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Ocean Surface Topography from Space
TRIDENT III. UK's contribution to improving altimetry through cal/val, algorithm development in the coastal zone and oceanographic analyses


Graham Quartly - (Plymouth Marine Laboratory)

  Val Byfield
Paolo Cipollini
Christine Gommenginger
Chris Hughes
Helen Snaith
Phil Woodworth
Peter Challenor
(National Oceanography Centre)
(National Oceanography Centre)
(National Oceanography Centre)
(National Oceanography Centre)
(National Oceanography Centre)
(National Oceanography Centre)
(University of Exeter)


TRIDENT III. NOC's contribution to improving altimetry through cal/val, algorithm development in the coastal zone and oceanographic analyses
Oceanographic researchers at PML, NOC and the University of Exeter will be working on a diverse set of projects from rain-flagging and evaluation of wind speed algorithms to improve use of altimetry in the coastal zone and the application of improved data on scales from the mesoscale to global.
This proposal details the breadth of altimetry activity carried out by the UK's National Oceanography Centre (NOC) at its sites in both Southampton and Liverpool, along with its collaboration with Plymouth Marine Laboratory and the University of Exeter. The range of work planned will build on our expertise in three distinct areas of importance to the OSTST community, with the analysis individually and jointly of data from the TOPEX/Jason series, the ESA satellites and those from other international players.

The first prong of the work relates to the cross-calibration of new sensors, determining the best data-editing criteria, and producing robust expressions relating output from the new instruments to their predecessors, thus allowing the continuation of a highly precise climate data record. The main focus of this effort will be on the metocean data, building on comparisons of backscatter strength (σ0), wave height and rain detection from the Jason-1/Jason-2 overlap period to achieve the same for the Jason-2/Jason-3 tandem phase. There will also be evaluation of wind speed, wave height and rain algorithms for ESA's Sentinel-3 and the first Ka-band altimeter, AltiKa. We will also be investigating in detail the oceanographic data from Cryosat-2 to demonstrate their accuracy and performance in both conventional and SAR modes and how they can be melded with other altimeter data.

The second line of investigation will be a reappraisal of the processing of altimeter waveform data, especially for applications in the coastal zone, where land-related artefacts have hitherto prevented their widespread use. We will be testing approaches that both "clean" the data by removing signals from strong contaminants, and also those that fit a more complicated model to the waveform data, allowing for peaks in addition to the ocean returns. In addition, we plan to reassess the applicability of sea state bias models in the coastal regime.

The third tine corresponds to the application of altimeter data to tackle oceanographic questions, covering both global patterns of sea level rise and shorter temporal and spatial scale variability such as aspects of ocean tides and coastal processes. Changes in altimetric sea level will be authenticated with respect to the global tide gauge network, with a critical evaluation helping to address whether errors in the geophysical corrections may contribute to the observed variability. The strong statistical relations found between altimetry and tide gauges will also allow us to reconstruct changing patterns in sea level rise using in situ records that extend back more than a century. Data from altimetry, gravimetry and in situ instruments will further be combined to assess how the total mass of the ocean is changing. The spectrum of variability present in the 20-yr satellite record will be contrasted with that shown by many modern climate models to focus attention on which of them have the correct intrinsic variability. Finally, synergistic studies in the southwest Indian Ocean will combine altimetric records of eddies with ocean colour data and with in situ observations to help us understand the depth profiles of oceanic features and how they affect biological productivity.

All these aspects of the UK's altimetry research programme may potentially feed into our contribution to international initiatives to develop capacity in coastal and marine applications of remote sensing. This can be through the development of distance-learning resources, contribution to international training courses and participation in fellowship schemes to increase the capacity of developing countries to use altimetry with other data and model output. Such activities will enable them to support environmental management, plan sustainable development, and reduce the risk to coastal populations from hazards such as sea level rise, coastal erosion and storm surges.

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