SAR freeware: NEST

The European Space Agency (ESA) is a leading provider of free and open software tools. Amongst the packages available are:

– BEAM: for processing MERIS and other VIS-IR imagery

-NEST: a SAR processing package

-PolSARPro: polarimetric SAR tools

Here I want to discuss NEST: the Next ESA SAR Toolbox and successor to the Basic ESA SAR Toolbox (BEST).

NEST is produced by Array Systems, a Canadian software and geomatics company. It uses the same platform as BEAM, and uses Java. It can be downloaded for free and is regularly updated and upgraded. Furthermore, NEST processing and be integrated with PolSARPro to extend the range of tools and applications. So far so good.

As with much Freeware, NEST lacks the ‘bells and whistles’ that the increasingly expensive professional packages offer (e.g. ENVI/SARScape, ERDAS, PCI). The GUI is not exactly easy on the eye, but then you are not paying for classy finishing and the programmers at Array and Brockmann Consult (responsible for BEAM) presumably have better things to do. One issue with NEST and BEAM is memory handling and file sizes: I find it prudent to close the software after a while to clean out the memory. NEST also writes a large number of large files: disk space and large virtual memory are needed!

NEST does provide a valuable service. When working with standard data formats, such as ESA ERS CEOS data, NEST enables you to process the imagery to a high standard and to create the most fundamental of products: a calibrated, geocoded and speckle filtered image. ERS processing also supports orbital refinement using Delft Orbits (up to 2005 I think), and Antenna Pattern correction. Envisat data are supported, as would be expected, as are ALOS, TerraSAR-X and Radarsat-2. Support for more formats are being added with every upgrade. Furthermore, InSAR processing is being gradually implemented and currently allows interferogram and coherence generation.

The downsides of NEST include:

-weak analysis tools: (but then this package is supposed to provide the fundamentals),

-help information (and error messages) that was apparently compiled by someone with the pedagogic skills of an idiot savant on Red Bull,

-poor integration that leads to some functions failing for unknown reasons (SAR Sim Terrain Correction being a particular pain): building graphs to process chains of operations seems to increase the processing time exponentially,

Reading between the lines of forum posts, and from my own experience, I would argue that using NEST is all about trial and error. In NEST you need to find your own work flow that provides you with the result you need. That process may take some time (more than with many packages) but hopefully, you will see light at the end of the tunnel: then you have a practical, quite powerful and free piece of software.

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