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Measuring global ocean wave skewness by retracking RA-2 ENVISAT waveforms

Measuring global ocean wave skewness by retracking RA-2 ENVISAT waveforms
Measuring global ocean wave skewness by retracking RA-2 ENVISAT waveforms
For early satellite altimeters, the retrieval of geophysical information (e.g., range, significant wave height) from altimeter ocean waveforms was performed on board the satellite, but this was restricted by computational constraints that limited how much processing could be performed. Today, ground-based retracking of averaged waveforms transmitted to the earth is less restrictive, especially with respect to assumptions about the statistics of ocean waves. In this paper, a theoretical maximum likelihood estimation (MLE) ocean waveform retracker is applied to the Envisat Radar Altimeter system (RA-2) 18-Hz averaged waveforms under both linear (Gaussian) and nonlinear ocean wave statistics assumptions, to determine whether ocean wave skewness can be sensibly retrieved from Envisat RA-2 waveforms. Results from the MLE retracker used in nonlinear mode provide the first estimates of global ocean wave skewness based on RA-2 Envisat averaged waveforms. These results show for the first time geographically coherent skewness fields and confirm the notion that large values of skewness occur primarily in regions of large significant wave height. Results from the MLE retracker run in linear and nonlinear modes are compared with each other and with the RA-2 Level 2 Sensor Geophysical Data Records (SGDR) products to evaluate the impact of retrieving skewness on other geophysical parameters. Good agreement is obtained between the linear and nonlinear MLE results for both significant wave height and epoch (range), except in areas of high-wave-height conditions.
0739-0572
1102-1116
Gomez-Enri, J.
52626f7d-16f6-4d53-99bc-82ea43d90aef
Gommenginger, C.P.
f0db32be-34bb-44da-944b-c6b206ca4143
Srokosz, M.A.
1e0442ce-679f-43f2-8fe4-9a0f0174d483
Challenor, P.G.
a7e71e56-8391-442c-b140-6e4b90c33547
Benveniste, J.
5b37343a-1a74-4d97-bd74-a46b2669712a
Gomez-Enri, J.
52626f7d-16f6-4d53-99bc-82ea43d90aef
Gommenginger, C.P.
f0db32be-34bb-44da-944b-c6b206ca4143
Srokosz, M.A.
1e0442ce-679f-43f2-8fe4-9a0f0174d483
Challenor, P.G.
a7e71e56-8391-442c-b140-6e4b90c33547
Benveniste, J.
5b37343a-1a74-4d97-bd74-a46b2669712a

Gomez-Enri, J., Gommenginger, C.P., Srokosz, M.A., Challenor, P.G. and Benveniste, J. (2007) Measuring global ocean wave skewness by retracking RA-2 ENVISAT waveforms. Journal of Atmospheric and Oceanic Technology, 24 (6), 1102-1116. (doi:10.1175/JTECH2014.1).

Record type: Article

Abstract

For early satellite altimeters, the retrieval of geophysical information (e.g., range, significant wave height) from altimeter ocean waveforms was performed on board the satellite, but this was restricted by computational constraints that limited how much processing could be performed. Today, ground-based retracking of averaged waveforms transmitted to the earth is less restrictive, especially with respect to assumptions about the statistics of ocean waves. In this paper, a theoretical maximum likelihood estimation (MLE) ocean waveform retracker is applied to the Envisat Radar Altimeter system (RA-2) 18-Hz averaged waveforms under both linear (Gaussian) and nonlinear ocean wave statistics assumptions, to determine whether ocean wave skewness can be sensibly retrieved from Envisat RA-2 waveforms. Results from the MLE retracker used in nonlinear mode provide the first estimates of global ocean wave skewness based on RA-2 Envisat averaged waveforms. These results show for the first time geographically coherent skewness fields and confirm the notion that large values of skewness occur primarily in regions of large significant wave height. Results from the MLE retracker run in linear and nonlinear modes are compared with each other and with the RA-2 Level 2 Sensor Geophysical Data Records (SGDR) products to evaluate the impact of retrieving skewness on other geophysical parameters. Good agreement is obtained between the linear and nonlinear MLE results for both significant wave height and epoch (range), except in areas of high-wave-height conditions.

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Published date: June 2007

Identifiers

Local EPrints ID: 44065
URI: http://eprints.soton.ac.uk/id/eprint/44065
ISSN: 0739-0572
PURE UUID: c0abecf6-7017-416a-9677-57400bf9c6a7

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Date deposited: 12 Feb 2007
Last modified: 15 Mar 2024 09:00

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Contributors

Author: J. Gomez-Enri
Author: C.P. Gommenginger
Author: M.A. Srokosz
Author: P.G. Challenor
Author: J. Benveniste

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