ENVISAT ASAR ScanSAR Complex Focusing & Interferometry

1. ENVISAT ASAR ScanSAR Complex Focusing & Interferometry A. Monti Guarnieri Dipartimento di Elettronica e Informazione - Politecnico di Milano C. Cafforio, P. Guccione Dipartimento di Elettronica ed Elettrotecnica - Politecnico di Bari

2. sensor 44° 16° ~ 700 m ENVISAT ASAR ScanSAR geometry ScanSAR is a particular SAR that achieves a very wide swath coverage by periodically switching the antenna pointing in several range subswaths. The sensor acquires for short bursts by ciclycally scanning all the subswaths

3. Range Azimuth Footprint (TF) ScanSAR Wide Swath look computation Each burst gives a focused look. Looks partially overlap in time (3 for WSM), but not in frequency. They are kept separated and will be averaged at interferogram level. Frequency (Hz) Azimuth (ms)

4. Wide Swath complex product Focused ScanSAR Wide Swath data will be arranged in a new complex product: Wide Swath Mode Single Look Complex (WSM SLC) where attention is paid particularly to the phase preserving and time annotations, as focused bursts overlap. The outputs of an ENVISAT ASAR ScanSAR focusing processor must be focused bursts (written sequentially) of all the processed swaths, all resampled on a coherent sampling grid.

5. Burst Windowing Zero-Padding (2-3 X) Azimuth Focusing Mosaicking Complex Interpolation (subsampling) ScanSAR rgc data (1 burst) Focused data (1 burst) Focusing schemes Direct Convolution Modified Specan Range Doppler Chirp Scaling w-k Deramp and filter Deramped filtering Chirp Scaling Chirp-Z transform WSS: WSM Complex Product

6. WSS: WSM Complex Product ASA_WSS is a single range look (full bandwidth) phase pres. level-1 product. It is a collection of bursts / swaths all sampled on the same grid. It is intended for interferometry, large scale analysis and see/ice applications. It can be post-processed do derive all the other WSS products.

7. Multimode interferometry: implementation MASTER IMAGE IM/AP pp focused MMSE Slave Image Reconstruction Hermitian multiplication & look averaging Differential interferogram SLAVE IMAGE IM/AP /WSM MMSE Master Image Reconstruction p.p. focusing (WSM) Co-registration Coherence map Interferogram adaptive filtering Mosaicking & Geocoding Doppler parameters Co-registering map and Scan pattern. Synthetic fringes Ancillary and Orbits Geocoded Differential Interferogram Geocoded Coherence Map Synthetic fringes and geometric information processor Full. res. DEM

8. WSS Product: Computing Time • ASA__WS0 53000 packets (30 sec) – 330 MB (1 byte / complex sample) • CPU: Mobile Pentium 1000 • Processor: POLIMI/POLIBA Reference Processor (0th ord. block w-k + dechirping & GLS filter bank). • Sampling interval (16 MHz)-1 x 10 ms (7 m x 130 m) – 1 GB (4 byte / complex sample) • Data extraction & preconditioning (FBAQ decoding, gain droop, ….)*: 16 min • Range Focusing*: 8 min • Azimuth Focusing: 20 x 5 = 10 m Total computing time 2 h. Steps (*) can be otpimized. Specan focusing > 30% more efficient.

9. Monitoring by IM/WSM InSAR WSM/IM combination provide frequent interferometric capability at a good resolution vs phase accuracy tradeoff. The same baseline range as for IM/IM can be exploited. In case that synchronized scans acquisitions could be programmed, WSM/WSM combinations could provide large scale interferograms. Small baselines are mandatory.

10. WSM/IM Interferometry Las Vegas Geocoded phase+ampl Bn: 35 m. IS2. WSS: 14/3/03, IMS: 29/11/02. SRTM DEM

11. WSM/IM: phase No scalloping !

12. Monitoring by WSM/WSM InSAR Latitude (o) 0-30 30-55 >75 Revisit time* (days) 3-4 2-3 <1 (*) ascending + descending orbits In case that synchronized scans acquisitions could be programmed, WSM/WSM combinations could provide large scale interferograms. Small baselines are mandatory.

13. Flevoland Phase+ampl Bn 400 m. 1/12/02, 5/1/03 Ellipsoid Flattening 400 x 400 km