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POLinSAR 2007 Session Summaries and Recommendations
POLinSAR 2005 Session Summaries

POLinSAR 2007 Seed Questions

 

ALOS PALSAR First Results - Session

 

1) The ALOS/PALSAR commissioning phase has been completed, including the polarimetric calibration. How well does the calibration fulfil the user requirements for Pol-SAR and Pol-InSAR applications?

 

2) The use of dual-pol mode relaxes the SAR systems constraints caused by the increase of the PRF. Which applications require the use of fully polarimetric data? What is the recommendation for future SAR systems?

 

3) Based on the current operation plan, the incidence angle is almost fixed to 21.5 degrees, and it is possible to select only between 9.9 degrees and 26 degrees. For the time of the future operation plan setting (probable 3 years after), which application needs smaller and larger off-nadir angles?

 

 

Theoretical Studies – Session

 

1) Surface and Subsurface Scattering Theory: One key motivation for using radar polarimetry is the ability to employ ratios for robust surface parameter estimation, primarily the decoupling of surface roughness and moisture/salinity in a single pass sensor.  What is the current status of the estimated accuracy and market impact of near and deep surface retrieval algorithms?

 

2) Are the requirements of SP algorithms compatible with existing sensor geometries,  for example: a) Quad vs Dual Pol, b) those that use cross polarisation vs. copolar ratios c) high angle of incidence requirements for dynamic range and d) spatial resolution requirements vs. bandwidth restrictions of low frequency sensors)?  Is there any mismatch between planned sensor deployments and requirements of scattering models?

 

3) Vegetation Scattering: Most quantitative inversion algorithms for vegetation parameter estimation employing polarimetric interferometry require a dominance of volume over temporal and environmental effects. What are the prospects for space borne single pass Pol-InSAR systems and can theory help inform the potential new products and increased accuracies achievable using such systems. Is there a preference for standard or ping-pong interferometry for vegetation applications?

 

4) Multidimensional Filtering: are the current filters we use adequate for quantitative inversion, especially for algorithms employing coherence optimisation and eigenvalue analyses? In particular what is the effect of coherence bias on algorithm inversion accuracies and are there better techniques we could use to remove bias, reduce speckle effects and improve retrievals in multi-parameter surface and vegetation polinsar applications?

 

5) Bistatic Polarimetry Theory: Does the use of bistatic polarimetry offer new products or better accuracy in surface and volume scattering applications? In particular does it allow better estimation of vegetation biomass and surface moisture/roughness? What is the importance of the HV-VH channel in bistatic polarimetry and how do we calibrate such new information channels if reciprocity can no longer be used?

 

6) Optimisation Algorithms: there are now many forms of optimisation used in radar polarimetry and polinsar. Can these be used for practical product development or are they more useful in the algorithm development/research phase. If so, given their increased complexity, what software tools are available to implement these ‘optimum’ processing strategies in the application sector?

 

 

Advances in POLSAR and Pol-InSAR - Session

 

1) Is there any demonstrated benefit of multi-baseline Pol-InSAR (e.g. improved classification, more stable parameter estimation, tomography etc.)? What are the prospects for spaceborne MB (ALOS-2, Tandem-X etc.) and do they match the requirements of the algorithms?

 

2) ALOS-PalSAR is the first fully polarimetric space-borne sensor that will provide polarimetric data in a systematic way.

  • What are the potential polarimetric (PolSAR) applications that can be validated and established with that data? Are the associated experiments and data secured?
  • What are the potential Pol-InSAR applications that can be demonstrated and established with it?  Are the associated experiments and data secured?
  • Is the polarimetric SAR community prepared to face in a systematic way this unique opportunity? 

 

3) What are the potential new applications that can be demonstrated / validated on the basis of multi-temporal polarimetric data sets as provided by ALOS-PalSAR.

 

4) With ALOS on the sky and RadarSAT-2 and TerraSAR-X on the horizon, a multi-frequency observation scenario will be feasible at least for a set of experimental observations. What are the potential applications that can be demonstrated / validated on the basis of multi-frequency polarimetric datasets?

 

Applications: Forestry - Session

 

1) What can we expected from ALOS PALSAR for forest application through the knowledge learned from the validation studies carried out till now, and what kinds of products can be derived from PALSAR?

 

2) Based on our current knowledge, how do L and P band compare for forest height and biomass estimation in a Pol-InSAR configuration? How do they compare for other configurations (single band,  polarimetry...). What are their respective advantages?

 

3) Based on previous or on-going studies, what is the best compromise for forest biomass estimation as far as configuration: Pol-InSAR, full polarimetry, compact polarimetry, single channel (which one?).

 

4) How do the Pol-InSAR techniques compare to the other available techniques for measuring tree height or characterising the canopy? Are there still key technical issues hampering routine operations? How do Lidar measurements and Pol-InSAR measures compare?

 

Applications: Other - Session

 

1) Which is the current state of the art on retrieving physical information from snow or ice covered regions? Is this retrieval affected by environmental conditions? Are multifrequency techniques necessary to retrieve reliable information?

 

2) The analysis of polar, sub-polar and snow covered areas is critical since they are perhaps the first Earth environments affected by global warming. Could all these regions be analyzed using the same approaches and scattering models? Or should their study be considered separately?

 

3) During the last years the research community has started to focus on the study of wetland areas. Which is the objective of the analysis of these areas? Which physical parameters need to be retrieved? Which is the optimum configuration of a multichannel SAR system for the study of these regions?

 

4) The technique reported by B. Mercer and Q. Zhang has considered Pol-InSAR data from densely vegetated areas. Would it be possible to use the same approach in areas with different morphology, as for instance, the Mediterranean forest characterized by being less vegetated?

 

Compact Polarimetry

 

1) Faraday effects: What are the effects of Faraday rotation on compact polarimetry measurements? This is particularly important for L- Band and P-Band observations.

 

2) Calibration: How would one calibrate measurements made by such a system from space? Is there enough information to remove cross-talk, channel phase and amplitude imbalance etc. using the data itself or does this have to be done in pre-flight characterization?

 

3) Polarization ‘habits’: The planetary radar science community, using Earth-based radars to observe planetary bodies, adopted circular polarization precisely because of the problem of Faraday rotation. Their algorithms, excellent as they are, are based on having high-fidelity R and L circular polarization data available for more than 3 decades. A switch to linear polarization at this stage would be a very difficult transition for that community because of the wealth of literature built up using circular measurements.

 

The Earth Science community has more than 15 years worth of algorithm, publications, and empirical relationships built up based on the high-fidelity data available - which has linear polarization. Why should they find it easier to make the switch to a hybrid measurement? Remember science communities (as opposed to remote sensing technique or instrument developers) are very conservative. Think for example about the time it took for radar interferometry to evolve from an interesting technique (first demonstrated in space on Magellan in the early 90's) to the point where it is an accepted science measurement technique used by a wide community.

 

4) Antenna trade-offs: Fully polarimetric (quad-pol) measurements tend to be swath-limited (due to ambiguities) because the SAR antennas we use are often designed for single-pol operation. What if we were able to fly big enough antennas that the swath limitation went away?

 

5) Loss of information and continuity linked to the hybrid pol scheme: The comparison between information content of compact polarimetry of that of full polarimetry is difficult to achieve and must be addressed in the light of a given application. Hence the question could be: compact polarimetry, for what application? For one given application, what is the loss of compact polarimetry vs. full polarimetry in terms of information content?

 

Moreover, there are some cases where a switch to a hybrid pol scheme could in fact be detrimental to the science. There are few examples involving circular polarization in the literature for Earth observations (e.g. Rignot contribution that showed that the sensitivity to forest biomass for circularly polarized backscatter at P-Band was significantly worse than that for HV polarization). We are also beginning to see long-term land surface and ice sheet deformation emerge from the ERS and Radarsat measurements, which are both linear polarization. Switching to a hybrid polarization would do what to the coherence of such long-term measurements?

 

6) Information processing strategy: Two approaches can be addressed regarding compact polarimetric information processing: 1) Defining compact polarimetric parameters derived from the compact polarimetric acquisition (approach followed by K. Raney) 2) Estimation of a reconstructed full polarimetric information based on symmetry assumptions of the observed media (followed by J.C. Souyris et al.). To what extent can the two approaches be merged? How do the errors introduced in reconstructing the full polarimetric data compare with the standards for polarimetric calibration generated by the CEOS WG on SAR calibration?

 

7) Power budget: The choice of a mixed polarisation basis leads to a mismatch between transmitter and receiver with regards to polarisation. This mismatch is expected to reduce the power link by approximately 3 dB on one receiving channel. Moreover, in fully polarimetric systems we take advantage of the reciprocal nature of the scattering to coherently combine HV and VH to give an effective 3 dB improvement in SNR, as was first pointed out by Keith Raney. This may be lost in the case of compact polarimetry. Hence a new working point must be selected accordingly to this drawback. What are the most appropriate solutions: polarisation synthesis? Increase of the pulse peak power? Others?

 

Polarimetry and PSI – Session:

 

1) In which ways the polarimetric information increases the detectability and the utility of the PS?

 

2) In order to maximize the number of PS, which is the optimum balance between resolution and polarimetric information?  And is the number of PS a reasonable figure of merit, or do we have a better one, in the polarimetric case?

 

3) Is the Faraday rotation detectable and is it possible to find countermeasures, using Persistent Scatterers?

 

4) Apart calibrating the gain and the antenna directivity, could we use the PS to calibrate the polarimetric matrix of the system too?

 

 

 

 

 

 

 

Applications: Land-Agriculture

 

1) Techniques based on multi-temporal acquisitions are very well adapted to crop identification and auxiliary parameter estimation. Would Multi-Baseline Pol-InSAR acquisitions help to improve the accuracy of physical information estimation (plant biomass, height, density, …) in terms of sensitivity and ambiguity reduction?

 

2) Which major modifications would be required to export forest volume parameter estimation procedures based on Pol-InSAR coherence models to the case of agricultural crops?

 

3) Are Pol-InSAR inversion results influenced by artefacts due to agricultural field quasi-periodic structures?

 

4) C-band POLSAR data have been widely used for crop monitoring. Are X-band (Single pass) Pol-InSAR acquisitions well adapted to agricultural volume analysis or should C-band data be preferred?

 

5) Do the outputs of current POLSAR/Pol-InSAR processing techniques meet end-user needs in terms of usefulness and accuracy?

 

6) Classification techniques using the whole PolSAR/PolinSAR information segment pixels according their global scattering behaviour. In order to provide more specific results, would it be preferable to limit the input information to some indicators, highly linked to physical parameters (humidity, roughness, density …)?

 

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