The ESA NRT River&Lake System J.L. Wheeler P.A.M. Berry R.G. Smith J.L. Wheeler P.A.M. Berry R.G. Smith

Overview Context / Background River&Lake Processor Altimeter products used Global Statistics Example products Data analysis and validation River&Lake website User analysis Discussion Context / Background River&Lake Processor Altimeter products used Global Statistics Example products Data analysis and validation River&Lake website User analysis Discussion

Context Ability of satellite radar altimeters to obtain accurate inland water heights known for several years Lakes were the first focus as they are large targets and it is relatively straightforward to obtain measurements Rivers are more complex as they are smaller and often located within steep terrain Improvements in retracking and accurate target location have make it possible to retrieve water heights globally Ability of satellite radar altimeters to obtain accurate inland water heights known for several years Lakes were the first focus as they are large targets and it is relatively straightforward to obtain measurements Rivers are more complex as they are smaller and often located within steep terrain Improvements in retracking and accurate target location have make it possible to retrieve water heights globally

River&Lake Processor – overview Mask selects R&L WaveformsMask selects R&L Waveforms Retracker corrects heightRetracker corrects height Boxes fix target locations (local corrections for geoid and seasonal mean heights)Boxes fix target locations (local corrections for geoid and seasonal mean heights) Filter removes ‘noisy’ heightsFilter removes ‘noisy’ heights Average of heights used for RLH productAverage of heights used for RLH product

River&Lake Processor – overview Mask: selects R&L Waveforms (1 pixel = 30”x30” = 1km at equator) Retracker: identifies ‘wet echoes’ and corrects height Boxes : fix target locations (correct for local geoid and seasonal mean heights) Filter : removes noise from height profile Mean: mean height used for RLH product Mask: selects R&L Waveforms (1 pixel = 30”x30” = 1km at equator) Retracker: identifies ‘wet echoes’ and corrects height Boxes : fix target locations (correct for local geoid and seasonal mean heights) Filter : removes noise from height profile Mean: mean height used for RLH product

Near-Real-Time altimeter products used EnviSat RA2:IGDR + Level1B repeat cycle:35 days Orbits in cycle:501 Track separation:80km (equator) Data availability:2-3 days Archived data:6½ years EnviSat RA2:IGDR + Level1B repeat cycle:35 days Orbits in cycle:501 Track separation:80km (equator) Data availability:2-3 days Archived data:6½ years Jason-2:SIGDR(replaces Jason-1) repeat cycle:10 days Orbits in cycle:124 Track separation:315km (equator) Data availability:1-2 days Archived data:1 year Jason-2:SIGDR(replaces Jason-1) repeat cycle:10 days Orbits in cycle:124 Track separation:315km (equator) Data availability:1-2 days Archived data:1 year

Global target coverage Total targets: 1341EnviSat: 1229Jason-2: 112

Lake Erie

Lake Michigan

Lake Tana

Lake Tanganyika

Lake Victoria

Data analysis – alongtrack height dispersion Measurement uncertainty: Mean uncertainty indicates data quality: Height dispersion >= 0.3m Height dispersion < 2cm

Data analysis - curve-fit R 2 Fit 8 th order sinusoid to timeseries. Coefficient of determination (R 2 ) is an indication of data quality Fit 8 th order sinusoid to timeseries. Coefficient of determination (R 2 ) is an indication of data quality Timeseries with a strong sinusoidal trend Curve-fit not possible

Data anlaysis - curve-fit residuals Standard deviation of curve-fit residuals can provide an indication of measurement error Timeseries having residuals < 0.5m of sinusoidal model

River and Lake Website Updated daily * Automated product delivery * ~120 registered users * ~160 subscriptions * Updated daily * Automated product delivery * ~120 registered users * ~160 subscriptions *

Website usage according to city Widespread global usage Main users: research centres Remote user interest continues to grow Widespread global usage Main users: research centres Remote user interest continues to grow

Discussion Jason-2 successfully replaced Jason-1 as a data source and has augmented the number of global targets for the river and lake processor Although some targets will disappear when EnviSat enters a geodetic orbit phase (Sep 2010) we hope to replace these with data from CryoSat2 and Sentinel3 Next generation altimeters will offer potential enhancements to the River&Lake processor due to their increased along- track sampling rate Work is underway to improve the global mask resolution and will potentially reveal smaller river targets The River&Lake website’s global user community continues to grow – including interest from the developing world Jason-2 successfully replaced Jason-1 as a data source and has augmented the number of global targets for the river and lake processor Although some targets will disappear when EnviSat enters a geodetic orbit phase (Sep 2010) we hope to replace these with data from CryoSat2 and Sentinel3 Next generation altimeters will offer potential enhancements to the River&Lake processor due to their increased along- track sampling rate Work is underway to improve the global mask resolution and will potentially reveal smaller river targets The River&Lake website’s global user community continues to grow – including interest from the developing world

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