The Extraction of InSAR Information from The Extraction of InSAR Information from Imagery of a Wind-Blown Imagery of a Wind-Blown

Tree Canopy with a Ground-Based SARTree Canopy with a Ground-Based SAR

Keith Morrison & Muhammad YasinKeith Morrison & Muhammad Yasin

Department of Aerospace, Power and Sensors, Department of Aerospace, Power and Sensors, University of Cranfield, Shrivenham, UKUniversity of Cranfield, Shrivenham, UK

& & DLR, Institut für Hochfrequenztechnik und RadarsystemeDLR, Institut für Hochfrequenztechnik und Radarsysteme

Weßling, GermanyWeßling, Germany

The GB-SAR SystemThe GB-SAR System

• Portable SAR / InSAR Imaging System

• All-weather

• L through X-band (1-12GHz)

• Fully polarimetric VV,HH,VH,HV

RationaleRationale

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)

PresentationPresentation

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 ?

SAR Imaging of TreeSAR Imaging of Tree

Sweet Chestnut Sweet Chestnut (castanea sativa mills)(castanea sativa mills)

Tree spatially isolated Tree spatially isolated in grassy parklandin grassy parkland

Tree DimensionsTree 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

9.6m

14m

25m

5m

Winter View, Winter View, from backfrom back

Radar ParametersRadar Parameters

SF-CW Radar Type13th July 2005 Date of observation4.000GHz Start frequency (GHz)6.000GHz End frequency1601 Number of frequencies per sweep1.25MHzFrequency step interval3000Hz VNA IF bandwidth+8dBm Effective transmit power at antennaVV Polarisation20mm Aperture elemental sampling, dx3680mmAperture size, D185 Number of aperture samples1 or 8 Data averaging factor9.6m Antenna height above ground0.9s Tsweep, frequency sweep time1.1s Tmove, antenna movement time

Scan Start Time End Time Duration Averaging Lapsed

1 16:02:18 16:08:58 6.7 min 1 -

2 16:32:37 16:39:18 6.7 min 1 0 min

3 16:41:18 16:47:58 6.7 min 1 8.7 min

4 16:48:46 16:55:27 6.7 min 1 16.2 min

5 16:57:10 17:03:51 6.7 min 1 24.6 min

6 17:04:44 17:11:24 6.7 min 1 32.1 min

7 17:12:50 17:19:30 6.7 min 1 40.2 min

8 17:20:45 17:27:25 6.7 min 1 48.1 min

9 17:28:34 17:35:15 6.7 min 1 56.0 min

10 17:38:00 18:08:08 30.1 min 8 77.1 min

11 18:13:06 18:43:13 30.1 min 8 112.2 min

Scans 1-9. Av. Factor 1

Scans 10 & 11. Av Factor 8

Antenna & Space-loss Antenna & Space-loss

Corrected ImagesCorrected Images

Bulk Averaging - TreeBulk Averaging - Tree

Canopy AttenuationCanopy Attenuation

InSAR DecorrelationInSAR Decorrelation

γ = γNoise . γSpatial . γSystem . γTemporal

1/(1+SNR-1)

22

43

min 4 mNNN

FLL

GG

R

P

P

avxf

rt

rtt

r

Coherence AnalysisCoherence Analysis

Coherence vs AmplitudeCoherence vs Amplitude

Coherent SummationCoherent Summation

Distribution of CoherenceDistribution of Coherence

Regression AnalysisRegression Analysis

y = m.x + cy = m.x + c

Regression Fit – Gradient (m)Regression Fit – Gradient (m)

Regression Fit - Constant (c)Regression Fit - Constant (c)

Standard Deviation From FitStandard Deviation From Fit

Model SimulationsModel Simulations

Effects of Wind-MotionEffects of Wind-Motion

Motion Motion SimulationSimulation

Sim_1a vs Sim_1b Sim_1a vs Sim_2a

InSAR PhaseInSAR Phase

InSAR Phase vs CoherenceInSAR 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.

Non-Zero BaselineNon-Zero Baseline

ConclusionsConclusions

• 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

Investigation into whether the GB-SAR system can be used for InSAR & PolInSAR