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SAR Polarimetric Interferometry (Polinsar)

POLinSAR Workshop 2003


Session Title: SAR Polarimetric Interferometry

Chair(s): E. Pottier and K.P. Papathanassiou

All five papers in the session were presented. The first three dealt with forest height estimation from Pol-InSAR data (papers 1 and 2 reviewed the main results that have been achieved in the frame of the two ESA studies on “Applications of SAR Polarimetry”). It was shown that forest height estimation over temperate forest test sites can be achieved with an accuracy of about 10% - independently on topographic variations and without using any a-priori information. This was one of the most important results presented. Also height validation results were presented based on direct coherent modeling of forest scattering using detailed 3-D tree architectural models.

In paper 4, for the first time, airborne Pol-InSAR data at X-band has been demonstrated and a first order comparison between DEMs at different polarizations has been performed. Finally, in paper 5 the estimation of building heights from Pol-InSAR data has been addressed.

Questions for Round Table discussion.

Question 1.  What is the value added by Quad-Pol Interferometry compared to Dual-Pol Interferometry and (Pseudo) Dual-Pol Interferometry?

Question 2. What is the effect of temporal decorrelation on the applicability and on the inversion performance of the actual models?

Do we need single pass Pol-InSAR systems in space? Is their realization possible?

Question 3. Are the available data sets complete / sufficient for the validation / development of new applications?

Question 4. What is the status of direct coherent (polarimetric / interferometric) modeling for Forestry, Agriculture, Ice applications?

The discussion about questions 1-3 can be summarized in following points:

- Fully polarimetric (Quad-Pol) Single-pass interferometry is the optimum and desired configuration for the developed (forest parameter) inversion schemes.

- Some of the individual parameters (e.g. underlying ground topography) may be estimated from reduced dual-pol observation vectors.

- The scheduled Quad-pol SAR missions (ALOS/PalSAR, RadarSAT 2, TerraSAR-X) will operate in a repeat pass interferometric mode. A quantitative study of the effects of temporal decorrelation on parameter retrieval accuracy is therefore urgently required.

- The implementation of single-pass Quad-Pol interferometry based on passive micro-satellite technology is not likely to happen in the near future due to technological / financial limitations.

- Multi-baseline scenarios at two polarizations are more probable to be realized in the near future in terms of passive micro-satellite technology.

- The available data sets over temperate forests are sufficient for the validation of tree height estimation accuracy.

- Pol-InSAR data over Boreal and Tropical Forest environments complemented by  good ground measurements are missing completely.

- There is a demand for Pol-InSAR data (and ground measurements) for the development of agricultural and land ice applications.

In parallel with future airborne trials and data analysis there is a need to further develop validated coherent vector scattering models for forestry, ice and agriculture applications of Pol-InSAR
 

Conclusions and Recommendations:

In the time between 1999 (CEOS Workshop in Toulouse, France) and 2003 (POLinSAR Workshop in Frascatti, Italy) Pol-InSAR has clearly matured (scientifically and technologically) from a “first-results” to a “science“ status.
 

Recommendation 1:
A Pol-InSAR Airborne validation Experiment over Tropical Forest is highly recommended in order to prove the performance of Pol-InSAR inversion as well as to compare the inversion performance at L-band and P-band.
 

Recommendation 2:
Forcing the communication with bio- / geo-chemical experts in order to establish algorithm and sensor specific requirements and to develop new products.
 

Recommendation 3:
 Exploration of potential Agriculture and Ice applications of Pol-InSAR.
 

Recommendation 4:
Exploration of potential X-band Pol-InSAR applications. Especially the combination of the long term temporal stability of point scatterers with their strong polarimetric behavior, can be a challenge for high resolution systems as TerraSAR-X.
 
 

The long-term goal is a space-borne single-pass fully polarimetric InSAR system.

Recommendation 5:
Until then the potential off

· limited polarimetric InSAR configurations

· repeat-pass Quad-Pol InSAR configurations

 has to be investigated / validated.

In summary we consider that POLInSAR, the combination of (quad- / light-) polarimetry with (single- multi-baseline) interferometry is a significant break through in quantitative parameter estimation of combined surface and volume scatterering.
 
 

 

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