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| Titel |
Investigating short wavelength correlated errors on low resolution mode altimetry |
| VerfasserIn |
Jean-Christophe Poisson, Pierre Thibaut, Gérald Dibarboure, Sylvie Labroue, Yannick Lasne, Francois Boy, Nicolas Picot |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082199
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| Zusammenfassung |
| Although conventional radar altimetry products (Jason1, Jason2, LRM CRYOSAT2, etc) have
a spatial resolution as high as 300 m, the observation of ocean scales smaller than 100 km is
limited by the existence of a “spectral hump”, i.e. a geographically coherent error. In the
frame of the future altimetry missions (SAR for Cryosat -2 and Sentinel-3 missions and
interferometry for the SWOT mission) it becomes crucial to investigate again and to
better understand the signals obtained at small scales by conventional altimeter
missions.
Through an analysis of simulations, we show that heterogeneous backscattering scenes
can result in the corruption of the altimeter waveforms and retracked parameters. The
retrackers used in current ground processors cannot well fit the Brown model during
backscattering events because this model has been designed for a homogeneous scene. The
error is also propagated along-track because of the size and shape of the low resolution mode
(LRM) disc-shaped footprint.
The hump phenomenon is shown to be almost ubiquitous in the ocean, yet more
intense at low latitudes and in the Indian Ocean and Western Pacific Ocean, where
backscattering events are more frequent. Its overall signature could be a Gaussian-like
random signal smooth for wavelengths smaller than 15 km, i.e. white noise on 1 Hz
products.
The analysis of current data from 5 altimetry missions highlights the influence of the
instrument design and altitude, and the influence of the retracker used. The spectral hump is a
systematic response to random events and it is possible to mitigate it with new
processing.
Simulations and geographically limited datasets from the synthetic aperture radar mode
(SARM) of Cryosat-2 show that the thin stripe-shaped synthetic footprint of SARM might be
less sensitive to the artifact. |
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