1,721,013 research outputs found
A study of " Prestige" oil spill by the combined use of ENVISAT/ASAR, quikSCAT scatterometer and limited area model simulations
No full textThe "Prestige" tanker wreck of November 2002 was a major disaster affecting the environment of north-western coasts of Spain (Galicia). The consequences of "Prestige" accident have been studied by several research groups in the last two years. Hereafter we present a study of "Prestige" oil spill by means of a combined use of remote sensing tools and limited-area model simulations.Two Envisat/ASAR Wide Swath (WS) images over the area of the disaster, Nov. 17 and Dec. 3, were retrieved from ESA archive. ASAR WS processing consists of 2 main steps: 1. Ingestion and geo-location, performed by means of the commercial software package TeraScan (www.seaspace.com); and 2. Speckle filtering and segmentation, performed according to the algorithms described in [1] and [2].A major question in oil spill detection with SAR images is the discrimination between "real" oil slicks and "lookalikes". To operate this distinction we adopted an approach, based on local meteo-marine condition analysis, which implies:1. Wind and wave information retrieval from SAR image itself, performed according to the methods described in [3] and [4];2. QuikSCAT scatterometer wind data from the 2 daily passes of the satellite, as obtained from PODAAC/JPL;3. Simulations by means of the limited-area meteorological model Eta [5], a three-dimensional, primitive equation, grid-point model currently operational at the National Center for Environmental Prediction of the U.S. National Weather Service.We shall present and discuss the results of the analysis outlined above.[1] A. Baraldi and F. Parmiggiani, "A refined Gamma MAP SAR speckle filter with improved geometrical adaptivity", IEEE Trans. Geosci. Remote Sensing, vol. 33, No. 5, (1995), 1245-1257.[2] A. Baraldi, P. Blonda, F. Parmiggiani and G. Satalino, "Contextual clustering for image segmeation", Optical Engineering, vol. 39 (2000), no. 4, pp. 1-17[3] P. Wadhams, F. Parmiggiani and G. De Carolis, "The use of SAR to measure ocean wave dispersion by frazil-pancake ice fields", J. Phys. Oceanography, Vol. 32 (2002), no. 6, 1721-1746.[4] Giacomo De Carolis, Flavio Parmiggiani and Elena Arabini, "Observations of wind and ocean wave fields using ERS Synthetic Aperture Radar imagery", Int. J. Remote Sensing, Vol. 25, No. 7-8 (2004) 1283 - 1290.[5] D. Cesini, S. Morelli, F. Parmiggiani, "Analysis of an intense bora event in the Adriatic area", Natural Hazards and Earth System Sciences, (2004) vol. 4, Issue 2: 323 - 337
Wind over Terra Nova Bay (Antarctica) during a polynya event: Eta model simulations and satellite microwave observations
No full textA study of Terra Nova Bay (TNB) winter polynya, based on the combined use of satellite observations and limited area model simulations, is presented. First, data from passive microwave observations are used to investigate the polynya area daily variability. Second, Eta model is run to simulate the low level wind over a defined TNB polynya, located in according to the satellite images, during the period 15 – 17 September 2003. A preliminary set up of initial and boundary conditions is used. Eta model is initialized with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, with National Centers for Environmental Prediction (NCEP) of the U.S. National Weather Service data and with information from satellite images providing a realistic extension of the polynya under study. Eta model simulates a katabatic wind system which develops qualitatively in agreement with the polynya extent, as shown from satellite images during the same period. The results demonstrate the strong effect of the polynya when included in the initialization of model integrations: the low level wind is intensified by the presence of the warm area corresponding to polynya, it is spatially variable and significantly different from one simulated along the coast of the Nansen Ice Sheet. The results of numerical simulations with different surface temperature in the polynya area are shown as well, thus an assessment of the range of variability of the wind intensity in relation to polynya surface temperature is provided
Surface-Atmosphere Interactions during a Polynya Event at Terra Nova Bay (Antarctica).
No full textNumerical three-dimensional weather simulations, satellite imagery and automatic weather station (AWS) data are used to study a real event of coastal polynya at Terra Nova Bay (TNB), Antarctica. The event, detected with satellite images, occurred in the period 12–17 July 2006. The atmospheric simulations are performed by the limited area Eta Model. Passive microwave satellite images, which are not affected by cloud cover, are used to evaluate the daily polynya size, while thermal infrared satellite images are only used to follow cloud dynamics. The synoptic and sub-synoptic fields are very well represented by the model results when they are compared with AVHRR imagery. Comparisons between simulated data and wind measurements by Manuela AWS are presented as well. The results are considered satisfactory. Simulation results show the striking relationship of surface winds and temperatures with the development of the polynya as inferred by satellite image
Atmospheric response to a realistic coastal polynya in Terra Nova Bay (Antarctica) simulated by ETA model
No full textCoastal polynyas are areas of open water (and/or very thin ice) which form adjacent to coasts or blocking feature in polar regions during the wintertime, when the sea water is expected to be ice covered. They are thought to be maintained by strong offshore winds blowing over these area and/or by ocean currents. Sea ice is removed as it forms and drifted offshore. In polynya areas a direct contact is established between the relatively warm sea water and the cold, dry atmosphere. As a consequence, the physical characteristics of the atmospheric boundary layer change. The work presented here concerns a real polynya event in the region of Terra Nova Bay (TNB), Antarctica, where a recurring coastal polynya occurs nearby the Italian Antarctic Base. The aim is the study of atmospheric response to the presence of a open water area of realistic size by three-dimensional numerical simulations. Atmospheric numerical modelling is a fundamental tool for the study of air - polynya interactions in the remote polar regions, where observational data are difficult. The numerical model used for the simulations is a recent version of ETA model (Mesinger et al., 2006), with the addition of a piecewise linear advection for the wind field. ECMWF and NCEP data provided the initial and boundary conditions. A previous version of the model had already been successfully used in the Antarctic area (De Carolis et al, 2006, Casini and Morelli, 2007). As a first step to analyze the polynya event, numerical simulation was performed for the period from 12 to 17 July 2006 in order to study the development of the katabatic wind (Morelli and Casini, 2008; Morelli, 2008). Daily satellite images, concerning the period, display that a sea ice free area formed on 15 and 16 July, reaching its maximum extension of about 4000 km2 on 16 July (Morelli et al.,2007). In order to gain insight on the atmospheric response to open water area within a sea ice field, ETA model runs were carried out from 15 to 17 July 2006 both with and without the polynya (as derived by satellite image) included in the initial conditions. Results from these experiments will be presented. Simulations were performed with 50 layers in the vertical from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0,125x0,125 transformed degrees (about 20kmx20km). Numerical simulations show that the polynya had significant effects on temperature, specific humidity, vertical velocity and horizontal wind speed throughout the boundary layer. The effects are found over and downwind the sea ice free area. The presence of polynya produced significant thermal modifications in atmosphere. Turbulent kinetic energy also responded to its presence and the low level wind speed changed over the open water area. References: Casini, G., Morelli, S. (2007) ‘Katabatic wind and Terra Nova Bay polynya: a study using two different versions of ETA model’, Geophysical Research Abstract, vol. 9, 02656.De Carolis G., Morelli, S., Parmiggiani, F., and Casini G. (2006) ‘Terra Nova Bay polynya: a study by satellite microwave observations and Eta model simulations’,Geophysical Research Abstract, vol. 8, 08433Mesinger F., Jovic D., Sin Chan Chou, Gomes J.L., Bustamante J.F. (2006) ‘Wind forecast around the andes using the sloping discretization of the Eta coordinate’, Proceedings of 8 ICSHMO, Foz do Iguacu, Brazil, 24-28 April 2006, INPE.Morelli S., Casini G., Parmiggiani F. (2007) ‘Wintertime katabatic event and polynya at Terra Nova Bay: a study by ETA simulations and AMSR-E images’, Extended Abstract of 2nd Antarctic Meteorological Observation, Modeling and Forecasting (AMOMF) Workshop, June 2007.Morelli S., Casini G. (2008) ‘Antarctic katabatic winds and their interaction with a coastal polynya in Terra Nova Bay, studied by ETA model simulations and satellite images’, Geophysical Research Abstract, vol. 10.Morelli S. (2008) ‘ETA Model simulation of winter katabatic events over the Terra Nova Bay area, Antarctica’. Third ICTP conference on "Current Efforts Toward Advancing the Skill of Regional Weather Prediction. Challenges and Outlook", 8-10 October 2008
ETA Model Simulations and AMSR Images to Study an Event of Polynya at Terra Nova Bay, Antarctica
No full textIn the Terra Nova Bay (TNB) region, the near-surface winds are persistently strong (in particular during the winter season) and blow offshore with a high degree of directional constancy. This region is also known as a preferential zone of coastal polynyas. Polynyas are recurring areas of open waters/thin ice surrounded by an ice covered sea. Coastal polynyas form along ice bound coasts; they are believed to be due to strong and persistent offshore winds and/or ocean currents which drive the sea ice away. As the ice is removed from the region of origin, open water is exposed, refrozen and the new ice is pushed away, so that coastal polynyas provide a source of new ice production. The horizontal surface temperature differences among the land ice, water and sea ice are strong, because the open water is close to the freezing point (-1.8 °C for typical salt water). The energy exchange between the ocean and the atmosphere in the Antarctic marginal sea ice zone is influenced by the extent of sea-ice cover. While the sea ice acts as insulation, a direct contact is established in areas with open water and intense energy exchanges occur, due to the large difference of temperature between the water and the air above it. This implies that the polynyas are areas where the ocean exchanges energy with the atmosphere and as a result they have an effect on the polar meteorology/climate. In Antarctica, the atmospheric numerical models which provide good results at the mid latitude, are put to the test, because the observations are scarce, the initial and boundary conditions are sometimes inadequate, complex terrain, sea ice and polynyas are present. Here, the numerical simulation of a real event of coastal polynya at TNB is shown, using a recent version of the Eta Model. The horizontal resolution is approximately 20 km and 50 level are considered in the vertical up to 25 hPa. Initial and boundary conditions are obtained from ECMWF analyses. The event, occurred from 12 to 18 July 2006, was selected by the analysis of the sequence of daily AMSR- derived Sea-Ice Concentration (SIC) maps. The computation of the sea ice free area provided information on the temporal development of the polynya which reached its maximum extent of about 4000 km2 on 16 July. Therefore, a realistic polynya size was included in the initial conditions for the simulation of the period 15 – 17 July. The Eta Model reproduces very well the evolution of upper and mid-level conditions in agreement with AVHRR observations. Also, the evolution of the simulated 10m wind is strictly correlated to the observed extent of the polynya. In order to isolate the effect of the presence of the open water area on the structure of the atmospheric boundary layer and on the atmospheric circulation, a further simulation was performed without the presence of the polynya, i.e. with its extent covered with sea ice. The numerical simulations show that the polynya acts to increase the speed of the air above it and strong heat fluxes warm the air. As a result, the polynya modifies the atmosphere over a long distance from its location and till to a height of several hundred meters
Synergic use of SAR imagery and high resolution atmospheric model to estimate marine wind fields : an application in presence of an atmospheric gravity wave episode.
Full text linkA study aimed at retrieving sea surface wind fields of semi-enclosed basins from combined use of SAR imagery and a high resolution mesoscale numerical atmospheric model, is presented. Two consecutive ERS-2 SAR frames and a set of NOAA/AVHRR and MODIS images acquired over the North Tyrrhenian Sea on March 30, 2000 were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved using the semi-empirical backscatter models CMOD4 and CMOD-IFREMER. Surface wind vectors predicted by the meteorological ETA model were exploited as guess input to SAR wind inversion procedure. ETA is a three-dimensional, primitive equation, grid-point model currently operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The model was adapted to run with a resolution up to about 4.0 Km. It was found that the inversion methodology was not able to resolve wind speed modulations due to the action of an atmospheric gravity wave, called “lee wave”, which occurred in the analyzed area. A simple atmospheric wave propagation model was thus used to account for the SAR observed surface wind speed modulation. Synergy with ETA model outputs was further exploited in simulations where atmospheric parameters up-wind the atmospheric wave were provided as input to the lee wave propagation model
An experiment of comparison of SAR wind analysis with Eta Model output in the North Thyrrenhian Sea
No full textAn experiment of comparison between SAR wind analysis and Eta model output for the North Thyrrenhian Sea is presented. Two consecutive SAR frames, covering large part of the North Thyrrenhian Sea, from ERS2 pass of March 30, 2000, were acquired from ESA. The empirical backscatter model CMOD4 was used to obtain wind stress while wind direction could be resolved without ambiguity either from PODAAC/JPL archive of QuikSCAT satellite data or from ECMWF. In situ reference data were supplied by the open sea ODAS Italia1 buoy located at 43.8N, 9.1E. The meteorological Eta model is used to study the features in the area. Eta is a three dimensional, primitive equation, grid point model which is operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The SAR wind analysis was applied to a region north of Corsica and to a region between Corsica and the continent which is in the shadow of the wind coming from NW. We will show how the Eta model outputs perfectly match the SAR analysis in the same regions. To complete the study, we also applied the SAR wave analysis to the two regions cited above
Synergic use of Sar Imagery and High- Resolution Atmospheric Model to Estimate Wind Vector over the Mediterranean Sea
No full textAn experiment whose aim is the retrieval of surface wind fields from SAR imagery coupled to a high resolution mesoscale numerical atmospheric model in semi-enclosed sea basin, is presented. A sea region belonging to North-Western Mediterranean Sea, which spans in W-E direction from Corsica (8.8 E) to Italian coast (10.5 E) and in N-S direction from Lygurian Sea (44.0 N) to North Tyrrhenian Sea (42.2 N), was selected as test area. Two consecutive ERS-2 SAR frames from the pass of March 30, 2000, along with a set of NOAA/AVHRR and MODIS images acquired on the same day were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved from predictions of the semi-empirical backscatter models CMOD4 and CMOD-IFREMER, which describe the dependency of the normalized radar cross section (NRCS) on wind vector and ERS-2 SAR image geometry. Surface wind vectors predicted by the meteorological ETA model were exploited as guess input to SAR wind inversion procedure to describe atmospheric conditions in the area, according a Bayesian approach recently proposed in literature. ETA is a three-dimensional, primitive equation, grid-point operational model running at the National Centers for Environmental Prediction of the U.S. National Weather Service. The model was adapted to run on selected regions of the Mediterranean basin with a nested very high, up to about 4.0 Km, resolution. The latter feature makes ETA model particularly suitble for its use in combination with SAR images. Besides, to simulate and predict several specific atmospheric weather phenomena, ETA outputs also include the vertical distributions of physical parameters such as air pressure, temperature, moisture up to about 25 Km. Apart some discrepancies in sparse and small areas, an overall agreement between SAR inversion results and ETA predictions was found. More importantly, it was found that the inversion methodology was not able to resolve wind speed modulations due to the manifestation of an atmospheric gravity wave, which occurred in the analyzed area as a result of the terrain disturbance to the air flow imposed by the peninsula located North of Corsica. Temporal evolution of the wave propagation phenomenon was allowed by inspection of NOAA/AVHRR and MODIS images through the detection of a cloud band associated to the atmospheric wave. A wave propagation model describing waves in the atmosphere owing to the disturbing action on the primary air flux by terrain features was thus used to account for the observed surface wind speed modulation on SAR image. Synergy with ETA model outputs was further exploited as atmospheric parameters up-wind the atmospheric wave were considered as input to the wave propagation model
Wave and wind field extraction from ERS SAR imagery
No full textThis paper deals with the analysis of SAR imagery of the Mediterranean Sea to estimate the directional wave spectrum and the wind vector. As case study an ERS-2 SAR acquired on 13 November 1997 (orbit 13417, frame 2889) which includes Lampedusa Island in the Sicily Channel was selected. Lampedusa was chosen as test site because of its privileged location in the centre of the Mediterranean and because it hosts a fully equipped meteorological station. Besides, the selected SAR image shows a striking feature from which the wind direction can be reliably estimated. Wave field and wind vector from SAR image were compared with predictions from the WAM wave model and the wind output of the ECMWF atmospheric model, respectively. The retrieval of directional two-dimensional wave spectrum from SAR image was carried out by means of the classical Hasselmann & Hasselmann inversion scheme and the SAR image cross-spectrum methodology, respectively. Assuming the wind direction is known independently, SAR data was then analyzed to retrieve the wind speed by using the predictions from empirical backscatter models, such as CMOD4 and CMOD-IFREMER. Wind vector retrieval results were validated against in situ measurements provided by the Lampedusa airport anemometer
RETRIEVAL OF TROPOSPHERIC ASH CLOUDS OF MT. ETNA FROM AVHRR DATA
No full textThis paper focuses on three eruptiveevents of the Mt. Etna volcano: July 22nd 1998,April 26th 2000 and the recent eruption of July-August 2001. Such eruptions may be a severethreat to aircraft safety, as in the April 2000event. From the AVHRR visible images theheight of the top of the clouds is estimated,using geometrical methods, knowing bothNOAA satellite and Sun positions. The resultsare then compared with information derivedfrom radio-sounding data etc.. The volcanic ashparticles with diameters of 1-10 mm are notdetectable by aircraft radar but they may beremotely sensed using thermal infrared data.The well-known algorithm, based on theAVHRR channel 4 and channel 5 brightnesstemperatures difference [Prata, 1989; Schneideret al. 1994], is here applied to highlight the ashclouds of Mt. Etna volcano. Even though it wastypically used to detect and follow the volcanicclouds of stratospheric eruptions, here it is succesfullytested for tropospheric plume too.Some good results of this technique are presentedtogether with some basic problems. Thiswork points out that it could be useful to preparea procedure to monitor Mt. Etna eruption cloudsanalysing TIR data. Such a procedure shouldautomatically alert (in real time, using the newMeteosat Second Generation satellite) and indicatethe cloud direction on the basis of atmosphericradio-sounded and/or predicted data
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