Improving GDAL's support for Polarimetric SAR
The goal of this project is to improve the support int GDAL to much more easily provide access to multichannel SAR datasets. The initial push in this project will be to standardize on metadata items representing:
- the matrix representation of the data in the file (i.e. scattering, covariance, coherency, etc...)
- whether or not the data is symmetrized
- which matrix element each band represents
The bulk of this work will be undertaken by Phil Vachon (a.k.a. pvachon or philv on IRC), since it is mostly self-serving.
Drivers and Representations Provided
There are a number of SAR CEOS "subdrivers" and a few drivers that will provide access to polarimetric SAR data. These include:
- jaxapalsar (Scattering matrix) (DONE)
- sarceos (PALSAR L4.1 ERSDAC products, symmetrized covariance matrix; CCP CEOS products, scattering matrix) (DONE; there is an issue with reading PALSAR data)
- rs2 (Scattering matrix) (DONE)
- airsar (symmetrized covariance) (DONE)
- raw/cpgdataset (symmetrized covariance, scattering) (DONE)
- tsx (Scattering Matrix, when they start doing data) (DONE)
- pcidsk (all representations) (requires a lot of work)
Matrix Representation Metadata
For the above formats, a "MATRIX_REPRESENTATION" metadata item will be added to the dataset. The presence of this metadata item indicates whether or not the dataset is polarimetric or not. Valid entries for the MATRIX_REPRESENTATION metadata item are:
- SCATTERING (implies 4 bands)
- SYMMETRIZED_SCATTERING (implies 3 bands)
- COVARIANCE (implies 10 bands) nb: is hermitian
- SYMMETRIZED_COVARIANCE (implies 6 bands) nb: is hermitian
- COHERENCY (implies 10 bands) nb: is hermitian
- SYMMETRIZED_COHERENCY (implies 6 bands) nb: is hermitian
- KENNAUGH
- SYMMETRIZED_KENNAUGH
Band Identifiers
Each band has a POLARIMETRIC_INTERP metadata item. This indicates which entry in the matrix representation of the file the band represents.<br>
For a SCATTERING Matrix, the following are valid band POLARIMETRIC_INTERP values: HH, HV, VH, VV
For a SYMMETRIZED_SCATTERING Matrix, the following are valid band POLARIMETRIC_INTERP values: HH, HV, VV
For a COVARIANCE matrix, the proper POLARIMETRIC_INTERP value is of the form Covariance_ij, where 1 >= i >= 4 and 1 >= j >= 4. Note that this is a hermitian matrix, so only the upper triangle of values is required.
For a SYMMETRIZED_COVARIANCE matrix, the proper POLARIMETRIC_INTERP value is of the form Covariance_ij, where 1 >= i >= 3 and 1 >= j >= 3. Note that this is a hermitian matrix, so only the upper triangle of values is required.
COHERENCY and KENNAUGH are TBD.
Sensor Band
Perhaps it would be worthwhile to provide a metadata item indicating what band the sensor operates in (i.e. P, L, C, X, Ku, etc...). This of course goes beyond simply Polarimetric SAR data. Perhaps a worthwhile goal for GDAL 1.6.0.
