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
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
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
- 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
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
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
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
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
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?
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
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
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
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
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
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
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 …)?