Amici, S.

Buongiorno, M. F.

Burton, M.

Carli, C.

La Spina, A.

Murè, F.

Neri, M.

Earth-prints Repository



 
 
 
 
INFRARED SPECTRAL CHARACTERISATION OF SOME VOLCANIC 
ROCKS ON MT. ETNA WITH IN-SITU INSTRUMENTS, JUNE 2007 
 
 
S. Amici1, A. La Spina2, M. Burton2, M. Neri2, M. F. Buongiorno1, C. Carli3 and F. Murè2 
 
 
1 Istituto Nazionale di Geofisica e Vulcanologia, Sede di Roma - CNT 
2 Istituto Nazionale di Geofisica e Vulcanologia, Sede di Catania 
3 Università degli studi di Parma - Dipartimento Scienze della Terra 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Index 
 
 
Introduction          5  
  
1 Instruments background        5 
 
1.1 FTIR instruments for emissivity measurements      5 
     
1.2 The ASTER instrument         8  
  
2 Campaign description        10 
 
2.1 Test site description        10 
 
3  Preliminary results         11 
 
3.1 Torre del Filosofo test site (ash and lava flow)     11 
 
3.2 Piana Provenzana test site        13 
 
3.3 Pian del lago  test site        13 
 
Conclusions          14 
 
Acknowledgement         14 
 
Bibliography          14 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 5 
Introduction   
 
Mount Etna volcano is the tallest and most active volcano in Europe. It is characterised by four craters 
(Northeast Crater, Voragine, Bocca Nuova, Southeast Crater (Figure 1) and a maximum height of 3315m 
above sea level (asl). Etna produces frequent eruptions of basaltic magma that consist of voluminous lava 
flows, scoria-generating explosions and ash-generating explosions [Behncke et al., 2005]. Since the late 
1970s, summit eruptions have shown an increase in their intensity, with a high rate of short-lived paroxysmal 
eruptive episodes [Behncke and Neri, 2003]. Such events can produce lava fountains that reach heights of 
several hundred meters and are accompanied by the generation of abundant tephra and scoriae that can fall 
tens of kilometres away from the volcano. The surface of Etna is highly dynamic, changing rapidly as lava 
flows are emplaced, ash falls deposit and pyroclastic cones grow. Such a system has naturally become the 
focus of air- and space-borne remote sensing studies, focussed on detecting thermal anomalies and 
measuring volcanic gas emissions. The efficacy of such studies is strongly dependent on accurate studies of 
the wavelength-dependent emissivity and reflectance of surface rocks. In order to obtain improved 
constraints on these parameters for Etna we conducted a campaign of in-situ ground-based spectroscopic 
measurements on Etna in June, 2007. A series of target sites, representative of both the present-day and 
oldest volcanic surfaces, were geologically and spectrally characterized. Measurements were made using an 
ASD FieldSpec Pro portable spectrometer operating in the 300-2500nm wavelength range for reflectance 
while an FTIR Bruker OPAG-22 was used for emissivity measurements in the mid-infrared. Here we present 
the preliminary results of the campaign and compare with satellite data. 
 
 
Figure 1  Summit Craters of Mount Etna: Bocca Nuova (BN1 and BN2),Voragine (VOR), Northeast Crater 
(NEC) and Southeast Crater (SEC). 
 
 
1 Instruments background  
 
1.1 FTIR instruments for emissivity measurements  
In June 2007 spectra were collected with an OPAG-22 FTIR (Bruker Daltonics, Germany). The 
instrument weighs 19 kg and has dimensions of 37x40x26 cm (see Figure 1). The spectrometer collects 
spectra at up to 0.5 cm-1 resolution, using a ZnSe beamsplitter and LN2-cooled MCT detector, over a 
wavenumber range from 500 to 6000 cm-1. The field of view of the instrument is 30 mrad. 
 
 
 
 6 
 
 
 
Figure 2  Optical layout of the Bruker OPAG-22 viewed from above, with inset highlighting the three 
apertures of the aperture wheel. In red the radiation path 1- Interferometer; 2- Elettronic; 3- Detector; 4- 
Laser HeNe. 5- Wheel A, B and C are the three openings. 
 
 
Radiation enters the instrument through a wheel with three openings: A- open; B and C hot and cold black-
bodies respectively. The wheel is controlled by software on a connected PC. In position A the instrument can 
be used to collect spectra, whereas B and C positions are used for instrument calibration during both tests 
and emissivity measurements. Input radiation, after reflection from two plane mirrors, passes through the 
interferometer block, which consists of two corner-cube reflectors on a pendulum mount. HeNe laser light 
from an internal source travels in parallel with the input radiation in order to measure the position of the 
moving mirrors. The output of the interferometer is a modulated signal measured with the detector. 
Interferograms are recorded on the hard disk of the PC and Bruker OPUS software allows conversion to 
absorption spectra, using a variety of apodization functions.  
In order to determine emissivity of the radiation source, we have utilized the black-body to calibrate the 
spectrometer and then extracted the temperature of the surface by fitting a Planck curve to the calibrated 
spectrum. Using this temperature we produced an emissivity spectrum from the measured spectra.  
In 2002/03 further FTIR measurements were collected on Etna with the objective of characterizing the 
emissivity of lava flows. The instrument used was the Model 102F spectrometer developed by Design and 
Prototypes for field measurements of  Earth’s surface and atmosphere spectral radiance. The spectrometer, 
called µFTIR (see Figure 3), operates at wavelengths ranging from 2 to 16 µm with a spectral resolution of 2 
cm-1. It has two liquid nitrogen cooled detectors, HgCdTe (or MCT) and InSb, for measurements collection 
in the 8-14 µm and 3-5 µm atmospheric windows respectively.  
 
 
 
 
 
 
 
 
 
 
 7 
 
 
                
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3  (a) Schematic diagram of the model 102F portable FTIR by Design & Prototypes, LTD; (b) 
Snapshot of the instrument. 
 
 
This instrument was used on 2003 Mount Etna field campaign to measure emissivity.  
 
The µFTIR software uses the following algorithm to compute the surface spectral emissivity: 
 
( )
( )
)(),(
)(
!!
!!
!"
DWRSBB
DWR
LTL
LL
#
#
=
                         (1) 
 
 
where L(λ) is the spectral radiance field measured by the spectrometer, LDWR(λ) is the downwelling 
radiance field reflected from the sample into the spectrometer, LBB(TS,λ) is the spectral radiance field of a 
Black Body (BB) at temperature TS , ε(λ) is the target spectral emissivity. The downwelling radiance of the 
hemisphere above the target is measured with a golden plate reflector located on the target. A golden plate 
with emissivity ε = 0.040 on the instrument spectral range is provided with the µFTIR. Moreover the sample 
temperature TS must be found by direct independent measurement .The instrument calibration is carried out 
by means of two blackbody measurements at two different temperatures. The measurement acquired data in 
the Pian del Lago area (Figure 4) during the 2003 campaign. 
       
 
 
a 
b 
 8 
 
 
Figure 4  View from the helicopter of Pian del Lago area, partially covered by the 2001 eccentric cone. 
 
 
1.2 The ASTER instrument  
ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is an international 
project funded by Japan’s Ministry of Economy Trade and Industry and flying on NASA’s TERRA satellite 
and launched in December 1999. The ASTER instrument has three separate optical subsystems: the visible 
and near-infrared (VNIR) radiometer, the shortwave-infrared (SWIR) radiometer, and the thermal infrared 
(TIR) radiometer [Pieri, D.C. and Abrams, M.J., 2004]. Table 1 summarizes the baseline performance of 
ASTER. 
 
 
 
 
Table 1  Spectral and spatial characteristics of ASTER. 
 9 
Reflected and emitted electromagnetic radiation from Earth’s surface are detected and recorded by 
ASTER VNIR, SWIR and TIR sensors as raw instrument data. Data are calibrated, geometrically corrected 
and released as Level 1B data. These data are used to produce higher–level data products and are distributed 
by ASTER GDS (Ground Data System). Two surface reflectance products are available, one each for VNIR 
and SWIR. These products are atmospherically and topographically corrected basing on available 
climatological data and on global digital elevation data sets respectively [Gillespie, A. et al., 1998]. The data 
set are expressed in unitless reflectance; the percent reflectance can be derived from the product by 
multiplying each value by 0.001 [Bailey G.B., 2007]. 
The surface emissivity is obtained using the five atmospherically corrected TIR bands as derived from 
temperature/emissivity separation algorithm [Realmuto V.J, 1990]. The possible range of emissivity values 
between 0 and 1 are encoded as value between 0 and 1000 in the product.  
On-demand ASTER acquisition was requested for June 19th 2007 with the objective of 
contemporaneously measuring satellite and ground-based data. In Figures  5 and 6 we show VNIR and TIR 
Mount Etna ASTER data acquired on July 2003 in the frame of a previous campaign and  the data acquired 
on June 19th 2007. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5  ASTER data acquired on July 19th 2003: (a) day Visible channels and (b) TIR channels during day 
acquisition. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6  ASTER data acquired on June 19th 2007 (a) day 09:59 GMT and (b) TIR channels, night 21:03 
GMT. The TIR data is interesting because shows the hot areas that interested the lava flow during 2006-2007 
activity. 
a 
a 
b 
b 
 10 
2 Campaign description 
 
From 19th-23rd June 2007 a field campaign was carried out on Mt. Etna, Sicily, Italy with the objective 
of quantitatively characterising the spectral characteristics of some lava flows on the volcano during an on-
demand overpass by the ASTER instrument, on board the NASA TERRA satellite. Spectral data in the 
visible, near-infrared and mid-infrared  were acquired using three different instruments in order to constrain 
the emissivity of the surface over a wide wavelength range. 
 
2.1 Test site description  
A number of sites with different characteristics were chosen, which are believed to represent the great  
variety of recent volcanic surfaces that is encountered at Mt. Etna (Table 2). Normally there are two types of 
volcanic surface: lava flows and pyroclastic deposits.  
In order to obtain a record as representative as possible, sites were chosen on lavas on different flanks 
and of different age, and with pyroclastic covers that show different characteristics. The locations of the 
measurement sites are shown in Figure 7. 
 
2006-2007: intermittent summit activity concentrated in vents at and around the Southeast Crater. Lavas 
characterized by “aa” type morphology. In 2006 the eruptive activity affected mainly the eastern and western 
flanks of the Southeast Crater, producing long lived Strombolian eruptions, occasionally accompanied by 
lava emission from fissures opened at the base of the carter. The eruptive activity in 2007 consisted of 
several paroxysmal episodes with activity ranging from intense Strombolian explosions to lava fountaining, 
accompanied by lava outflow. 
 
2002-2003: Second flank eruption characterized by the activation of the same two magmatic plumbing 
systems (central-lateral and eccentric) active in 2001. In this case the eruption was coupled with  a major 
flank slip on the eastern and southeastern sides of the volcano. Lavas characterized by “aa” type 
morphology. A wide cover of pyroclastic products were emitted from the eccentric vents, which cover the 
Pian del Lago area. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 7  Historical Mount Etna lava Flows on DEM.  
 
 
 
FTIR points 
Pian del Lago 
TdF 
Piano Provenzana 
 11 
3 Preliminary results  
 
The infrared (8-12 µm) spectral region has the minimum thermal emission from Earth and is positioned in a 
good atmospheric window. It is characterized by important absorption bands in emissivity spectra also for 
silicate and basalts that allows the study of a surface (Lythology). Measurements of emissivity realized on 
2007 and 2003 [Amici et al.,2006; Amici et al. 2007] on three different points on Mount Etna have been 
compared with ASTER data (Table 2). 
 
 
Site feature FTIR 2003 FTIR 2007 ASTER 2003 ASTER 2007 
Site  name Lava flow Latitude  Longitude 
Latitude 
Longitude 
Latitude 
Longitude 
Latitude  
Longitude 
Piana  
Provenzana 
(PP) 
 Point 29 
2002/03          - 
 
N 37° 47’ 40.56” 
E 15° 01’ 24.42” 
 
N 37° 47’ 32” 
E 15° 01’ 26” 
N 37° 48’ 16.51” 
E 15° 02’ 24.7” 
Pian del Lago 
(PDL)  
N 37° 43’ 42” 
E 15° 00’ 30.6”            - 
N 37° 43’ 41.1” 
E 15° 00’ 30.29” 
N 37° 43’ 22.5” 
E 15° 00’ 25.63” 
Ash Torre del 
Filosofo  (TDF) 
Point 26 
2006          - N 37° 44’ 18.66” E 14° 59’ 54.60”     - 
N 37° 44’ 17.8” 
E 14° 59’ 57.4” 
 
Table 2  Test sites geo-location in situ and on satellite respectively. 
 
 
3.1 Torre del Filosofo test site (ash and lava flow) 
Torre del Filosofo test site is characterized by two different kind of surfaces: pyroclastic ash from 
2006 Etna activity and lava flow from 2007 Etna eruption. Despite it was later spring time in the area were 
present some ice residual as shown in Figure 8. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 8  (a) Torre del Filosofo as seen by ASTER June 19th 2007 visible bands 15m spatial resolution and 
(b) the in field site characterized by FTIR. 
 
a b 
 12 
Emissivity measurements were realized on Ash 2006 to ASTER emissivity data acquired on July 19th 2003 
and on 19th June 2007. Due to the spatial resolution (90m) of the TIR band used for emissivity retrieval, the 
Aster emissivity is probably a mixture of the different components. 
In Figure 9 is the plot of the emissivity of the two different kind of surfaces compared with ASTER data 
acquired on 2007. 
0.7
0.75
0.8
0.85
0.9
0.95
8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13
Emissivity of LAVA 07 T=315.6 °K
Emissivity of ASH T=306.8 °K
ASTER 07 Lava
ASTER 07 Ash
wavelenght (micron)
E
m
is
si
vi
ty
 
 
 
Figure 9  Torre del Filosofo N 37° 44’ 18.66”    E 14° 59’ 54.20” Ash 2006 ; N 37° 44’ 18.66” E 14° 59’ 
54.60” (lava 2007) ash and lava ground emissivity measurement are compared with the corresponding 
ASTER. 
 
In Figure 10 the emissivity of Ash is compared with ASTER data acquired on 2003 and 2007. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 10  Torre del Filosofo N 37° 44’ 18.66”    E 14° 59’ 54.20” Ash 2006. On ground emissivity 
measurement is compared with ASTER 2003 acquisition (green values) and ASTER 2007 (pink values). 
Emissivity of ASH 2006and lava flow 2007
0.7
0.75
0.8
0.85
0.9
0.95
1
8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13
wavelength (micron)
E
m
is
s
iv
it
y FTIR07 N37 44 18.66 E14 59 54.20 (Ash06)
Aster03 N37 44 18.87 E14 59 53.93
Aster07 N37 44 20.17 E14 59 53.45
T of ground (ash): 306.5  K  
 13 
3.2 Piana Provenzana test site  
On ground emissivity spectrum was retrieved deriving the ground temperature by fitting the Plank function. 
The absorption bands can be due to the vibration in the silicon-oxygen group in amorphous groundmass 
(Figure 11).  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 11  (a) N 37° 47’ 40.56”   E 15° 01’ 24.42” corresponding to point 29 of Table 2 - Piana Provenzana 
area: (b) measured on ground emissivity on 2007 compared with ASTER 2007 same day (red) and ASTER 
2003 (green).  
 
3.3 Pian del Lago test site  
Pian del Lago is a slightly tilted surface of cineritic scoria of centimeter range diameter located 
between the Valle del Bove scarp, the two new 2003 eruption craters and  the 2001 eruption new crater on 
the southeast flank of the volcano.  
The spectrum shows a clear, wide emissivity inflection at 10 micron, that can be attributed can be due 
to the vibration in the Al-O-Si group, possibly in plagioclase (Figure 12).  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 12  (a) N 37° 43’ 42’’   E 15° 00’ 30.6’’ is the point PDL of Table 2 and (b) measured on ground 
emissivity on 2003 compared with ASTER 2003 (green) and ASTER 2007 (red). 
 
 
 
 
 
0.7
0.75
0.8
0.85
0.9
0.95
1
8 8.5 9 9.5 10 10.5 11 11.5 12
Wavelenght [micron]
E
m
is
s
iv
it
y
FTIRpoint29
ASTER07point29
ASTER03point29b a 
0.7
0.75
0.8
0.85
0.9
0.95
1
8 8.5 9 9.5 10 10.5 11 11.5 12
Wavelenght [micron]
E
m
is
s
iv
it
y
FTIR03
Aster07
Aster03
a b 
 14 
Conclusions 
 
The in field campaign carried out on Mount Etna was devoted to the validation of satellite data. 
In particular, in this technical note, we report the results obtained for the Nir-IR spectral range. 
Measurements obtained by FTIRs instruments was compared with standard products by ASTER sensor in 
the same spectral range. 
A good agreement between the two kind of data was found for Piana Provenzana and Pain del Lago.  
Future work will be devoted to understand the differences in the Torre del Filosofo test site: for instance 
planning a new series of in-situ measurements by using Micro FTIR and Bruker OPAG-22 jointly and cross 
calibrated. Geochemical analysis results of samples acquired in the test sites will be used to interpret the 
spectral features. 
Further, ASTER radiance data will be processed applying local atmospheric profile for the atmospheric 
correction and the retrieved emissivity will be compared with ASTER standard data. 
 
 
Acknowledgement 
 
The authors would like to thank Dr. Boris Behncke (INGV-Catania) for assistance with him, knowledge of 
Mount Etna area. A special thank to Dr Dave Pieri, ASTER science Team Member, for the data planning 
support.  
  
 
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SPIE       Vol 6361 6361113-1.  
 
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Canadian Journal of Earth Sciences, 40: 1405-1411, DOI: 10.1139/E03-052. 
 
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Telerilevamento-2007-39-19-31. 
 
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Infrared spectral characterisation of some volcanic rocks on Mt. Etna with in-situ instruments, June 2007

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Infrared spectral characterisation of some volcanic rocks on Mt. Etna with in-situ instruments, June 2007

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