1,721,002 research outputs found
Rapid Climate Change (RAPID) - a new UK programme (abstract of poster to be presented at: AGU Ocean Sciences Meeting, 26-30 January 2004, Portland, Oregon)
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Retrieval of the surface wind speed from satellite radio-altimeter data: a review of algorithms
No full textWe give a review of surface wind-speed retrieval algorithms using satellite radio-altimeter data and analyze the efficiency of these algorithms. The data processing by new radio altimeters (JASON and ENVISAT) showed that the two-parameter algorithm developed for the satellite “Topex A” effectively operates with the data of the new radio altimeters and exceeds in accuracy the conventional algorithm by 5–10%. We discuss two main reasons for the wind-speed retrieval errors: (i) ambiguous relationship between the wind speed and the backscattering cross section and (ii) regional features of the wave climate formation. Within the framework of a two-parameter algorithm, we propose a new approach for the wind-speed retrieval problem, in which two-mode structures (wind waves and a swell) are taken into account. The data processing confirmed that the new approach allows one to reduce the error related to regional features of the wave climate formation by another 5–7%
Future exploitation of in-situ wave measurements at Station Mike
No full textAs part of a UK-SOLAS (Surface Ocean-Lower Atmosphere Study) project the National Oceanography Centre (NOCS) has instrumented the Norwegian weather ship Polarfront with the directional wave radar “WAVEX”. This system complements the Polarfront’s existing ship borne wave recorder which was installed by the Norwegian Meteorological Institute in 1978. The Polarfront and its predecessors have occupied Station Mike (66°N, 2°E) all year round for nearly 60 years. NOCS also equipped the ship with digital cameras and the autonomous air-sea flux system “AutoFlux”. The NOCS systems were installed in September 2006 and will operate continuously for at least 3 years. Project information and real-time data from the ship can be found via http://www.noc.soton.ac.uk/ooc/CRUISES/HiWAS/index.php . The sea-state dataset being obtained on the Polarfront is unparalleled in that the SBWR provides reliable wave height data but no directional information, whereas the wave radar provides excellent directional wave spectra but infers wave heights indirectly. It is believed that, until now, the two systems have never been deployed together for more than brief periods. On Polarfront the two systems provide very comprehensive information on sea state, in a region of the world’s oceans which experience a wide range of conditions (e.g. 3-hourly significant wave height of 15.5 m in November 2001). The main research aim of the project is the parameterisation of the air-sea fluxes, including wind stress, in terms of wind speed, sea state etc. However, the wave data set being collected has potential uses which fall outside the project aims and we would welcome proposals for collaboration from members of the remote sensing and modelling communities. Here we describe initial results which show that the two wave systems agree reasonably well for wave period, but that significant wave heights from the WAVEX are overestimated in the presence of swell
Tropical Atlantic salinity variability: New insights from SMOS
Full text linkObservations from the SMOS satellite are used to reveal new aspects of Tropical Atlantic sea surface salinity (SSS) variability. Over an annual cycle, the variability is dominated by eastern and western basin SSS “poles,” with seasonal ranges up to 6.5 pss (practical salinity scale), that vary out of phase by 6 months and largely compensate each other. A much smaller SSS range (0.08 pss) is observed for the region as a whole. The dominant processes controlling SSS variability are investigated using GPCPv2.2 precipitation (P), OAFlux evaporation (E), and Dai and Trenberth river flow (R) data sets. For the western pole, SSS varies in phase with P and lags R by 1–2 months; a more complex relationship holds for the eastern pole. The synthesis of novel satellite SSS data with E, P, and R enables a new approach to determining variability in Tropical freshwater fluxes and its potential impacts on the Atlantic ocean circulation
A rotating knife-beam altimeter for wind-swath remote sensing of ocean: wind and waves
No full textThe use of a nadir altimeter radar with a rotating knife-beam antenna pattern isconsidered for improved measurements of the sea surface wind and wave parameters over a wide swath. Theoretical calculations suggest the antenna beam rotating about the vertical axis is able to provide wide swath of order 250-350 km. Processing of the signals using time or Doppler sampling techniques results in the division of the antenna footprint into elementary scattering cells of the order of 14x14 km. The theoretical algorithms developed here indicate that the system may be used to retrieve the variance of large-scale slopes, the direction of wave propagation and the wind speed in each cell. The possibility of measuring significant wave height is also analyzed. The combination of linear motion of the radar and the rotation of the knife-beam antenna can be exploited to build up a two-dimensional map of the surface, which enables better understanding of wave processes and to study their structure and temporal dynamics using repeated observations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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