I would like to subset the GRD file with python based on lat/lon range. However, when i read the original tiff file with GDAL and there is no projection information. Anyone has any thoughts for how to get the lat/lon information from the original GRD file rather than using GIS software?
the tif file does not contain all the metadata required to process the raster properly.
You might have a look at the snappy libraries which use SNAP functionalities within Python.
instead of the tif file you import Sentinel-1 by the manifest.safe file.
Full workflow (including subset): http://remote-sensing.eu/preprocessing-of-sentinel-1-sar-data-via-snappy-python-module/