Tree height estimation from multi-temporal ERS SAR interferometric phase

1. 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

2. 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?

3. 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?

4. 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

5. 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

6. Interferometric tree height Seasonality? Frozen Winter Frozen Snowfall Multitemporal

7. 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

8. 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

9. 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

10. 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