DOI: 10.5285/d96406df-ec66-45bb-979a-4338061ad289
title: UCL CPOM CryoSat2 Polar Ocean Significant Wave Height 2011-2019

description: We present the significant ocean surface wave heights in the Arctic and Southern Oceans from CryoSat-2 data. We use a semi-analytical model for an idealised synthetic aperture satellite radar or pulse-limited radar altimeter echo power. We develop a processing methodology that specifically considers both the Synthetic Aperture and Pulse Limited modes of the radar that change close to the sea ice edge within the Arctic Ocean. All CryoSat-2 echoes to date were matched by our idealised echo revealing wave heights over the period 2011-2019. Our retrieved data were contrasted to existing processing of CryoSat-2 data and wave model data, showing the improved fidelity and accuracy of the semi-analytical echo power model and the newly developed processing methods. We contrasted our data to in situ wave buoy measurements, showing improved data retrievals in seasonal sea ice covered seas. We have shown the importance of directly considering the correct satellite mode of operation in the Arctic Ocean where SAR is the dominant operating mode. Our new data are of specific use for wave model validation close to the sea ice edge and is available at the link in the data availability statement. NERC NE/R000654/1 Towards a marginal Arctic sea ice cover.
description: We take CryoSat2 Level 1B radar data (Baseline D was used at the time of processing, though other NetCDF file based product releases are applicable). These records are from 2 satellite modes, LRM and SAR. We only take data either above 60N or below 50S. The data is first filtered by using pulse peakiness and echo standard deviation to leave only data for the open ocean surface. The remaining 20Hz satellite echos are down sampled to 1Hz averaged records. The 1Hz averaged echoes are then analysed by our semi-analytical physical retracker to create the closest matching idealised radar echo. A different idealised echo is used for the different instrument modes. The parameters used to create the idealised echo represent the significant wave height of the ocean surface. The individual wave height data records are saved as satellite tracks similar to the initial CryoSat2 files. We then create gridded data product for easier use. This collects all satellite records onto a daily 100km polar stereographic projection. Prior to gridding we filter the data to those with acceptable retracker fit, the difference between the idealised and recorded radar echo. A wave height dependent LRM to SAR mode offset was apparent and this bias was analysed, parameterised and removed to make the gridded data.
description: CryoSat2 LRM and SAR mode radar altimeter.
description: The retracker fit metric is supplied alongside the individual data records to indicate the accuracy of the retrieved data. For the gridded data product, data accuracy filtering and mode debiasing was performed. The gridded data is give daily with many empty grid cells where the satellite did not cross for that day. These data celss have nan values. Data is supplied over all locations where a record was retrieved. This can be over sea ice. We supply a sea ice mask within the file to indicated which data points are for the open ocean. We provide data for all open ocean surfaces as defined by the spatial coverage. We give particular attention for data filtering to avoid sea ice contaminated data retrievals, but to also obtain data as close to the sea ice edge as possible. We analyse NSIDC sea ice concentration data to compare our data to the sea ice extent .