IEEE IGARSS Vancouver, July 27, 2011 On the potential of TanDEM-X for the retrieval of agricultural...

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


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.


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)


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


Methodology• Examples OVoG: alternate-tx, and

single-tx with direct groundOVoG: single-tx with

double-bounce from ground

Coherences are no longer aligned


Methodology• Examples

RVoG with both ground contributions

OVoG with both ground contributions

Alternate-tx Single-tx

Alternate-txSingle-tx


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…


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


Wallerfing: RGB composite

HH-VVVVHH


Wallerfing: coherence maps

HH-VVVV

HH HH+VV


Wallerfing (sample): RGB composite

Sample extracted from the image

HH-VVVVHH


Wallerfing (sample): coherence maps

HH-VVVV

HH HH+VV


Wallerfing (sample): backscatter

VV

HH


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



• 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



• Application to these data: HH, and similar for VV

Measured Estimated from SNR



• Application to these data: HH+VV




• Application to these data: HH-VV



Wallerfing (sample): coherence set

Set of 6 coherences:HH, VVHH+VV, HH-VVOptimum (1st and 2nd)


Wallerfing (sample): interf. phases

HH-VVVV

HH HH+VV


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


Wallerfing (sample): PolSAR

Entropy

Average alpha

alpha1


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


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.)

IEEE IGARSS Vancouver, July 27, 2011 On the potential of TanDEM-X for the retrieval of agricultural...

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