Keith Morrison & Muhammad Yasin

1. The Extraction of InSAR Information from Imagery of a Wind-Blown Tree Canopy with a Ground-Based SAR Keith Morrison & Muhammad Yasin Department of Aerospace, Power and Sensors, University of Cranfield, Shrivenham, UK & DLR, Institut für Hochfrequenztechnik und RadarsystemeWeßling, Germany

2. The GB-SAR System • Portable SAR / InSAR Imaging System • All-weather • L through X-band (1-12GHz) • Fully polarimetric VV,HH,VH,HV

3. Rationale • Particular open questions relate to the conditions under which PolInSAR produces accurate measurements of biomass, with respect to: • canopy structure (species, density, height distribution) • technical sensor specifications • imaging conditions (spatial and temporal)

4. Presentation Can the GB-SAR system be used to obtain meaningful PolInSAR measurements of forest canopies? Considerations GB-SAR imaging timescale on order of tens of minutes Can expect wind-induced target motion Can the results be related to air- and space-borne ?

5. SAR Imaging of Tree

6. Sweet Chestnut (castanea sativa mills)

7. Tree spatially isolated in grassy parkland

8. Tree Dimensions • Trunk Height = 25m • Trunk diameter at DBH = 1.7m • Trunk Circumference at DBH = 5.6m • Maximum tree width (2m from ground) = 15m • Tree width at ¾ of tree height = 12 m • Maximum tree depth = 18m • Tree depth at ¾ of tree height = 11m

10. 5m 9.6m 25m 14m

11. Winter View, from back

12. Radar Parameters SF-CW Radar Type 13th July 2005 Date of observation 4.000GHz Start frequency (GHz) 6.000GHz End frequency 1601 Number of frequencies per sweep 1.25MHz Frequency step interval 3000Hz VNA IF bandwidth +8dBm Effective transmit power at antenna VV Polarisation 20mm Aperture elemental sampling, dx 3680mm Aperture size, D 185 Number of aperture samples 1 or 8 Data averaging factor 9.6m Antenna height above ground 0.9s Tsweep, frequency sweep time 1.1s Tmove, antenna movement time

14. Scans 1-9. Av. Factor 1 Figure 4.1: The log-amplitude images of Scans (top to bo

15. Scans 10 & 11. Av Factor 8 Figure 4.2: The log-amplitude images of Scans 10 (top) and 11. The plots are 3-29m in rang

16. Antenna & Space-loss

17. Corrected Images

18. Bulk Averaging - Tree

20. Canopy Attenuation

21. 1/(1+SNR-1) InSAR Decorrelation γ = γNoise . γSpatial . γSystem.γTemporal

22. Coherence Analysis Figure 8.7: Coherence maps of (top left): Scans 2 & 3; (top right) Scans 8 & 9; (bottom left) Scans

23. Coherence vs Amplitude

24. Coherent Summation

25. Distribution of Coherence

27. Regression Analysis

29. y = m.x + c

30. Regression Fit – Gradient (m)

31. Regression Fit - Constant (c)

32. Standard Deviation From Fit

33. Model Simulations

35. Effects of Wind-Motion

36. Motion Simulation

37. Sim_1a vs Sim_1b Sim_1a vs Sim_2a

39. InSAR Phase

40. InSAR Phase vs Coherence The curves show the frequency of occurrence with phase for varying coherence ranges. The outermost curve is over the entire coherence range 0-1. The next innermost curve shows the distribution 0.1-1, then 0.2-1, and so on. The innermost curve shows the phase distribution 0.9-1.

41. Non-Zero Baseline

42. Conclusions Investigation into whether the GB-SAR system can be used for InSAR & PolInSAR • Meaningful SAR Imaging of trees is feasible • Wind motion produces spreading of IPR into broadband unstructured azimuthal arcs • Good coherences obtained by observation in low wind conditions • Recovery of ‘static’ backscatter pattern by temporal averaging • Averaging also improves the coherence • However, latter might bias InSAR phase / height retrieval to stronger coherent features in canopy