H. Snaith | University of Southampton (original) (raw)

Papers by H. Snaith

Altimetry is a key component of the remote-sensing work at Southampton Oceanography Centre. We ha... more Altimetry is a key component of the remote-sensing work at Southampton Oceanography Centre. We have used data from most previous missions, and those from Jason-1 are an integral part of our future plans. We will make use of all the geophysical parameters obtainable over the ocean — sea surface height, wave height, wind speed and rain rate, both separately and in combination. Our proposed work with Jason-1 will focus on four main areas — CALVAL, global climatologies, long-term monitoring and comparison with other datasets and models. CALVAL

Coastal Altimetry, 2010

Page 255. Coastal Challenges for Altimeter Data Dissemination and Services 10 HM Snaith and R. Sc... more Page 255. Coastal Challenges for Altimeter Data Dissemination and Services 10 HM Snaith and R. Scharroo Contents 10.1 Introduction..... 248 10.2 Generating Custom Products..... ...

Page 1. REPROCESSING ALTIMETER DATA RECORDS ALONG EUROPEAN COASTS: LESSONS LEARNED FROM THE ALTIC... more Page 1. REPROCESSING ALTIMETER DATA RECORDS ALONG EUROPEAN COASTS: LESSONS LEARNED FROM THE ALTICORE PROJECT Vignudelli S. (1), Kostianoy A. (2), Ginzburg A. (2), Sheremet N. (2), Lebedev ...

Remote Sensing of the Changing Oceans, 2011

Chapter 11 Satellite Altimetry: Sailing Closer to the Coast Stefano Vignudelli, Paolo Cipollini, ... more Chapter 11 Satellite Altimetry: Sailing Closer to the Coast Stefano Vignudelli, Paolo Cipollini, Christine Gommenginger, Scott Gleason, Helen M. Snaith, Henrique Coelho, M. Joana Fernandes, Clara Lázaro, Alexandra L. Nunes, Jesus Gómez-Enri, Cristina Martin-Puig, Philip ...

As part of the GOCE User Toolbox Specification (GUTS) project, the GUTS team has carried out a sc... more As part of the GOCE User Toolbox Specification (GUTS) project, the GUTS team has carried out a scientific trade-off study, to select the best algorithms to fulfil the user requirements for the toolbox. In some cases the selection is straightforward. However, in other cases, the choice depends on scientific applications as well as the algorithm efficiency and more practical considerations. Studies need to be performed to demonstrate the best possible algorithm. One example is the selection of filtering functions and the choice of interpolation schemes used in calculation of a mean dynamic topography from combined GOCE and satellite altimeter data. The trade-off study has also selected the functionality of the toolbox, given the user requirements and the recommended algorithms. In this paper we present the proposed functionality of the toolbox, and the most important algorithm selections. As part of the scientific trade-off, a pilot application is investigating validation of mean dynamic topography, generated from pseudo observations using proposed toolbox algorithms, against ocean model data. The study includes results from research into methods of calculation of mean dynamic topography and filtering methods presented at this workshop.

Environmental research requires access to quality controlled, calibrated data. Satellite altimete... more Environmental research requires access to quality controlled, calibrated data. Satellite altimeter data are used in a range of environmental research, including oceanography, ice and land surface studies. Users who are not altimeter specialists may not be aware of, or have access to, the latest updates and most appropriate corrections to use for their application. We propose a GRID based methodology to give all users access to the best possible altimeter data product at the time of the request, tailor made for their specific application. A data portal system would be based on a "Network of Trust" consisting of the data providers and a certificating authority. Data could be served through a fully interactive web 'front-end' or directly from within analysis programmes. This system would build on the experiences gained in combining two existing Altimeter Data services (GAPS and RADS) to produce a coherent data service with alternative web interfaces and configurable users access.

OCEANS 2009, 2009

In this paper, we will showcase the main outcomes of the COASTALT project, including improved cor... more In this paper, we will showcase the main outcomes of the COASTALT project, including improved corrections (with special emphasis on the tropospheric effect) and novel re-tracking techniques built on established research results and the processing chain development with the generation and validation of ENVISAT test data sets over a selection of regional sites. We will also dive in further and explore how coastal altimetry might be exploited to its full potential in the coastal zone. This should be of interest to a broad range of data integrators that have an interest in using these improved altimeter data in their operational products or services.

Remote Sensing of Environment

The CryoSat-2 satellite, primarily dedicated to precise monitoring of the Cryosphere, is demonstr... more The CryoSat-2 satellite, primarily dedicated to precise monitoring of the Cryosphere, is demonstrating its capability to provide valuable altimetric data also over the ocean. Here we present the results of a global assessment and validation of the new Geophysical Ocean Product (GOP) distributed by the European Space Agency (ESA) since April 2014, focusing on the sea surface height anomaly (SSHA), the significant wave height (SWH), and the wind speed. Our assessment involves only Low Resolution Mode (LRM) and Pseudo LRM (PLRM) data, since full SAR processing is not already operationally implemented in the GOP. The global assessment is conducted on the basis of measurement noise and along-track spectral and crossover analysis, whereas the validation is performed against a variety of in situ observations such as tide gauges, buoys and Argo floats as well as data from the WaveWatch III (WWIII) model. The performance of the GOP is compared to that of Jason-2 and CryoSat-2 data from the Radar Altimeter Database System (RADS). The mean value of the 20-Hz SSHA noise at 2 m SWH is 6.3 cm for LRM and 10.2 cm for PLRM, and the standard deviation of the crossovers is ~ 5.4 cm. The mean 20-HZ SWH noise over the global oceans is 49.4 cm and 69.8 cm, for LRM and PLRM respectively. CryoSat-2 and Jason-2 show almost identical performance when SSHAs are validated against tide gauges, with a median correlation and root mean square difference (RMSD) of 0.78 and 7.1 cm for the GOP, 0.76 and 7.3 cm for Jason-2, and 0.79 and 7.8 cm for CryoSat-2 from RADS. The median correlation with Argo-derived steric heights is 0.68 for the GOP, 0.74 for Jason-2, and 0.67 for CryoSat-2 from RADS. However, the correlation shows a strong latitudinal dependence, with higher values at low latitudes (median value larger than 0.80 in the 10°S-10°N band). The median RMSD between the SSHAs and steric heights is 5.3 cm for the GOP, 4.6 cm for Jason-2, and 5.1 cm for CryoSat-2 from RADS. The GOP and Jason-2 show also identical performance when SWHs are compared to buoy data, with a slope and RMS error of 0.98 and 15 cm for GOP, 0.97 and 16 cm for Jason-2, and 1.05 and 17 cm for CryoSat-2 from RADS. On the other hand, the GOP wind speed exhibits a bias of about 2 m/s relative to both Jason-2 and to buoy data. Differences between the GOP and WWIII SWH are smaller than 20% of the SWH almost everywhere. In summary the GOP products are fit for oceanographic applications.

Canadian Journal of Remote Sensing, 1993

Des donnees altimetriques saisies par le satellite GEOSAT ont servi a l'etude des variations ... more Des donnees altimetriques saisies par le satellite GEOSAT ont servi a l'etude des variations de la hauteur significative des vagues, de la vitesse du vent et du niveau de la mer dans les eaux de la...

Russian Journal of Earth Sciences, 2008

The Gravity and Ocean Circulation Explorer - GOCE - satellite mission is a new type of Earth obse... more The Gravity and Ocean Circulation Explorer - GOCE - satellite mission is a new type of Earth observation satellite that will measure the Earth gravity and geoid with unprecedented accuracy. The objective of the GOCE User Toolbox development project is in close collaboration with ESA's High-Level (Level 1 - Level 2) Processing Facility (HPF) effort to develop algorithms and input and output specification for a GOCE user toolbox that is required by the general science community for the exploitation of GOCE level 2 and ERS- ENVISAT altimetry. Combining GOCE geoid models with satellite altimetric observations of the sea surface height substantial improvements in the modelling of the ocean circulation and transport are foreseen. No ocean circulation products are planned to be delivered as level-2 products as part of the GOCE project, so a strong need exists, for oceanographers, to further process the GOCE level-2 geoid and merge it with Radar Altimetry. The primary requirement of oce...

ABSTRACT Two existing Altimeter Data services, both with significant numbers of users, have been ... more ABSTRACT Two existing Altimeter Data services, both with significant numbers of users, have been interlinked to produce a coherent data service with alternative web interfaces and configurable users access. We will discuss issues of migrating users from existing services to new services such as this. The GAPS (Global Altimeter Processing Scheme) database provides collocated ocean altimeter data. The system has several stages: read the incoming Geophysical Data Records and convert to a consistent format, applying all known data updates and corrections; determine and apply a consistent set of geophysical corrections; collocate to an along track grid. The output includes collocated values of applied corrections so they can be removed or replaced. The system has remained relatively static for several years, giving a stable, but dated, product. The RADS (Radar Altimeter Database System) system, at the Technical University of Delft, is a sophisticated database system that is more flexible in its approach. The system carries out the first 2 stages of the GAPS scheme, allowing users to retrieve non-collocated altimetric parameters. The geophysical corrections are applied at the time of extraction via user-defined corrections sets, allowing more frequent updates to the database. A new system uses RADS as the input data source to create a reference GAPS data set, allowing users to easily extract a collocated, internally consistent dataset with recommended geophysical parameters. The extraction process allows any field in the RADS database to be collocated to the reference grid with little additional computational overhead and no storage overhead. Users can also extract their preferred parameters, using their preferred correction set, either with or without collocation, as required. This system is efficient, but requires the database operator to decide which fields to maintain in the database. Additional data fields must be calculated for all available data, even if never used. A further development of this system is now planned, to make use of recent GRID services advances. The source database will be replaced by a system that retrieves source data on request from remote certified sources.

Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society, 2010

The last few years have witnessed the foundation and development of a new discipline, coastal alt... more The last few years have witnessed the foundation and development of a new discipline, coastal altimetry, and the coalescence of an active community of researchers who are now enthusiastically developing the topic. In the present community white paper, we summarize the technical challenges that satellite altimetry faces in the coastal zone, and the research that is currently being carried out to overcome those challenges. We introduce the new coastal altimetry data that are becoming available, and describe how we can calibrate/validate those data. Then we show several of the possible applications of coastal altimetry and conclude by looking at the future of the discipline, and at how we can build capacity in coastal altimetry.

Journal of Marine Systems, 2001