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.