ALOS_preprocessor - August 11, 2008

Main authors:
Rob Mellors    - San Diego State University rmellors@geology.sdsu.edu
David Sandwell - Scripps Institution of Oceanography dsandwell@ucsd.edu

plus contributions by P. Rosen, H. Zebker, and E. Fielding. 
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NEW STUFF Aug 2008

- supposed to read SAR mode (high-resolution, wide observation, or
polarimetry) from the leaderfile and set parameters accordingly 
- can force it to assume quad polarimetry data with -quad
- supposed to handle quad pol data (prf, chirp_slope and chirp_ext)
(prf is divided in half; chirp_slope set to -871580000000.0 and chirp_ext = 500)
[chirp_slope value from H. Zebker as the leaderfile seems to be wrong]
- spacecraft height defined at beginning and end
- handle prf changes in data file by creating new files rather
than quitting

Note: This does not really support ScanSAR data yet
although you could with effort - each burst/swath is a prf change
so it will create lots of files which could be glued back together
and processed, if you had a scansar processor.

I think it all works but...but you get what you pay for....

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This code is used to preprocess ALOS PALSAR data in L1.0
format.  It had been tested with both FBS and FBD mode data
at a variety of look angles.  The main functions of the code are:

1) ALOS_pre_process - Takes the raw ALOS PALSAR data and 
aligns the data in the near range.  In addition it produces
a parameter files in the SIOSAR format and or ROI_PAC containing the essential 
information needed to focus the data as Single Look Complex (SLC)
images. In case of a PRF change during reading, will create a new
data and header file PRF. 

2) ALOS_baseline - Takes two parameter files of an
interferometric pair and calculates the approximate shift parameters 
needed to align the two images as well as the accurate interferometric
baseline at the beginning and end of the frame.

Known bugs: gives incorrect results for end baseline 
if one file is much shorter than another.

3) ALOS_merge - Appends two raw image files and eliminates duplicate lines.
In addition it makes a new PRM file representing the new longer frame.

4) ALOS_fbd2fbs - Converts a raw image file in FBD mode (14 MHz) to an FBS mode
(28 MHz) by fourier transformation of each row of the image file (one echo)
and padding the spectrum with zeros in the wavenumber domain.  A new parameter
file is created to reflect the new data spacing and chirp parameters.   A complementary
ALOS_fbs2fbd program is also available but not automatically compiled with the
makefile.  The interferograms made from the FBD2FBS conversion have lower noise than the 
interferograms made from the FBS2FBD conversion.

A version of ALOS_fbd2fbs that works with fftw is also in the ALOS_fbd2fbs
directory under ALOS_fbd2fbs_fftw.

Questions: email rmellors@geology.sdsu.edu