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Reduced ascending/descending pass bias in SMOS salinity data demonstrated by observing westward-propagating features in the South Indian Ocean

Reduced ascending/descending pass bias in SMOS salinity data demonstrated by observing westward-propagating features in the South Indian Ocean
Reduced ascending/descending pass bias in SMOS salinity data demonstrated by observing westward-propagating features in the South Indian Ocean
The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite has been providing data, including sea surface salinity (SSS) measurements, for more than five years. However, the operational ESA Level 2 SSS data are known to have significant spatially and temporally varying biases between measurements from ascending passes (SSSA) and measurements from descending passes (SSSD).

This paper demonstrates how these biases are reduced through the use of SSS anomalies. Climatology products are constructed using SMOS Level 2 data to provide daily, one-degree by one-degree climatologies separately for ascending and descending passes using a moving window approach (in time and space). The daily, one-degree products can then be averaged to provide values of climatological SSS at different spatial and/or temporal resolutions.

The averaged values of the SMOS climatology products are in good general agreement with data from the World Ocean Atlas 2013. However, there are significant differences at high latitudes, as well as in coastal and dynamic regions, as found by previous studies. Both the mean and standard deviation of the differences between data from ascending passes and data from descending passes for the anomalies are reduced compared with those obtained using the original salinity values.

Geophysical signals are clearly visible in the anomaly products and an example is shown in the Southern Indian Ocean of westward-propagating signals that we conclude represent the surface expression of Rossby waves or large-scale non-linear eddies. The signals seen in salinity data agree (in speed) with those from sea surface temperature and sea surface height and are consistent with previous studies.
Ocean salinity, Rossby wave, Planetary wave, Soil moisture and ocean salinity satellite, SMOS, Indian Ocean, Sea surface salinity, Salinity anomaly
0034-4257
154-163
Banks, C.J.
5d65ec1e-ed5f-48fc-9b05-3e46f24c35dc
Srokosz, M.A.
f1701d3e-01b3-43d0-8993-9fd523032a79
Cipollini, P.
276e356a-f29e-4192-98b3-9340b491dab8
Snaith, H.M.
40f759ed-8c90-4d76-8e9c-7d7a4c264adf
Blundell, J.R.
88114f32-6b76-46b2-b2d8-d6ef64a82b0d
Gommenginger, C.P.
f0db32be-34bb-44da-944b-c6b206ca4143
Tzortzi, E.
8f70c6da-e897-40b3-b20e-6d0aba9cf153
Banks, C.J.
5d65ec1e-ed5f-48fc-9b05-3e46f24c35dc
Srokosz, M.A.
f1701d3e-01b3-43d0-8993-9fd523032a79
Cipollini, P.
276e356a-f29e-4192-98b3-9340b491dab8
Snaith, H.M.
40f759ed-8c90-4d76-8e9c-7d7a4c264adf
Blundell, J.R.
88114f32-6b76-46b2-b2d8-d6ef64a82b0d
Gommenginger, C.P.
f0db32be-34bb-44da-944b-c6b206ca4143
Tzortzi, E.
8f70c6da-e897-40b3-b20e-6d0aba9cf153

Banks, C.J., Srokosz, M.A., Cipollini, P., Snaith, H.M., Blundell, J.R., Gommenginger, C.P. and Tzortzi, E. (2016) Reduced ascending/descending pass bias in SMOS salinity data demonstrated by observing westward-propagating features in the South Indian Ocean. Remote Sensing of Environment, 180, 154-163. (doi:10.1016/j.rse.2016.02.035).

Record type: Article

Abstract

The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite has been providing data, including sea surface salinity (SSS) measurements, for more than five years. However, the operational ESA Level 2 SSS data are known to have significant spatially and temporally varying biases between measurements from ascending passes (SSSA) and measurements from descending passes (SSSD).

This paper demonstrates how these biases are reduced through the use of SSS anomalies. Climatology products are constructed using SMOS Level 2 data to provide daily, one-degree by one-degree climatologies separately for ascending and descending passes using a moving window approach (in time and space). The daily, one-degree products can then be averaged to provide values of climatological SSS at different spatial and/or temporal resolutions.

The averaged values of the SMOS climatology products are in good general agreement with data from the World Ocean Atlas 2013. However, there are significant differences at high latitudes, as well as in coastal and dynamic regions, as found by previous studies. Both the mean and standard deviation of the differences between data from ascending passes and data from descending passes for the anomalies are reduced compared with those obtained using the original salinity values.

Geophysical signals are clearly visible in the anomaly products and an example is shown in the Southern Indian Ocean of westward-propagating signals that we conclude represent the surface expression of Rossby waves or large-scale non-linear eddies. The signals seen in salinity data agree (in speed) with those from sea surface temperature and sea surface height and are consistent with previous studies.

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Accepted/In Press date: February 2016
Published date: July 2016
Keywords: Ocean salinity, Rossby wave, Planetary wave, Soil moisture and ocean salinity satellite, SMOS, Indian Ocean, Sea surface salinity, Salinity anomaly
Organisations: Physical Oceanography, Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 388186
URI: https://eprints.soton.ac.uk/id/eprint/388186
ISSN: 0034-4257
PURE UUID: 3592b791-d869-48fe-9c81-8aadec4fc7bb

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Date deposited: 19 Feb 2016 16:55
Last modified: 09 Jan 2018 18:15

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Contributors

Author: C.J. Banks
Author: M.A. Srokosz
Author: P. Cipollini
Author: H.M. Snaith
Author: J.R. Blundell
Author: C.P. Gommenginger
Author: E. Tzortzi

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