805 research outputs found
Volcanic Water Vapour Abundance Retrieved Using Hypespectral Data
In the present study a remote sensing differential
absorption technique, already developed to calculate the atmospheric water vapour abundance, has been adapted to calculate water
vapour columnar abundance in tropospheric volcanic plume. Water
vapour is the most abundant gas of a volcanic plume released into the atmosphere from an active volcanic system. The technique is based on the correlation between the dip in the spectral curve measured by the spectrometer were water vapour absorptions bands are presents, and the precipitable water content in the column.
Airborne and satellite remote sensing images in the infrared
wavelength range were used. The technique has been applied to data acquired over two different degassing volcanoes. The Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) acquired data over the Hawaiian PuâuâOâo Vent cone of the Kilauea volcano on April 2000. The Hyperion sensor on EO-1 satellite has been requested to acquire data on July 2003, during a ground-based measurements campaign on Mt. Etna (Italy). The result is the spatial distribution of water vapour abundance of the Mt. Etna and of the Pu`u` O`o Vent volcanic plumes. A comparison between the two results has been done, showing the differences in the volcanic activity. The algorithm produces reliable results compared to the ground based measurements in the plume area acquired during a measurements campaign over Mt. Etna
Near real-time routine for volcano monitoring using infrared satellite data
An Advanced Very-High-Resolution Radiometer (AVHRR) routine for hotspot
detection and effusion rate estimation (AVHotRR) using AVHRR
infrared space-borne images is presented here for the monitoring of active
lava flow. AVHotRR uses directly broadcast National Oceanic and
Atmospheric Administration (NOAA)-AVHRR remotely sensed data. The
2006 summit eruption of Mount Etna provided the opportunity to test the
products generated by AVHotRR for monitoring purposes. Low spatial
and high temporal resolution products can also be used as inputs of flow
models to drive numerical simulations of lava-flow paths and thus to
provide quantitative hazard assessment and volcanic risk mitigation
Aerosol optical thickness of Mt. Etna volcanic plume retrieved by means of the Airborne Multispectral Imaging Spectrometer (MIVIS)
Within the framework of the European MVRRS project (Mitigation of Volcanic Risk by Remote Sensing
Techniques), in June 1997 an airborne campaign was organised on Mt. Etna to study different characteristics of
the volcanic plume emitted by the summit craters in quiescent conditions. Digital images were collected with
the Airborne Multispectral Imaging Spectrometer (MIVIS), together with ground-based measurements. MIVIS
images were used to calculate the aerosol optical thickness of the volcanic plume. For this purpose, an inversion
algorithm was developed based on radiative transfer equations and applied to the upwelling radiance data measured
by the sensor. This article presents the preliminary results from this inversion method. One image was selected
following the criteria of concomitant atmospheric ground-based measurements necessary to model the atmosphere,
plume centrality in the scene to analyse the largest plume area and cloudless conditions. The selected image was
calibrated in radiance and geometrically corrected. The 6S (Second Simulation of the Satellite Signal in the Solar
Spectrum) radiative transfer model was used to invert the radiative transfer equation and derive the aerosol optical
thickness. The inversion procedure takes into account both the spectral albedo of the surface under the plume and
the topographic effects on the refl ected radiance, due to the surface orientation and elevation. The result of the
inversion procedure is the spatial distribution of the plume optical depth. An average value of 0.1 in the wavelength
range 454-474 nm was found for the selected measurement day
Volcanic CO2 Abundance of Kilauea Plume Retrieved by Meand of AVIRIS Data
Absorbing the electromagnetic radiation in several regions of the solar spectrum, CO2 plays an important role in the Earth radiation budget since it produces the greenhouse effect. Many natural processes in the Earth s system add and remove carbon dioxide. Overall, measurements of atmospheric carbon dioxide at different sites around the world show an increased carbon dioxide concentration in the atmosphere. At Mauna Loa Observatory (Hawaii) the measured carbon dioxide increased from 315 to 365 ppm, in the period 1958 2000 [Keeling et al., 2001]. While at the large scale, the relationship between CO2 increase and global warming is established [IPCC, 1996], at the local scale, many studies are still needed to understand regional and local sources of carbon dioxide, such as volcanoes. The volcanic areas are particularly rich in carbon dioxide; this is due to magma degassing in the summit craters region of active volcanoes, and to the presence of fractures and active faults [Giammanco et al., 1998]. Several studies estimate a global flux of volcanic CO2 (34+/-24)10(exp 6) tons/day from effusive volcanic emissions, such as the tropospheric volcanic plume (Table 1) [McClelland et al., 1989]. Plumes are a turbulent mixture of gases, solid particles and liquid droplets, emitted continuously at high temperature from summit craters, fumarolic fields or during eruptive episodes. Inside the plume, water vapour represents 70 90% of the volcanic gases. The main gaseous components are CO2, SO2, HCl, H2, H2S, HF, CO, N2 and CH4. Other plume components are volcanic ash, aqueous and acid droplets and solid sulphur-derived particles [Sparks et al., 1997]. Volcanic gases and aerosols are evidences of volcanic activity [Spinetti et al., 2003] and they have important climatic and environmental effects [Fiocco et al., 1994]. For example, Etna volcano is one of the world s major volcanic gas sources [Allard et al., 1991]. New studies on volcanic gaseous emissions have pointed out that a variation of the gas ratio CO2/SO2 is related to eruptive episodes [Caltabiano et al., 1994]. However, measurements and monitoring of volcanic carbon dioxide are difficult and often hazardous, due to the high background presence of atmospheric CO2 and the inaccessibility of volcanic sites. Hyperspectral remote sensing is a suitable technique to overcome the difficulties of ground measurement. It permits a rapid, comprehensive view of volcanic plumes and their evolution over time, detection of all gases with absorption molecular lines within the sensor s multispectral range and, in general, measurement of all the volatile components evolving from craters. The molecular and particle plume components scatter and absorb incident solar radiation. The integral of the radiation difference composes the signal measured by the remote spectrometer. The inversion technique consists of retrieving the plume component concentrations, hence decomposing the signal into the different contributions. The accuracy of remote sensing techniques depends primarily on the sensor capability and sensitivity
The OPERA magnetic spectrometer
The OPERA neutrino oscillation experiment foresees the construction of two
magnetized iron spectrometers located after the lead-nuclear emulsion targets.
The magnet is made up of two vertical walls of rectangular cross section
connected by return yokes. The particle trajectories are measured by high
precision drift tubes located before and after the arms of the magnet.
Moreover, the magnet steel is instrumented with Resistive Plate Chambers that
ease pattern recognition and allow a calorimetric measurement of the hadronic
showers. In this paper we review the construction of the spectrometers. In
particular, we describe the results obtained from the magnet and RPC prototypes
and the installation of the final apparatus at the Gran Sasso laboratories. We
discuss the mechanical and magnetic properties of the steel and the techniques
employed to calibrate the field in the bulk of the magnet. Moreover, results of
the tests and issues concerning the mass production of the Resistive Plate
Chambers are reported. Finally, the expected physics performance of the
detector is described; estimates rely on numerical simulations and the outcome
of the tests described above.Comment: 6 pages, 10 figures, presented at the 2003 IEEE-NSS conference,
Portland, OR, USA, October 20-24, 200
SO2 AND ASH VOLCANIC PLUME RETRIEVALS FROM THE 24 NOVEMBER 2006 Mt. ETNA ERUPTION USING MSG-SEVIRI DATA: SO2 VALIDATION AND ASH CORRECTION PROCEDURE
Estimation of the daily trend of sulfur dioxide and ash from the thermal infrared measurements of the Spin Enhanced Visible and Infrared Imager (SEVIRI), on board the Meteosat Second Generation (MSG) geosynchronous satellite, has been carried out. The SO2 retrieval is validated vicariously by using satellite sensors and with ground measurements. The 24 November 2006 tropospheric eruption of Etna volcano is used as a test case. MSG-SEVIRI is an optical imaging radiometer characterized by 12 spectral channels, a high temporal resolution (one image every 15 minutes), and a 10 km2 footprint. The instrumentâs spectral range includes the 7.3 and 8.7 mm bands (channels 6 and 7) used for SO2 retrieval and the 10.8 and 12.0 mm (channels 9 and 10) split window bands used for ash detection and retrievals. The SO2 columnar abundance and ash are retrieved simultaneously by means of a Look-Up Table least squares fit procedure for SO2 and using a Brightness Temperature Difference algorithm for ash. The SO2 retrievals obtained using different satellite sensors such as AIRS and MODIS have been carried out and compared with SEVIRI estimations. The results were validated using the permanent mini-DOAS ground system network (FLAME) installed and operated by INGV on Mt. Etna. Results show that the simultaneous presence of SO2 and ash in a volcanic plume yields a significant error in the SO2 columnar abundance retrieval in multispectral Thermal Infrared (TIR) data. The ash plume particles with high effective radius (from 1 to 10 mm) reduce the top of atmosphere radiance in the entire TIR spectral range, including the channels used for the SO2 retrieval. The net effect is a significant SO2 overestimation. To take this effect into account a novel ash correction procedure is presented and applied to the retrieval
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