POLinSAR 2005 Summaries & Recommendations
These recommendations from the
POLinSAR 2005 workshop are based on round table discussions initiated by a set
of seed questions proposed by the session chairpersons. The chairpersons
summarized the round table discussions and presented the summaries in the
dedicated summary sessions. In the summaries and recommendations the session
seed questions are indicated in italic.
SAR Polarimetric Interferometry Session
Chairpersons: W.-M. Boerner, S.
Pol-InSAR was developed originally for tree height estimation.
How mature is this product now and are there any gaps in the understanding of
the performance of Pol-InSAR in different forest types? Is this the best way to
get at biomass from radar coverage? There appear to be no saturation effects
but how accurate is biomass from height and how robust are the allometric
mature Pol-InSAR Application is forest height, there are more than 6 different
forest test sites with in-situ comparisons.
support idea of an L-Band Spaceborne Pol-InSAR for global biomass mapping. Key
No saturation means high biomass with L-band space technology (> 300
Robust performance across diverse forest systems
Key development is demonstrated capability in Tropical Forests (to be
Temporal decorrelation is an error source in inversion (needs to be
Height-to-biomass is an error source (need clarification on product
requirements from users (‘global’ Forestry)) This is a shared
problem with Lidar. Radar provides direct estimate of
‘forest’height, not ‘tree’ height…a good thing?
What are the prospects for exploiting Pol-InSAR using
existing/near future satellite sensors? What are the key limitations on
performance? Do we need to wait until the next generation of multi-satellite
clusters? Are there sufficient programs in place to try and fully exploit
Pol-InSAR for ALOS-PALSAR, Envisat ASAR, Radarsat II and Tandem-X?
There are 2 levels of application to consider:
Low Frequency repeat pass (L-band) quadpol to combat temporal
decorrelation + optimise parameter estimation. Some operational performance
possible even for dualpol (HH/HV) systems like ALOS/PALSAR
High Frequency (C and X band)
Vegetation operation seems possible for low biomass
(forestry and agriculture) but requires single-pass or short temporal
applications (Persistent Scatterer InSAR)…have good prospects in 2 ways:
Increasing the density of PS for better performance in D-InSAR
New physical parameters (rotations and twists)…
is the role of full vs. partial polarimetry in Pol-InSAR products? Can dual pol
systems be used for height/biomass estimation with wide swath coverage for
provides more robust performance but Pol-InSAR information is
‘column’ rather than ‘diagonal’ based in the S matrix
(unlike POLSAR) so single TX pol dual RX can provide inversion products
(forestry height). An assessment is needed to decide if degraded product
quality is acceptable for applications.
is the role of advanced signal processing issues based on coherence
optimisation, coherent target decomposition etc. Are these crucial to product
development or can simpler processing schemes based on standard linear
polarisations, Pauli channels etc. be used just as well?
development of algorithms has demonstrated improvement in robustness but
optimum algorithm is application specific.Therefore there is a need to provide
tools to users with guidance and recommendations for different applications.
This is input to development of software tools like POLSARPRO/RAT…etc
What are the prospects for wide area vector tomographic
imaging from space? Are there any fundamental problems in processing, data
collection etc. or are the requirements well within the limits of existing
technology and algorithm maturity? What would be the advantage of tomographic
imaging over interferometry? What new products would emerge
Processing techniques demonstrate
practical application to air/space borne data…
Polarimetry is demonstrated to be of
importance for image interpretation
number of baselines so well suited to future constellations. ‘system of
systems’ An interesting area is the overlap between MBPI and PolTomo.
What about exploiting polarimetry in differential or
D-InSAR applications? Are there any clear application areas where this will be
important? What extra performance can we expect to get for D-Pol-InSAR vs.
classical D-InSAR systems?
Still early developments, more data sets are needed.
But urban applications (Persistent Scatterer InSAR)…have good prospects
in 2 ways:
Increasing the density of PS for better performance in D-InSAR
New physical parameters (rotations and twists)…
Dubois-Fernandez, D. Hoekman
Which are the most promising approaches for forest biomass
estimation, and what are the limitations?
Is it possible to estimate forest height with L- and/or P-band
over tropical forest?
Can we identify a set of forest types over which the different techniques
should be tested, validated? Have tests being conducted over these types of
forests? What are the estimated limits of each of the identified techniques
over these different biotopes?
Can we develop robust biophysical parameter retrieval techniques
for complex targets such as heterogeneous, hilly and textured natural forests?
What are the needed biophysical parameters? Biomass, tree height, forest
Most tests have been conducted with airborne data. Is this
representative for spaceborne data? Is resolution an issue for this type of
applications? Is the typically steeper spaceborne incidence angle a difficult
Tropical forests are disappearing at alarming rates. Could
ENVISAT ASAR be utilized better to mitigate this problem?
Estimation of forest height using Pol-InSAR data and the RVoG
model was given much attention. Results of validation experiments over a number
of European test sites (Papathanassiou) showed consistent results and fair
performance over a wide range of forest types, forests heights and biomass
levels. The appropriateness of the h100 measure was discussed. Since results
seem to depend on vertical forest structure either more complicated height
measures or more complicated models may be necessary to improve results
further. Since straightforward application of the RVoG model and the use of a
single baseline may limit possibilities other approaches were considered.
Possible sources of error were indicated such as temporal
decorrelation, too much attenuation, non-optimal baseline, and orientation
effects in plantations. Also canopy roughness was indicated as an error source
(Garestier). Slope effects were not considered to be a major problem
(Papathanassiou). Dual polarization InSAR in principle allows forest height
estimation and, thus, may be applicable on a larger scale from space, however
is not very accurate. Dual baseline space observation (PALSAR polarimetric
mode) is expected to meet accuracy requirements. Most of the Pol-InSAR
inversion presented in this session was performed at L-band. One
presentation however, presented results at X-band. Garestier showed significant
penetration at X-band and differential penetration with polarisation, providing
evidence that Pol-InSAR biomass inversion can be performed at these higher
frequencies. This is of great importance for the future planned system like
TerraSAR-X, TandemXSAR or the future C-band system from ESA.
Besides dual baseline approaches to mitigate problems hybrid
methods involving both classification and parameter estimation were proposed
(Lee, Ferro-Famil). For example, prior classification of forest area using
PolSAR data, followed by unsupervised classification of forests by Pol-InSAR
data yielded promising results. Though classes can be separated in terms of
structure, height and biomass it is still not completely clear how to link
unsupervised results to groundtruth. Also the use or additional use of X- and
P-band DEM and DTM were discussed (Aulinger). In this paper, the authors
identified a bias to the estimate of the ground height obtained from the HH
P-band interferometry information clearly correlated to biomass. Brian Mercer
indicated that previous studies by Infoterra showed that using the optimised
polarisation does not have such a bias.
The applicability of allometry (Mette) as a means to estimate
biomass from height was discussed for a wide range of forest types. Besides
errors and unknowns in allometry, such as ecosystems without light competition
or tropical forests it was remarked that the Pol-InSAR height estimation may
not work accurate in discontinuous open forests or heterogeneous forests.
Repeat-pass C-band coherence was shown to be exploitable in the
Northern Taiga regions of Siberia, under favourable conditions (Wiesman). A
larger range for biomass retrieval is expected from PALSAR.
Knowledge on the relation between biomass and P-band intensity
data at high incidence angles is of importance for space application. It
was shown that results from previous research, at medium incidence angles, are
comparable. The only exception being that low biomass areas are confused with
bare areas, but this problem could be mitigated by prior classification. This
positive result is of importance for the BIOMASCA proposal (Dubois).
For applications, which parameters are needed, and at which
accuracy? Is forest height a meaningful parameter? Soil moisture, for
example, is hard to describe with a single number because in general the soil
moisture vertical profile is not uniform. In analogy, could we derive a height
distribution? Application areas are not limited to forestry. Numerical weather
prediction models or climate models need the aerodynamical roughness of forests
to describe the atmospheric boundary layer. Ecologists need data such as crown
closure, species clumping, gap dynamics, disturbance. If we only invert for
average height and consider canopy roughness as a source of error, we throw
away very useful data.
And what about biomass? One issue is clearly the global
estimation of biomass for which SAR could provide useful information. However
biomass information is crucial for other purposes. In carbon offset trading
issues, for example, very accurate carbon sequestration figures are needed,
above and below ground. This can only be achieved in small permanent sample
plots. The role of SAR in this case would be assessing for which areas such
sample plots are representative or to detect disturbances. The temporal
resolution of this information is also extremely important. Clearly more
discussion with user communities is required.
Chairpersons: E. Pottier, M. Sato
In this session, we discussed on
some original and new applications for POL-SAR and Pol-InSAR, such as:
- Urban area (segmentation,
coherent points + PS)
- Target detection (dual-freq +
dual aspect angle, FOPEN)
- Snow monitoring
- Ocean (surface RCS, oil spill
detection, Oyster farming)
In each application: Obviously
- Polarimetry and Polarimetry +
Interferometry play an important key role
- Result improvement
- Physical interpretation
In each measurement, what kind of “unique”
calibration and ground truth will be required?
For further development of new technical approaches, what kind of
validation data (which include SAR data, but also other physical measurements)
should be needed? Are these data or measurements already available?
Who should be involved in order to achieve the final aims of the
Is multi-frequency + polarimetry very important for future
applications, and what would be the limitations and gains.
Ground Truth - Very detailed
ground truth is necessary to:
explain the variability observed on data
be adapted to end-user needs
At the same time, in many
cases, we still do not know what the SAR system is looking.
Calibration - Calibration is
playing more and more an important rule:
- Interferometry + Polarimetry
-> effects on correlation and interferometric terms.
- More sensitivity (dynamic
range) is required for forest studies
- Same comments as CEOS - CalVal
Data Exchange - A priori
information is always useful in classification
- Data sets -> yes
- Ground truth: more difficult
- Photographs of the test site
- Information about the
A list of available data sets
will be quite useful to obtain new users.
In general, multi frequency
will be useful, however, in practice, it has to be limited.
We have to continue the
discussion on the useful frequency.
For a given application :
o What can we do with multi-channels SAR data
(Polarimetry + Interferometry, Polarimetry + Multi-Frequency)?
o Best configuration?
Solution (?) - For a given
application <-> select a test site:
o Collect data from Space borne sensors
Envisat – ASAR (C-Band)
+ auxiliary data (optical
data, multi-spectral data …)
o POLSAR / Pol-InSAR / POLfreSAR analysis ->
Comparison / Test / Validation
coherent / incoherent models
Ground truth (?)
Possibility in the frame of a
general / common SO between agencies?
Land-Agriculture Applications Session
Chairpersons: P. Lombardo, M.
How do spatial resolution and revisit time affect the
usefulness of SAR remote sensing data for agricultural application? Can
recommendations be made for future missions or experiments, especially based on
Is it still general opinion that X-band carries lower information
content on agricultural areas compared to L-band and C-band?
What is the relative importance of multi-frequency vs. polarimetric
SAR/InSAR data for agricultural applications?
In terms of importance for the agricultural application, in which
order would you list the following items and their combinations: Spatial
resolution, radiometric resolution, multifrequency, polarimetry,
interferometry, revisit time?
Are data fusion techniques (with reference both to multiple types of
SAR images and multiple sensors) for the agricultural applications completely
assessed? Would you consider useful to have an opportunity to compare techniques
developed by different institutions in an open contest? (in which case what
should be the rules to make it useful?)
A reference single-pass Pol-InSAR data set would be
extremely useful to assess processing techniques and compare results among different
However, the data set would consist of a significant amount of
images to represent many different cover types, each one collected with short
revisit times (the definition of a significant data set might be hard work
A potential solution to mitigate difficulty in collecting
such data set would be to make a large use of ground-based sensors
However time is becoming very short for new recommendations on
next spaceborne C-Band system, there is a general agreement that the Pol-InSAR
community should encourage building fully polarimetric sensors, because:
Not having it would be a step back!
Even X-band has a penetration useful for biomass estimation, and
C-band is expected to allow useful measurements (something in between L and X)
Non-polarimetric C-band has now only simple applications (except
A document has been prepared as a result of POLinSAR 2005 that
motivates this recommendation of polarimetry at C-band from a scientific
point of view.
Another important issue that should be pushed for, together
with C-band polarimetry, is the shorter repetition time (possibly 6
days). In this direction potential interactions with other Space Agencies could
Theoretical Modelling Session
Chairpersons: I. Hajnsek, T. Le
Strong evolution in theoretical
modelling since last POLinSAR 2003
Is there a benefit to introduce (more) physical modelling in
algebraic modelling in Pol-InSAR? How to link the two communities?
There is already a strong use of structural models in Pol-InSAR
A link between the direct modelling community is partially
established and is strongly recommended to be further developed
How reliable are incoherent / coherent forest scattering models
today in terms of polarimetric and interferometric observables at X, C, L and P
bands? Where are the main limitations?
There are a set of models established and validated for coherent
modelling, but there is still a strong need for further work to be done
(forest, soil, agriculture, ice)
What is the potential of coherent agriculture soil and vegetation
modelling and where are the main limitations?
The potential is high, but it needs more development
Are the existing (coherent) ice scattering models capable for
Pol-InSAR applications? What are the required developments?
No presentation concerning land-ice or sea ice was present
A need for more understanding, coherent model and experimental
For mission operation design and performance analysis, data sets
with relevant ground data are required for scattering modelling. How large and
reliable are the existing data sets and how to make them available?
There exist forest data for initialisation of direct models
(available for all?)
There is a need also for agricultural data for initialisation
What was the progress with respect to the recommendations of the
POLinSAR 2003 WS about:
- Modelling of vertical
extinction in tree and forest canopies
- Introduction of higher order
scattering for soil surfaces
- Polarisation behaviour of
microwaves measurements of crops
- Modelling of polarimetric
phase difference in sea ice
In summary there is a evolution recognised in direct modelling
There would be the need to focus the work and to compare the
different models(in terms of sensor close development)
Development of coherent modelling for land (forest, soil,
agriculture, ice) is still needed
Effort in development of theoretical modelling dedicated to
relevant topics (e.g. applications of high scientific priority, critical gaps)
Observation/ database is crucial for theoretical modelling, Data
need to be available to the community
Emphasis on well defined ground data (discussion on common data
Airborne Pol-InSAR Campaigns Session
Chairpersons: S. Hensley, H.
Is there a need for an airborne campaign where multiple sensors
collect Polarimetric Interferometric and/or Polarimetric data at multiple
frequencies with associated in situ ground truth data for cross-calibration and
algorithm comparisons purposes? What sites would be recommended for such
No specific recommendation was put forward.
Can any significant gaps be identified in Polarimetric
Interferometric and/or Polarimetric data sets for validation and development of
existing and new techniques, i.e. is there a need for campaigns that fill these
gaps for different applications (e.g. forest, hydrology, agriculture, and
ice). If so, what applications, modes, frequencies, sites etc. would be
recommended for such campaigns.
- Several areas were recommended
for dedicated measurement campaigns- urban (use square loop), soil
moisture in vegetated regions,
- Any suggested campaign must be
linked to the context of planned missions with specific applications.
Is there a need for Single Pass Polarimetric interferometric
systems to help quantify the influence of temporal decorrelation on repeat pass
results? If so what frequencies would be the most useful to implement?
- Yes, was suggested in the
context of biomass applications. Certainly would he useful at all frequencies
but particularly at L-band.
Are the geophysical or biological systems that would benefit from
persistent polarimetric interferometric observations that may be possible with
UAV type systems? What would be the desired operating characteristics of such
- Persistent monitoring of
volcanoes, pre and post seismic observations, landslide prone an
anthropogenic induced deformations could benefit from such systems.
Are there synergistic opportunities for spaceborne/airborne joint
campaigns similar to ones previously conducted for the ERS, JERS and SIR-A, B-C
- No specific recommendations
were put forward. One suggestion would be with ALOS PALSAR. Make repeat
observations of temporal intervals of time intervals up to 46 days with
increased resolution compared to PALSAR to better understand temporal
decorrelations and resolution limitations of PALSAR.
- Care must be made in going from
airborne to spaceborne applications to properly compensate for resolution
Are there any new ideas about new Polarimetric Interferometric
observation techniques, such as bi- and multistatic techniques and
multi-frequency techniques that require new campaigns.
Are there any new applications areas for Polarimetric
Interferometry that requires new campaigns for proof of concept, demonstration
Spaceborne Missions for Pol-InSAR
Chairpersons: A. Moreira, J.-C.
What future missions have a great potential for Pol-InSAR
applications? What recommendations can be given in this respect?
Pol-InSAR vs. "Single-pol multi-baseline" : Pol-InSAR
& "Single-pol multi-baseline" interferometry are different
acquisitions configurations (for e.g. for DEM extraction over vegetated
areas). What are the advantages/drawbacks of such architectures in the
framework of spaceborne missions for vegetation studies?
Spaceborne Pol-InSAR for a global biomass product: Future
spaceborne Pol-InSAR missions are expected to provide global biomass estimation
with an unprecedented accuracy. What accuracy range, in terms of altimetric
& planimetric resolution, localisation, is necessary to allow new
applications, in the field of biomass estimation (carbon cycle) ?
Pol-InSAR and bi-static effects: One possibility of achieving
low-cost space-borne Pol-InSAR missions is to use a constellation of low cost
passive receivers in the vicinity of an illuminating SAR partner (cartwheel,
pendulum, ... principles). In this case, the Pol-InSAR acquisition is conducted
under a bistatic configuration. What kind of alteration of the received signal
is expected? If any, give recommendation on the maximum bistatic angle that can
Future spaceborne SAR missions will have polarimetric
capabilities and will allow the further development of polarimetric and Pol-InSAR
Temporal decorrelation will be a limiting issue for Pol-InSAR
Polarimetric and D-InSAR (potential to be further explored)
Need for a single-pass L-band Pol-InSAR mission (A. Moreira, J.C.
Souyris, S. Cloude, K. Papathanassiou and?)
Single-pass polarimetry will be possible by utilising a passive
micro-satellite constellation together with an active SAR-satellite.
Justification for including a fully polarimetric
Capability for future C-Band Satellite Missions
In , for a particular classification experiment in the
Flevoland agricultural area, it is shown that single polarization (HH or VV)
achieves an accuracy under 40 %, dual polarization achieves a result of
60%-70%, and full polarimetry achieves 90%.
 Hoekman, D.H., and
M.A.M. Vissers, 2003. A new polarimetric classification approach evaluated for
agricultural crops, IEEE Transactions on Geoscience and Remote Sensing, Vol.41,
No.12, December 2003, pp.2881-2889.
Classification accuracy using fully polarimetric data increases
by ca. 20% when compared with dual-pol 
 J.S. Lee, M. R. Grunes and E. Pottier,
“Quantitative Comparison of Classification Capability: Fully polarimetric
versus Dual- and Single polarization SAR,” IEEE TGRS, November 2002
Fully polarimetric information is required for an unsupervised
crop classification scheme providing robust classification of important crops
(ref. Skriver, Quegan, LeToan)
Supervised Wishart classification of multitemporal C-band Pol-InSAR
data showed an improvement of ca. 15 % from dual-pol to full polarized data
(Skriver et al, 2000).
A key parameter for discriminating crop types and monitoring the
state of crop development is the height of the crops. Simulations, laboratory
measurements and actual data have shown that it is possible to measure crop
heights using polarimetric interferometric techniques at high frequencies. By
incorporating short temporal baselines, C-band polarimetric interferometry
proves to be a potential operational tool for agricultural applications (Scott
Hensley et al).
Fully polarimetric data is essential for accurate snow
classification since an optimization of the polarimetric contrast and other
polarimetric parameters are needed for discrimination between dry snow and
uncovered areas. Algorithm is also robust against topographic effects (ref. A.
Martini, L. Ferro-Famil, E. Pottier)
Phase difference is important for discrimination between thin ice
and open water (H. Skriver, W. Dierking)
Strategic & Programmatic Issues
A full polarimetric capability for C-band satellites represents a
new dimension for product development
Radarsat-2 SOAR statistics demonstrate the strong request for
full polarimetric data that will foster the development of a variety of new
Complementarity and compatibility to RADARSAT-2 and RADARSAT-3
satellites with full polarimetric capabilities