A Satellite Perspective on
Jökulhlaup in Greenland
location of potential jökulhlaup lakes
and
calculation of water discharges using
remote sensing techniques
Morten Larsen
M.Sc. Water and Environment
Asiaq – Greenland Survey
13-02-2012
INUTEK Nytårskur 2012
Table of contents
1. Introduction
2. Study area
3. Location of potential jökulhlaups lakes
4. Water volume assessment
5. Verification
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1. Introduction
What is a jökulhlaup?
A jökulhlaup is a very intense flood where a water reservoir releases a
large amount of water abruptly.
The water reservoir is filled by water over time and when the level
reaches a critical point the reservoir is emptied.
GeoBasis August 11th, 2009
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GeoBasis August 12th, 2009
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1. Introduction
The aim of the work:
• To develop a remote sensing method for locating potential
jökulhlaup lakes
• To develop a remote sensing method for assessing the water
volume during a jökulhlaup.
• To build up knowledge about remote sensing in Greenland
Why developing the methods?
1. Jökulhlaups influences the ecosystem
2. Jökulhlaups are a risk for human activity in downstream areas
3. Jökulhlaups affects the design and construction of hydro power
plants
4. Jökulhlaup frequency and magnitude can be used in climate
change research
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Table of contents
1. Introduction
2. Study area
3. Location of potential jökulhlaups lakes
4. Water volume assessment
5. Verification
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2. Study area
Study area 16.000 km2
Lake North
Maps by: KMS
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Hydrological station
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Lake South
Table of contents
1. Introduction
2. Study area
3. Location of potential jökulhlaups lakes
4. Water volume assessment
5. Verification
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3. Location of potential jökulhlaups
Mapping
lakes
Mapping
glaciers
Spatial
location
analysis
Potential
jökulhlaup lakes
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Mapping
surface
anomalies
3. Location of potential jökulhlaups
1st task - Mapping lakes
• Tasseled cap transformation
• Surface classified as water if the brightness
index > 0.4 and the wetness index > 0
• Multi-year observation: Time series of LANDSAT
scenes from late summers 2003-2009
• If surface is classified as water in at least 5 out
of 6 years it is mapped as water
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3. Location of potential jökulhlaups
2nd task - Mapping glaciers
• New image produced as average of
the Tasseled cap parameters in the
LANDSAT time series
• Unsupervised classification with 50
spectral classes
• Spectral classes thematically coded
into glacier ice or non-glacier ice
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3. Location of potential jökulhlaups
3rd task - Mapping surface anomalies
The NDVI anomaly is the
difference between NDVI for a
given year and mean NDVI for
all years in the LANDSAT time
series.
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3. Location of potential jökulhlaups
4th task – Spatial location analysis
Area selection Number of potential
threshold
jökulhlaups
No restriction
336
Glacier ice
50.000 m2
73
250.000 m2
20
1.000.000 m2
5
Surface anomaly
Lake
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3. Location of potential jökulhlaups
Results
Discussion
• All in all the method showed good
results
• Ice covered lakes were difficult to
classify; Two known jökulhlaups
were not selected due to this
problem
• Further development in
discriminating between glacier and
lake ice is needed
• Only jökulhlaup with great changes
in the surface area are mapped
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Table of contents
1. Introduction
2. Study area
3. Location of potential jökulhlaups lakes
4. Water volume assessment
5. Verification
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4. Water volume assessment
Developing a method only based on satellite images
Water volume difference:
water volume (before jökulhlaup)
=
water volume (after jökulhlaup)
water volume (jökulhlaup)
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The method:
• Extract a DEM from ASTER stereo
images at lowest possible water level
• Find a relation between the surface
area and the volume in the lake
• Estimate water surface areas from a
LANDSAT time series
• Calculate water volumes in the lake
from the relation
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4. Water volume assessment
DEM extracted for Lake North
August 8th, 2004
Relation between the water
surface area and the volume
1.80E+09
1.60E+09
Volume [m3]
1.40E+09
1.20E+09
1.00E+09
8.00E+08
6.00E+08
4.00E+08
2.00E+08
0.00E+00
0.00E+00
1.00E+07
2.00E+07
Area
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[m2]
3.00E+07
4.00E+07
4. Water volume assessment
The water surface area time series
LANDSAT scenes from 1999-2010
3.50E+07
3.00E+07
2.00E+07
1.50E+07
1.00E+07
5.00E+06
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2012/04/01
2010/11/18
2009/07/06
2008/02/22
2006/10/10
2005/05/28
2004/01/14
2002/09/01
2001/04/19
1999/12/06
0.00E+00
1998/07/24
Area [m2]
2.50E+07
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4. Water volume assessment
Water volumes
2.0E+09
2.0E+09
1.5E+09
1.5E+09
1.0E+09
1.0E+09
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Accumulated positive degree days
12,000
8,000
6,000
4,000
2,000
0
2012/04/01
2010/11/18
2009/07/06
2008/02/22
2006/10/10
-5.0E+08
2005/05/28
-5.0E+08
2004/01/14
0.0E+00
2002/09/01
0.0E+00
2001/04/19
5.0E+08
1999/12/06
5.0E+08
10,000
R² = 1,00
1,98 km3
1998/07/24
Lake volume [m3]
R² = 0,99
Table of contents
1. Introduction
2. Study area
3. Location of potential jökulhlaups lakes
4. Water volume assessment
5. Verification
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Hydrological station
5. Verification
Lake North
Lake South
Lake North
Lake South
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Lake South
5. Verification
ISTA water balance equation:
Q jökulhlaup * dt + Qinflow * dt = QISTA * dt + dVOLISTA
where
Q jökulhlaup is inflow from jökulhlaup [m3/s]
Qinflow is inflow from other sources [m3/s]
QISTA
is discharge out of Lake ISTA [m3/s]
t
is time [s]
VOLISTA is volume of water stored
in Lake ISTA [m3]
Qinflow
Q jökulhlaup
VOLISTA
Qinflow
QISTA
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Qinflow
5. Verification
Estimating Qinflow :
Q jökulhlaup * dt + Qinflow * dt = QISTA * dt + dVOLISTA
Inflow to Lake ISTA per month
[m3]
Qinflow is mainly from the glacier
3.5E+08
3.0E+08
Qinflow
R² = 0,95
2.5E+08
2.0E+08
1.5E+08
1.0E+08
Qinflow
5.0E+07
Qinflow
0.0E+00
0
50
100
150
200
250
300
Positive degree days per month
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5. Verification
Estimating the water volume:
Q jökulhlaup * dt + Qinflow * dt = QISTA * dt + dVOLISTA
120
Water level [m]
118
116
114
VOLISTA
112
110
108
106
104
102
0.0E+00
2.0E+08
4.0E+08
6.0E+08
8.0E+08
1.0E+09
Volume in Lake ISTA [m3]
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5. Verification
Estimating QISTA:
Q jökulhlaup * dt + Qinflow * dt = QISTA * dt + dVOLISTA
QISTA
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5. Verification
RS
Water balance
Results
Discussion
Lake North
Lake South
Lake South
September
2002
August
2003
September
2007
QISTA·dt [m3]
1,25·109
0,06·109
0,05·109
VOLISTA[m3]
0,64·109
0,24·109
0,15·109
Qinflow ·dt [m3]
0,03·109
0,02·109
0,02·109
Q jökulhlaup·dt [m3]
1,85·109
0,28·109
0,18·109
Vjökulhlaup[m3]
1,98·109
0,28·109
0,19·109
7%
0,4 %
2%
Difference
The method showed reliable results for
the two test lakes
Challenge to obtain ASTER stereo images
immediately after a jökulhlaup
Challenge to derived reliable surface
areas from LANDSAT due to ice, shadows
and clouds
The method is less accurate for lakes
with a steep bathymetry
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The project was funded by:
The Commission for Scientific Research in
Greenland
The project was carried out by:
Eva Mätzler
Asiaq
Bo Naamansen
Asiaq
Morten Larsen
Asiaq
Christian Tøttrup
GRAS
Dorthe Petersen
Asiaq
Kisser Thorsøe
Asiaq
13-02-2012
INUTEK Nytårskur 2012