1,721,045 research outputs found
Spectral emissivity and temperature maps of the Solfatara crater from DAIS hyperspectral images
Full text linkQuantitative maps of surface temperature and spectral emissivity have been retrieved on the Solfatara crater at Pozzuoli (Naples) from remote sensing hyperspectral data. The present study relies on thermal infrared images collected on July 27, 1997 by the DAIS hyperspectral sensor owned by the German aerospace center (DLR). The Emissivity Spectrum Normalization method was used to make temperature and emissivity estimates. Raw data were previously transformed in radiance and corrected for the atmospheric contributions using the MODTRAN radiative transfer code and the sensor response functions. During the DAIS flight a radiosonde was launched to collect the atmospheric profiles of pressure, temperature and humidity used as input to the code. Retrieved temperature values are in good agreement with temperature measurements performed in situ during the campaign. The spectral emissivity map was used to classify the image in different geo-mineralogical units with the Spectral Angle Mapper method. Areas of geologic interest were previously selected using a mask obtained from an NDVI image calculated with two channels of the visible (red) and the near infrared respectively
Volcanic ash and SO2 in the Kasatochi and Okmok eruptions: Interference and impact on quantitative retrievals
No full textAsh and SO2 were detected in the eruptions of Kasatochi and Okmok by infrared and UV sensors, including MODIS, AIRS and OMI. The simultaneous presence of ash and SO2 in these clouds presents a problem for retrieving SO2 column abundance because ash absorbs strongly near the 8.7 mm SO2 absorption feature. This leads to a overestimation of the MODIS SO2 abundance, unless the effects of ash are taken into account. Here, we use a new radiative transfer scheme to correct for the effects of ash on SO2 retrieval at 8.7 mm and also account for the effects of ash on SO2 retrieval at 7.3 mm, although this is much less severe, as we will demonstrate. The retrievals provide an improved quantitative description of the ash and SO2 in volcanic eruptive clouds and will assist in developing warnings for aviation. A comparison between MODIS retrievals and contemporaneous OMI SO2 retrievals and AIRS ash and SO2 retrievals has been also presented.UnpublishedAGU Fall Meeting
15-19 December San Francisco1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcaniope
Fine Tuning Eruption Source Parameters to Improve Ash Dispersion Simulations: An Example From Eyjafjallajökull 2010
No full textVolcanic ash dispersion simulations and remote sensing of ash clouds are conducted by volcano observatories and Volcanic Ash Advisory Centres to monitor and forecast the evolution of volcanic ash clouds in space and time in order to mitigate the risk posed by these events on civil aviation. Despite constant improvements in terms of technology and modern capabilities, both numerical simulations and monitoring are still affected by variable degrees of uncertainty. To initialize the rate of emission and position of the volcanic ash in the ash dispersion simulation computational domain of the numerical model used for forecasting the ash clouds, in particular, currently relies on the preliminary simulation of the volcanic plume. The source modeling is generally carried out using simplified plume models that depends on parameters that cannot be accurately measured in real time, for example, the wind entrainment coefficient and the plume centerline height in case of wind affected (bent-over) plumes. In this work, we test recently proposed correction factors for these parameters for two of the most widely used simplified plume models and compare with ash cloud satellite observations retrieved during the Eyjafjallajökull eruption. Specifically, we compare modeling results obtained with and without applying the corrections of the top plume height and wind entrainment coefficient. We show that, by applying the corrections, we significantly reduce the discrepancy between the simulated and satellite-retrieved ash cloud observations
Correzioni atmosferiche di dati MIVIS
Full text linkIn questa presentazione sono brevemente illustrate le procedure di correzione atmosferica utilizzate nell'elaborazione dei dati MIVIS acquisiti sull'Etna e sull'isola di Vulcano nel 1994 e nel 1997. I metodi utilizzati sono basati su modelli di trasferimento radiativo e differiscono a seconda della regione spettrale considerata. In particolare, nella regione spettrale 0.4 + 2.5 um la procedura sviluppata fa un uso combinato dei modelli di trasferimento radiativo 6S e MODTRAN, mentre per i canali nell'infrarosso termico è usato esclusivamente il MODTRAN. Nel primo caso le correzioni atmosferiche sono state utilizzate per la valutazione della riflettanza superficiale, nel secondo caso per la mappatura termica e per valutazione del flusso di SO2 emesso dall’Etna
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
Simulazione di immagini ASTER da immagini MIVIS per la stima del flusso di SO2 dall'Etna
Full text linkLo scopo di questo lavoro è la verifica della possibilità di determinare il flusso di SO2 emesso dal17Etna da immagi-ni simulate ASTER nel TIR. L'ASTER è uno degli strumenti montati a bordo di Terra, il primo satellite del progetto EOS lanciato il 18 dicembre del 1999, le cui immagini non sono ancora disponibili. La simulazione delle immagini ASTER è stata eseguita utilizzando le immagini MIVIS acquisite durante la campagna di misura "Sicily '97". Le mappe di contenuto colonnare di SO2, mostrate in questo lavoro, sono state ottenute utilizzando un algoritmo basato sulla tecnica Split- Window e precedentemente applicato alle immagini MIVIS. I risultati sono in ottimo accordo con quelli ottenuti direttamente dalle procedure d'inversione delle immagini MIVIS e alle misure COSPEC effettuate durante la campagna di misura
Volcanic ash and SO2 in the Kasatochi and Okmok eruptions: Interference and impact on quantitative retrievals
No full textAsh and SO2 were detected in the eruptions of Kasatochi and Okmok by infrared and UV sensors, including MODIS, AIRS and OMI. The simultaneous presence of ash and SO2 in these clouds presents a problem for retrieving SO2 column abundance because ash absorbs strongly near the 8.7 mm SO2 absorption feature. This leads to a overestimation of the MODIS SO2 abundance, unless the effects of ash are taken into account. Here, we use a new radiative transfer scheme to correct for the effects of ash on SO2 retrieval at 8.7 mm and also account for the effects of ash on SO2 retrieval at 7.3 mm, although this is much less severe, as we will demonstrate. The retrievals provide an improved quantitative description of the ash and SO2 in volcanic eruptive clouds and will assist in developing warnings for aviation. A comparison between MODIS retrievals and contemporaneous OMI SO2 retrievals and AIRS ash and SO2 retrievals has been also presented.UnpublishedAGU Fall Meeting
15-19 December San Francisco1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcaniope
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