Two-dimensional phase unwrapping is the process of recovering
unambiguous phase data from a 2-D array of phase values known only
modulo 2pi rad. SNAPHU is an implementation of the Statistical-cost,
Network-flow Algorithm for Phase Unwrapping proposed by Chen and
Zebker (see references below). This algorithm poses phase unwrapping
as a maximum *a posteriori* probability (MAP) estimation
problem, the objective of which is to compute the most likely
unwrapped solution given the observable input data. Because the
statistics relating the input data to the solution depend on the
measured quantity, SNAPHU incorporates three built-in statistical
models, for topography data, deformation data, and smooth generic
data. The posed optimization problem is solved approximately with use
of network-flow techniques. SNAPHU always produces complete unwrapped
solutions, and, in our tests, its accuracy is comparable to or better
than that of other available algorithms. As SNAPHU uses an iterative
optimization procedure, its execution time depends on the difficulty
of the interferogram. In single-tile mode the required memory is on
the order of 100 MB per 1,000,000 pixels in the input interferogram.
The software is written in C and should run on most Unix/Linux
platforms. It is freely available to the public, subject to the
conditions outlined in the README file included with the distribution.

The latest version of the code is 1.4.2 (February 2003).

Download the full source distribution here:

snaphu-v2.0.0tar.gz
(gzipped tar file, 140 kB)

For compatibility here is the previous version:

snaphu-v1.4.2.tar.gz
(gzipped tar file, 140 kB)

The following files are included in the full distribution, but are
listed separately here as well for convenience:

Distribution README file:
README
(text, 5 kB)

Text version of man page:
snaphu_man1.txt
(text, 30 kB)

HTML version of man page:
snaphu_man1.html
(text, 48 kB)

Full template runtime configuration file:
snaphu.conf.full
(text, 23 kB)

Brief template runtime configuration file:
snaphu.conf.brief
(text, 11 kB)

C. W. Chen and H. A. Zebker, ``Network approaches to two-dimensional
phase unwrapping: intractability and two new algorithms,'' Journal of
the Optical Society of America A, vol. 17, pp. 401-414 (2000).
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C. W. Chen and H. A. Zebker, ``Two-dimensional phase unwrapping with
use of statistical models for cost functions in nonlinear
optimization,'' Journal of the Optical Society of America A, vol. 18,
pp. 338-351 (2001).
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C. W. Chen and H. A. Zebker, ``Phase unwrapping for large SAR
interferograms: Statistical segmentation and generalized network
models,'' IEEE Transactions on Geoscience and Remote Sensing, vol. 40,
pp. 1709-1719 (2002).
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Go]

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