Alaska Satellite Facility - Distributed Active Archive Center

Sentinel-1 – FAQ

Frequently Asked Questions About Sentinel-1 Data

Also see the more general SAR FAQ page and other help pages at Tutorials.

Sentinel-1 data products acquired in Stripmap, Interferometric Wide Swath, and Extra Wide Swath modes, generated by the Payload Data Ground Station, are distributed at three levels of processing:

Level-1 products can be one of two product types — either Single Look Complex (SLC) or Ground Range Detected (GRD). Level-2 Ocean (OCN) products can have different components available depending on the acquisition mode. Products are designated based on their acquisition mode, product type and, in the case of Level-1 GRD, resolution. All products are processed directly from the Level-0 product. Each mode can potentially generate Level-1 SLC, Level-1 GRD and Level-2 Ocean products. For Wave (WV) mode, the Level-0 and Level-1 products are not distributed. Level-2 Ocean Swell Spectra (OSW) component is not available from the TOPSAR modes.

Sentinel-1 satellites carry a C-band SAR instrument to provide a combined all-weather, day-and-night supply of imagery of Earth’s surface every six days. The four SAR modes — described in more detail on the Data and Imagery page — are Extra Wide Swath, Interferometric Wide Swath, Stripmap, and Wave.

The naming convention is explained in the graphic below. For more data information, see the Sentinel-1 Data and Imagery page.

You must be logged in to Vertex in order to download Sentinel-1 data from ASF.  If you don’t already have a user account at ASF, please create one on Earthdata.

To filter by data product, use the drop-down menu titled at the bottom of the results column. Use the menu to select only those products you want added to your download queue. The bar, at the top of the results column, lets you filter your results by typing in keywords displayed in the granule description, such as path or flight direction.

For more detailed sorting, use the and features, and add the results to your download queue. Click the button, and import the resulting file into a spreadsheet. Use the tools in your spreadsheet to sort the metadata — for example, by polarization. Copy and paste the resulting granule names into the window to the left of the map and click .

Find additional Vertex help through the tab at the top left of the page.

Use the geographic search option in the Vertex Data Portal to identify your area of interest and download Sentinel-1 products available from ASF DAAC.

Sentinel-1 data products are distributed using a Sentinel-specific variation of the Standard Archive Format for Europe (SAFE) format specification. The SAFE format has been designed to act as a common format for archiving and conveying data within ESA Earth Observation archiving facilities. The format wraps a folder containing image data in a binary data format and product metadata in XML. This flexibility allows the format to be scalable enough to represent all levels of Sentinel-1 products.

A Sentinel-1 product refers to a directory folder that contains a collection of information. It includes:

  • a ‘’ file which holds the general product information in XML
  • subfolders for measurement datasets containing image data in various binary formats
  • a preview folder containing ‘quicklooks’ in PNG format, Google Earth overlays in KML format and HTML preview files
  • an annotation folder containing the product metadata in XML as well as calibration data
  • a support folder containing the XML schemes describing the product XML.

Also see SAR Product Formatting on the ESA website.

The default Windows file extraction utility will often fail because of long Sentinel-1 filenames. The open-source utility 7-Zip can be used to extract the .zip files downloaded from ASF and ESA.

These beam modes incorporate an acquisition technique (TOPSAR) that produces wide swaths from multiple sub-swaths, or bands, acquired in the direction the satellite is moving. This can create “seams” that are more noticeable in cross-polarized images (HV and VH). IW is acquired using three sub-swaths and EW five sub-swaths. See Image Quality for examples.

Stepped ends, as in the image to the right, are an artifact of the multi-beam scanning technology of TOPSAR and the way that ESA “slices” a data take into discrete, manageable units. See Image Quality for more information on image artifacts and anomalies.

Single polarization (HH, VV) images are in grayscale, while dual polarization (HH/HV, VV/VH) images have had color assigned to each polarization channel.

The Sentinel-1A browse is a geocoded jpeg image displayed in a polar stereo map projection at latitudes above 65° north and south. The Vertex map always displays a granule in a Mercator projection. The browse image below is also an example of stepping (question #10). See Image Quality for more information on image artifacts and anomalies.

The European Space Agency (ESA) uses slices instead of frames to divide a Sentinel-1 datatake into more manageable units, without any overlap or duplicated lines between slices. Stripmap and Interferometric Wide Swath slices consist of approximately 25 seconds of acquisition, and Extra Wide Swath slices consist of approximately 60 seconds. Each band within a product slice is kept to under 2 GB in size. Depending on the terrain being imaged, slices in the same datatake can have different dimensions in the azimuth direction.

ASF DAAC assigns frames to Sentinel-1 product slices that refer to the same point temporally and geographically. In Vertex, search results then display all the products available over a point and time instead of listing the products for the same point individually. For example, a single Sentinel-1 slice can produce RAW, SLC, GRD and OCN products. ASF DAAC uses the internally generated frame number to group these products into a single Vertex search result and to create InSAR stacks or stacks used to color code Vertex results on the map to indicate approximate quantity of repeating observations with the same relative orbit and frame number.

This situation can happen when ESA just released new data and ASF DAAC is still waiting to get the product, or when ESA has processed a scene multiple times. In the latter case, ASF DAAC only keeps the most recent copy of each product type, but ESA may keep older copies available for distribution. If you have a specific product that does not seem to fit either of these two possibilities, please contact ASF DAAC through [email protected].

ASF DAAC generates thumbnail and browse images from the geocoded GRD product produced by the European Space Agency (ESA). If a granule in Vertex is missing a thumbnail and browse image, ASF has not received the GRD product yet, and only RAW, SLC or OCN products are currently available to download.
Note: OCN (Wave mode) products never have browse or thumbnail images available.

This ability is currently not available to individual researchers. Acquisition requests are determined by the requirements of the Copernicus program and ESA/EU member states. ESA does make upcoming acquisition planning available to download and view in Google Earth. More information about ESA’s background planning strategy is available on the ESA Sentinel-1 Observation Scenario web page.