International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
ANOMALY DETECTION AND COMPARATIVE ANALYSIS OF HYDROTHERMAL 
ALTERATION MATERIALS TROUGH HYPERSPECTRAL MULTISENSOR DATA IN 
THE TURRIALBA VOLCANO 
J. G. Rejas ad J. Martinez-Frias ® J. Bonatti *, R. Martínez d and M. Marchamalo ? 
? National Institute for Aerospace Technology, INTA. Ctra. de Ajalvir km 4 s/n 
28850 Torrejón de Ardoz (Spain), rejasaj@inta.es 
^Astrobiology Centre-Spanish National Research Council, INTA/CAB-CSIC. Ctra. de Aj alvir km 4 s/n 
28850 Torrejón de Ardoz (Spain), jmfrias(d)cab.inta-csic.es 
* Costa Rica University, UCR. Campus UCR-San Pedro de Montes de Ocas s/n, 
0125 San José (Costa Rica), jbonatti2011(@gmail.com 
“Technical University of Madrid, UPM. Ramiro de Maeztu, 7, 
28040 Madrid (Spain), ruben. martinez@upm.es, miguel. marchamalo@upm.es 
Commission VII, WG VII/3 
KEY WORDS: Spectral Anomaly, Hydrothermal Alteration, Hyperspectral, Multispectral, Multisensor. 
ABSTRACT: 
The aim of this work is the comparative study of the presence of hydrothermal alteration materials in the Turrialba volcano (Costa 
Rica) in relation with computed spectral anomalies from multitemporal and multisensor data adquired in spectral ranges of the 
visible (VIS), short wave infrared (SWIR) and thermal infrared (TIR). We used for this purposes hyperspectral and multispectral 
images from the HyMAP and MASTER airborne sensors, and ASTER and Hyperion scenes in a period between 2002 and 2010. 
Field radiometry was applied in order to remove the atmospheric contribution in an empirical line method. HYMAP and MASTER 
images were georeferenced directly thanks to positioning and orientation data that were measured at the same time in the acquisition 
campaign from an inertial system based on GPS/IMU. These two important steps were allowed the identification of spectral 
diagnostic bands of hydrothermal alteration minerals and the accuracy spatial correlation. Enviromental impact of the volcano 
activity has been studied through different vegetation indexes and soil patterns. Have been mapped hydrothermal materials in the 
crater of the volcano, in fact currently active, and their surrounding carrying out a principal components analysis differentiated for a 
high and low absorption bands to characterize accumulations of kaolinite, illite, alunite and kaolinite+smectite, delimitating zones 
with the presence of these minerals. Spectral anomalies have been calculated on a comparative study of methods pixel and subpixel 
focused in thermal bands fused with high-resolution images. Results are presented as an approach based on expert whose main 
interest lies in the automated identification of patterns of hydrothermal altered materials without prior knowledge or poor 
information on the area. 
Previous works have shown the applications of ranges of the 
spectrum in MIR (Medium Infrared) and TIR, combined with 
other sources (Nasrabadi, 2008; Cipar et al., 2011). 
1. INTRODUCTION 
Detection of spectral anomalies aims at extracting automatically 
pixels that show significant responses in relation of their 
surroundings. Several methods have been developed in the last 
decades, allowing a better understanding of the relationships 
between hyperspectral data dimensionality and the optimization 
of search procedures (Duran and Petrou, 2007; Shaum, 2005; 
Stein ef al., 2002) as well as the sub-pixel differentiation of the 
spectral mixture and its implications in anomalous responses 
(Bar et al., 2010; Eismann et al., 2009; Manolakis and Shaw, 
2002). 
In other sense, image spectrometry has proven to be efficient in 
the characterization of minerals based on statistical methods 
using specific reflection and absorption bands. Hyperspectral 
configurations in SWIR and VNIR (Visible-Near Infrared) have 
been successfully used for mapping hydrothermal alteration 
materials in different geological scenarios (Antôn-Pacheco et 
al., 2001; Crosta et al., 2003). 
An important aim in this research was to establish relationships 
that allow linking spectral anomalies with what can be called 
information anomalies and, though, identify information related 
to anomalous responses rather than simply spotting differences 
from the background. We aim at analysing the information 
obtained form detected anomalous responses. 
This work presents a multi-source approach, applied to the 
analysis of the correlations between spectral anomalies and 
hydrothermal materials in the Turrialba volcano complex, 
located in the Central Volcanic Range (Costa Rica). We analyse 
the influence of spectral resolution in the determination of the 
background, a critical aspect in the detection of anomalies. 
Results are compared with vegetation and soil indeces in an 
active volcanic environment. The increasing activity of this 
complex requires special attention and survey, because of its 
proximity to main urban areas in Costa Rica.