Pulse-Pair (Doppler) Processing of Envisat Individual Echoes

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1 Pulse-Pair (Doppler) Processing of Envisat Individual Echoes R. Abileah 1, S. Vignudelli 2 1 jomegak, San Carlos CA, USA 2 CNR Istituto di Biofisica, Pisa, Italy

2 Outline Envisat individual echoes (IE) data Coherence between echoes Doppler processing of IE data Open ocean Coastal, tangential track Conclusions More complex examples presented in our companion poster presentation Coastal, perpendicular tracks Lakes 2

3 Envisat Individual Echoes (IE) Data Recordings Sample of worldwide distribution of 1-second IE records 1-second record (amplitude, phase not shown) 1 second = 7 km = 1984 samples 3

4 IE Inventory Data collection started on September GB / year 1 second out of every 1 minute 1800 Hz Global coverage Level 1b processed data available via GPOD 4

5 Prior IE Exploitations Incoherent Methods J. TOURNADRE, Signature of Lighthouses, Ships, and Small Islands in Altimeter Waveforms, 2007 ESA RAIES project ESA SAMOSA Philippa Berry, et al., Global Analysis of EnviSat Burst Echoes Over Inland Water, IEEE Transactions on Geoscience and Remote Sensing, 50 (5), , Specular returns from inland waters 5

6 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 6

7 Doppler Processing 7

8 Interpretation of Doppler Velocity Projected orbital vertical + horizontal velocities At Nadir the Doppler velocity corresponds to satellite vertical velocity (H_rate in data header) 8

9 Pulse Pair Processing (PPP) Descriptions of the Doppler Spectrum Zero-lag power M = z z 0 * m nm, nm, n = 1,..., 1984 m = 1,, 128 à n = 1,, 1984 à One-lag power Velocity M = z z +. 1 * m nm, n 1, m n = 1,..., V = ar g( z z ) * m n, m n+ 1, m π n = 1,..., 1984 Magnitude coherence (at 1 lag) γ = M / M m m m 9

10 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 10

11 Doppler Filtered PPP Waveform z n Passband filter M 0 Conventional waveform M 0 H_rate Doppler filtered waveform 11

12 Open Ocean Example (1/2) 12

13 Open Ocean Example (2/2) 13

14 Coastal Example (1/2) 14

15 Coastal Example (2/2) 15

16 Remarks & 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 16

17 Our companion Poster presentation includes - Coherence vs. sea state - Ground tracks perpendicular to coastline - Slopping sea surface topography 17

18 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 18

19 Thank you & special thanks to the CAWS committee for organizing a meeting in this beautiful place. 19

20 Appendix Magnitude Coherence

21 Statistics of Magnitude Coherence γ 1 * * γ z z / z z m nm, n+ 1, m nm, nm, n n = 1 var( ˆ γ) = 1 2n ( 2 ˆ ) 2 γ 1 var( ˆ γ γ = 0) = 2n E ( ˆ γ γ = 0) = 1 2 π n 21

22 PPP (red) vs. Power Spectrum (blue) velocity estimates 22

Scientific Applications of Fully-Focused SAR Altimetry

Scientific Applications of Fully-Focused SAR Altimetry Alejandro Egido (1,2), Walter Smith (2) (1) UMD/CICS-MD, United States (2) NOAA, United States CICS Science Conference Nov 29, 30 & Dec 1, 2016 College