Values in file csv

snap
#1

Good morning,

I have worked with Grd products and, after Terrain Correction, I’ve obtained several images and now I would like to draw histogram, for example, with Matlab.

I must use csv files, not other format, but I’m not able to get histogram with these csv files, for example, in Matlab .

In csv file what are those values?
I think that they aren’t digital number (DN) from this post:

Thanks in advance.

#2

if you didn’t calibrate or select the topographic normalization, these values are still intensities.

How did you export the csv values? Maybe you can post your file here.

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#3

Thanks dear Andreas,

after terrain correction I have made
file -> export -> csv.

This is a csv file for example
https://mega.nz/#!y5J3UaKY!MZc6yfX0AJcZ5USbwbhk4cm5v9AsC8acTig8anH4ZSg

#4

I think these are just the Pixel intensities in a table.

If you can ge them into a list, Matlab should be able to create a histogram out of it but I’m not experienced with Matlab.

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#5

Please, what is the difference between pixel intensities and digital number?

When I obtain from Snap, for example, an image in jpeg, not file csv, in matlab there are 256 gray level for X-axis in hystogram because image is already quantized, is it correct?

When I use file csv there should be along X-axis values of pixel intensities i.e values of the band because amplitude is the measurement of SAR sensors, is it right?

Thank you very much.

Problem using " Terrain flattering" on GRD IW products
#6

I personally read the term Digital Number (DN) only when using optical data, but I guess it’s kind of the same:
DN is the measurement before calibration while reflectance is the proportion of radiation hitting a surface to the radiation reflected away from it (as for optical data).

DN can be compared with amplitude A, the raw format of backscattering. A² is intensity I, still not calibrated but the proportion of microwave backscattered from that area on the ground. To get comparable values of SAR backscatter, calibration is needed. Calibration corrects intensity according to sensor specifications and (local) incidence angle.

  • Beta Nought (ß) is the radar brightness (or reflectivity) coefficient. The reflectivity per unit area in slant range is dimensionless. This normalization has the virtue that it does not require knowledge of the local incidence angle (e.g. scattering area A).
  • Sigma Nought (σ), the backscattering coefficient, is the conventional measure of thestrength of radar signals reflected by a distributed scatterer, usually expressed in dB. It is a normalized dimensionless number, which compares the strength observed to that expectedfrom an area of one square metre. Sigma nought is defined with respect to the nominally horizontal plane, and in general has a significant variation with incidence angle, wavelength, and polarization, as well as with properties of the scattering surface itself.
  • Gamma (γ) is the backscattering coefficient normalized by the cosine of the incidence angle.

Source: http://www.sarmap.ch/pdf/SAR-Guidebook.pdf

Converting to jpeg loses this information because it usually renders the values (scaling 0-255)

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When used Sigma0, Betta0 or Gamma0?