asf-tools 0.3.0

Tools developed by ASF for working with SAR data

ASF Tools for Python

asf_tools is a Python package for working with Synthetic Aperture Radar (SAR) data. It was designed for working with datasets generated by HyP3, but several of the tools have the potential to be used with a variety of rasters, including non-SAR datasets.

Install

In order to easily manage dependencies, we recommend using dedicated project environments via Anaconda/Miniconda. It is also possible to use Python virtual environments, but installation of non-python dependencies (e.g., gdal) can be challenging.

asf_tools can be installed into a conda environment with

conda install -c conda-forge asf_tools

or into a virtual environment with

python -m pip install asf_tools

Quick Usage

Local Resolution Weighted Composite

The make_composite tool allows you to create a local-resolution-weighted composite from a set of Sentinel-1 RTC products (D. Small, 2012). It is intended to be used with RTC products generated by ASF HyP3.

You will need to request RTC products using the Include Scattering Area option, then download and unzip them into an empty directory.

To generate a composite of the co-polarization images, navigate to the directory containing the unzipped RTC products and run:

make_composite VV-composite */*VV.tif

To generate a composite of the cross-polarization images, navigate to the directory containing the unzipped RTC products and run:

make_composite VH-composite */*VH.tif

Usage Tip

Because the imagery has been radiometrically terrain corrected (RTC), geometric and radiometric distortions have been removed from the files to be composited. One the strong points of LRW composites is that you combine both ascending and descending datatakes into a single product. In this manner no layover or shadow masks are required - what is shadowed on an ascending pass is visible in a descending pass and vice-versa. Thus, not only is it possible to combine ascending and descending, but it is highly encouraged. Using many datatakes from both the ascending and descending satellite passes will make the best composites possible.

About Local Resolution Weighting (LRW)

In an LRW composite, each satellite pass contributes to creating the output pixels. The amount of this contribution is scaled by the inverse of the scattering area used during terrain correction (thus the need for requesting the area map option of HyP3 RTC). The inverse of the surface scattering area, also referred to as local resolution, is multiplied by each pixel's backscatter value. The results of all of the images covering any single pixel are then summed. This total is then divided by the sum of the weights used to get the output average backscatter.

Water extent mapping

The water_map tool allows you to create a surface water extent map from a Sentinel-1 dual-pol (VV+VH) RTC product. It is intended to be used with RTC products generated by ASF HyP3.

Additionally, a HAND (height above nearest drainage) GeoTIFF that is pixel aligned to the RTC images is required, and preferably derived from the same DEM used to correct the RTC images -- the quality of the HAND used is directly tied to the quality of the output water extent map.

To make a water extent map, run:

water_map [OUT_RASTER] [VV_RASTER] [VH_RASTER] [HAND_RASTER]

For more information and to see the options available, see:

water_map --help

For details on the algorithm see the asf_tools.water_map.make_water_map docstring.