Separation of Wind-Sea and Swell Wave Heights Using Altimeter Data

Abstract Satellite altimetry provides an immensely valuable source of operational significant wave height (Hs) data. Currently, altimeters on board Jason-1 and Envisat provide global Hs observations, available within 3–5 h of real time. In this work, Hs data from these altimeters are validated against in situ buoy data from the National Data Buoy Center (NDBC) and Marine Environmental Data Service (MEDS) buoy networks. Data cover a period of three years for Envisat and more than four years for Jason-1. Collocation criteria of 50 km and 30 min yield 3452 and 2157 collocations for Jason-1 and Envisat, respectively. Jason-1 is found to be in no need of correction, performing well throughout the range of wave heights, although it is notably noisier than Envisat. An overall RMS difference between Jason-1 and buoy data of 0.227 m is found. Envisat has a tendency to overestimate low Hs and underestimate high Hs. A linear correction reduces the RMS difference by 7%, from 0.219 to 0.203 m. In addition to wave height–dependent biases in the altimeter Hs estimate, a wave state–dependent bias is also identified, with steep (smooth) waves producing a negative (positive) bias relative to buoys. A systematic difference in the Hs being reported by MEDS and NDBC buoy networks is also noted. Using the altimeter data as a common reference, it is estimated that MEDS buoys are underestimating Hs relative to NDBC buoys by about 10%.

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Accuracy of altimeter data in inner and coastal seas

10.5194/os-2018-81 ◽

2018 ◽

Cited By ~ 1

Author(s):

Luigi Cavaleri ◽

Luciana Bertotti ◽

Paolo Pezzutto

Keyword(s):

Wind Speed ◽

High Frequency ◽

Adriatic Sea ◽

Wave Model ◽

Altimeter Data ◽

Northern Adriatic Sea ◽

Large Wave ◽

Northern Adriatic ◽

Wave Heights ◽

One Year

Abstract. We carry out an inter comparison among four different altimeters, Cryosat, Jason2, Jason3, Sentinel-3. This is done checking the altimeter data versus the same wind and wave model results of a given area, the Mediterranean Sea, for one year period. The four datasets are consistent for wind speed, but they show substantial differences for wave heights. The verification of a Sentinel-3 pass close to coast in the Northern Adriatic Sea shows irregular spiky large wave height values close to coast. The problem worsens using high frequency altimeter data.

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Global Assessments of Surface Winds and Waves From an Ensemble Forecast System Using Satellite Data

Volume 7B: Ocean Engineering ◽

10.1115/omae2019-96627 ◽

2019 ◽

Author(s):

Ricardo Martins Campos ◽

C. Guedes Soares

Keyword(s):

Satellite Data ◽

Ensemble Forecast ◽

Altimeter Data ◽

Forecast System ◽

Significant Wave ◽

Error Metrics ◽

Control Member ◽

Ensemble Mean ◽

Wave Heights ◽

Significant Wave Heights

Abstract This paper evaluates the 10-m wind intensities and significant wave heights from the NCEP Ensemble Forecast System using altimeter data. A total of 20 perturbed members plus a control member (deterministic run) compose the ensemble. The assessment is focused on the comparison between the control run and the ensemble mean, in terms of benefits presented by four error metrics. Four satellite missions are selected for the assessments, obtained from AVISO and NESDIS/NOAA databases. Results show that the scatter components of the errors strongly depends on the latitude, were extra-tropical locations at longer forecast times present large errors. A significant improvement using the ensemble forecast compared to deterministic runs was verified at these locations, where the RMSE of day 10 was reduced from 5 to 3.5 m/s for U10 and from 1.8 to 1.3 meters for Hs.

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Accuracy of altimeter data in inner and coastal seas

Ocean Science ◽

10.5194/os-15-227-2019 ◽

2019 ◽

Vol 15 (2) ◽

pp. 227-233 ◽

Cited By ~ 4

Author(s):

Luigi Cavaleri ◽

Luciana Bertotti ◽

Paolo Pezzutto

Keyword(s):

Wind Speed ◽

High Frequency ◽

Adriatic Sea ◽

Wave Model ◽

Altimeter Data ◽

Data Sets ◽

Northern Adriatic Sea ◽

Large Wave ◽

Northern Adriatic ◽

Wave Heights

Abstract. We carry out an inter-comparison of four different altimeters: Cryosat, Jason-2, Jason-3, and Sentinel-3. This inter-comparison is undertaken by checking the altimeter data against the wind and wave model results of a given area, the Mediterranean Sea, for a 1-year period. The four data sets are consistent for wind speed, but they show substantial differences with respect to wave heights. The verification of a Sentinel-3 pass close to the coast in the northern Adriatic Sea shows irregular, spiky, large, wave height values close to the coast. This problem worsens when using high-frequency altimeter data.

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Numerical Investigation of Typhoon Waves Generated by Three Typhoons in the China Sea

10.5194/os-2019-111 ◽

2019 ◽

Author(s):

Qing Shi ◽

Jun Tang ◽

Yongming Shen ◽

Yuxiang Ma

Keyword(s):

Wind Speed ◽

Wind Field ◽

Wave Model ◽

Satellite Observations ◽

Altimeter Data ◽

Correction Coefficient ◽

Wind Fields ◽

China Sea ◽

Wave Heights ◽

Typhoon Waves

Abstract. The typhoon waves generated in the China Sea during the Chan-hom (1509), Linfa (1510) and Nangka (1511) typhoons that occurred in 2015 were numerically investigated. The wave model was based on the a third generation spectral wind-wave model SWAN, in which the wind fields for driving waves were derived from the ERA-interim (ECMWF), CFSv2 (The NCEP Climate Forecast System Version 2) and CCMP (Cross-Calibrated Multi-Platform) datasets. The numerical results were validated using buoy data and satellite observation data. The simulation results under the three types of wind fields were in good agreement with the observed data. The CCMP wind data was the best in simulating waves overall, and the wind speeds pertaining to ERA and CCMP were notably smaller than those observed near the typhoon centre. The Holland wind model was used to revise and optimize the wind speed pertaining to the CCMP near the typhoon centre, and the wind speed correction coefficient, correction formula and corresponding parameters were determined. Based on these findings, the CCMP and CCMP/Holland blended wind fields were used to simulate the typhoon waves generated during the Meranti (1614), Rai (1615) and Malakas (1616) typhoons that occurred in September 2016. A comparison between the simulated wave heights and those obtained from the Jason-2 altimeter data indicated that all correlation coefficients between the simulated values and the satellite observations were greater than 0.75. The blended wind field was better overall in simulating the wave heights. The simulated maximum wave heights were more similar to the satellite observations, and the root mean square error of the blended wind field was 0.223 m lower than that of the CCMP. The results demonstrated that the CCMP wind-driven SWAN model could appropriately simulate the typhoon waves generated by three typhoons in China Sea, and the use of the CCMP/Holland blended wind field could effectively improve the accuracy of typhoon wave simulations.

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Comparison of Envisat ASAR Ocean Wave Spectra with Buoy and Altimeter Data via a Wave Model

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecho529.1 ◽

2009 ◽

Vol 26 (3) ◽

pp. 593-614 ◽

Cited By ~ 10

Author(s):

Jian-Guo Li ◽

Martin Holt

Keyword(s):

Wave Height ◽

Spectral Characteristics ◽

Wave Model ◽

Ocean Wave ◽

Global Ocean ◽

Altimeter Data ◽

Wave Spectra ◽

Envisat Asar ◽

Comparison Results ◽

Wave Heights

Abstract The Advanced Synthetic Aperture Radar (ASAR) on board the Envisat satellite is an important resource for observation of global ocean surface wave spectra. However, assessment of this valuable dataset is not straightforward as a result of a lack of other independent ocean wave spectral observations. The radar altimeter (RA-2) on board the same satellite measures ocean wave height at the same time as the ASAR but at a location about 200 km distant. A small number of moored buoys produce one-dimensional (1D) ocean wave spectra but few ASAR spectra fall on the buoy positions in a given period. Indirect comparison of the Envisat ASAR 2D wave spectra with the RA-2 wave heights and 1D spectra of three selected buoys from July 2004 to February 2006 is facilitated by a wave model, which provides coherent spatial and temporal links between these observations. In addition to the conventional significant wave height (SWH), four spectral subrange wave heights (SRWHs) are used to illustrate the spectral characteristics of these observations. A comparison of three Envisat ASAR 2D spectra with the closest model and buoy spectra is also attempted to illustrate the qualities of these different observations and to demonstrate the restrictions to their direct comparison. Results indicate that these three independent observations are in good agreement in terms of SWH, though the Envisat ASAR shows the largest variance. Comparison of SRWHs indicates that the ASAR spectra agree well with buoy and model in moderately long waves, but the ASAR instrument does not resolve high-frequency waves, especially along the satellite track.

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