Azimuthal SAR Interferogram (azisar) Sylvain Barbot, Institute of Geophysics and Planetary Sciences, Scripps Institution of Oceanography, University of California at San Diego

forward look interferogram backward look interferogram range direction double difference interferogram double difference suppresses topography and most of troposphere delays. measurement is still ambiguous, but no more relative (  0  ||  r||.cos  = 0) Geometry

efficient look direction antenna width wavelength first fringe  occurs for ||   r||  = 3L/8=3.75m (no wavelength dependence)  is the efficient look angle angular energy distribution angle first moment from energy distribution Real Aperture Radar

insardbldiff still not measured plane of sight azimuth (satellite track)incidence quake slip Azimuth View Angle

azimuth emitted pulse h=800 km S=5 km L=10 m fo=5.3 GHz range Synthetic Aperture Radar

Doppler frequency Instantaneous phase Total Doppler bandwidth nearest range Illumination duration T int Azimuth Compression

sensor target How to filter for look directions ? Range and look direction variation with time Look Direction

Doppler analysis

lines of equi-Doppler lines of equidistance flight line illuminated area Range/Doppler reference system How to filter for look direction ? Local ground incidence angle Doppler analysis

case of a zero Doppler centroid Doppler frequency varies linearly with time Doppler analysis Doppler frequency variation with time/space

Frequency spectrum in azimuth (antenna pattern modulation) Doppler centroid Doppler analysis Image spectrum=Doppler frequency *antenna spectrum * scene impulse response

zero Doppler centroid Doppler analysis Non-zero Doppler centroid case non-zero Doppler centroid forward look backward look

Doppler Power Spectrum Doppler frequency / PRF Aliasing Limit (DFT) Doppler centroid ~ 0.75 Doppler analysis backward look forward look backward look

Doppler analysis Doppler shift (freq. domain) = azimuth modulation (time domain) Doppler with range f d (r)/f 0 =a 2 r 2 +a 1 r+a 0 Doppler at acquisition Doppler centroid modulation Now easy to take backward and forward look shifted to center DFT backward forward

no need for Doppler compensation Hector Mine azimuth interferogram