Monitoring and Retrieving Rice Phenology by means of Satellite SAR Polarimetry at X-band
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Transcript of 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
IEEE IGARSSVancouver, July 27, 2011
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
IEEE IGARSSVancouver, July 27, 2011
Site
• Mouth of the Guadalquivir river, Sevilla (SW Spain)
30km x 30km
IEEE IGARSSVancouver, 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)
– 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
IEEE IGARSSVancouver, July 27, 2011
Satellite data
2008
2009
TerraSAR-X images provided by DLR in the framework of projects LAN0021 and LAN0234
Failed orders
Available images
IEEE IGARSSVancouver, July 27, 2011
Analysis of observations• TerraSAR-X, 30 deg, 2009: Temporal evolution
HH VV HH-VV
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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)
IEEE IGARSSVancouver, July 27, 2011
• 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
IEEE IGARSSVancouver, July 27, 2011
• Correlation between HH and VV
Analysis of observations vs phenology
Magnitude Phase (PPD)
Vegetative phase
Reproductive phase
Maturation Vegetative phase
Reproductive phase
Maturation
IEEE IGARSSVancouver, July 27, 2011
• Eigenvalue decomposition
Analysis of observations vs phenology
Entropy Alpha (dominant)
Vegetative phase
Reproductive phase
Maturation
Wind induced roughness
Double-bounce+
IEEE IGARSSVancouver, July 27, 2011
Retrieval of phenology from TSX data• Basic retrieval approach with a single acquisition (TSX)
– Four parameters• HHVV coherence and phase difference
• Entropy and alpha1
IEEE IGARSSVancouver, July 27, 2011
Retrieval of phenology from TSX data• Basic retrieval approach with a single acquisition (TSX)
– Five phenological intervals
– Decision plane
IEEE IGARSSVancouver, 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
– Percentage of pixels assigned to each stage within a parcel
Parcel B
Parcel C
IEEE IGARSSVancouver, July 27, 2011
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
IEEE IGARSSVancouver, 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
– 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)
IEEE IGARSSVancouver, July 27, 2011
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