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Product Description

Description

Product Specifications

Table

Satellite altimetry is one of the most common techniques used to measure ocean wave height. It involves using radar to measure the height of the ocean surface from space. The Significant Wave Height (SWH) is the average height of the highest one-third of waves in a given sample period (European Space Agency, n.d.-m; NASA, n.d.-e). Satellite altimeter data of significant wave height (SWH) from Jason-3 and Sentinel-3A were available in real-time since July 2017, covering the global ocean.
Satellite altimeter data of SWH from multiple missions were available since 1986, covering 30 years of continuous records.
In the specific, two wave products are available at Copernicus Marine Service from altimeter satellite along-track sea surface heights anomalies (SLA) as: SEALEVEL_GLO_PHY_L3_NRT_OBSERVATIONS_008_044 for single altimeter, and WAVE_GLO_PHY_SWH_L4_NRT_014_003 which is the merged product of multi-mission altimeters.
As the spatial coverage of altimeters data is not homogeneous and the data refer to short time intervals, waves spectra available from altimeters could be not reliable if extracted far from the altimeter’s tracks. More homogenous wave data over the Arctic are provided by wave models, as for the ARCTIC ANALYSIS FORECAST WAV_002_014 dataset. This product is originated by the WAM model at 3 km resolution forced with surface winds and boundary wave spectra from the ECMWF (European Centre for Medium-Range Weather Forecasts), together with currents and ice from the ARC MFC analysis (Sea Ice concentration and thickness). WAM runs twice daily providing one hourly 10 days forecast and one hourly 5 days forecast. From the output variables the most used are peak period and mean direction of the significant wave height.Significant wave height is an average measurement of the largest 33% of waves.

Product Specifications

BUSINESS PROCESS	SC, SCE, IN, SO, ELD
DESCRIPTION	Wave heights describe the average height of the highest third of the waves (defined as the significant wave height – see diagram below). It is measured by the height difference between the wave crest and the preceding wave trough (Bureau of Meteorology, n.d.).
EO INFORMATION OF INTEREST	Sea wave height (SWH)
MAIN PROCESS STEPS	Observation: Altimeters emit microwave radar signals towards the ocean surface. The signal bounced back contains information about the sea state, as the variance of the surface elevation within the footprint (σ) inversely relates to SWH. Model: WAM is forced by DMI’s numerical weather prediction model Harmonie and ECMWF’s global weather prediction model, which provides wind forcing. Wave energy is primarily driven by surface wind. The variance of the surface elevation within the footprint (σ) inversely relates to SWH. Sea ice is included in the model, but sea current interaction is not considered. The water depth is assumed to be constant, and effects due to varying sea levels (tides or storms) are not incorporate.
INPUT DATA SOURCE	Observation: Gridded significant wave height level-4 product based on all available significant wave height level-3 products: · SAR spectral integral parameter level-3 product based on Sentinel-1A, Sentinel-1B and CFOSAT off-nadir measurements. · Altimetry along-track significant wave height level-3 product based on Sentinel-6A, Jason-3, Sentinel-3A, Sentinel-3B, Saral/AltiKa, Cryosat2, CFOSAT nadir, SWOT nadir, Hai Yang-2B and Hai Yang-2C measurements. Model: WAM input includes the following components 1. 10 m wind fields provided by numerical weather prediction, 2. A parametrization of the source term represented by the energy transfer between wind and wave, 3. Data assimilation scheme (satellites, buoys), 4. Validation.
SPATIAL RESOLUTION AND COVERAGE	Observation: 7x7km Model: 3 × 3 km, Arctic Ocean, from Lat 63° to 90°; Lon -180° to 180°
ACCURACY / CONSTRAINS	Observation: The accuracy of satellite derived data on wave (typically of few centimetres) depends on several factors, such as the type of satellite sensor, the wave parameter, atmospheric conditions, the sea state condition, and the validation method (e.g. 0.3 – 1 m altimeter vs SAR).The Copernicus Marine Service aims to provide accurate and reliable sea level data by combining observations from multiple altimeter missions. Model: WAM can be run at different resolutions (e.g., 50 km, 10 km, and 4 km). Higher resolution models tend to perform better. WAM relies on surface wind data (usually from numerical weather prediction models) to drive wave simulations. Accurate wind input improves model accuracy. Comparing WAM results with observations (e.g., EnviSat Radar Altimeter and in-situ data) helps assess accuracy. Changes in model resolution and forcing data impact accuracy. WAM’s spatial resolution determines its ability to capture small-scale features. Coarser resolutions may miss localized effects
LIMITATIONS	Some of the challenges of wave monitoring from satellite are: 1. The limited spatial and temporal resolution of satellite data, which may not capture the fine-scale features and variability of ocean waves 2. The interference of sea ice, rain, clouds, and other atmospheric conditions on the satellite signals, which may affect the accuracy and reliability of wave measurements . 3. The complexity of retrieving wave parameters from different types of satellite sensors, such as radar altimeters, scatterometers, synthetic aperture radars, and radiometers, which may require different algorithms and assumptions (Dohan & Maximenko, 2010; Dubovik et al., 2021; Hauser et al., 2023) Model: limitations in the assumptions in the Spectral Shape in Representation of Physical Phenomena, etc
TEMPORAL RESOLUTION	Hourly, products available since 3 Dec 2017
FREQUENCY UPDATE	Daily – Following day at 4:00 UTC and 16:00 UTC
DELIVERY / OUTPUT FORMAT	NetCDF-4
ACCESSIBILITY	Copernicus Marine Service, AVISO - CNES data center.