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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Sea Level CCI Annual Review #1 WP2700 Coastal sea level corrections : Coastal Proximity Parameter Paolo Cipollini (NOC)

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Rationale In order to determine how ‘close to the coast’ we can reach with climate-quality data, we need to screen data and corrections versus some independent variable –‘Distance from coast’ is crude because it does not capture the enormous variability in 1) morphology and 2) coastal conditions Example: Elba Island, Tuscan Archipelago distance from coast(km)

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Coastal Proximity P A new parameter to be used as independent variable –initially aim at capturing differences in coastal morphology problem is well defined once geometry and instrumental params are fixed (orbital height, antenna beamwidth, pulse length, number of gates) and a good DEM is available –later, if possible, include peculiarities in coastal ocean (for instance peculiarities in coastal wave field) more tentative The P parameter is expected to improve screening (impact on the regional variability in coastal regions –with reference to distance from coast

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Defining P increasing from ocean land smaller over tips/peninsulas, larger in bays for easier comparison with distance (which is zero at coastline), P can be remapped: –-1 over open ocean –0 at idealized, straight coastline –1 inland P > 0 P = 0 P < 0

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Computing P - DEM We need to simulate the effects of land on waveforms we fly a virtual altimeter over a DEM Need a good DEM: ACE2 ACE2 produced by De Montfort University using altimetry to correct (‘warp”) and integrate SRTM available at various resolutions: we used the highest one –3 arcmin, i.e.~90 m at equator

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example1: small tall island

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Computing P - two effects near land power deficit due to “missing ocean” –land, even if it is at z=0, will usually have much lower backscatter than ocean (there are exceptions, but they are difficult to model!) land returns in various gates depending on land elevation –i.e. we get echoes from land elements in various gates (before and after leading edge) depending on the land height

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example 2: flat straight coast Ocean Land z=0.001

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example 2: “Dover cliff” Ocean Land z=100

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Computing P - parameterise the two contributions We assume them to be independent and parameterise them as ‘worst cases’, and compute, gate by gate : 1.power deficit due to “missing ocean”: assume sigma0 land =0 for this effect where n ocean is the return from the ocean elements only; and n ocean0 the return from ocean elements if there was no land at all 2.land returns in various gates depending on land elevation: assume sigma0 land =sigma0 ocean for this effect where n land is the return from the land elements only Finally we weight P 1, P 2 by gate position, sum them and rescale them to [-1,1]

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example of P 1, P 2 and weighting

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Example of P

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Example of P

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Example of P Global map of P at 0.02° resolution (CoastalProximity_v1.nc) available on SL CCI FTP server

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Next steps Refining P –account for peculiarities of coastal ocean, like wave field variable spread for the gaussian weights based on wave models/wave climatology? –difficult to do it globally Validating P –it is the independent variable – goes on the x axis –so we need to plot parameter errors, correction ‘errors’ or any equivalent cost functions against P –…and if needed, refine the algorithm to improve the effectiveness of the parameter in making errors monotonic and easy to put a threshold on

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Validating P distance from coast Error or cost function LAND coastal proximity P

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Sea Level CCI – Annual Review #1 – 19 th - 20 th September 2011 Comments/Suggestions Welcome!

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