sar interferometry and gps studies at guagua

European Geophysical Society, Nice, March 2001
SAR INTERFEROMETRY AND GPS STUDIES AT GUAGUA-PICHINCHA AND COTOPAXI VOLCANOES (ECUADOR)
S. Bonvalot (1,2), G. Gabalda (1), D. Rémy (1), P. Briole (2), J.-L. Froger (3), P. Mothes (4), P. Hall (4), G. Lopez (5)
(1)
IRD (Institut de Recherche pour le Développement),(2) Institut de Physique du Globe de Paris, (3) UBP Clermont-Ferrand, (4) Instituto Geofisico, EPN, Quito, (5) Aeromapa, Quito
[email protected]
Objectives
Technical data overview
20˚N
SAR data acquisition and processing
15˚N
Quito
SAR (Synthetic Aperture Radar) interferometry and
GPS techniques have been combined on two stratovolcanoes in Ecuador with the following objectives :
10˚N
0˚
5˚S
10˚S
15˚S
(1) to evaluate the potentialities of using
interferometric data for ground deformation
studies in remote or dangerous areas where
geodetic networks cannot be easily maintained
due to the rough field conditions (large volcanoes,
high elevation, vegetation, access difficulties),
20˚S
85˚W
80˚W
75˚W
70˚W
65˚W
60˚W
55˚W
GPS data acquisition and processing
Equipment :
12 channels dual frequency receivers with full wavelength
data (Ashtech Z12 receivers).
Field procedures :
Pichincha (4785 m) : Landsat satellite image drapped over topography showing the
dense vegetation on the western side of the volcano (green areas) and the proximity
of Quito urban area.
(1) static measurements (sampling rate 30 sec) using 3
to 4 receivers simultaneously during sessions of few hours
to few days according with the baseline characteristics and
the required accuracy (max baseline length 17 km).
(3) to validate on these volcanoes protocols for
GPS data acquisition and processing (static
and kinematic measurements) that could improve
the volcano monitoring tasks.
(3) base stations : at least two fixed base stations were
operated during the whole survey. The main reference is the
permanent GPS station located in Quito (2923 m) and operated by NIMA (USA) and IGM (Ecuador).
Processing procedures :
Digital topography database
Software : Bernese 4.0, Gamit 9.9, WinPrism 2.1,
Geogenius
Digital topographic map of the Ecuatorian Andes in the area
of Quito obtained from map digitization (1/50000 scale) by
IRD and Municipio of Quito (Souris et al.). The D.E.M. with horizontal resolution 30 m has been used to remove topography
contribution from SAR interferograms
ITRF Solutions : computed from IGS stations (Kourou, Galapagos, Arequipa, Bogota) and precise orbits data.
4600
5
4400
2
7
8
00
9
10
Figure 4 : Example of DEM inaccuracies
on Cotopaxi as revealed by interferometry
data.
4a : 1 month ERS interferogram.
4b : DEM used for topographic correction.
4c : high resolution interferometric DEM
SAR interferometry data
767
769
Latitude (mm)
10
10
5
5
0
0
-5
-5
-10
-10
-10
0
4
2
4
2
0
2
-2
-4
GT
9
6
08
08
08
5
7
0
-2
-4
3
0
-2
-4
BE
4
4
2
0
-4
4
2
0
TMP
40
BOS
SN2
SN3
SN4
SN5
LAG
MAR
-0.65
REF
NAS
107
106
011
010
00
LOM
SN1
4000
-0.70
4000
VC1
HIE
TBO
MUR
4000
4000
4000
00
40
-0.75
ASH
40
00
-0.80
40
-78.55
-78.50
Figure 2d : interferogram orbits 12633-13635
Period : 97/09/19 97/11/28
Altitude of ambiguity : 55 m
-78.45
-78.40
LONGITUDE (degres)
-78.35
COTOPAXI GPS NETWORK
Figure 6b :
COMPARISON OF VARIOUS SURVEYS
USGS (11/1993)
IRD (11/1996)
reference
IRD (03/2000)
LATITUDE (sec)
0.004
0.003
0.002
0.001
0.000
-0.001
-0.002
-0.003
-0.004
BO
S0
NA
S1
RE
F0
VC
10
MA
R0
NA
S0
TM
P0
LA
G0
SN
O2
TB
O0
HIE
0
LO
M0
SN
O3
SN
O5
SN
O1
SN
O4
LA
T0
AS
H0
MU
R0
Figure 4b : Digital Elevation Model of Cotopaxi
generated from 1/50000 map digitisation and
used in this study (IRD & Municipio Quito)
LONGITUDE (sec)
0.004
0.003
0.002
0.001
0.000
-0.001
-0.002
-0.003
-0.004
250
200
09918
BO
S0
NA
S1
RE
F0
VC
10
MA
R0
NA
S0
TM
P0
LA
G0
SN
O2
TB
O0
HIE
0
LO
M0
SN
O3
SN
O5
SN
O1
SN
O4
LA
T0
AS
H0
MU
R0
12633
100
Apr97
S ep98
Figure 1 : Dataset of ERS images used in this study
(acquisition date versus perpendicular baseline in meter)
The color of the line indicates the quality of the computed
interferogram (red-yellow-green-blue from very good to
poorly coherent interferograms)
Figure 3 :Collective mask of coherence on Cotopaxi computed from the whole dataset of interferograms (see figure
1). The red and yellow pixels inicate the pixels where the
coherence is mainained over 4 years (i.e. below the ice
cap and along the lahar deposit areas).
Guagua Pichincha
SAR interferometry
(10/1992–01/2000)
Cotopaxi
(05/1992–05/1997)
ERS availability
poor (1992-2000)
poor (1992-1997)
Spatial coherence
limited (eastern flank, summit)
quite good (below ice cap, lahars)
39
Figure 4c : Digital Elevation Model produced
by radar interferometry (NASA Topography Mission, Space Shuttle, march 2000)
Conclusions
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
-0.20
71
m
38
07 B O S
m
0
48
68 N A S
m
1
41
03 R E F
m
0
37
12 V C 1
m
0
MA
38
06
R
m
0
38
04 N A S
m
0
38
94 TM P
m
0
41
04 LA G
m
0
40
08 SN O
m
2
44
T
32 B O
m
0
38
95 HIE
m
0
42
L
52 O M
m
0
46
19 SN O
m
3
39
60 SN O
m
5
43
96 SN O
m
1
29
41 SN O
m
4
40
59 LA T
m
0
45
47 A SH
m
0
MU
R0
Dec95
ALTITUDE (m)
Figure 5 : Static and kinematics GPS measurements
on Cotopaxi (surveys 1996 and 2000).
The kinematics surveys have been tested for rapid
network control.
50
J ul94
STATIONS
Acknowledgments
We thank :
S. Arceniegas (IGM, Quito), D. Chase and J. Tomasovich (NIMA, USA), C. DeMets (Univ. Madison, USA) for
providing us the GPS data of the Quito permanent station,
Temporal coherence 6 months
up to few years (lahars deposits)
E. Reyes, J. Zamora (CLIRSEN Quito) and E. Lascano (CLIRSEN Cotopaxi) for their help in the ERS data
selection,
Observed changes
no significant (10/1992–01/2000)
none (05/1992-05/1997)
M. Souris and B. Lortic (IRD) for providing us the D.E.M. of Ecuador,
Potentialities
short term deformations
short to mid terms deformations
F. Bondoux, F. Khan, C. Luro, J.P. Metaxian (IRD) and J. Stix (Univ. Montreal) for their assitance in the GPS
field works,
GPS data
(11/1998–03/2000)
Network / Baseline
26 stations (since 1998)
Network accuracy
Static (1 to 3 cm)
Kinematics controls (2 to 5 cm)
Observed changes
Below network accuracy
< 2 cm (horiz), < 5 cm (vert.)
(11/1996–03/2000)
18 stations (since 1996)
Static (1 to 3 cm)
Kinematics controls (2 to 5 cm)
Below network accuracy
< 2 cm (horiz), < 5 cm (vert.)
WP
5
-5
-0.60
300
04407
Mar93
10
2
4000
Phase variations
0
Oct91
-4
Levelling benchmarks : IGM (1961-1992)
EDM Baseline (EPN ground deformation network)
We show on Figure 6b a comparison of the adjusted coordinates of the 4 sites determined by USGS during the
1993 survey (J. Ewert, USGS, communication) and reoccupied during our 1996 survey. Comparison between the
1996 adjusted coordinates (reference) and those determined by kinematics surveys are also reported. The consistency between the data sets indicates that (1) no ground
deformation occurred since 1993 (2) that kinematics survey
can be successfully used for rapid network control on
Cotopaxi.
Figure 4a : Interferogram orbits 12132-12633
Period : 97/08/15 - 97/09/19
Altitude of ambiguity : 44 m
13635
-2
-4
GPS surveys : USGS/EPN (11/1993)
GPS surveys : IRD/EPN (11/1996)
GPS surveys : IRD/EPN (03/2000)
The first GPS survey has been carried out by USGS (John
Ewert) in 11/1993 (4 stations). In 11/1996, we reoccupied
the USGS sites and installed 14 new sites distributed from
the base of the volcano to the ice cap (4850 m) as shown
on Figure 6a. A short control survey has been realized in
03/2000 using kinematics measurements.
Figure 2b : interferogram orbits 09918-12633
Period : 93/06/08 - 97/09/19
Altitude of ambiguity : 44 m
12132
-2
-4
COTOPAXI GPS NETWORK
0
-p/2
Results
Figure 2c : interferogram orbits 12132-13635
Period : 97/08/15 - 97/11/28
Altitude of ambiguity : 211 m
0
-2
-2
Figure 6a :
p/2
p
Field surveys
Using the whole dataset of interferograms, we computed a
collective mask of coherence (Figure 3). Such mask points
out the areas where SAR interferometry might be successfully used for ground deformation studies over several years.
4
2
0
-4
Coherence analysis
150
Longitude (mm)
We present on figure 9b the results of
repeated kinematics measurements in
the summit area. It can be noted that the
rim of the caldera has not been affected
by significant horizontal change during
the last period of activity.
GPS data
Figure 2a : interferogram orbits 09918-13635
Period : 93/06/08 - 97/11/28
Altitude of ambiguity : -63 m
-4
4
2
0
-2
5 ERS-1 and ERS-2 images (descending orbits) ranged
between 1992 and 1997 (Figure 1). Only interferograms with
altitude of ambiguity greater than 40 m are considered.
2 types of phase variations can be identified from this dataset : (1) an E-W phase variation (Figure 2c) assumed as a
tropospheric effect (related with local distinct meteorological
pattern between amazonian and inter-Andean influences),
(2) high frequency signals related with DEM inaccuracies
(Figures 4a to 4c).
768
LONGITUDE (km)
Dataset
As evidenced on the computed interferograms (Figure 2a to
2d), the coherent areas are limited to the lower part of the
volcano, below the ice cap (i.e. from 3000 to 4900 m). It can
be noted that lahar deposits area remain coherent over long
periods of time.
-4
4
4000
Application to Cotopaxi volcano
-4
009
5b : after october 1999
11
766
0
-2
008
Figure 5 : Stack of images of radar amplitude
before (5a) and after (5b) the eruption
of october 1999.
6d : orbits 44101-24428
(99/12/21-99/12/22, 47 m)
2000-1998
4
2
0
-2
007
6c : orbits 20053-24929
(95/05/16-00/01/26, 152 m)
Figure 6 : Examples of interferogram on the actiive
caldera computed for various periods between 07/1993
and 01/2000. 6a and 6b are 2 years and 1 month
interferograms before the last magmatic reactivation.
6c is a 5 years interferogram encompassing the whole
period of activity. 6d is a tandem interferogram acquired
after the october 1999 eruption.
2000
4
2
0
Figure 9b :
Results of the kinematic survey around the caldera
(1998-2000). See station number on map figure 7b.
Results of kinematic surveys
in caldera area (11/1998 to 03/2000)
REF1
44
9980
1998
4
2
106
3
Figure 9a :
Results of data processing for
Quito-REF1 baseline (1998-2000)
-2
2
107
00
9981
5a : before october 1999
(2) no significant change affected the
REF1 position within 11/1998 and
03/2000.
4600
44
LATITUDE (cm)
(1) The
solutions
of
baseline
measurements obtained with various
software are consistent within +/- 3cm
(horiz.) and +/- 5 cm (vert.).
9982
6b : orbits 20053-20554
(95/05/16-95/06/20, 1467 m)
Vertical (mm)
LATITUDE (km)
Kinematic GPS survey (caldera)
Static measurements
6a : orbits 8186-20554
(93/07/02-95/06/20, -148 m)
Despite of the very low coherence level of the interferograms, we analysed detailed images on the caldera area to evaluate the potentialities of SAR data
for measuring topographic changes related with the
recent activity. To enhance possible changes, we
present here stacked images of amplitude and a series
of interferograms acquired before and after the main
eruption (October 1999). Changes in the dome morphology and enlargement of the crater are visible (see
Figures 4, 5a, 5b). Detailed interferograms (Figure 6)
show that no large scale deformation affected the volcano before and during the recent volcanic crisis. This
result is consistent with the results of the GPS measurements realized during 1998-2000.
350
We show on figure 9a the results of the
determination of the QUITO-REF1 baseline over several days in 1998 and 2000
and the measured changes between the
two epochs.
Kinematic measurements
The recent volcanic activity on Guagua-Pichincha is
concentrated in the summit caldera. The last reactivation, started during summer 1998 is characterized
by repetitive dome growth and destruction accompanied by explosions of various magnitude. A paroxysmal explosion occurred in October 1999 producing
partial dome destruction and ash fall over Quito.
400
Results for QUITO-REF1 baseline
(11/1998 to 03/2000)
1
Figure 7b
Figure 2d : interferogram orbits 44101-21428
Period : 99/12/21 - 99/12/22
Altitude of ambiguity : 125 m
WIN PRISM (WP)
GEO GENIUS
30
Figure 2c : interferogram orbits 20053-20554
Period : 95/05/16 - 95/06/20
Altitude of ambiguity : 1467 m
Temporal evolution and detailed imaging
of the caldera
BERNESE (BE)
30
Figure 1 : Dataset of ERS images used in this study (acquisition date
versus perpendicular baseline in meter). The color of the line indicates the quality of the computed interferogram (red-yellow-green-blue
from very good to poorly coherent interferograms)
1999
COMPARISON OF VARIOUS SURVEYS
GAMIT (GT)
30
May01
1998
PICHINCHA GPS NETWORK
005
J an00
5 : Rate = 3.3+/- 0.5 mm/yr : WRMS = 13.4 mm
1997
DeMets/UW-Madison
780
003
S ep98
LONGITUDE (km)
# Outliers =
0
Apr 16 19:29
00
Apr97
775
5 : Rate = 2.8+/- 0.3 mm/yr : WRMS = 8.6 mm
50
Dec95
LATITUDE (km)
J ul94
770
LONGITUDE (cm)
Figure 4 : View of the caldera
and the active dome
20053
20554
08186
765
# Outliers =
0
40
06683
Mar93
760
5 : Rate = 11.5+/- 0.2 mm/yr : WRMS = 5.8 mm
30
1996
9970
755
# Outliers =
20
-30
GMT
LATITUDE (degres)
0
A permanent GPS station located in Quito and operated by NIMA (Figures 7a, 8) has been used as a reference site for the GPS static surveys. The kinematic
surveys in the summit area were realized from REF1
reference station (Figure 7b).
4061
CIN1
ALTITUDE (cm)
24929
SFO1
SJO1
9975
BASELINE (cm)
44101
100
42
00
200
3000
8
300
10
-20
CRZ1/CRZ2
7
24428
400
4000
29
500
REF1
29
18917
21422
600
20
002
16412
700
00
30
9980
A total number of 34 stations have been determined
(21 in the summit area on the eastern side of the
active crater). The western part of the volcano has
not been investigated due to the bad field conditions
(absence of access path, dense vegetation) that would
require high difficulties for network installation and reiteration. For same reasons, other monitoring networks
(seismic stations, tiltmeters, EDM bases, etc.) are also
deployed only on the eastern part of the volcano.
30
0
LATITUDE (cm)
Figure 3 : Collective masque of coherence
on Quito area computed from the best
interfergrams (see figure 1). The red and
yellow pixels indicate the pixels where
the coherence is maintained up to 6
months
9985
TNK1
LONGITUDE (cm)
Figure 2b : interferogram orbits 06683-08186
Period : 92/10/25 - 93/02/07
Altitude of ambiguity : 84 m
40
-10
3000
3000
Figure 2a : interferogram orbits 20053-24429
Period : 95/06/20 - 00/01/26
Altitude of ambiguity : 200 m
LUL1
00
30
9990
The network contains reference stations out of the
active zone (few kilometers away) and a series of stations distributed around the crater area (Figures 7a,
7b). In addition, existing benchmarks from the national
geodetic network (IGM) or from the geophysical monitoring network have been also included (ex : seismic
and tiltmeter stations, base sites for EDM measurements, etc.).
QITO Coordinate changes
50
FAN1
00
30
2000
3000
800
200
Oct91
00
30
9995
Network design
As evidenced on the computed interferograms (see
Figures 2a to 2d), the coherent areas are limited to
the eastern side of the volcano and on the urban area
of Quito. Intense vegetation in western part explains
the absence of coherence.
100
10000
A first GPS survey has been carried out in October
1998, consecutively to the reactivation of the volcano.
The network has been complemented during 1999
(EPN, Aeromapa) and controlled in March 2000.
3000
Coherence analysis
Surveys
3000
Quito
Kinematic measurements
RE
F1
Pichincha volcano
-p/2
12 ERS-1 and ERS-2 images (10 descending, 2
ascending) ranged between 10.1992 and 01.2000
(Figure 1). Only interferograms with altitude of ambiguity greater than 40 m are considered.
Figure 8 :
Data from the Quito permanent GPS station
1996-1999 (C. DeMets, personal communication).
This station operated by NIMA (USA) and IGM
(Ecuador) is used as reference station for the
Pichincha GPS network).
Static measurements
00
Dataset
0
4000
p
Quito permament station (NIMA/IGM)
GPS data
p/2
Using the best coherent interferograms, we computed
a collective mask of coherence over 6 months (Figure
3). Such mask points out the areas where SAR interferometry might be successfully used for ground deformation studies (i.e. eastern flank of the volcano and
summit area).
Pichincha GPS network
Figure 7a
SAR interferometry data
08
Application to Pichincha volcano
4000
Cotopaxi (5911 m) : Spot satellite image drapped over topography showing
the permanent ice cap (from 4900 m) and the main lahar deposit areas.
30
The two selected volcanoes [Guagua Pichincha,
4785 m and Cotopaxi, 5911 m] are located in the
vicinity of the capital Quito (1,5 Million Inhab.). Both of
them have been very active in the historical times, but
only the Guagua-Pichincha has undergone eruptive
activity within the last decades (repetitive dome
growth and destruction). They are also representative
of South American strato-volcanoes that constitute
extreme cases for SAR interferometry applications
(steep slopes, variable vegetation, possible ice cap,
etc.).
(2) pseudo-static and kinematic measurements (sampling
rate 3 sec) acquired for sessions up to 15 minutes (pseudostatic) in the range of few km away from a reference station
(typically within 2 km)
00
(2) to set up precise GPS repetition networks
and determine baseline measurements between
stable and active areas to better characterize
possible ground deformations induced by the
volcanic activity,
The differential interferograms have been generated from
ERS-1 and ERS-2 data using Diapason software (Cnes).
The datasets have been selected in order to compute interferograms from various time periods (from several years to
one day) for coherence analysis between 1992 to 2000.
5˚N
P. Lebellegard and S. Calmant (IRD, Noumea) for their contribution to the data processing with Bernese,
GDR INSAR, N. Pourthié (Cnes) and F. Beauducel (IPG Paris) for their help in SAR data analysis,
ERS images have been acquired from SPOT Image, Eurimage and Clirsen agencies
This study was supported by IRD (DME) and INSU (PNRN)
00
-78.30