monitoring and retrieving rice phenology by means of satellite sar polarimetry at x-band

IEEE IGARSSVancouver, July 27, 2011

Monitoring and Retrieving Rice Phenology by means of Satellite SAR Polarimetry at

X-band Juan M. Lopez-Sanchez

J. David Ballester-Berman

Signals, Systems & Telecommunications GroupUniversity of Alicante

Shane R. Cloude

AEL Consultants


Motivation

• Motivation: examples of known demands from rice farmers in Spain– Timely information for:

• Effective germination measurements• When all plants have emerged they count their number. If low, more seeds are added

• Nitrogen fertillization stop• Once all panicles in a field have appeared, fertilization is not longer needed

• Excessive fertilization may cause an increase in pests

– Detection of cultivation problems due to water salinity: areas with delayed development

• Objective: Is it possible to retrieve the current phenological stage from a single acquisition?

• Approach:– Analysis and interpretation of the polarimetric behavior of rice at different

phenological stages– If possible, proposal of a retrieval approach based on scattering properties


Site

• Mouth of the Guadalquivir river, Sevilla (SW Spain)

30km x 30km


Ground campaign

• Campaigns: 2008 and 2009

• Ground measurements over 5-8 parcels provided by the local

association of rice farmers (Federación de Arroceros de Sevilla)

– Weekly (defined at field level):• Phenology: BBCH stage (0-99)

• Vegetation height

– Additional information:• Sowing and harvest dates

• Plantation density: plants/m2, panicles/m2

• Yield (kg/ha)

• Important:

– A water layer is always present at ground during the campaign

– Sowing is carried out by spreading seeds (from a plane) randomly over flooded

fields


Satellite data

2008

2009

TerraSAR-X images provided by DLR in the framework of projects LAN0021 and LAN0234

Failed orders

Available images


Analysis of observations• TerraSAR-X, 30 deg, 2009: Temporal evolution

HH VV HH-VV


Coherent acquisition of co-pol channels

Analysis of observations• TerraSAR-X HHVV dual-pol images: List of observables

– Backscattering coefficients and HH/VV ratio– Backscattering coefficients at the Pauli basis (HH+VV, HH-VV)– Correlation between HH and VV: magnitude and phase (PPD)– Correlation between 1st and 2nd Pauli channels: mag. and phase– Eigenvector decomposition (H2): Entropy and alpha– Model-based decomposition: Random volume + polarized term (rank1)


• Power

Analysis of observations vs phenology

HH and VV power

Wind induced roughness

Double-bounce

Vertical orientation:differential extinction

Development

Increasing randomness

Nearly random volume

Vegetative phase

Reproductive phase

Maturation


• Correlation between HH and VV


Magnitude Phase (PPD)

Vegetative phase

Reproductive phase

Maturation Vegetative phase

Reproductive phase

Maturation


• Eigenvalue decomposition


Entropy Alpha (dominant)

Vegetative phase

Reproductive phase

Maturation

Wind induced roughness

Double-bounce+


Retrieval of phenology from TSX data• Basic retrieval approach with a single acquisition (TSX)

– Four parameters• HHVV coherence and phase difference

• Entropy and alpha1


Retrieval of phenology from TSX data• Basic retrieval approach with a single acquisition (TSX)

– Five phenological intervals

– Decision plane


Retrieval of phenology from TSX data• Retrieval results (parcel F)


Retrieval of phenology from TSX data• Retrieval results: Comparison against ground data

– Percentage of pixels assigned to each stage within a parcel

Parcel B

Parcel C


Retrieval of phenology from TSX data• Comments on the approach

– Useful tracking of phenology:• At parcel level: BBCH agrees with the stage assigned to the

majority of pixels inside the parcels (with some exceptions)

• At (multi-looked) pixel level: parts with different development within

a parcel are well identified

– But not perfect..• The algorithm is very ‘simple’: parameters and thresholds have

been selected manually (it could be optimized)

• An ambiguity between plant emergence (BBCH 18-21) and last

stages (BBCH +50) is still present at some areas. Both are

characterized by high entropies


Conclusions

• Coherent dual-pol data provided by TerraSAR-X have been useful for retrieving phenology of rice fields with a single acquisition

– Advantages when compared to other possible approaches:• 11-days revisit rate with the same sensor & mode• High spatial resolution • Retrieval with a single pass is possible (single-pol and incoherent dual-pol

are not enough)

– Limitations:• There remain some ambiguities that might be solved with full-pol data (e.g.

using anisotropy), but not in operational mode with TSX• Low coverage: TSX dual-pol swath is 15 km on ground• Some measurements are below or close to the noise level of TSX (-19 dB)


Future lines of research• Multi-temporal approaches (time series)

– Time coordinate provides extra information

• Multi-angular (and multi-temporal) integration– Ideal to reduce refresh time or increase spatial coverage

• Development of an operational scheme with farmers

• Pending issues:– Presence of rain– Other species within the rice fields (mixture)

• Application to rice under different farming practices:– Plantation procedures and arrangements– Dry ground at some moments

monitoring and retrieving rice phenology by means of satellite sar polarimetry at x-band

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