Monitoring of water level variations of inundation areas ... · Study area: Pantanal 5 Pantanal...

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Monitoring of water level variations of

inundation areas within the Pantanal Wetland

Denise Dettmering, Christian Schwatke, Anne Braakmann-Folgmann, and Eva Börgens

Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM)

email: denise.dettmering@tum.de

Motivation

• Monitoring of water levels is essential for various applications, such as water resource management, disaster monitoring, …

• Monitoring of water levels in remote areas is difficult.

Satellite Altimetry is able to provide water level estimations on a global scale without ground access.

However, the temporal resolution is limited to some days or month depending on the satellite‘s orbit. The orbit also defines the spatial resolution.

• Number of freely available in-situ gauging stations is declining since 1980.

• Station distribution is inhomogeneous.

Satellite Altimetry – Measurement Principle

water level =

satellite height – (corrected) range

WL = hsat - ralt

Ellipsoid

water surface

Challenges of Inland Altimetry

Inundation areas are even more challenging than lakes and rivers due to irregular water coverage

• Altimeter footprint covers not only water but also land areas.

• This leads to land contamination of the radar echos (waveforms).

Combination of different altimeter missions in order to improve temporal and spatial resolution

Special data pre-processing necessary (retracking)

Rigorous outlier detection helpful

typical ocean returns land-contaminated returns

• Small waters and extreme events may be missed due to data resolution

Study area: Pantanal

Pantanal national park: about 15 000 km²

One of the largest wetlands worldwide; located in central South America

56.4 – 58° W

16.4 – 18° S

Landsat, April 2003

Landscape

http://ulab.cca.edu/wp-content/uploads/2012/10/pantanal-ponds1.jpg http://pompei-hotels.com/travel-and-architecture-design/Aerial-View-Of-Floodlands-In-Pantanal.jpg

http://www.unique-national-parks.com/uploads/O6/Xg/O6XgsYad6Rq2Ff_RIecV9A/Pantanal-floods.jpg http://gezimanya.com/sites/default/files/lokasyonResimleri/pantanal-a-maior-area-alagada-do-mundo.jpg

Data Coverage

56.4 – 58° W

16.4 – 18° S

Envisat (2002-2010)

Saral (2013-2015) repeats every 35 days

TOPEX (1992-2002)

Jason-1 (2002-2009) Jason-2 (2008-2015)

repeats every 10 days

• Separation of the area in small grid cells (0.1 by 0.1 degree)

106 out of 256 grid cells (~42%)

some are not usable due to topography: land or mountains

• Only part of the grid cells are covered by satellite observations

Sample time series

Grid cell: ID 504

longitude: 303.25°, latitude: -17.35°

Rio Sao Lourenco

Pass#37 of TOPEX/Jason-1/Jason-2

mean water level: 107.898 ± 0.518 m

mean formal error: 6.6 cm

Validation

Blue: altimetry

Green: in-situ (shifted)

RMSE: 27.2 cm R=0.9424

Offset=97m

Grid cell: ID 504

longitude: 303.25°, latitude: -17.35°

Rio Sao Lourenco

Pass#37 of TOPEX/Jason-1/Jason-2

In-situ gauging station within the grid cell (about 3 km from the center)

data from ANA*; starting mid 2005

* Agencia National de Aguas (http://ana.gov.br)

Animation of water level variations

Water level time series [m] 2008 – 2015

(mean value per time series subtracted)

no data for Envisat/Saral between Oct. 2010 and March 2013

Fitting of annual signal - 3 examples

Fitting an harmonic signal with fixed annual frequency in each time series

Clear annual period with

regular amplitude R = 0.9336

R = 0.8938

Clear annual period with

changing amplitude

R = 0.5154

Annual behavior hardly detectable;

only occasional flooding

Fitting of annual signal - correlations

correlation R between signal and annual fit

Annual signal is able to represent the signal for most parts of the area

Fitting an harmonic signal with fixed annual frequency in each time series

#106 grid cells covered by observations in the central part of the Pantanal national park

#82 grid cells with correlation coefficient R.>.0.7 (77%)

Amplitude and Phases of annual signal

estimated amplitudes [m] month of maximum water level

82 grid cells in the central part of the Pantanal national park

only signals with correlation coefficient R > 0.7

Rio Paraguay

Rio Canabu Rio Sao Lourenco

Larger amplitudes in rivers and its surroundings

Shift of the water maximum from north to south

Conclusions

• Satellite Altimetry provides reliable water level time series for wetlands and can help to monitor remote areas in ungauged basins.

• Absolut physical heights with dm-accuracy are available for a maximum time period of more than 20 years (depending on satellite mission).

• Due to the sparse spatial resolution a complete acquisition/coverage of the Pantanal region is not possible

• Most of the area show clear annual signals with maximal amplitude of about 1.5 m.

• The month of maximum amplitude varies between March (North-East) and June (South-West).

• Water level time series from satellite altimetry for different inland water bodies are available via DAHITI.

DAHITI

• DGFI-TUM provides water level time series for inland water bodies via web interface

• Database for Hydrological Time Series of Inland Water (DAHITI)

• Easy access to about 260 inland water targets (lakes and rivers)

http://dahiti.dgfi.tum.de

Monitoring of water level variations of inundation areas ... · Study area: Pantanal 5 Pantanal...

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