Absolute calibration of Jason radar altimeters from GPS kinematic campaignsGPS kinematic campaignsover the Lake Issykkul

Legos (FR)Legos (FR)IWPB (KG)OCA (FR)CPRM (BR)CPRM (BR)OSU (USA)GRGS (FR)Univ Conception (CH)Univ Conception (CH)

J‐F Crétaux, S. Calmant, V. Romanovski, F. Perosanz, S. Tashbaeva,P. Bonnefond, D.Moreira, C.K. Shum, F. Nino, M. Bergé‐Nguyen, S. Fleury, P. Gegout, R. Abarca Del Rio, F. Lyard, and P. Maisongrande

OSTST 2011, San diego, October 19‐21

Cal / Val of radar altimetry for continental water at Legos

Ojectives:

comparison of level time series deduced from altimetry and in situ level when availablePerform GPS field campaigns (rivers and lakes) for establishment of error budget for different parameters (impact of retracking mode, geophysical correction) and to compute absolute /relative altimetric bias 

2 Sites operatingp g

Lake Issykkul

Cal/Val: T/P GFO

Amazon Basin

Cal/Val: T/P, GFOJS1‐2, envisat, Icesat

Preparation of future missions:Altika, Jason‐3, Sentinel‐3, SWOT

Absolute calibration on lakes: caracteristics and advantages

‐ Waves, Electromagnetic Bias, tides and inverse barometer negligible‐ In‐Situ data (limnigraphs) are useful for comparison and easy to install‐Multi satellite calibration is possible on one single site‐ Possibility to quantify errors in the corrections (wet and dry troposphere)‐ Assessment of performance of tracking/retracking algorithms

/‐ densification of absolute calibration sites in continental area / oceanic sites

GPS profile over an Envisat track

Campagnes de calibrations 2008, à 2010. 

6 field campaigns between 2004 and 2010 for multi satellite Cal/ValResults for Jason‐1 and Jason‐2 over 2 campaigns in 2009

In the frame of the FOAM project funded by CNESIn the frame of the FOAM project funded by CNES

Dry Tropospheric Correction (DTC)

Tropo Seche (GDR/Pistach) Cycle 32 weather stations were installed in Cholpon Ata (North coast: permanent) and on the Vessel (Multur) for the time of the campaigns. Another one installed permanently in June 2011 on the East coast near an Envisat / altika trackTropo Seche (GDR/Pistach) Cycle 3

-185

-184

-183

Limit of the Jason-2 track over the lake Issykkyl

Another one installed permanently in June 2011 on the East coast near an Envisat / altika track

189

-188

-187

-186

DTC

(cm

) GRD Jason2

-192

-191

-190

-189D

In Situ measurement taken along the Jason2 trackPistach

DTC Jason 2 Track centered

-19342,1 42,2 42,3 42,4 42,5 42,6 42,7 42,8

Latitude (°)

Discrepancies between In situ GDR of JS2 and DTC, Jason 2, Track centered

-1 89-1,88-1,87 In Situ

GDR, Jason2

Discrepancies between In situ , GDR of JS2 and Pistach products are within 1 cm

-1 93-1,92-1,91

-1,91,89

m

-1,95-1,94-1,93

2008,5 2009 2009,5 2010 2010,5

i f 3 diff

Wet Tropospheric Correction (WTC)

computation from 3 different ways:

The radiometers (problem of footprint)The models (CLS & GRGS)The models (CLS & GRGS)The GPS data along the coast ( more precise but problem of spatial variability)

Best coherence were obtained using GRGS model and GPS data (better than 1 cm)

Relative bias between Jason‐1 and Jason‐2 during tandem phase

JS2‐JS1 relative bias: 8.1 +/‐ 1 cm

GPS data processing

- Fixed reference point from GINS software (GRGS)p ( )- Mobile point from TTC and now from GINS in PPP mode- Correction of Height antenna from regular comparisons between shoreline reference point or permanent GPS at Kyzyl Suu and the mobile GPSreference point or permanent GPS at Kyzyl Suu, and the mobile GPS- Correction of floatability of the boat depending on the velocity

1568,4 Effect of boat velocitiy (STORM, campaign 2010)

1568,359 km/h

1568,3~6cm

1568,25

13 km/h

1568,277,25 77,252 77,254 77,256 77,258 77,26 77,262 77,264 77,266

For 2010 campaign, a correction of 1.5 cm/km/h must be appliedFor 2009 campaigns, the correction was lower (other boat): 5 mm/km/h

Relative bias Ocean / Ice1:23 +/‐ 4 cm

Relative Ocean / Ice1 retracker and absolute Jason‐2 biases

/

Same relative bias as calculated with Envisat incalculated with Envisat in Crétaux et al., 2009

Absolute JS2 (tracker ocean) bias: 16.2 +/‐ 4.2 cm( ) /

Absolute Bias of Jason‐1

Absolute Jason-1 bias calculated from Issykkul of 96 mm +/-40 mm

Absolute Bias of Jason‐2

Absolute Jason-2 bias calculated from Issykkul of 162 mm +/-42 mm

0 1

0,15Detection of Seiche and possible tides. Comparison with altimeters

0,05

0,1

0

-0,05

-0,12010,68 2010,73 2010,78 2010,83 2010,88 2010,93

Hi t i lHistorical limnigraph not precise enough and temporaly a d te po a ysampled for detection of high frequency level

i tivariations

Future campaigns, instrumentations, and data processing

Spring 2012

- One new permanent GPS close to the lake shore along the north coast (cooperation- One new permanent GPS close to the lake shore along the north coast (cooperation with institute of seismology) with collocated weather station for troposphere assessment

O th t t f th l k f l l i ti t hi h t l- One new gauge on the west coast of the lake for level variation at high temporal resolution to better observe the Seiche effect and measure instantaneous water level - Experiment with one GPS reflectometer for the observation of instantaneous lake

f i h f f h i f i isurface in the frame of the preparation of SWOT mission - One boat campaign along Altika tracks after the launch in April 2012

GPS data processing

- All computation (fixed and mobile) with GINS software in PPP mode

P i f i i GPS i Af i l kOther lakes

All computation (fixed and mobile) with GINS software in PPP mode

- Preparation of new in situ GPS campaign over an African lake (Victoria,Tanganyka, Malawi ?)

CONCLUSIONS 

Potential of absolute calibration of multi‐mission Altimetry and interferometry over lakes

Operating Cal/Val sites needed

P i i f f ti t

For next missions:Altika, Jason‐3, Sentinel‐3 and SWOT

Precision of few centimeters multi‐year time series availableIn situ data availableInformation on geophysical correction & retracking algorithms and error budgetInformation on geophysical correction & retracking algorithms and error budgetNecessary redundancy with other Cal/Val sitesNecessary of new site over lakes (Africa) to be investigated