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General

What SAR products are supported? #

NEST supports ENVISAT, ERS-1, ERS-2, and RADARSAT-2 fully.

NEST also supports TerraSAR-X, Cosmo-Skymed, ALOS PALSAR, RADARSAT-1 and JERS with the exception of some special product types.

For more details on what product types are supported, please refer to the supported products spreadsheet.

How is NEST licensed? #

NEST is licensed under the GNU GPL

If I write an application using NEST API am I forced to distribute that application? #

No. The license gives you the option to distribute your application if you want to. You do not have to exercise this option in the license.

If I wanted to distribute an application using NEST what license would I need to use? #

The GNU GPL

I am a commercial user. Is there any restriction on the use of NEST? #

NEST can be used internally ("in-house") without restriction, but only redistributed in other software that is under the GNU GPL unless permission is granted from all copyright holders.

I can't open an ENVISAT product. #

First, try to open the products with Enviview. If that works then it could be a version not supported by NEST. Let us know and we'll try to get it supported asap. If both Enviview and NEST are not able to read the product, then it could be that the file is corrupt or compressed.

Some users have had difficulty when decompressing files using Winzip. Deactivate the CR/LF translation option in winzip (this option is activated by default).

When I open a RADARSAT-2 image I don't get any metadata #

A RADARSAT-2 product should be opened through it's product.xml file to ensure that the RADARSAT-2 product reader will recognize all files and import the whole product.

How do I import a PolSARPro result? #

Use the PolSARPro reader and select the folder containing all the individual band files. When imported, all individual bands will show up within one product.

What method is used for Oil Spill Detection? #

The method currently implemented in NEST for oil spill detection is an adaptive thresholding dark spots detection algorithm. It first estimates the mean backscatter level in a large window, then set a threshold which is k decibel below the estimated mean backscatter level. Pixels with backscatter values lower than the threshold are considered as potential oil spill. Finally the detected pixels are clustered and discriminated. Only those clusters that are larger enough will be saved as detection result. Here in the algorithm, the user has fully control of the window size for estimating the mean backscatter level, the parameter k for setting the threshold, and the minimum cluster size.

The method is based on the following reference in which a much more complicated pyramid approach was proposed. In NEST however one level detection is implemented.

A. S. Solberg, C. Brekke and R. Solberg, "Algorithms for oil spill detection in Radarsat and ENVISAT SAR images", Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International, 20-24 Sept. 2004, page 4909-4912, vol.7.

Can I use the Apply-Orbit-File Operator on JERS-1, Radarsat-1. ALOS, etc.? #

No. The orbit corrections are only for ENVISAT, ERS-1 and ERS-2. If the orbit state vectors in your products are not accurate then this would be a problem when orthorectifying. You should be using the SARSimulation Terrain Correction to coregister your image with a simulated SAR image generated from the DEM and then terrain correcting.

What external DEM does NEST support? #

Currently only WGS84-latlong (P? , P?, Ph) DEM in meters is accepted as geographic system. User can specify one tile (i.e. one file) of the DEM. What are the definitions of local incidence angle and projected local incidence angle?

The local incidence angle is defined as the angle between the normal vector of the backscattering element (i.e. vector perpendicular to the ground surface) and the incoming radiation vector (i.e. vector formed by the satellite position and the backscattering element position).

The projected local incidence angle is defined as the angle between the incoming radiation vector (as defined above) and the projected surface normal vector into range plane. Here range plane is the plane formed by the satellite position, backscattering element position and the earth center.

For more information on the definitions, derivations and calculations of the angles please see section 14.3.4 in "SAR Geocoding: Data and Systems" by Gunter Schreier.

In coregistration I get "Not enough valid GCPs in slave". How can I fix this? #

Some products can have a significant error in their georeferencing. You may need to set the coarse registration window in the GCP Selection tab to something larger such as 512 or 1024. Also, increasing the number of GCPs will give you a better chance of having more surviving. For fine registration, you could reduce the coherence threshold. In the warp, check 'show residuals' to see a summary of where GCPs are being shifted to and what their RMS values are. Set the RMS threshold to a value where you can get lots of representative GCPs at the smallest RMS.

I've closed my tool views (world map, layer manager, navigation, etc). How can I get them back? #

In the top menu go to View -> Manage Layout and select Reset Layout or Load Tabbed Layout.

Why can I not orthorectify my image over the Arctic? #

It will depend on the DEM and output map projection. The default SRTM DEM is only available from +60 to -60 deg latitude. At the polar regions you will need to use either the low resolution GETASSE30, ASTER GDEM up to 83 deg or your own external DEM. Also, for the polar regions, using a polar map projection will give you a better result.

Why won't my graph from a previous NEST version work with the latest NEST version? #

if you are using a GRAPH derived with a previous release of NEST 4C-1.1, your graph could have some troubles running to NEST 4C-1.1.

The reason of this is linked to the fact that the XML DOM library that we use was renamed.

There are 2 solutions to solve this inconvenience:

1) Edit your graph file and rename any Xpp3DomElement to XppDomElement

2) Create a new graph with NEST 4C-1.1

Also, some operators may now include new parameters which may be incompatible with older graphs.

Is training and support available for NEST? #

ESA provides introductory training at some conference workshops and support for technical problems through the NEST website forum. Personalized training courses and technical support subscriptions are available by contacting Array.

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