IEEE IGARSS Vancouver, 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 IGARSS Vancouver, July 27, 2011 Outline Motivation: final application Methodology – Direct models and inversion issues: experimental demonstration of theoretical models with TanDEM-X data – Influence of the acquisition mode and other parameters – Prediction of performance (baseline requirements) Analysis of available datasets Planned acquisitions and expected results

IEEE IGARSS Vancouver, 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 IGARSS Vancouver, 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 VOLUME GROUND Single-tx (bistatic)

IEEE IGARSS Vancouver, 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 IGARSS Vancouver, July 27, 2011 Methodology Examples OVoG: alternate-tx, and single-tx with direct ground OVoG: single-tx with double-bounce from ground Coherences are no longer aligned

IEEE IGARSS Vancouver, July 27, 2011 Methodology Examples RVoG with both ground contributions OVoG with both ground contributions Alternate-tx Single-tx Alternate-tx Single-tx

IEEE IGARSS Vancouver, 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. h amb = 3.14 m – TanDEM-X: Bn ~ 3 km (bistatic) or 1.5 km (alternate-tx) – Normal mode: Bn ~ m, kz ~ – Some sensitivity is expected…

IEEE IGARSS Vancouver, 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): degrees Height of ambiguity: m Perpendicular baseline: m InSAR sensitivity: Vertical wavenumber kz = For agricultural crops with hv = 1 m, kv = << 1

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing: RGB composite HH-VV VV HH

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing: coherence maps HH-VV VV HH HH+VV

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): RGB composite Sample extracted from the image HH-VV VV HH

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): coherence maps HH-VV VV HH HH+VV

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): backscatter VV HH

IEEE IGARSS Vancouver, 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:

IEEE IGARSS Vancouver, 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 IGARSS Vancouver, July 27, 2011 Wallerfing (sample): SNR effect Application to these data: HH, and similar for VV Measured Estimated from SNR

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): SNR effect Application to these data: HH+VV Measured Estimated from SNR

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): SNR effect Application to these data: HH-VV Measured Estimated from SNR

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): coherence set Set of 6 coherences: HH, VV HH+VV, HH-VV Optimum (1st and 2nd)

IEEE IGARSS Vancouver, July 27, 2011 Wallerfing (sample): interf. phases HH-VV VV HH HH+VV

IEEE IGARSS Vancouver, 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 IGARSS Vancouver, July 27, 2011 Wallerfing (sample): PolSAR Entropy Average alpha alpha1

IEEE IGARSS Vancouver, 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 IGARSS Vancouver, 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.)