GDAL

The Geospatial Data Abstraction Library (GDAL) is an open-source software library used to work with raster and vector geospatial data. There are a number of GDAL command line utilities that we can leverage to transform NISAR data.

Using GDAL to Transform NISAR Data¶

NISAR products are distributed in HDF5 format, and the files can be very large. Many users may want to transform the data by extracting just the datasets of interest from the HDF5 files and/or subsetting the data to a defined spatial extent.

We can use command line utilities from the GDAL software library to transform these files. Leveraging GDAL’s ability to stream data from Earthdata Cloud directly allows us to download only the data we need in the desired format.

Preparing GDAL to Access EDC¶

If you do not already have GDAL installed you can follow GDAL’s official guide.

In this guide we will be streaming products directly from NASA’s Earthdata Cloud (EDC) without downloading them first. To do so, we must allow GDAL to authenticate to EDC by placing a .netrc file in the home directory of our compute environment containing our Earthdata Login credentials.

~/.netrc

machine urs.earthdata.nasa.gov
    login <username>
    password <password>

Using a `gdalrc` File¶

Users can choose to generate a gdalrc file to simplify GDAL commands. This replaces the need to include --config flags for each command.

Create a file in ~/.gdal/gdalrc with the following content:

~/.gdal/gdalrc

[configoptions]
CPL_VSIL_CURL_CHUNK_SIZE=2097152
CPL_VSIL_CURL_CACHE_SIZE=67108864
GDAL_CACHEMAX=64000000
GDAL_DISABLE_READDIR_ON_OPEN=TRUE
GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES
GDAL_HTTP_MULTIPLEX=YES
GDAL_NUM_THREADS=ALL_CPUS
CPL_VSIL_CURL_CACHE_SIZE=1GB
GDAL_HTTP_NETRC=YES
GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt
GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

If you have a gdalrc file staged, you can skip all the --config flags included in the sample commands on this page.

Transform NISAR HDF5 Products¶

Users can transform NISAR data by using the gdal_translate or gdalwarp utility to extract and/or spatially subset data, reproject the data, and change the file format. For the examples provided here, we will output the data as a GeoTIFF.

You will need the download link for a NISAR product to run these commands. Use the Copy URL links available in the search results for Vertex, or use one of the other available search methods to find a NISAR product URL.

Screenshot of the Copy URL link for a NISAR product in Vertex. — Figure 1:Click the Copy URL link to get the download URL for a NISAR product in Vertex.

Extract Datasets¶

Run the following gdalinfo command, using the download URL for a NISAR product, to view information about the product, including the datasets it contains:

gdalinfo "/vsicurl/https://<DOWNLOAD URL>" \
         --config GDAL_HTTP_NETRC=YES \
         --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
         --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

Refer to the Data Products section for more information about the datasets included in NISAR products.

Utilize the following gdal_translate command to extract a specific dataset from an HDF5 product as a GeoTIFF:

gdal_translate -of GTiff \
                "/vsicurl/https://<DOWNLOAD URL>":<VARIABLE PATH> <OUTPUT FILE>.tif \
                --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
                --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
                --config GDAL_CACHEMAX 64000000 \
                --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
                --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
                --config GDAL_HTTP_MULTIPLEX=YES \
                --config GDAL_NUM_THREADS=ALL_CPUS \
                --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
                --config GDAL_HTTP_NETRC=YES \
                --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
                --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

The gdalwarp command is also suitable for this, and can be used as a drop-in replacement. However, using gdal_translate for simple dataset extraction operations may provide up to a 30% improvement in performance.

Example

First we will use gdalinfo to fetch information about the NISAR GCOV product used in this example:

gdalinfo "/vsicurl/https://nisar.asf.earthdatacloud.nasa.gov/NISAR/NISAR_L2_GCOV_BETA_V1/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001.h5"

This command returns a lot of information about the product, including the name and description for each dataset (or subdataset) contained in the HDF5 file.

Let’s look at the information about the first subdataset:

SUBDATASET_1_NAME=HDF5:"/vsicurl/https://nisar.asf.earthdatacloud.nasa.gov/NISAR/NISAR_L2_GCOV_BETA_V1/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001.h5"://science/LSAR/GCOV/grids/frequencyA/HHHH
SUBDATASET_1_DESC=[35928x36288] //science/LSAR/GCOV/grids/frequencyA/HHHH (32-bit floating-point)

We can garner a number of important details from this information:

The path of this dataset is /science/LSAR/GCOV/grids/frequencyA/HHHH, as specified by the second field of the SUBDATASET_1_DESC variable on the second line.
- This dataset is the Frequency A HHHH covariance dataset (HH polarization) of the GCOV product which we are using for our example.
The first and third field of the SUBDATASET_1_DESC variable specifies that the resolution of the dataset is 35928 by 36288 pixels with the type of 32-bit floating point.
The SUBDATASET_1_NAME variable provides the full string which we can utilize in a gdal_translate command.

The following gdal_translate command references the SUBDATASET_1_NAME string to form a command which outputs our chosen dataset as a GeoTIFF named output.tif:

gdal_translate -of GTiff \
                "/vsicurl/https://nisar.asf.earthdatacloud.nasa.gov/NISAR/NISAR_L2_GCOV_BETA_V1/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001.h5"://science/LSAR/GCOV/grids/frequencyA/HHHH output.tif \
                --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
                --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
                --config GDAL_CACHEMAX 64000000 \
                --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
                --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
                --config GDAL_HTTP_MULTIPLEX=YES \
                --config GDAL_NUM_THREADS=ALL_CPUS \
                --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
                --config GDAL_HTTP_NETRC=YES \
                --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
                --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt\

To extract other datasets, use the subdataset name displayed in the gdalinfo output for the desired dataset.

Spatial Subsetting¶

GDAL has many utilities which allow for spatial subsetting. In this section we will demonstrate spatial subsetting through the use of the gdalwarp utility with WKT spatial extent strings.

The gdalwarp utility allows describing spatial extents using a type of string known as a Well Known Text (WKT) Polygon or MultiPolygon string (we will refer to them as WKT spatial extent strings), which are utilized widely across geospatial applications (see examples of WKT formulation).

An easy method for defining a WKT spatial extent string is to set an Area of Interest (AOI) in Vertex. Once you’ve drawn an AOI in Vertex, the Area of Interest WKT field displays the WKT spatial extent string, and hovering over the field exposes a copy icon that you can use to capture the WKT.

A screenshot describing the location of the copy AOI string button in Vertex. — Figure 2:Click the **Copy to clipboard** icon in the Area of Interest WKT field in Vertex to copy the WKT spatial extent string to your system’s clipboard.

To perform spatial subsetting with gdalwarp, utilize the -cutline <WKT> flag alongside the -cutline_srs WGS84, -crop_to_cutline, and -dstalpha flags.

The command below demonstrates the use of these flags:

gdalwarp -of GTiff \
         "/vsicurl/https://<DOWNLOAD URL>":<VARIABLE PATH> <OUTPUT FILE>.tif \
         -cutline <WKT> \
         -cutline_srs WGS84 \
         -crop_to_cutline \
         -dstalpha \
         --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
         --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
         --config GDAL_CACHEMAX 64000000 \
         --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
         --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
         --config GDAL_HTTP_MULTIPLEX=YES \
         --config GDAL_NUM_THREADS=ALL_CPUS \
         --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
         --config GDAL_HTTP_NETRC=YES \
         --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
         --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

Example

In this example we will use the gdalwarp utility to perform spatial subsetting on the subdataset identified in the previous example.

We used Vertex to pick an area within our product and copied the AOI string, which is in a suitable WKT spatial extent string format:

POLYGON((-115.7994 43.887,-113.7599 43.887,-113.7599 44.9751,-115.7994 44.9751,-115.7994 43.887))

We will then input this string, and the full dataset string identified in the previous example, into the spatial subsetting snippet provided above.

This gives us the final command, which we can utilize to perform our spatial subsetting operation:

gdalwarp -of GTiff \
         "/vsicurl/https://nisar.asf.earthdatacloud.nasa.gov/NISAR/NISAR_L2_GCOV_BETA_V1/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001.h5"://science/LSAR/GCOV/grids/frequencyA/HHHH output.tif \
         -cutline "POLYGON((-115.7994 43.887,-113.7599 43.887,-113.7599 44.9751,-115.7994 44.9751,-115.7994 43.887))" \
         -cutline_srs WGS84 \
         -crop_to_cutline \
         -dstalpha \
         --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
         --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
         --config GDAL_CACHEMAX 64000000 \
         --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
         --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
         --config GDAL_HTTP_MULTIPLEX=YES \
         --config GDAL_NUM_THREADS=ALL_CPUS \
         --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
         --config GDAL_HTTP_NETRC=YES \
         --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
         --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

Reprojection¶

The gdalwarp utility can also be used to reproject datasets from the projection used for the source NISAR HDF5 product to a different spatial reference system.

In your gdalwarp command, set the -t_srs <SRS> flag, where <SRS> is the EPSG code for the desired output spatial reference system (such as EPSG:3857 for Web Mercator):

gdalwarp -of GTiff \
         "/vsicurl/https://<DOWNLOAD URL>":<VARIABLE PATH> <OUTPUT FILE>.tif \
         -t_srs <SRS> \
         -dstalpha \
         --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
         --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
         --config GDAL_CACHEMAX 64000000 \
         --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
         --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
         --config GDAL_HTTP_MULTIPLEX=YES \
         --config GDAL_NUM_THREADS=ALL_CPUS \
         --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
         --config GDAL_HTTP_NETRC=YES \
         --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
         --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

Example

We can utilize this snippet to project the product used in our previous examples into Web Mercator as follows:

gdalwarp -of GTiff \
         "/vsicurl/https://nisar.asf.earthdatacloud.nasa.gov/NISAR/NISAR_L2_GCOV_BETA_V1/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001/NISAR_L2_PR_GCOV_005_149_A_024_4005_DHDH_A_20251120T123755_20251120T123830_X05009_N_F_J_001.h5"://science/LSAR/GCOV/grids/frequencyA/HHHH output.tif \
         -t_srs EPSG:3857 \
         -dstalpha \
         --config CPL_VSIL_CURL_CHUNK_SIZE 2097152 \
         --config CPL_VSIL_CURL_CACHE_SIZE 67108864 \
         --config GDAL_CACHEMAX 64000000 \
         --config GDAL_DISABLE_READDIR_ON_OPEN=TRUE \
         --config GDAL_HTTP_MERGE_CONSECUTIVE_RANGES=YES \
         --config GDAL_HTTP_MULTIPLEX=YES \
         --config GDAL_NUM_THREADS=ALL_CPUS \
         --config CPL_VSIL_CURL_CACHE_SIZE=1GB \
         --config GDAL_HTTP_NETRC=YES \
         --config GDAL_HTTP_COOKIEFILE=/tmp/gdal_cookies.txt \
         --config GDAL_HTTP_COOKIEJAR=/tmp/gdal_cookies.txt

Using GDAL to Transform NISAR Data¶

Preparing GDAL to Access EDC¶

Using a gdalrc File¶

Transform NISAR HDF5 Products¶

Extract Datasets¶

Spatial Subsetting¶

Reprojection¶

Using a `gdalrc` File¶