Transcript Mask
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 •Retracker •Boxes •Filter •Mean : selects R&L Waveforms (1 pixel = 30”x30” = 1km at equator) : identifies ‘wet echoes’ and corrects height : fix target locations (correct for local geoid and seasonal mean heights) : removes noise from height profile : mean height used for RLH product Near-Real-Time altimeter products used EnviSat RA2: • • • • • repeat cycle: 35 days Orbits in cycle: 501 Track separation:80km (equator) Data availability: 2-3 days Archived data: 6½ years Jason-2: SIGDR • • • • • IGDR + Level1B (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: 1341 EnviSat: 1229 Jason-2: 112 Lake Erie Lake Michigan Lake Tana Lake Tanganyika Lake Victoria Data analysis – alongtrack height dispersion Measurement uncertainty: h Mean uncertainty indicates data quality: h 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 alongtrack 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 Thank you for listening.