The ESA NRT River&Lake System
description
Transcript of The ESA NRT River&Lake System
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: 1341 EnviSat: 1229 Jason-2: 112
Lake Erie
Lake Michigan
Lake Tana
Lake Tanganyika
Lake Victoria
Data analysis – alongtrack height dispersion
Measurement uncertainty:
Mean uncertainty indicates data quality:
€
σ h
€
σ h
Height dispersion >= 0.3m
Height dispersion < 2cm
Data analysis - curve-fit R2
Fit 8th order sinusoid to timeseries.Coefficient of determination (R2) 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 *
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
Thank you for listening.