, seabirds, fish, etc. (PhD on this topic closing date 15 April!). </li></ul>Peter Miller - firstname.lastname@example.org