Issue Extracting Numpy Array from Sentinel-1 GRD Image

development python
1

Hello,

I am stuck on what feels like should be simple task. I am following the documentation here:

and trying to follow the first contact step to get a numpy array from a S1 grd image.

‘’’
p = ProductIO.readProduct(‘C:/Users/f72w381/Downloads/S1B_IW_GRDH_1SDV_20201012T012004_20201012T012029_023773_02D2C9_779C.SAFE/manifest.safe’)

rad13 = p.getBand(‘Intensity_VV’)
w = rad13.getRasterWidth()
h = rad13.getRasterHeight()
rad13_data = np.zeros(w * h, np.float32)
rad13.readPixels(0, 0, w, h, rad13_data)
p.dispose()
rad13_data.shape = h, w
imgplot = plt.imshow(rad13_data)
imgplot.write_png(‘radiance_13.png’)
print(‘done’)
‘’’

This returns a numpy array still filled with zeros.

Things I have tried:

  1. trying with the zipped and unzipped files.

  2. exporting p as a GeoTiffs and BEAM-DIM fomats and trying with those formats.

  3. Performing the extraction for just a single line of pixels

  4. Checking the grd image in snap desktop to be sure it actually has values in it

  5. Trying with the other bands

What am I missing?

2

First, does the “First Contact” script work using MER_FRS_L1B_SUBSET.dim? Then, have a look at Preprocessing Sentinel 1 SAR Data using snappy, which mentions converting DN to Sigma Nought or Decibels.

3

It did work with the test visual image. I will check out that link and see if I need to convert first. Thanks!

4

I followed that documentation and converted to Sigma Nought and subset the image to a smaller portion in case it was a memory issue. No luck. All the images appear fine in the SNAP desktop, but still just getting an array of zeros.

5

Had to covert to dBs first to get the plot to appear.