Sea surface wind speed and sea state retrievals from dual-frequency altimeter and its preliminary application in global view of wind-sea and swell distributions

ABSTRACT

Altimeter radar backscatter intensity, in terms of the normalized radar cross section (NRCS), is known to be modulated by surface wind forcing and the state of wind-sea development. Based on a data set of collocated altimeters (including Topex/Poseidon, Jason-1 and Jason-2) and in situ measurements, different responses to various wind speeds and wave ages (i.e. the state of wind-sea development) were illustrated for altimeter dual-frequency NRCSs (K_u-band at 13.6 Hz and C band at 5.4 Hz), which can facilitate the retrieval of wind speed and wave age parameters. A statistical parametric algorithm was developed to retrieve the two dynamic parameters from the altimeter dual-frequency NRCSs using the neutral network method. The wind-sea significant wave height (SWH) was estimated from wind speed and wave age parameters, which partitions the swell SWH from the altimeter SWH measurement. All newly derived parameters were well validated by comparison against in situ buoy measurements. A preliminary application of the method in examining the swell or wind-sea contributions to global waves was performed; it was found the swell dominance in an open ocean, and the wind-sea dominance in marginal and semi-enclosed seas. The methods would benefit other applications such as studies of air–sea interactions, validation of wave model, determination of swell decay rate and studies of wave climate.

KEYWORDS:

• Altimetry
• sea state
• dual-frequency

Acknowledgements

This work was supported by the National Key Research and Development Programme of China (grant No. 2016YFC1401002 and 2016YFC1402000), the National Natural Science Foundation of China (grant No. 41606024 and No. 41506033), the CAS Innovative Foundation [grant no. CXJJ-16M111], High Technology program of China (863) under [grant No. 2013AA09A505], China Postdoctoral Science Foundation [grant No. 2014M561972], the NSFC Innovative Group [grant No. 41421005] and the NSFC-Shandong Joint Fund for Marine Science Research Centres [grant No. U1606402].

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Key Research and Development Programme of China (grant No. 2016YFC1401002 and 2016YFC1402000), the National Natural Science Foundation of China (grant No. 41606024 and No. 41506033), the CAS Innovative Foundation [grant no. CXJJ-16M111], High Technology program of China (863) under [grant No. 2013AA09A505], China Postdoctoral Science Foundation [grant No. 2014M561972], the NSFC Innovative Group [grant No. 41421005] and the NSFC-Shandong Joint Fund for Marine Science Research Centres [grant No. U1606402].