Coastal Proximity Parameter

Sea Level CCI Annual Review #1

WP2700 Coastal sea level corrections :Coastal Proximity Parameter

Paolo Cipollini (NOC)

Sea Level CCI Annual Review #1 19th - 20th September 2011RationaleIn 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 variableDistance 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)Sea Level CCI Annual Review #1 19th - 20th September 2011Coastal Proximity PA new parameter to be used as independent variableinitially aim at capturing differences in coastal morphologyproblem is well defined once geometry and instrumental params are fixed (orbital height, antenna beamwidth, pulse length, number of gates) and a good DEM is availablelater, 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 regionswith reference to distance from coastSea Level CCI Annual Review #1 19th - 20th September 2011Defining P increasing from ocean landsmaller over tips/peninsulas, larger in bays

for easier comparison with distance (which is zero at coastline), P can be remapped:-1 over open ocean0 at idealized, straight coastline1 inland

P > 0P = 0P < 0Sea Level CCI Annual Review #1 19th - 20th September 2011Computing P - DEMWe need to simulate the effects of land on waveforms we fly a virtual altimeter over a DEMNeed a good DEM: ACE2 ACE2 produced by De Montfort University using altimetry to correct (warp) and integrate SRTMavailable at various resolutions: we used the highest one3 arcmin, i.e.~90 m at equator

Sea Level CCI Annual Review #1 19th - 20th September 2011

example1:small tall islandSea Level CCI Annual Review #1 19th - 20th September 2011Computing P - two effects near landpower deficit due to missing oceanland, 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 elevationi.e. we get echoes from land elements in various gates (before and after leading edge) depending on the land heightSea Level CCI Annual Review #1 19th - 20th September 2011

example 2:flat straight coastOceanLand z=0.001Sea Level CCI Annual Review #1 19th - 20th September 2011

example 2:Dover cliffOceanLand z=100Sea Level CCI Annual Review #1 19th - 20th September 2011Computing P - parameterise the two contributionsWe assume them to be independent and parameterise them as worst cases, and compute, gate by gate :power deficit due to missing ocean: assume sigma0land=0 for this effectwhere nocean is the return from the ocean elements only; and nocean0 the return from ocean elements if there was no land at allland returns in various gates depending on land elevation: assume sigma0land=sigma0ocean for this effect

where nland is the return from the land elements onlyFinally we weight P1, P2 by gate position, sum them and rescale them to [-1,1]

Sea Level CCI Annual Review #1 19th - 20th September 2011

example of P1,P2and weightingSea Level CCI Annual Review #1 19th - 20th September 2011Example of P

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

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

Global map of P at 0.02 resolution (CoastalProximity_v1.nc)available on SL CCI FTP serverSea Level CCI Annual Review #1 19th - 20th September 2011Next stepsRefining Paccount for peculiarities of coastal ocean, like wave field variable spread for the gaussian weights based on wave models/wave climatology?difficult to do it globallyValidating Pit is the independent variable goes on the x axisso we need to plot parameter errors, correction errors or any equivalent cost functions against Pand if needed, refine the algorithm to improve the effectiveness of the parameter in making errors monotonic and easy to put a threshold onSea Level CCI Annual Review #1 19th - 20th September 2011Validating P distance from coastError or cost functionLANDcoastal proximity P Sea Level CCI Annual Review #1 19th - 20th September 2011Comments/Suggestions Welcome!Sea Level CCI Annual Review #1 19th - 20th September 2011