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The ESA NRT River&Lake System. 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.
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The ESA NRT River&Lake System 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 • 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 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 • 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
Data analysis – alongtrack height dispersion • Measurement uncertainty: • Mean uncertainty indicates data quality: • Height dispersion < 2cm • Height dispersion >= 0.3m
Data analysis - curve-fit R2 • Fit 8th order sinusoid to timeseries. • Coefficient of determination (R2) is an indication of data quality • Curve-fit not possible • Timeseries with a strong sinusoidal trend
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 * www.earth.esa.int/riverandlake/
Website usage according to city • 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
