(1) Cemagref de Montpellier , UMR TETIS Territoires, - - PowerPoint PPT Presentation

Nicolas BERCHER (1), Pascal KOSUTH (1), Jérôme BRUNIQUEL(2)

(1) Cemagref de Montpellier , UMR TETIS « Territoires, Environnement, Télédétection et Informations (1) Cemagref de Montpellier , UMR TETIS « Territoires, Environnement, Télédétection et Informations Spatiales », Spatiales », nicolas.bercher@teledetection.fr ; pascal.kosuth@teledetection.fr nicolas.bercher@teledetection.fr ; pascal.kosuth@teledetection.fr (2) Alcatel Alenia Space, Toulouse, France (2) Alcatel Alenia Space, Toulouse, France jerome.bruniquel@space.alcatel.fr jerome.bruniquel@space.alcatel.fr

Characterizing the quality of river water level time series Characterizing the quality of river water level time series derived from satellite radar altimetry: derived from satellite radar altimetry: Efforts toward a standardized methodology Efforts toward a standardized methodology

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series) “ex ante” quantification of the accuracy

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Radar Altimetry measurements :

• 10 to 35 days (theoretical),
• accuracy : unknown

In situ measurements :

• twice a day,
• accuracy : ~3 cm

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Introduction (1/3) - Expectations by Hydrologists “ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Ra d a r Altim e try m e a s u re m e n ts :

1 to 3 5 d a ys (th e

• re

tica l), a ccu ra cy : u n kn

• w

n

Ra d a r Altim e try m e a s u re m e n ts :

1 to 3 5 d a ys (th e

• re

tica l), a ccu ra cy : u n kn

• w

n

In situ measurements :

• twice a day,
• accuracy : ~3 cm

Radar altimetry measurements

• 10 days or 35 days
• with quantified accuracy
• reconstructed daily time series
• with quantified accuracy

Methods to characterize the “Quality” of water levels from radar altimetry accuracy and effective sampling frequency of radar altimetry Reconstruction of daily time series ; Resulting accuracy of daily time series Factors affecting the quality of reconstructed time series

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Introduction (2/3) - Expectations by Hydrologists “ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

One satellite

• verflight

Window size

Introduction (3/3) - Building time series of water levels from satellite radar altimetry

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Topex/Poseido n track 63

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Satellite Retracking Algorithm + corrections Selection of a unique value per cycle CAUTION : Internal dispersion of radar altimetry measures within the window during a cycle is not a quantification of the error

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series) “ex ante” quantification of the accuracy

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

215 89 165 241 63 139 102 254 76 152 228 50 178

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Radar Altimetry Data / In situ data

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Solimões River; Topex Poseidon; Track 63

Error Error structure

Ma na us Ma na us

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

High flow Mean flow Low flow

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

215 89 165 241 63 139 102 254 76 152 228 50 178

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Satellite / gauging station

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Quantification of the accuracy of radar altimetry measurements

Error Error structure

Ma n a u s Ma n a u s

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Satellite / gauging station

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Quantification of the accuracy of radar altimetry measurements

Error Error structure

Ta ba tinga Ta ba tinga

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Satellite / gauging station

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Quantification of the accuracy of radar altimetry measurements

Error Error structure

Ua ra cu Ua ra cu

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Ua ra cu Ua ra cu

Ta ba tinga Ta ba tinga

Ma n a u s Ma n a u s

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

215 89 165 241 63 139 102 254 76 152 228 50 178

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series) “ex ante” quantification of the accuracy

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Lower accuracy at low river stage is related to the area of open water (river width)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry Influence of river width on radar altimetry accuracy

Statistical analysis is under way to correlate accuracy and river width

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Manaus (Negro river)

1500 1750 2000 2250 2500 2750 3000 01/01/91 01/01/92 31/12/92 Time Water level (cm)

Sampling period 30 days

Manaus (Negro river)

1500 1750 2000 2250 2500 2750 3000 01/01/91 01/01/92 31/12/92 Time Water level (cm)

• 750
• 500
• 250

250 500 750 Error (cm)

Sampling period 30 days linear interpolation standard deviation : 38 cm

A.1-Effect of time sampling and sampling period

Effect of time sampling period on the error in water levels time series Manaus gauging station

• 150
• 100
• 50

50 100 150 200 5 10 15 20 25 30 Time sampling period (days) Error on water levels (cm)

Standard deviation (cm)

• max. negative error (cm)
• max. positive error (cm)

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

A.1-Effect of time sampling and sampling period

Manaus Obidos Tabatinga Uaraca

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Manaus

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Tabatinga

12.0-- 10.0-- 8.0-- 6.0-- 4.0--

Uaraca

Topex Poseido n ERS ENVISAT

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Manaus

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Tabatinga

12.0-- 10.0-- 8.0-- 6.0-- 4.0--

Uaraca

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry Spectral analysis of river water level time series

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy + effective

sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Coupled effects:

Sampling rate (days) Simulated additive noise (cm)

80 70 60 50 40 30 20 10 cm

RMS error (cm)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J. Coupled influence of measurement accuracy and effective sampling

frequency “ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Manaus

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Tabating a

12.0-- 10.0-- 8.0-- 6.0-- 4.0-- 2.0-- 0.0--

Uaraca

12.0-- 10.0-- 8.0-- 6.0-- 4.0--

40 cm 75 cm

100 cm

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Natural hydrological signal Oversampling (interpolation) method Quality of the river water level time series from Satellite radar altimetry depends on 4 elements Time sampling period Measurement Accuracy

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Introduction:

Expectations by hydrologists Building time series of water levels from satellite radar altimetry

“Quality” of sampled measurements (accuracy

+ effective sampling frequency)

Method for quantification of the “Quality” : accuracy and effective sampling period Influence of river width “ex ante” quantification of the accuracy

“Accuracy” of reconstructed river water level time series

Oversampling : building a “continuous” time series from satellite sampling Coupled influence of measurement accuracy and effective sampling frequency and influence of river hydrology Method for characterization of the quality of oversampled time series (reconstructed daily time series)

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

Method for characterization of the quality of oversampled time series

2. (Satellite K + retracking Algorithm Y) measures (river R on section S) with an accuracy of XXcm

Conclusions & Future

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry

2. (Satellite K + retracking Algorithm Y) measures (river R on section S) with an accuracy of XXcm The error cannot be represented by a single number (rms) 1. Dispersion of satellite measurements is not an estimate of the error of these measurements 3. Error is not gaussian. It is structured in relation with river level and must be represented by a variable error mean and standard deviation 5. A method is available for characterization of the quality of water levels time series from radar altimetry. It can be applied :

To quantify the uncertainty of near real time radar altimetry data To compare the accuracy of various retracking algorithms To identify the impact of factors such as : river width, river hydrology, …

1. Both effective sampling frequency and accuracy of satellite measurement influence the accuracy of reconstructed daily time series . 3. Error is not gaussian. It is structured in relation with river level and must be represented by a variable error mean and standard deviation 1. Both effective sampling frequency and accuracy of satellite measurement influence the accuracy of reconstructed daily time series .

Quality

• f Satellite data

Accuracy of reconstructed time series

ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 ESA – CNES “15 years of progress in radar altimetry” Symposium – Venice – March 2006 Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Characterizing the quality of river water level time series derived from satellite radar altimetry Efforts toward a standardized methodology Bercher N;, Kosuth P., Bruniquel J. Bercher N;, Kosuth P., Bruniquel J.

Access to all in situ data Access

• nly to past in situ

data Access to no in situ data

• perational
• perational
• perational
• perational

Statistical approach Statistical approach

Satellite Retracking algorithm River morphology + Sampling frequency River Hydrology Oversampling method

“ “Quality” of river water level time series derived from satellite radar altimetry Quality” of river water level time series derived from satellite radar altimetry Methods to characterize the Quality