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Purpose

 

Baseline and burst synchronisation are key factors, which determine the suitability of ASAR Wide Swath data pairs for interferometric purposes. This functionality enables to check these parameters before actually running the interferometric processing chain. The extracted parameters have to be intended as approximate measurements aimed at a preliminary data characterisation and interferometric quality assessment. The baseline value itself is not used in any part of the Interferometric processing chain.  

 

Technical Note

 

The input Data File List (Reference and Secondary data) are represented by intensity images resulting from a previous data import (Basic module) or data focusing (Focusing module) process. In this case the Orbit File List is not required.

 

Any number of data files (and corresponding orbit files in case of not imported products) can be entered; the baseline and burst synchronisation values for all possible combinations (i.e. pairs) will be provided.

 

It must be noted that the same input list cannot contain original and imported data.

 

Baseline

The generation of an interferogram is only possible when the ground reflectivity acquired with at least two antennae overlap. When the perpendicular component of the baseline (Bn) increases beyond a limit known as the critical baseline, no phase information is preserved, coherence is lost, and interferometry is not possible. The critical normal baseline Bn,cr, can be calculated as:

 

                   Bn,cr = λ R tan(θ)

           2 Rr

 

where λ is the wavelength, R is the range distance, Rr is the pixel spacing in range, and θ is the incidence angle. Note that the critical baseline can be significantly reduced by the topography.

 

Burst Synchronisation

ASAR Wide Swath data pair could be affected by burst synchronisation related problems, which make impossible to use them for interferometric product generation. Although ASAR Wide Swath mode was not designed to keep burst synchronisation between different acquisitions, there is a high percentage of synchronised Wide Swath data pairs. The European Space Agency provides a web based application to estimate the burst synchronisation percentage for a user selected set (based on satellite track number or area location) of ASAR Wide Swath mode products. The search can be eventually refined with specific time intervals. A similar result is provided, for specific data pairs (one or more than one), using this functionality.

 

Theoretically the interferometric processing can be attempted on all SAR pairs with minimum burst synchronisation percentage higher than zero. Of course the higher the percentage the larger the swath portion which is actually considered in the processing, thus a minimum burst synchronisation percentage of at least 50% is typically suggested.

 

DORIS

DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) data provide precise orbital information for ENVISAT ASAR. Two versions of DORIS data are available:

 

-The VOR (Verified ORbits) are the most precise ones, but they are made available not earlier than one month after the actual satellite acquisition.

-The POR (Precise ORbits) are slightly less precise than the VOR, but they are made available together with the ASAR data.

 

Access to DORIS data is provided by the ESA Earth Observation Help Desk.

 

Input Files

 

Input File List

List of data files (_pwr in case of imported data). This file is mandatory.

 

Orbit File List

List of orbit files (DOR_VOR or DOR_POR) corresponding to the Data File List (the same input order must be respected). This list is not required only in case of imported data type (e.g. _pwr).        

 

Output Files

 

Output Root Name

Name of the output root. If it is not provided the extracted parameters are written in the Log File.

 

Root Name        

A suffix, to identify which input pair the information are related to, is added to the Output Root Name. The following information are provided in the output text files:

 

-Minimum Burst Synchronisation

It corresponds to the synchronisation percentage value. Note that the synchronisation of the ASAR Wide Swath pair is proportional to the overlap between the same swath (1 to 5) of Reference and Secondary images. The algebraic sign (+/-) depends on the de-synchronisation direction. Zero value means that there is no synchronisation, between Reference and Secondary image, in at least one of the 5 swaths of which the entire ASAR Wide Swath acquisition is made of. In this case, the pair cannot be processed in interferometric mode. Otherwise, with synchronisation values other than zero, the interferometric processing can be attempted.

 

-Min Normal Baseline

Estimated value (meter) of the normal baseline. The provided value is the smallest amid the 5 swaths.

 

-Max Normal Baseline

Estimated value (meter) of the normal baseline. The provided value is the largest amid the 5 swaths.

 

The burst synchronisation and baseline value, specific for each swath of each pair, are provided in the log file at the process completion. They are named respectively "Overlap SubSwath" and "Baseline SubSwath".

 

General Functions

 

Exec

The processing step is executed.

 

Store Batch        

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

 

Close        

The window will be closed.

 

Help

Specific help document section.

 

 

Specific Function(s)

 

 

References

 

B. Rosich, A. Monti-Guarnieri, D. D’Aria, I. Navas, B. Duesmann, C. Cafforio, P. Guccione, S. Vazzana, O. Barois, O. Colin, E. Mathot: "ASAR Wide Swath mode interferometry: optimisation of the scan pattern synchronisation".

 

Monti Guarnieri A. and C. Prati: "ScanSAR focusing and interferometry". IEEE Transactions on Geoscience and Remote Sensing, Vol. 34, No. 4, July, 1996.

 

Monti Guarnieri A., P. Guccione, P. Pasquali, and Y.L. Desnos: "Multi-mode ENVISAT ASAR interferometry: Techniques and preliminary results". IEEE Proceedings on Radar, Sonar and Navigation, Vol. 150, No. 3, June, 2003.