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Tree height estimation from multi-temporal ERS SAR interferometric phase. M. Santor o (1) , J. Askne (2) , P. B. G. Dammert (3). (1) Friedrich-Schiller-University Jena (2) Chalmers University of Technology (3) Ericsson Microwave AB
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Tree height estimation from multi-temporal ERSSAR interferometric phase M. Santoro(1), J. Askne(2), P. B. G. Dammert(3) (1) Friedrich-Schiller-University Jena (2) Chalmers University of Technology (3) Ericsson Microwave AB Jena, Germany Gothenburg, Sweden Mölndal, Sweden
Introduction To answer this question it necessary to ... • ... know what affects the InSAR phase in forests • ... have test sites! • ... take into account atmospheric artefacts • ... understand the measurements interferometric tree height To retrieve the true height it is also necessary to ... • ... model the InSAR phase • ... compensate the InSAR tree height using the model Question: How feasible is tree height retrieval from ERS InSAR phase?
InSAR Phase Atmospheric delay Phase noise Topography + errors Interferometric tree height forest Filter atmospheric artefacts Deal with phase noise field The InSAR phase can be used to determine the topography of an area What happens in a forest?
Test sites • Kättböle, Sweden • Forest stands estate: 5.5 km2 • Intensively managed forest • Boreal coniferous • 42 stands > 2 ha • Tree height: 2-23 m • 9 ERS-1/2 pairs • Tuusula, Finland • Mixed forest landscape: 20 km2 • Intensively managed forest • Boreal, coniferous • 6 stands > 10 ha • Tree height: 10-27 m • 8 ERS-1/2 pairs • Bois de Boulogne, Paris • Park: ~ 9 km2 • Urban environment • Temperate, deciduous • 4 stands > 20 ha • Tree height: 18-23 m • 9 ERS-1/2 pairs • Thüringer Wald, Germany • Forests: ~ 40x10 km2 • Managed forests, mountains, fields • Temperate, coniferous • 5 ERS-1/2 pairs
Atmospheric artefacts Phase properties of a reference grid of scattering targets Good correction Dense grid of reference points (not available in forests) Estimation of atmospheric phase delays from meteo data Good agreement between modelled and measured phase Need of meteo data, GPS measurements, radiometer data Choose pairs that are NOT affected by the atmosphere Stable weather conditions and possibly no clouds Approaches to atmospheric filtering
Interferometric tree height Seasonality? Frozen Winter Frozen Snowfall Multitemporal
Interferometric Water Cloud Model The total forestcoherence is a sum of 2 contributions: Ground coherence, gr Vegetation coherence, veg Model considers tree attenuation (), gaps (), InSAR geometry () Interferometric tree height
Modelling Modelled coherence Modelled interferometric tree height • Estimate model unknowns: s 0veg, s 0gr, b,veg and gr. • Non-linear regression using (, V) and (s 0,V) measurements • Accurate measurements • 3. InSAR phase: does not affect the regression
Tree height retrieval Errors are due to: Phase noise (low forest coherence) Residual atmospheric artefacts Small contrast between ground and vegetation Vegetation height Interferometric tree height
Conclusions • More knowledge about InSAR phase properties in forests • IWCM describes the forest „topographic“ effects well • Compensation of atmospheric artefacts: difficult in large forests • Phase noise is dominant • Number of useful InSAR pairs is small • Tree height estimation is limited