Pulse-Pair (Doppler) Processing of Envisat Individual Echoes

R. Abileah1, S. Vignudelli2

1 jOmegak, San Carlos CA, USA 2 CNR – Istituto di Biofisica, Pisa, Italy

2Pulse-Pair (Doppler) Processing of Envisat IE

OutlineOutline

Envisat individual echoes (IE) dataEnvisat individual echoes (IE) data Coherence between echoesCoherence between echoes Doppler processing of IE dataDoppler processing of IE data

Open oceanOpen ocean Coastal, tangential trackCoastal, tangential track

ConclusionsConclusions

More complex examples presented in our More complex examples presented in our companion poster presentationcompanion poster presentation Coastal, perpendicular tracksCoastal, perpendicular tracks LakesLakes

3Pulse-Pair (Doppler) Processing of Envisat IE

Envisat Individual Echoes (IE) Data Recordings

Sample of worldwide distribution of 1-second IE records

1 second = 7 km

= 1984 samples

1-second record (amplitude, phase not shown)

4Pulse-Pair (Doppler) Processing of Envisat IE

IE Inventory

Data collection started on September 2004 330 GB / year 1 second out of every 1 minute 1800 Hz Global coverage Level 1b processed data available via GPOD

5Pulse-Pair (Doppler) Processing of Envisat IE

Prior IE Exploitations – Incoherent Methods

J. TOURNADRE, Signature of Lighthouses, Ships, and Small Islands in Altimeter Waveforms, 2007

ESA RAIES project  http://earth.esa.int/raies/

ESA SAMOSA http://www.satoc.eu/projects/samosa/

Philippa Berry, et al., Global Analysis of EnviSat Burst Echoes Over Inland Water , IEEE Transactions on Geoscience and Remote Sensing, 50 (5), 1980-1985, 2012-09-04

Specular returns from inland waters

6Pulse-Pair (Doppler) Processing of Envisat IE

Prior IE Exploitations – Coherent (Doppler) Methods

Christine Gommenginger et al., NEW SCIENTIFIC APPLICATIONS FOR OCEAN, COASTAL, LAND AND ICE REMOTE SENSING WITH ENVISAT RADAR ALTIMETER INDIVIDUAL ECHOES, 2006

Christine Gommenginger, Assessment of Envisat RA-2 Individual Echoes over ocean, 2009

Concluded that low coherence and frequency aliasing made IE data unsuitable for delay-Doppler processing

7Pulse-Pair (Doppler) Processing of Envisat IE

Doppler Processing

8Pulse-Pair (Doppler) Processing of Envisat IE

Interpretation of Doppler Velocity

At Nadir the Doppler velocity corresponds to satellite vertical velocity (H_rate in data header)

Projected orbital vertical + horizontal velocities

9Pulse-Pair (Doppler) Processing of Envisat IE

Pulse Pair Processing (PPP) Descriptions of the Doppler Spectrum

1 *, 1,

1,. . . ,1984m n m n m

n

M z z

0 *, ,

1,. . . ,1984m n m n m

n

M z z

*, 1,

1,. . . ,1984

9. 91arg( )m n m n m

n

V z z

1 1 0/m m m

M M

.

n = 1,…, 1984

m =

1,…

, 1

28

Zero-lag power

One-lag power

Velocity

Magnitudecoherence (at 1 lag)

10Pulse-Pair (Doppler) Processing of Envisat IE

Correlation of (unwrapped) PPP Doppler Velocity to Orbital Vertical Velocity (H_rate)

(Using many samples from open ocean)

Data fit σ=0.2 m/s

11Pulse-Pair (Doppler) Processing of Envisat IE

Doppler Filtered PPP Waveform

zn

M0

M0

Conventional waveform

Doppler filteredwaveform

H_rate

Passband filter

12Pulse-Pair (Doppler) Processing of Envisat IE

Open Ocean Example (1/2)

13Pulse-Pair (Doppler) Processing of Envisat IE

Open Ocean Example (2/2)

14Pulse-Pair (Doppler) Processing of Envisat IE

Coastal Example (1/2)

15Pulse-Pair (Doppler) Processing of Envisat IE

Coastal Example (2/2)

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Remarks & ConclusionsRemarks & Conclusions

Envisat’s 1800 Hz rate provides sufficient pulse-to-pulse coherence for Doppler processing

Filtering at known vertical velocity sharpens altimeter response on Nadir point

Producing one 7 km (1 sec) integrated waveform, or perhaps 2-3 segments

Doppler filters out land contamination

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Our companion Poster presentation includes …

- Coherence vs. sea state

- Ground tracks perpendicular to coastline

- Slopping sea surface topography

18Pulse-Pair (Doppler) Processing of Envisat IE

Acknowledgments

Salvatore Dinardo and Jérôme Benveniste of European Space Agency provided access to the IE archive

Roberto Cuccu of European Space Agency for his help in downloading data through the GPOD service

Walter Smith of NOAA suggested the crucial test linking measured Doppler velocity with satellite vertical velocity

Keith Raney of JHU/APL for review and comments

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Thank you& special thanks to the CAWS committee

for organizing a meeting in

this beautiful place.

Appendix

Magnitude Coherence

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Statistics of Magnitude Coherence |γ|

1ˆvar( 0)

2n

1 * *, 1, , ,/

m n m n m n m n mn n

z z z z

221ˆ ˆvar( ) 1

2n

1ˆ( 0)

2E

n

22Pulse-Pair (Doppler) Processing of Envisat IE

PPP (red) vs. Power Spectrum (blue) velocity estimates