Wind-Wave induced velocity in ATI SAR Ocean Surface Currents: First experimental evidence from an airborne campaign
Wind-Wave induced velocity in ATI SAR Ocean Surface Currents: First experimental evidence from an airborne campaign
Conventional and along-track interferometric (ATI) Synthetic Aperture Radar (SAR) sense the motion of the ocean surface by measuring the Doppler shift of reflected signals. Measurements are affected by a Wind-wave induced Artefact Surface Velocity (WASV) which was modelled theoretically in past studies and has been estimated empirically only once before with Envisat ASAR by Mouche et al., (2012). An airborne campaign in the tidally dominated Irish Sea served to evaluate this effect and the current retrieval capabilities of a dual-beam SAR interferometer known as Wavemill. A comprehensive collection of Wavemill airborne data acquired in a star pattern over a well-instrumented validation site made it possible for the first time to estimate the magnitude of the WASV, and its dependence on azimuth and incidence angle from data alone. In light wind (5.5 m/s) and moderate current (0.7 m/s) conditions, the wind-wave induced contribution to the measured ocean surface motion reaches up to 1.6 m/s upwind, with a well-defined 2nd order harmonic dependence on direction to the wind. The magnitude of the WASV is found to be larger at lower incidence angles. The airborne WASV results show excellent consistency with the empirical WASV estimated from Envisat ASAR. These results confirm that SAR and ATI surface velocity estimates are strongly affected by WASV and that the WASV can be well characterized with knowledge of the wind knowledge and of the geometry. These airborne results provide the first independent validation of Mouche et al., 2012, and confirm that the empirical model they propose provides the means to correct airborne and spaceborne SAR and ATI SAR data for WASV to obtain accurate ocean surface current measurements. After removing the WASV, the airborne Wavemill retrieved currents show very good agreement against ADCP measurements with a root mean square error (RMSE) typically around 0.1 m/s in velocity and 10° in direction.
ocean surface current, microwave remote sensing, ATI SAR, Doppler, wind, airborne
1640-1653
Martin, Adrien C.H.
8c4f9cad-a856-4638-a13d-1b27edb73c3c
Gommenginger, Christine
f0db32be-34bb-44da-944b-c6b206ca4143
Marquez, Jose
e450ae26-9831-405d-81a1-a89029fe9790
Doody, Sam
4dabe33d-160b-44e5-876d-4d046f9e0c2f
Navarro, Victor
f8b2656c-aa5b-49e7-bd93-61ee033682da
Buck, Chris
ac592950-f49d-44ee-9329-d12963c0a2ca
13 February 2016
Martin, Adrien C.H.
8c4f9cad-a856-4638-a13d-1b27edb73c3c
Gommenginger, Christine
f0db32be-34bb-44da-944b-c6b206ca4143
Marquez, Jose
e450ae26-9831-405d-81a1-a89029fe9790
Doody, Sam
4dabe33d-160b-44e5-876d-4d046f9e0c2f
Navarro, Victor
f8b2656c-aa5b-49e7-bd93-61ee033682da
Buck, Chris
ac592950-f49d-44ee-9329-d12963c0a2ca
Martin, Adrien C.H., Gommenginger, Christine, Marquez, Jose, Doody, Sam, Navarro, Victor and Buck, Chris
(2016)
Wind-Wave induced velocity in ATI SAR Ocean Surface Currents: First experimental evidence from an airborne campaign.
Journal of Geophysical Research: Oceans, 121 (3), .
(doi:10.1002/2015JC011459).
Abstract
Conventional and along-track interferometric (ATI) Synthetic Aperture Radar (SAR) sense the motion of the ocean surface by measuring the Doppler shift of reflected signals. Measurements are affected by a Wind-wave induced Artefact Surface Velocity (WASV) which was modelled theoretically in past studies and has been estimated empirically only once before with Envisat ASAR by Mouche et al., (2012). An airborne campaign in the tidally dominated Irish Sea served to evaluate this effect and the current retrieval capabilities of a dual-beam SAR interferometer known as Wavemill. A comprehensive collection of Wavemill airborne data acquired in a star pattern over a well-instrumented validation site made it possible for the first time to estimate the magnitude of the WASV, and its dependence on azimuth and incidence angle from data alone. In light wind (5.5 m/s) and moderate current (0.7 m/s) conditions, the wind-wave induced contribution to the measured ocean surface motion reaches up to 1.6 m/s upwind, with a well-defined 2nd order harmonic dependence on direction to the wind. The magnitude of the WASV is found to be larger at lower incidence angles. The airborne WASV results show excellent consistency with the empirical WASV estimated from Envisat ASAR. These results confirm that SAR and ATI surface velocity estimates are strongly affected by WASV and that the WASV can be well characterized with knowledge of the wind knowledge and of the geometry. These airborne results provide the first independent validation of Mouche et al., 2012, and confirm that the empirical model they propose provides the means to correct airborne and spaceborne SAR and ATI SAR data for WASV to obtain accurate ocean surface current measurements. After removing the WASV, the airborne Wavemill retrieved currents show very good agreement against ADCP measurements with a root mean square error (RMSE) typically around 0.1 m/s in velocity and 10° in direction.
Text
Martin_et_al-2016-Journal_of_Geophysical_Research__Oceans.pdf
- Version of Record
Text
martin_WASV_JGR-O_v2.pdf
- Other
Restricted to Repository staff only
Request a copy
More information
Published date: 13 February 2016
Keywords:
ocean surface current, microwave remote sensing, ATI SAR, Doppler, wind, airborne
Organisations:
Marine Physics and Ocean Climate
Identifiers
Local EPrints ID: 388180
URI: http://eprints.soton.ac.uk/id/eprint/388180
PURE UUID: e3e2a4f8-4066-46f1-8295-6bedf960e4c4
Catalogue record
Date deposited: 19 Feb 2016 15:16
Last modified: 14 Mar 2024 22:53
Export record
Altmetrics
Contributors
Author:
Adrien C.H. Martin
Author:
Christine Gommenginger
Author:
Jose Marquez
Author:
Sam Doody
Author:
Victor Navarro
Author:
Chris Buck
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics