Model based forest height estimation with ALOS/PalSAR: A first study.

Transcription

1 Model based forest height estimation with ALOS/PalSAR: A first study. K.P. Papathanassiou*, I. Hajnsek*, T.Mette*, S.R. Cloude** and A. Moreira* * (DLR) (DLR-HR) Oberpfaffenhofen, Germany ** AEL Consultants (AELc) Scotland, UK

2 Forest Height and Biomass Estimation Conventional Biomass Estimation based on Backscatter Saturation: Biomass Saturation Limit [T/ha] [Kg/(m^2)] % of Earths Vegetated Area % of Total Biomass Stock C-band 20* 2 25% 4% L-band 40* % 8% P-band 100* % 20-25% Biomass Estimation based on Forest Height: Tree Height % 80-99% The expected above ground biomass estimation accuracy is about 30%. Information about species and/or forest structure can increase the estimation accuracy * M. L. Imhoff, Radar Backscatter and Biomass Saturation: Ramifications for Global Biomass Inventoty,IEEE TGARS, Vol. 33, No. 2, March 1995

3 Forest Parameter Inversion using Pol-InSAR INTERFEROMETRIC POLARIMETRIC OBSERVABLES Step I: Modelling SAR Image HH COHERENT SCATTERING MODEL Interferometric Coherence in Three Polarisations FOREST PARAMETERS Forest Height Forest Extinction Underlying Topography Interferometric Phase in Three Polarisations

4 Forest Parameter Inversion using Pol-InSAR INTERFEROMETRIC POLARIMETRIC OBSERVABLES Step II: Inversion SAR Image HH COHERENT SCATTERING MODEL Interferometric Coherence in Three Polarisations FOREST PARAMETERS Forest Height Forest Extinction Underlying Topography Interferometric Phase in Three Polarisations

5 Polarimetric SAR Interferometry: Modeling Nature 30-70K Leaves, ~ 2K Branches, Leave Form, Branch Orientation Distribution, Tree height, Ground Moisture and Roughness Random Volume + Ground Model Volume height: h V Extinction: σ Topography: φ 0 G/V Ratio: m(polarisation) Single Baseline Single Frequency Inversion Scenarios: Single-Polarisation Interferometry Dual-Polarisation Interferometry Quad-Polarisation Interferometry 4 Parameters 2 Observables 5 Parameters 4 Observables 6 Parameters 6 Observables Underestimated Underestimated Solvable!!!

6 Scenario for Spaceborne Single-Pass PolInSAR: Passive Micro Satellite Configuration Receive-only micro satellites ( ) Illuminator ( ) PInSAR 3 Passive Micro-satellites Ant. Length (Rx): 3.0m Ant. Width.(Rx): 3.0m Weight (each) Kg PALSAR / ALOS Bandwidth: 28MHz Orbit Height: 691Km Ant. Length (Tx): 8.9m Ant. Width.(Tx): 3.1m Weight (ALOS): 4000Kg

7 Fichtelgebirge Test Site Topography: m a.s.l. (Schneeberg) Azimut Range L-band HH Image X-band Single Pass Inteferometric DEM Vegetation: typically even-aged stands up to 300 t/ha 95 % Norway spruce (Picea abies) 2 % european beech (Fagus sylvatica)

8 Test Site: Fichtelgebirge, Germany Beech Stands

9 Height Validation Fi04 Spruce afforestation Height: 8-9 m 30 Fi05 Heterogeneous spruce stand Height: m 30 Fi_i Homogeneous (rel.) mixed spruce beech stand Height: m height [m] height [m] height [m] Groundtruth Radar (Pol-InSAR) ESAR / Test Site: Fichtelgebirge, Germany

10 Forest Height & Biomass Maps ESAR / Test Site: Fichtelgebirge, Germany Azimut Range L-band HH

11 Scattering Model: Geometrical Interpretation Interferometric Coherence: ~ r γ ( w ) = ~ r γv + m( w ) exp( iφ0 ) r 1 + m( w ) ~ r γ ( w ) r ~ m( w ) ~ = exp( iφ0 ) γ V + r ( 1 γv ) 1 + m( w ) ~ r r γ ( w ) = exp( iφ0 ) ) [ B + X ( w A ] Equation of a straight line in the complex plane!!! - Line Slope := f (Baseline, Vegetation Height, and, Extinction ) - Line Length := f (Baseline, Vegetation Height, Extinction, and, Ground Scat. Amplitude) Frequency Dependent Parameters The optimal polarisations represent the limiting points of the visible line part

12 Temporal Decorelation of the Volume Scatterer Temporal Effect: Random movement of the scattering particles in the volume : Wind Effects. The 2nd order polarimetric properties of the ground [T G ] and the volume scatterer [T V ] remain the same: Ground / Volume amplitude ratios m (w r ) are unaffected r 0 γt f ( m ( w )) 1 Interferometric Coherence: is equal for all polarisations!!! ~ r ~ r γt γv + m( w ) γ ( w ) = exp( iφ0 ) r 1 + m( w ) ~ r γ ( w ) r ~ m( w ) ~ = exp( iφ0 ) γ T γv + r ( 1 γt γv ) 1 + m( w ) the line is preserved!!! φ 0 affects slope of the line but not the position of the points on the line. remains invariant under variations of. The estimation of is still possible!!! ~ γ V leads to an underestimation of and thus an overestimation of volume height. φ 0

13 Temporal Baseline: 24 Hours Line Comparison: C-Band vs. L-Band SIR-C / Test Site: Kudara,Russia Azimuth Pauli RGB Image Range C-band L-band

14 Temporal Baseline: 24 Hours Line Comparison: C-Band vs. L-Band SIR-C / Test Site: Kudara,Russia Azimuth Range Pauli RGB Image C-band L-band

15 C-band Line Validation: Boreal Forest SIR-C / Test Site: Kudara,Russia Azimuth Pauli RGB Image Range Chi-Square Image Validity Mask: Q > 80%

16 L-band Line Validation: Boreal Forest SIR-C / Test Site: Kudara,Russia Azimuth Range Pauli RGB Image Chi-Square Image Validity Mask: Q > 80%

17 Temporal Decorelation of the Volume Scatterer Ambiguity area Line of ct. extinction γ ~ V Volume Height Estimation: Assumption of the mean extinction value σ Estimate the corresponding ~ γ V value ~ V γ = h V 2 σ z' exp( iκz z') exp dz' cosθ 0 0 h V 2 σ z' exp dz' cosθ 0 0 h V

18 Inversion Performance Analysis = 1. 0 σ=±10% = 0. 8 σ=±10% = 0. 6 σ=±10% = 0. 4 σ=±10% k z =0.06 (2π-Height~ 100m), Look angle θ=40º, Looks=32

19 Inversion Performance Analysis = 0. 8 σ=±10% = 0. 8 σ=±20% Erroneous extinction values lead to An offset in the estimation only at high volume heights = 0. 8 σ=±30% = 0. 8 σ=±40% k z =0.06 (2π-Height~ 100m), Look angle θ=40º, Looks=32

20 Inversion Performance Analysis = 1. 0 σ=±10% = 0. 8 σ=±10% = 0. 6 σ=±10% = 0. 4 σ=±10% k z =0.06 (2π-Height~ 100m), Look angle θ=40º, Looks=32

21 Conclusions Temporal decorrelation makes in general accurate parameter inversion impossible. Moderate temporal decorrelation of the volume can be accounted in the RVoG inversion model. Experimental data demonstrate the validity of the model predictions -The line is preserved! The temporal decorrelation in the RVoG model cannot be inverted in a unique way without regularisation. Reqularisation by fixing the extinction coefficient is considered as a widely robust first approach The availability of a second temporal / spatial baseline may allow a more flexible / accurate regularisation

22 Experimental Airborne SAR: E-SAR Flexible multi-channel SAR- System P-, L-, S-, C- and X-Band Full polarimetric in P- and L- Band High-resolution Imaging (up to 0.5 m resolution in azimuth) Along- and Across-Track Interferometry Real-time SAR Processing Innovative Imaging Modes (polarimetric SAR interferometry and tomography)

23 Basic Imaging Geometry for SAR Tomography L z n r N-1 N Horizontal baseline [m] x Azimuth [m] y

24 Polarimetric E-SAR Image, L-Band ) spruce forest 2) buildings 3) cars 4) corner reflector

25 First Demonstration of Airborne SAR Tomography 1) 1) German Reigber, Aerospace A. et al: ìfirst Center Demonstration of Airborne SAR Tomography using Pol-InSAR Multibaseline Working L-Band Group Dataî. DLR IEEE HR Trans. on Geosc. and Remote Microwaves Sensing, and Vol. Radar 38 (5), Institute Sept. 20

26 Spruce Forest Backscattering Profiles (15-20 m height) 40 HH VV HV Height [m] Height [m] Height [m] HH+VV HH-VV 2*HV Height [m] Height [m] Height [m] Backscattering [db] Backscattering [db] Backscattering [db]