Spectral emissivity and temperature maps of the Solfatara crater from DAIS hyperspectral images

Quantitative 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

Spectral emissivity and temperature maps of the Solfatara crater from DAIS hyperspectral images

Quantitative 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 contributes 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 measures performed in situ during the campaign. The spectral emissivity map was used to classify the image in different geomineralogical 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 detection and retrievals using MODIS data by means of neural networks

Volcanic ash clouds detection and retrieval represent a key issue for aviation safety due to the harming effects on aircraft. A lesson learned from the recent Eyjafjallajokull eruption is the need to obtain accurate and reliable retrievals on a real time basis. <br><br> In this work we have developed a fast and accurate Neural Network (NN) approach to detect and retrieve volcanic ash cloud properties from the Moderate Resolution Imaging Spectroradiometer (MODIS) data in the Thermal InfraRed (TIR) spectral range. Some measurements collected during the 2001, 2002 and 2006 Mt. Etna volcano eruptions have been considered as test cases. <br><br> The ash detection and retrievals obtained from the Brightness Temperature Difference (BTD) algorithm are used as training for the NN procedure that consists in two separate steps: ash detection and ash mass retrieval. The ash detection is reduced to a classification problem by identifying two classes: "ashy" and "non-ashy" pixels in the MODIS images. Then the ash mass is estimated by means of the NN, replicating the BTD-based model performances. A segmentation procedure has also been tested to remove the false ash pixels detection induced by the presence of high meteorological clouds. The segmentation procedure shows a clear advantage in terms of classification accuracy: the main drawback is the loss of information on ash clouds distal part. <br><br> The results obtained are very encouraging; indeed the ash detection accuracy is greater than 90%, while a mean RMSE equal to 0.365 t km<sup>−2</sup> has been obtained for the ash mass retrieval. Moreover, the NN quickness in results delivering makes the procedure extremely attractive in all the cases when the rapid response time of the system is a mandatory requirement

Volcanic ash retrieval from IR multispectral measurements by means of Neural Networks

The lesson learned from the recent Icelandic Eyjafjallajokull volcanic eruption is the need to obtain accurate near real time retrievals in order to sample the phenomenon evolution. In particular, because of the harming effects of fine volcanic ash particles on aircrafts, the real time tracking of volcanic clouds is a key issue for aviation safety. The current mostly utilized procedure for the ash retrievals is based on the Brightness Temperature Difference (BTD) algorithm, using the 11 and 12 micron channels measurements and radiative transfer model computation. This latter requires many input parameters and is time consuming, preventing the utilization during the crisis phases. In this work a fast and accurate Neural Network (NN) approach has been developed to detect and retrieve volcanic ash cloud properties using multispectral IR measurements. The exploited data come from the Moderate Resolution Imaging Spectroradiometer (MODIS) acquired over Mt. Etna volcano during the 2001, 2002 and 2006 eruptive events. The procedure consists in two separate steps that uses the three MODIS channels 28, 31 and 32: the detection and the ash retrievals. The detection is reduced to a classification problem. In this context several classes can be individuated, such as free sea surface, meteorological clouds, and ash plume. To maintain the solution of the problem as easy as possible we have simplified the scenario identifying only two classes on the MODIS images: 'ash' and 'no ash' pixels. This approach is coherent with the philosophy of this work in which the time passed to obtain the result is a stringent factor. For the ash mass retrieval, the trained network replicates the model. In fact, in order to have a network able to learn a behavior and to represent it through a functional approximation, it is necessary to provide appropriate information by an ensemble of examples. These latter can be obtained from a model if a direct measure is not available. In this work the results obtained with the BTD procedure have been considered. The results obtained from the entire procedure are encouraging, indeed the confusion matrix for the test set has an accuracy greater than 90%. Moreover the ash mass retrieval shows a good agreement with that achieved by BTD procedure

Spectral emissivity and temperature maps of the Solfatara crater from DAIS hyperspectral images

Quantitative 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 tem- perature 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 Spec- tral 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

Synergistic use of Lagrangian dispersion and radiative transfer modelling with satellite and surface remote sensing measurements for the investigation of volcanic plumes: the Mount Etna eruption of 25–27 October 2013

Abstract. In this paper we combine SO2 and ash plume dispersion modelling with satellite and surface remote sensing observations to study the regional influence of a relatively weak volcanic eruption from Mount Etna on the optical and micro-physical properties of Mediterranean aerosols. We analyse the Mount Etna eruption episode of 25–27 October 2013. The evolution of the plume along the trajectory is investigated by means of the FLEXible PARTicle Lagrangian dispersion (FLEXPART) model. The satellite data set includes true colour images, retrieved values of volcanic SO2 and ash, estimates of SO2 and ash emission rates derived from MODIS (MODerate resolution Imaging Spectroradiometer) observations and estimates of cloud top pressure from SEVIRI (Spinning Enhanced Visible and InfraRed Imager). Surface remote sensing measurements of aerosol and SO2 made at the ENEA Station for Climate Observations (35.52° N, 12.63° E; 50 m a.s.l.) on the island of Lampedusa are used in the analysis. The combination of these different data sets suggests that SO2 and ash, despite the initial injection at about 7.0 km altitude, reached altitudes around 10–12 km and influenced the column average aerosol particle size distribution at a distance of more than 350 km downwind. This study indicates that even a relatively weak volcanic eruption may produce an observable effect on the aerosol properties at the regional scale. The impact of secondary sulfate particles on the aerosol size distribution at Lampedusa is discussed and estimates of the clear-sky direct aerosol radiative forcing are derived. Daily shortwave radiative forcing efficiencies, i.e. radiative forcing per unit AOD (aerosol optical depth), are calculated with the LibRadtran model. They are estimated between −39 and −48 W m−2 AOD−1 at the top of the atmosphere and between −66 and −49 W m−2 AOD−1 at the surface, with the variability in the estimates mainly depending on the aerosol single scattering albedo. These results suggest that sulfate particles played a large role in the transported plume composition and radiative forcing, while the contribution by ash particles was small in the volcanic plume arriving at Lampedusa during this event

Tecniche d'inversione per la stima dell'emissione di anidridesolforosa dell'Etna dalle immagini telerilevate dal MIVIS nell'infrarosso termico

Nell'ambito del Progetto Europeo Mitigation of Volcanic Risk by Remote Sensing (MVRRS) è stata effettuata una carnpagna di misure neii'area etnea (SICILIA '97) e diversi gruppi di ricerca hanno effettuato misure a terra contemporaneamente ai voli dell'hfkred and Visible Imaging Spectrometer (MIVIS). Nella presente memoria vengono descritte una soluzione analitica dell'equazione del trasferimento radiativo ed un algoritmo, basato sulla tecnica Split-Wmdow, per la determinazione del contenuto colonnare di SO2 nel plume dell'Etna. Entrambe queste procedure derivano da una precedente soluzione numerica dell'equazione di trasferimento radiativo, soluzione ottenuta utilizzando le simulazioni dei termini atmosferici effettuate con il modello di trasferimento radiativo MODTRAN 3.5. I contenuti colonnari di SO2, valutati con le metodologie descritte nel presente lavoro, hanno poi permesso, assieme alla misura della velocità orizzontale del vento all'altezza del plume, di stimare il flusso di SO2 emesso dall’Etna. I flussi medi ottenuti da ogni singola immagine MMS sono stati confrontati con le simultanee misure COSPEC effettuate da terra e da un aereo ultraleggero che volava al di sotto del plume. I valori ottenuti: circa 45 kg/s il 12 giugno 1997 e circa 30 kg/s il 16 giugno risultano in ottimo accordo con le misure COSPEC citate

Analisi spettrale di dati MIVIS: un caso di studio sull'isola di Vulcano

Si descrive un caso di studio mirato alla valutazione delle potenzialità del MIVIS in applicazioni di caratterizzazione della superficie. I1 data-set è costituito dai canali del Visibile e Infrarosso riflesso di un'immagine del cono vulcanico della Fossa (isola di Vulcano), trasformata in riflettanze superficiali. Lo studio comprende: una valutazione della qualità dei dati, l'applicazione di tecniche di classificazione spettrale, il confronto degli spettri MIVIS di alcune unità classificate con spettri misurati in laboratorio. I risultati mostrano come sia stato possibile individuare diversi tipi di depositi e alterazioni ed estrarre informazioni chimico-mineralogiche basandosi sull'identificazione delle bande di assorbimento, seppure con alcune limitazioni

CORREZIONI ATMOSFERICHE DEI DATI MIVIS

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Correzioni atmosferiche di dati MIVIS

In 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 \ue8 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\u2019Etna