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River and Lake Water Level Monitoring in Africa. Philippa Berry De Montfort University, UK & J é r ô me Benveniste European Space Agency . Overview. Radar Altimetry Missions ERS-1 ERS-2 ENVISAT Retracking Waveform sequence over Africa Near Real Time Pilot Demonstration

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River and lake water level monitoring in africa l.jpg

River and Lake Water Level Monitoring in Africa

Philippa Berry

De Montfort University, UK

&

Jérôme Benveniste

European Space Agency

Tiger Workshop 2006 - Cape Town


Overview l.jpg
Overview

  • Radar Altimetry Missions

    • ERS-1

    • ERS-2

    • ENVISAT

  • Retracking

    • Waveform sequence over Africa

  • Near Real Time Pilot Demonstration

    • Geographical River and Lake masks

    • Validation against river gauges

    • Validation against SGDR

  • Capabilities and limitations

    • Examples over lakes

    • Examples over rivers

  • The Envisat Radar Altimeter Ultra Stable Oscillator Correction

  • Discussion

Tiger Workshop 2006 - Cape Town


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ESA RA-1 & RA-2

  • ERS-2 long time series at 35 days sampling

  • Envisat continues time series, also additional mode allows terrain to be sampled even over mountains.

  • Near Real Time capability permits generating height data within within 3 days of measurement

Tiger Workshop 2006 - Cape Town


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ERS-2 waveform sequencing

across Africa

Ocean type echo

Very fat echofrom high surface roughness

Bright thin echo from still water

Tiger Workshop 2006 - Cape Town


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South American NRT Mask

To produce reliable NRT mask the Envisat SGDR data were run through the full mask to generate products, these were assessed and only the locations of clean time series were included in the final NRT mask.

NRT products are now generated globally. Work continues on enhancing the system to retrieve more targets (grey parts of mask).

Tiger Workshop 2006 - Cape Town


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NRT African Mask + Products

Tiger Workshop 2006 - Cape Town


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Global NRT mask

This is the first release of the global NRT mask. Work continues towards monitoring remaining targets by increasing the waveform analysis and retracking and enhancing the selections mask.

Tiger Workshop 2006 - Cape Town


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Requirement of an Accurate mask

To measure heights accurately using a fully automated system, a very detailed mask is needed, to select out only signals from water.

Tiger Workshop 2006 - Cape Town


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Validation

Extensive validation of results made against gauge stations. Example shown here from Amazon basin. Retracking enables accurate heights to be generated.

Tiger Workshop 2006 - Cape Town


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VALIDATION

Rio Negro

Tiger Workshop 2006 - Cape Town


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VALIDATION

Rio Amazonas

Tiger Workshop 2006 - Cape Town


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NRT over Lake Debo

This figure shows the continuing monitoring over lake Debo from ERS2 (blue), Envisat (red) with two NRT points plotted (cyan).

Tiger Workshop 2006 - Cape Town


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Histogram of NRT to SGDR differences over Africa

2 cm

Tiger Workshop 2006 - Cape Town



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Niger River

Niger River


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Time series over Congo

Congo time series

ERS2

ERS2

Envisat

ERS2

Tiger Workshop 2006 - Cape Town


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All Possible Measurements on the Congo

These pictures show everywhere that we have useable waveform data over the Congo. Every circle is another measurement.

We are working on the River and Lake system with the aim of retrieving measurements from every location shown.

Tiger Workshop 2006 - Cape Town


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Example ERS2 Time Series over Africa

Lake Kariba

Lake Kivu

1995

1995

2004

2004

River Nile

River Niger

Tiger Workshop 2006 - Cape Town


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Envisat RA-2 Time Series over Africa

Lake Kariba

Lago do Cahoro Bassa

2002

2002

2006

2006

Congo

Lake Upemba

Tiger Workshop 2006 - Cape Town


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Time Series over African Rift Valley lakes from ERS2

Red dots show mean position of altimeter measurements - one time series for each dot.

Note that the best time series are selected for distribution within the NRT system using the NRT mask.

Tiger Workshop 2006 - Cape Town


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Time series from ERS2

Lake Malawi

Lake Malawi

Tiger Workshop 2006 - Cape Town


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Time series from ERS2

Lake Tanganika

Tiger Workshop 2006 - Cape Town


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Time series from ERS2

Lake Victoria

Tiger Workshop 2006 - Cape Town


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Lake Volume Change - first results

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME DEMONSTRATION PILOT

  • Radar Altimeter waveforms and geophysical corrections are fetched directly from the Envisat ground segment

  • The near real time River&Lake processor is run as soon as the data is received

  • The “River&Lake for Hydrology” (RLH) output product is stored in the web site

  • The longest lag is the availability of the DORIS Interim orbit (3~4 days)

  • This will improve to 3 hours when the DORIS Navigator orbit is fully processed in real time

Tiger Workshop 2006 - Cape Town


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Near-real Time Products:

  • NRT system demo is on since October 2005

  • Stopped since March 2006, restarted November 2006

  • Data within 3 days

  • Very good agreement indeed with SGDR data, meaning that the NRT heights are accurate within a few cm

  • Outputs will be assessed and mask upgraded to include additional sites periodically

Tiger Workshop 2006 - Cape Town


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River and Lake Products Website

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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A typical Time Series

SAMPLE PAGE FOR HISTORICAL PRODUCTS

Each sample page has the same layout

Information

Time series

Products download

Tiger Workshop 2006 - Cape Town


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SAMPLE PAGE FOR NEAR REAL TIME PRODUCTS

THE NEAR REAL TIME IS MADE AVAILABLE VIA THE RIVER AND LAKE WEB SITE

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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SAMPLE PAGE FOR NEAR REAL TIME PRODUCTS

THE NEAR REAL TIME IS MADE AVAILABLE VIA THE RIVER AND LAKE WEB SITE

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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SAMPLE PAGE FOR NEAR REAL TIME PRODUCTS

Lake Debo

NRT

Validation NRT

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME PRODUCTS

AFRICA - Lake Volta

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME PRODUCTS

AFRICA - Lake Rudolph

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME PRODUCTS

amount of data for one day

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME PRODUCTS

All Data generated in Near Real Time over one 35 day cycle

Location of data since 25 October

Tiger Workshop 2006 - Cape Town


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ENVISAT RA2 USO Anomaly

  • RA2 has shown (since Feb 2006) an anomalous behaviour of the Ultra Stable Oscillator (USO) clock period.

  • The anomaly consists of an offset of about 5.6 m and orbital oscillations of ~20 cm in the EnviSat RA-2 range values

  • Consequence  geophysical applications of RA-2 sea level measurements have been hindered since USO anomaly started

    • The River and lake NRT system has been halted

Tiger Workshop 2006 - Cape Town


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20 cm

1 orbit

Tiger Workshop 2006 - Cape Town


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EnviSat RA2 USO anomaly

  • Solutions: Two different models and corrective algorithms have been implemented since then:

    • The first model, developed by CLS (France)

      • currently being used to correct the geophysical range values (at 1s rate). Only the corrections (and not the corrected output L2 products) have been provided (through the ESA web portal http://earth.esa.int/pcs/Envisat/RA2) so that users can correct their own products.

    • The second model, developed by R. Scharroo (Altimetrics LLC, USA)

      • has been implemented and used at ESRIN to correct the L1b RA2 products, that are given as input to the River & Lake processor for further computation of the elevations.

Tiger Workshop 2006 - Cape Town


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EnviSat RA2 USO anomaly

  • A comparison between the two corrective models has been performed in order to assess their validity.

  • The following plot illustrates the differences between the two models, applied to ~6 h of data on 14th October 2006.

  • Differences of up to ~100 picoseconds in the Ku-band window delay are shown, that are equivalent to a difference of up to13 mm in range or elevation

Tiger Workshop 2006 - Cape Town


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EnviSat RA2 USO anomaly

13 mm

Tiger Workshop 2006 - Cape Town


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River and Lake processor results

  • The uso corrected Level 1b products, as well as non-USO-corrected L2 IGDR products (needed for the geophysical corrections) are now given as input to the River & Lake processor for a correct determination of river and lakes water level.

Tiger Workshop 2006 - Cape Town


River and lake processor results42 l.jpg
River and Lake processor results

  • The following African rivers are processed in near real time by the River&Lake system :

    • Senegal, Niger/Benue, Volta, Nile, Congo, Zambezi, Limpopo and Orange

  • The following African lakes are processed in near real time by the River&Lake system:

    • Albert, Aswuan, Bangweulu, Cahora Bassa, Chad, Chilwa, Ndombe, Edward, George, Kainji, Kariva, Kivu, Kyoga, Lac de Buyo, lac de Kossou, lac de lagdo, lac de Manantali, lac de Selingue, Malawi, Mbakaou, Mweru, Mweru Wantipa, Nasser, Niangay, Nyasa, Shiroro, Tana H’ay’k, Tanganyika, Turkana, Victoria

Tiger Workshop 2006 - Cape Town



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River and Lake processor results

  • RA2 data from 2005 have been given as input to the R&L processor to illustrate the outputs of the processor over Africa

  • The plotted values are elevation differences with respect to climatological mean values.

Tiger Workshop 2006 - Cape Town


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River and Lake processor results

[m]

Tiger Workshop 2006 - Cape Town

-20

0

-10

10

20


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NEAR REAL TIME PRODUCTS

THE MASK CAN BE ENHANCED TO ATTEMPT RETRIEVAL OVER YOUR PROJECT’S AREA

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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NEAR REAL TIME PRODUCTS

SIGN UP IN THE DISTRIBUTION LIST

OF THE NRT PILOT DEMO

VIA THE RIVER AND LAKE WEB SITE

or write at

[email protected]

http://earth.esa.int/riverandlake

Tiger Workshop 2006 - Cape Town


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BURST ECHOES - RESEARCH CONTINUES

Tiger Workshop 2006 - Cape Town


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BURST ECHOES - RESEARCH CONTINUES

Tiger Workshop 2006 - Cape Town


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Discussion

  • The ERS2 measurements have allowed generation of long time series of inland water heights over Africa.

  • ENVISAT continues this valuable time series: additionally, its Near-Real Time capability allows generation of heights within 2-3 days of measurement.

  • The spatial sampling permits data over a huge number of inland water targets to be gathered; the drawback is the low temporal sampling which permits annual and seasonal variations to be observed but does not allow high frequency changes to be identified.

  • These data are provided by ESA to Users: work continues to enhance this pilot system and recover heights from all the available water crossings worldwide.

Tiger Workshop 2006 - Cape Town


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