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