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Q. - In the Digital Elevation Model Extraction step, the required DEM tiles are not retrieved or in some cases they are only partially downloaded. How is it possible if those DEM tiles actually exist in the relevant WEB site?

 

A. - This problem is typically due to a temporary failure of the internet connection or to a change of the reference FTP or HTTP address (the FTP or HTTP protocols are used depending on the required DEM). In case one of the DEM tiles is not found in the internet, or the internet connection fails before or during the data downloading, a message is written in the Process.log file where the required DEM tiles (i.e. file name) are mentioned. The user can do an attempt to download those data using a dedicated FTP or HTTP too and then store them in the working directory.

The internet addresses, which are used by the program to download the Digital Elevation Model of the different supported products, are subject to changes. They are written (and they can eventually be modified) in the relevant Preferences.

 

Q. - How does SARscape calculate the slope (easting, northing, and combined) in the Convertion DEM to Slope tool?

 

A. - This functionality generates the following files:

•_S2N_slope, which is a real number corresponding to the slope inclination (degrees) in South-North direction.

•_W2E_slope, which is a real number corresponding to the slope inclination (degrees) in West-East direction.

•_slope, which is a complex number corresponding to the South-North slope inclination (imaginary part) and to the West-East slope inclination (real part).

 

The slope computation in a point P is done by calculating the angles ΘB and ΘA, which are related respectively to the previous and to the next pixels:

ΘB = atan2( (ZP-ZB) /D) * (180/Π)

ΘA = atan2( (ZA-ZP) /D) * (180/Π)

 

Z is the height difference of the point P with respect to the previous (B) and to the next (A) pixels; D is the distance on the ground between the points P and A.

 

Q. - Can I use original geocoded data (i.e. standard products such as GEC or GTC formats) as input to the Mosaicing tool?

 

A. - All geocoded products (in SARscape format) can be mosaiced using either the Conventional Mosaicing or the Gradient Mosaicing tool: either original geocoded standard products or slant/ground range original data geocoded with SARscape.

It remains the fact that we strongly suggest to start from Slant Range Single Look products (instead of Ground Range Resampled data) in order to preserve at the best both radiometry and geometry.

 

Q. - Can I use original geocoded data (i.e. standard products such as GEC or GTC formats) as input to the Mosaicing tool? We have around 7 adjacent paths of PALSAR data to mosaic, each with around 5-6 scenes along the path; what is the best method to create a full mosaic?

 

A. - The following steps shall be executed in your case:

1.Import your original standard product; GEC and GTC formats are already geocoded but they MUST be imported before any SARscape process is executed.

2.Cut the image border of each scene in case you have corrupted (bad value) pixels.

3.Last overlay mosaic of the 5-6 scenes along each path.

4.Gradient mosaic of the 7 adjacent mosaicked paths. Check both flags: "Absolute Calibration" (aimed at removing constant and linear trends simultaneously in each mosaicked path) and "Local Calibration" (aimed at refining the image matching close to the cut line where two mosaicked path are actually stuck together); the "Use Existing Shape" flag can be possibly checked in a second mosaic iteration (typically not needed), in case you want to edit - and then use - the cut line which was automatically drawn in the first process iteration.

 

Q. - Is it possible to Mosaic Interferograms?

 

A. - In order to mosaic Interferograms the following procedure must be followed:

1.Interferogram geocoding - Note that both the "Radiometric Calibration" and "Radiometric Normalization" flags must not be checked.

2.Conversion (Complex to Phase and Module) - The geocoded interferograms are split into the phase (_phase) and module (_mod) components.

3.Conventional Mosaicing - The "Last Pixel" method shall be adopted to mosaic - separately - the module and the phase components of the interferograms. The result will be a mosaiced module and a mosaiced phase.

4.Conversion - Phase and Module to Complex - The mosaiced phase and module are combined in order to reconstruct the original complex interferogram.

 

Q. - I have some acquisitions affected by Orbital Inaccuracies, which cause Geolocation Errors. I can solve the problem by manually identifying one Ground Control Point that I use as input in the Geocoding and Radiometric Calibration step. However I wondered if there is a tool, which allows correcting the relevant orbital parameters without looking for GCPs.

 

A. - The Automatic Orbital Correction tool can be used for this purpose. The correction must be performed before the geocoding step.

 

Q. - After the Update Orbital Data step is executed, processing steps such as the Geocoding, the Interferogram Flattening and the Baseline Estimation still provide wrong results (i.e. geolocation error, only null values in the synthetic phase, wrong baseline estimation value). Why does it happen?

 

A. - The correction of the orbits does not involve the correction of parameters, such as the slant range distance and the acquisition start time, which are used in the above mentioned processing steps. In case these parameters were wrong, the error can be corrected by either using a Ground Control Point in the processing steps where it is foreseen (e.g. Geocoding and Radiometric Calibration, Interferometric Workflows, Orbit Correction, etc.) or by automatically calculating - and applying - the correction parameters with the relevant Orbit Correction tool.

 

It must be noted that also the coregistration process can be affected by orbital inaccuracies, unless the Initialisation from Orbit checkbox is set off.

 

Q. - When do I have to perform the PRF Correction?

 

A. - We found that in some cases geocoding Radarsat-1 data with 1 GCP produced an accurate geolocation close to the GCP while the product became shifted if observed in areas far from the GCP (this was evident when moving, from the GCP position, in azimuth direction). We attributed this problem to a wrong value reported for the Pulse Repetition Frequency (PRF) and, for this reason, we introduced the PRF Correction tool. Considered that, I would suggest to check - running a Geocoding process - whether the above mentioned geolocation problem exists using one GCP only, if it does not you do not need to correct the PRF. Vice versa if you identify a geocoded product shift in areas far from the GCP it means that you must correct the PRF. In case of interferometric processing, this correction has to be executed before flattening the Interferogram.

 

Q. - Is it possible to Cut RAW Data by means of the Sample Selection tool?

 

A. - Raw data cannot be resized. The "Sample Selections" tool can be used only after the data have been focussed.