Snaphu Data Export

Exporting NEST data for SNAPHU processing

Important note

It is strongly advised before executing graph for exporting NEST data for SNAPHU processing for user to get familiar with general principles of doing phase unwrapping in NEST.

SNAPHU Data Export Graph

The main purpose of SNAPHU data export functionality is three-fold:

  1. To export NEST data (bands) in the format compatible for SNAPHU processing,
  2. To build a SNAPHU configuration file (snaphu.conf), the file where processing parameters for SNAPHU are being stored,
  3. To construct a container NEST product that will store metadata and bands to be used when SNAPHU results are being ingested back into NEST.

The export graph is visualized in the figure below.


In the export graph, there are two readers, and two writers. The argumentation for two readers is, that as input for SNAPHU export operation both Interferometric, and Coherence product are needed. The interferometry product is needed for the metadata and (complex) phase, while the coherence product is required for the coherence information that is used for weighting in the process of unwrapping. The reason for two writers is, that one writer saves the phase product that, as already introduced, serves as a container for the data exchange with SNAPHU, especially in the data ingestion step. While the other writer saves (exports) the data and builds a configuration file for SNAPHU software.

Phase product part of the export graph

Part indicated in the blue box in the figure bellow performs the following:

1-Read:
Reads the interferometric product.
3-BandSelect:
Selects bands that are to be stored in the "phase" product. It is recommended that only phase band is selected.
5-Write:
Writes "phase product" in the standard NEST/BEAM DIMAP format.
SNAPHU product part of the export graph

Branches groupd by the red box in the figure bellow performs the following:

1-Read:
Reads the interferometric product.
2-Read:
Reads the coherence product.
4-SnaphuExport:
Selects bands that are to be stored in the SNAPHU product, required bands are phase and coherence. Also in this step parameters for SNAPHU are being defined. For more details about the SNAPHU processing parameters please refer to SNAPHU manual.
6-Write:
Write SNAPHU product, using a SNAPHU writer. Note that as output format "Snaphu" format is being predefined.

External processing with SNAPHU

Given that the SNAPHU software is properly installed and configured, unwrapping of exported NEST product is quite straightforward. In the directory where the SNAPHU product is being saved, the following command is to be executed:

snaphu -f snaphu.conf YOUR_PHASE_BAND.img 99999

where YOUR_PHASE_BAND.img stands for the name of the phase band that is to be unwrapped, and 99999 represents the number of lines of the YOUR_PHASE_BAND. Note that the command to be externally called for the phase unwrapping is listed in the header of snaphu.conf file that is created with the SNAPHU writer.

Again, it is strongly recommended that before doing any processing with SNAPHU user becomes familiar with the software and process control flags.