On the potential of TanDEM-X for the retrieval of agricultural crop parameters
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Transcript of On the potential of TanDEM-X for the retrieval of agricultural crop parameters
IEEE IGARSSVancouver, July 27, 2011
On the potential of TanDEM-X for the retrieval of agricultural crop parameters
by single-pass PolInSAR
Juan M. Lopez-Sanchez and J. David Ballester-Berman
Signals, Systems and Telecommunications Group University of Alicante, Spain
IEEE IGARSSVancouver, July 27, 2011
Motivation• Final application: information for helping farming practices
– Requirement: Timely and local information about crop phenology, condition, and other indicators
– TanDEM-X: proof-of-concept
– High spatial resolution (1-3 m)
– Short revist time (11 days)
– Single-pass interferometry
• Parameters of interest to be retrieved with single-pass PolInSAR:
– Vegetation height: correlated to phenology in many crops (especially during the vegetative phase)
– Structural parameters related to phenology and crop condition:
– Extinction
– Vertical profiles (using PCT)
– Other physical features (target decomposition): randomness, orientation of leaves and branches, water content, etc.
IEEE IGARSSVancouver, July 27, 2011
Methodology• A number of direct models have been developed in the last years:
– General: Homogeneous volume over ground
– Model: Analytical expression of the complex interferometric coherence, as a function of polarization channel
1
2
Alternate-tx
(monostatic)
Random Oriented
Direct
Double-bounce
Both
VOLUM
E
GRO
UND
Single-tx (bistatic)
IEEE IGARSSVancouver, July 27, 2011
Methodology• Examples
RVoG: single-tx with double-bounce from ground
RVoG: alternate-tx, and single-tx with direct ground
• All coherences are aligned
• Line depends on scene
and interferometer
IEEE IGARSSVancouver, July 27, 2011
Methodology• Examples OVoG: alternate-tx, and
single-tx with direct groundOVoG: single-tx with
double-bounce from ground
Coherences are no longer aligned
IEEE IGARSSVancouver, July 27, 2011
Methodology• Examples
RVoG with both ground contributions
OVoG with both ground contributions
Alternate-tx Single-tx
Alternate-txSingle-tx
IEEE IGARSSVancouver, July 27, 2011
Methodology• Baseline requirements
– If too small: no decorrelation, hence all coherences in a small cluster (i.e. insensitive)
– If too large: extreme volume decorrelation, hence low coherence and presence of phase noise
– Important: kz * hv (or kv = kz*hv/2)
– Ideal case: kv = 1 [Cloude 2009]
• Typical example for crops: hv = 1 m
– With the mentioned criterion: kz = 2, i.e. hamb = 3.14 m
– TanDEM-X: Bn ~ 3 km (bistatic) or 1.5 km (alternate-tx)
– Normal mode: Bn ~ 250-300 m, kz ~ 0.2-0.4
– Some sensitivity is expected…
IEEE IGARSSVancouver, July 27, 2011
Available data set: Wallerfing (Germany)
• Date: April 12, 2011 (no ground truth, but scarce agriculture is expected)
• Mode: Bistatic
• Polarizations: HH VV
• Incidence angle (scene center): 32.66 degrees
• Height of ambiguity: 133.4 m
• Perpendicular baseline: 76.56 m
• InSAR sensitivity:
• Vertical wavenumber kz = 0.0471
• For agricultural crops with hv = 1 m, kv = 0.0236 << 1
IEEE IGARSSVancouver, July 27, 2011
Wallerfing: RGB composite
HH-VVVVHH
IEEE IGARSSVancouver, July 27, 2011
Wallerfing: coherence maps
HH-VVVV
HH HH+VV
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): RGB composite
Sample extracted from the image
HH-VVVVHH
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): coherence maps
HH-VVVV
HH HH+VV
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): backscatter
VV
HH
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): SNR effect
• Low backscattering levels are expected from agriculture fields
– Data sample: bare fields or with scarce vegetation: below -10 dB
• NESZ in these TSX/TDX images (from annotated info): - 21 to -24 dB
• Decorrelation due to SNR:
SNR
SNR 11
1
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): SNR effect
• If NESZ = -22 dB is assumed, decorrelation due to SNR can be estimated from backscattering levels:
Example: Typical values for HH and VV over rice fields with TSX
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): SNR effect
• Application to these data: HH, and similar for VV
Measured Estimated from SNR
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): SNR effect
• Application to these data: HH+VV
Measured Estimated from SNR
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): SNR effect
• Application to these data: HH-VV
Measured Estimated from SNR
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): coherence set
Set of 6 coherences:HH, VVHH+VV, HH-VVOptimum (1st and 2nd)
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): interf. phases
HH-VVVV
HH HH+VV
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): diff. interf. phases
Phase HH – Phase VV Phase HH+VV – Phase HH-VV
Height HH – Height VV Height HH+VV – Height HH-VV
IEEE IGARSSVancouver, July 27, 2011
Wallerfing (sample): PolSAR
Entropy
Average alpha
alpha1
IEEE IGARSSVancouver, July 27, 2011
Planned acquisitions• Generic: various types of crops
– Barrax (Albacete), SE Spain
– Types: wheat, barley, maize, etc.
– Farming practices information and optical images available
– Measurements of LAI, vegetation height, phenology, soil moisture
– Roseworthy farm (Adelaide), S Australia
– Types: wheat, barley, legumes, peas, beans, canola.
– Measurements of vegetation height, phenology, etc.
• Thematic:
– Rice fields in Sevilla, SW Spain
– Weekly measurements of phenology, height, condition changes
– Extra data: sowing & harvest date, plantation density, yield
IEEE IGARSSVancouver, July 27, 2011
Expected results• Better results are expected for the planned acquisitions (Jun-Aug 2011):
– Baselines: 240 – 300 m
– Many acquisitions in alternate bistatic mode
• Regarding the application: Expected limitations:
– Noise
– Reduced swath: small spatial coverage
– Potential solution: combination of passes (asc, desc, etc.)