In this paper we show the applicability of orbital Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) with multiple images for  terrain deformation episodes monitoring. This paper is focused on the Coherent Pixels Technique (CPT). This technique has been tested with ERS SAR and ENVISAT ASAR data for the period 1992-2008 from 

The Itoiz and Yesa reservoirs. These ones, located in Navarra, northern Spain, are constructed gravity dams 

that stores the water from the Irati and the Urrobi rivers, 

and the Aragón river respectively. The results has been 

compared with theoretical results obtained using an 

analytical model

Arjona, Alicia

Fernández, Jose

Luzón, F.

Mallorquí, J.

Monells, D.

Pallero, Jose L. G.

Prieto Morin, Juan Francisco

Prieto, E.

Santoyo, M.A.

Seco, Andrés

In this paper we show the applicability of orbital Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) with multiple images for terrain deformation episodes monitoring. This paper is focused on the Coherent Pixels Technique (CPT). This technique has been tested with ERS SAR and ENVISAT ASAR data for the period 1992-2008 from The Itoiz and Yesa reservoirs. These ones, located in Navarra, northern Spain, are constructed gravity dams that stores the water from the Irati and the Urrobi rivers, and the Aragón river respectively. The results has been compared with theoretical results obtained using an analytical model

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On the applicability of an advanced DInSAR techniques near Itoiz and Yesa reservoirs, Navarra, Spain

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

 ON THE APPLICABILITY OF AN ADVANCED DINSAR  TECHNIQUE 
NEAR ITOIZ AND YESA RESERVOIRS, NAVARRA, SPAIN. 
 
Arjona, A.(1), Santoyo, M.A.(1), Fernández, J.(1), Monells, D.(2), Prieto, J.F.(3), 
Pallero, J.L.G-(1), Prieto, E.(4), Seco, A.(4), Luzón, F.(5), Mallorquí, J.(2) 
 
(1) Instituto de Astronomía y Geodesia (CSIC-UCM), Plaza de Ciencias 3, 28040-Madrid, Spain. 
Email: jft@mat.ucm.es, alicia_arjona@mat.ucm.es, msantoyo@ual.es. 
(2) Universitat Politècnica de Catalunya, Departament de Teoria del Senyal i Comunicacions. 
D3 - Campus Nord, UPC, Barcelona, Spain, Email: dmonells@yahoo.es, mallorqui@tsc.upc.edu. 
(3) Departamento de Ingeniería Topográfica y Cartografıa, ETSI Topografıa, Geodesia y Cartografıa, 
UPM, Km 7.5 Autovıa de Valencia, E-28031 Madrid, Spain. 
(4) Universidad Pública de Navarra, Campus de Arrosadía s/n 31006,  Pamplona, Navarra, Spain, 
Email: andres.seco@unavarra.es, epc@unavarra.es. 
(5) Departamento de Física Aplicada, Universidad de Almería, Cañada San Urbano S/N, 04120 Almería, 
Spain, Email: fluzon@ual.es. 
 
 
 
ABSTRACT 
In this paper we show the applicability of orbital 
Synthetic Aperture Radar (SAR) Differential 
Interferometry (DInSAR) with multiple images for 
terrain deformation episodes monitoring. This paper is 
focused on the Coherent Pixels Technique (CPT). This 
technique has been tested with ERS SAR and 
ENVISAT ASAR data for the period 1992-2008 from 
The Itoiz and Yesa reservoirs. These ones, located in 
Navarra, northern Spain, are constructed gravity dams 
that stores the water from the Irati and the Urrobi rivers, 
and the Aragón river respectively. The results has been 
compared with theoretical results obtained using an 
analytical model. 
 
1. INTRODUCTION 
The Itoiz reservoir, located in Navarra, northern Spain, 
is a newly constructed gravity dam that stores the water 
from the Irati and the Urrobi rivers. The dam has a total 
height of 121 m, a total length of 525 m and a maximum 
water storage volume of 410 hm3. Moreover, as Yesa 
reservoir is included into the Itoiz’s scene we have 
considered a good opportunity to study this region. The 
Yesa reservoir drains an area of 2.181 km2 in the upper 
Aragón river closed to Itoiz reservoir. See [3], [7] and 
[8] for more details and Fig.1. 
Satellite Radar Interferometry (InSAR) has 
been proven to be a useful and powerful tool in tectonic 
areas for surveying subtle surface deformations over 
several years related to geodynamic phenomena. An 
advanced DInSAR observation technique, called the 
Coherent Pixel Technique (CPT) [2, 4 ,6], is being 
applied to study the existence of deformation areas in 
order to obtain mean velocities and time series of 
deformation.  
We have studied the applicability of this 
technique to study the surface displacement field during 
the impoundment of the Itoiz water reservoir, and 
possible displacements in the surrounding of Yesa’s 
dam. Specifically, we focus on the analysis of the 
stability of the left slope of the Itoiz and Yesa water 
reservoirs. See [3] for more details. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 1. Situation of the Itoiz and Yesa water 
reservoirs. 
 
 In both of the studies the stacks used are 
composed by ENVISAT and ERS descending and 
ascending images concerning to the 2003-2008, and 
1992-2008 periods respectively. We compare the 
observation results with an analytical model. Surface 
_____________________________________________________ 
Proc. ‘Fringe 2009 Workshop’, Frascati, Italy, 
30 November – 4 December 2009 (ESA SP-677, March 2010) 
 water loads and the associated displacements are 
computed by means of the Boussinesq solution for a 
vertical pixel load on a homogeneous elastic half-space.  
 
2. APPLIED METHODS  
2.1 The Coherent Pixel Technique 
 
We have applied an advanced DInSAR algorithm 
known as the Coherent Pixel Technique (see [2], [4] and 
[6]) in order to obtain deformation nearby Itoiz and 
Yesa water reservoir. To obtain DInSAR deformation 
maps, with both linear and non-linear terms of 
deformation, we have followed the procedure described 
in Fig. 2.  
 
Figure 2. Block diagram for the linear (PRISAR) and 
non-linear (SUBSOFT) parts of CPT (see [2]). 
 
We start with images focused from raw data. 
Using PRISAR software, we carry out the co-
registration between each image to obtain 
interferometric phase. Both satellite orbits and Digital 
Elevation Model are used in order to generate 
differential interferograms. The result will be linear 
deformation maps from a set of low resolution 
interferograms (multi-looked) after estimating the DEM 
errors and the atmospheric artefacts.  
With advanced DInSAR we will have more 
information from interferograms. For example by 
requesting a threshold so that the baseline from couple 
of images do not exceed a given value. This part of 
processing is carried out by SUBSOFT software. The 
selection criterion of the pixels to be processed is based 
on their coherence stability. This selection is related to a 
Delaunay triangulation. All this information is used to 
calculate the non-linear component of movement and 
the atmospheric artefacts by means of spatial low pass 
filtering and temporal high pass filtering. For this last 
step we apply the Single Value Decomposition (SVD) 
method for interferograms unwrapping. 
 
2.2   Water load 
 
On the other hand, surface water loads evolution is 
computed based on the Time Histories of the Lake 
Levels (THLL) and on the Digital Elevation Model 
(DEM) of the zone. THLL covers the period between 
19/1/2004 to 10/5/2008 with a daily sampling rate. The 
combination of these two data sets gives us an 
opportunity to perform a highly accurate estimation of 
the evolution of the water loads and the space 
distribution in time, due to the relatively high spatial 
sampling rate of elevations in the DEM (25m x 25m). 
Surface deformations due to the evolution of water 
loads are computed for a homogeneous elastic 
halfspace. The surface vertical forces can be expressed 
by means of F(x,y,t) = ρgsh(x,y,t) where ρ is the water 
density, g is the gravity aceleration, s is the area of the 
spatial sampling rate from a digital elevation model of 
Itoiz area and h(x,y,t) is the water column height that 
depends on the spatial location at surface (x,y) and the 
time t during the reservoir impoundment (see [1] and 
[9]). Given the deformation due to a surface pixel load, 
the total contribution of the entire lake water loads is 
computed by the sum of subsurface deformations due to 
the two dimensional array of forces of the lake. The 
time varying deformations due to the time varying 
reservoir loads, are then obtained by the computation of 
deformations due to the lake water level at a given time. 
 
3. RESULTS 
3.1   Itoiz results from ascending images 
  
We do not have a good coherence (see Fig. 3) so the 
number of interferograms is less than the number of 
images. For this reason, the triangulation between pixels 
(see Fig. 3) do not allows us to obtain pixels on the right 
side of the dam. Pixels with a coherence greater than 
0.25 in more than 45% of the interferograms are chosen. 
These are meshed using Delaunay triangulations, with 
arcs no longer than 2000 m. Close to the dam LOS 
displacements lower than ± 8 cm in 12 years are 
measured. (see Fig. 4 and 5)  
 
 
 
 
 
 
 
Figure 3. Amplitud image, selected pixels using the 
coherence criterion and Delaunay triangulations of 
study area (red square). Line colour indicates for the 
quality of the relationship between neighbouring pixels. 
Darker colour means higher quality. 
  
Figure 4. Deformation map. Darker colour means 
positive  and softer colour means negative LOS velocity 
of displacements. 
 
A 
 
B 
 
C 
 
Figure 5. Time serie of A-C pixels. ERS data dates 
in red. ENVISAT data dates in blue. 
 
3.2   Itoiz results from descending images 
 
In this case we only have obtained good interferogram 
from ENVISAT images, with similar processing 
parameters of ascending processing. Five different 
pixels (A-E) have been selected in order to represent 
their temporal deformation series (see Fig. 7 and 8). We 
obtain better coherence so triangulation between pixels 
(see Fig. 6) allow us to obtain some pixels on the slope 
left of the dam. The pixels show a slight LOS 
displacement or stability.  
 
 
 
 
 
 
 
Figure 6. Amplitud image, selected pixels using the 
coherence criterion and Delaunay triangulations of 
study area (red square). Line colour indicates for the 
quality of the relationship between neighbouring pixels. 
Darker colour means higher quality. 
 
 
 
 
Figure 7. Deformation map. Darker colour means 
positive  and softer colour means negative LOS velocity 
of displacements. 
 
A 
 
B 
 
C 
 
D 
 
E 
 
Figure 8. Time serie of A-E pixels. ENVISAT data dates. 
 
 3.3        Yesa results 
 
For the two ascending processing of Yesa we do 
not have a good coherence so triangulation between 
pixels do not allows us to connect pixels. As in the 
Itoiz processing, we do not obtain more 
interferograms than images due to the low 
coherence in the area. 
For descending processing coherence is 
better, and considering pixels with a coherence 
greater than 0.25, more than 45% of the 
interferograms are chosen. These are meshed using 
Delaunay triangulations, with arcs no longer than 
2000 m. 
 
 
 
 
 
 
 
 
 
Figure 9. Amplitud image, selected pixels using the 
coherence criterion and Delaunay triangulations of 
study area (red squares). Line colour indicates for 
the quality of the relationship between 
neighbouring pixels. Darker colour means higher 
quality. 
 
Eight different pixels (A-H) have been selected 
in order to represent their temporal deformation series 
(see Fig. 11). Some pixels show a maximum LOS 
displacement of around -12 cm in 15 years. 
 
Figure 10. Deformation map of two interesting areas of 
Yesa. Darker colour means positive  and softer colour 
means negative LOS velocity of displacements. 
 
 
 
3.4  Water loads: Itoiz 
 
For the computation of elastic displacement we assume 
a Poisson’s ratio of υ=0.27 and a Young Modulus of 
0.90 Mbar. Fig. 12 shows vertical displacement 
(positive downward) at four different times.  
 
 
Figure 11. Time series of A-E pixels. ERS data dates in 
red. ENVISAT data dates in blue. 
 
a)                                               b) 
 
 
c)                                               d) 
 
 
 
 
 
 
A 
 
E 
 
B 
 
F 
 
C 
 
G 
 
D 
 
H 
 
Figure 12.  Vertical surface elastic displacements due to 
water loads (cm). a) 18/09/2004 (earthquake 
mainshock, Mw=4.7); b) 01/06/2006, c) 01/07/2007, d) 
18/04/2008 (maximum capacity), (see [1]). 
 
 
4. CONCLUSIONS 
We have obtained some results by means of the 
advanced radar interferometry Coherent Pixel 
Technique in order to study the possible deformations in 
Itoiz and Yesa water reservoir nearby. For this purpose, 
 we have used a set formed by ENVISAT and ERS 
ascending and descending images from 1992-2008 
period. The DInSAR technique cannot estimate 
deformation in a complete way within the surrounding 
of Itoiz and Yesa dam due to existing vegetation, the 
low coherence found, layover, foreshortening and 
shadowing effects. But, despite those problems some 
interesting results have been obtained.  
For ascending images from Itoiz, we have 
processed ENVISAT and ERS images from the 1996-
2008 period. We get 56 interferograms from 54 images 
in order to obtain the deformation map. The results 
show slight deformation; a maximum deformation of 3 
cm/year. The pixel closer to dam has a maximum 
subsidence of around 7 cm in 12 years. We cannot 
obtain coherence pixels on the slope left of the dam. 
Concerning descending images from Itoiz, we only have 
used ENVISAT images from 2004-2007 period due to 
the absence of good interferograms using whole stack of 
images. Measured displacements are located in the left 
slope of the Itoiz reservoir showing a maximun 
subsidence of about 4 cm in 3 years.   
 After processing ascending images from Yesa 
we show the impossibility to obtain good interferograms 
despite of the large number of images.  Concerning to 
descending radar images processing from Yesa we 
obtain some results for the 1992-2009 period. Mainly 
subsidences with a maximum magnitude between 6 and 
15 cm in the 15 years period studied.  
On the other hand, theoretical vertical 
displacements in the vicinity of the Itoiz dam has 
maximum values of about 1.0 cm, occurring when the 
dam is at its maximum capacity and near and around the 
lake, as expected. The maximum value of deformations 
of the DInSAR results is about the same order of 
magnitude as the maximum displacements obtained by 
the theoretical elastic analysis.  
Concluding, the results for Itoiz show a clear 
need of installing corner reflectors which will allow 
having control pixels in order to improve displacements 
detection capability. The installation of these corners 
have been done during August 2009. They are located in 
the surroundings of the Itoiz dam (see Fig. 13). 
A complementary GPS observation network is 
going to be carried out around Itoiz dam area.  GPS 
allows us to obtain 3D deformations continuous in time, 
but only with a few surface pixels, so both techniques 
could be combined in order to get better spatio-temporal 
resolution of the areas. More detailed CPT-DInSAR 
processing and combination of ascending and 
descending results and a more in depth comparison 
between observational and theoretical results will be 
done in the near future with the new necessary images. 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 13. Corner reflectors installed in Itoiz. 
 
 
ACKNOWLEDGMENTS 
 
This work has been mainly supported by the “Advanced 
studies in the Itoiz reservoir: analysis and modeling of 
natural and induced processes.” (115/SGTB/2007/8.1) 
funded by the “Ministerio de Medio Ambiente y Medio 
Rural y Marino” of Spain, and the ESA Category-1 
project 5284 “Landslides and deformationmonitoring 
nearby Itoiz and Yesa water reservoirs by means of 
Advance Radar Interferometry”. It has been also 
partially supported by the GEOMOD (CGL2005-05500-
C02) and PEL2G (CGL2008-06426-C02/BTE) research 
projects funded by the Spanish Ministry of Science and 
Innovation. 
 
 
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On the applicability of an advanced DInSAR techniques near Itoiz and Yesa reservoirs, Navarra, Spain

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