Tree Height Estimation from Multi-temporal Ers Sar Interferometric Phase

Multi-temporal sets of ERS-1/2 SAR interferometric (InSAR) phase have been evaluated at several test sites in Europe for tree height estimation. Atmospheric artefacts affected a large number of image pairs. These were generally well compensated in case of large-scale artefacts over small forests, whereas for large forests their effect could only be assessed. Hence, the amount of pairs utilizable for further investigation considerably decreased. The interferometric tree height, i.e. the forest “topography” seen by an InSAR system, did not show temporal consistency because of the target phase noise, ranging from slightly below the ground level to slightly above the true tree height. With a multi-temporal combination, the estimates were below the true tree height, depending on the canopy closure. To retrieve the total true height from InSAR tree height measurements, the Interferometric Water Cloud Model was used. Modelled InSAR tree heights resulted generally in reasonable agreement with observations. Nevertheless, because of the strong noise components and the weak contrast between ground and vegetation coherence, the compensated tree height showed an almost constant value, independent of the true height. Hence, the several sources of error and uncertainty strongly limit the usefulness of C-band repeat-pass SAR interferometry for tree height estimation.