Monitoring and Retrieving Rice Phenology by
means of Satellite SAR Polarimetry at X-band
Juan M. Lopez-Sanchez
J. David Ballester-Berman
Shane R. Cloude
Signals, Systems & Telecommunications Group
University of Alicante
AEL Consultants
IEEE IGARSS
Vancouver, July 27, 2011
Motivation
• Motivation: examples of known demands from rice farmers in Spain
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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
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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:
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Analysis and interpretation of the polarimetric behavior of rice at different
phenological stages
If possible, proposal of a retrieval approach based on scattering properties
IEEE IGARSS
Vancouver, July 27, 2011
Site
• Mouth of the Guadalquivir river, Sevilla (SW Spain)
30km x 30km
IEEE IGARSS
Vancouver, July 27, 2011
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)
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Weekly (defined at field level):
• Phenology: BBCH stage (0-99)
• Vegetation height
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Additional information:
• Sowing and harvest dates
• Plantation density: plants/m2, panicles/m2
• Yield (kg/ha)
• Important:
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A water layer is always present at ground during the campaign
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Sowing is carried out by spreading seeds (from a plane) randomly over flooded
fields
IEEE IGARSS
Vancouver, July 27, 2011
Satellite data
2008
2009
Failed orders
Available images
TerraSAR-X images provided by DLR in the framework of projects LAN0021 and LAN0234
IEEE IGARSS
Vancouver, July 27, 2011
Analysis of observations
• TerraSAR-X, 30 deg, 2009: Temporal evolution
HH VV HH-VV
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Analysis of observations
• TerraSAR-X HHVV dual-pol images: List of observables
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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 (H2a): Entropy and alpha
Model-based decomposition: Random volume + polarized term (rank1)
Coherent acquisition
of co-pol channels
IEEE IGARSS
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Analysis of observations vs phenology
HH and VV power
• Power
Nearly random volume
Wind induced
roughness
Increasing randomness
Development
Vegetative
phase
Double-bounce
Reproductive
phase
Maturation
Vertical orientation:
differential extinction
IEEE IGARSS
Vancouver, July 27, 2011
Analysis of observations vs phenology
• Correlation between HH and VV
Magnitude
Vegetative
phase
Reproductive
phase
Phase (PPD)
Maturation
IEEE IGARSS
Vancouver, July 27, 2011
Vegetative
phase
Reproductive
phase
Maturation
Analysis of observations vs phenology
• Eigenvalue decomposition
Entropy
Alpha (dominant)
Vegetative
phase
Wind induced
roughness
+
Double-bounce
IEEE IGARSS
Vancouver, July 27, 2011
Reproductive
phase
Maturation
Retrieval of phenology from TSX data
• Basic retrieval approach with a single acquisition (TSX)
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Four parameters
• HHVV coherence and phase difference
• Entropy and alpha1
IEEE IGARSS
Vancouver, July 27, 2011
Retrieval of phenology from TSX data
• Basic retrieval approach with a single acquisition (TSX)
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Five phenological intervals
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Decision plane
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Vancouver, July 27, 2011
Retrieval of phenology from TSX data
• Retrieval results (parcel F)
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Retrieval of phenology from TSX data
• Retrieval results: Comparison against ground data
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Percentage of pixels assigned to each stage within a parcel
Parcel B
Parcel C
IEEE IGARSS
Vancouver, July 27, 2011
Retrieval of phenology from TSX data
• Comments on the approach
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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
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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
IEEE IGARSS
Vancouver, July 27, 2011
Conclusions
• Coherent dual-pol data provided by TerraSAR-X have
been useful for retrieving phenology of rice fields with a
single acquisition
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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)
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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)
IEEE IGARSS
Vancouver, July 27, 2011
Future lines of research
•
Multi-temporal approaches (time series)
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Time coordinate provides extra information
Multi-angular (and multi-temporal) integration
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Ideal to reduce refresh time or increase spatial coverage
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Development of an operational scheme with farmers
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Pending issues:
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Presence of rain
Other species within the rice fields (mixture)
Application to rice under different farming practices:
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Plantation procedures and arrangements
Dry ground at some moments
IEEE IGARSS
Vancouver, July 27, 2011