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Backscatter SigmaO S1
Added by Naeem Shahzad about 6 years ago
Greetings, Dr. Charles. Sir, I am trying to process a single S1 image for a simple backscatter sigmaO image. I have tried to follow the Sentinel1 processing user guide for GAMMA, but I am not getting the outputs similar to the those which are shown in user guide? I am following:
1. par_S1_SLC
2. SLC_mosaic_S1_TOPS
3. multi_look
4. gc_map and geocode_back (simple image looks better than beck geo-coded data(attached))
Maybe I am missing something, to get a smooth regular image other than pixelated noisy image (screenshot attached).
regards
naeem
| back_geocode_s1.png (49.2 KB) back_geocode_s1.png | |||
| mli_image_s1.png (658 KB) mli_image_s1.png |
Replies (4)
Backscatter SigmaO S1 - Added by Charles Werner about 6 years ago
Hello,
Somewhere the line size is wrong. Obviously if the MLI image is wrong, you can't
geocode.
The correct process to get an MLI image correct is
par_S1_SLC
multi_S1_TOPS (will be renamed to ScanSAR_burst_MLI in the next release)
Once you have created a mosaicked MLI image, then it is as any other MLI image
from stripmap SAR.
The scripts mk_geo_radcal is what I use for terrain geocoding and may be useful
to you.
See the html documentation for information
gamma_doc mk_geo_radcal
There are examples for running the current version of the Gamma Software (20180702):
Gamma Software Users with a valid license or evaluation license can download the
Gamma Software Demo examples here:
account: http://www.gamma-rs.ch/userdata/Gamma_Software_demo
user: gamma_user
password: RBS_821
The examples with Sentinel-1 data should be useful.
Best regards,
Charles
RE: Backscatter SigmaO S1 - Added by Naeem Shahzad about 6 years ago
Dear Sir
Thank you for this.
During the process of mk_geo_radcal, the output "XX_map.mli" image contains dB values when open via 'dispwr'.It can also be seen in the "XX_map.mli.bmp". When I convert this bmp or even .mli file to tif or ras format, it only shows the values ranges from 0 to 255. why its not transforming the actual dB values in tif file, even using 'float_math applied on xx_map.mli file. Anyguidance? What I need is basically a tif file with dB values so that I can compare this with other data sets.
regards
Naeem
RE: Backscatter SigmaO S1 - Added by Charles Werner about 6 years ago
The process to convert the intensity values in the _geo.mli file to dB values
and then into GeoTIFF format is as follows:
1.The MLI data are power, not dB values. The bmp file is a greyscale
visualization of the intensity data. To convert to dB use the program
float_math. You should know the
number of samples/line in the geocoded image. This value is stored in the DEM
parameter file (dem_par) as the width.
float_math XX_map.mli - XX_map.dB width 4
alternately, if you have the LAT package:
linear_to_dB XX_map.mli XX_map.dB width 0
2.Save the floating point dB values as a GeoTIFF file:
data2geotiff DEM_par XX_map.dB 2 XX_map_dB.tiff
Documentation is available for all these programs
gamma_doc float_math
gamma_doc linear_to_dB
gamma_doc data2geotiff
best regards,
Charles