Sentinel-1 – Image Quality

Users of Sentinel data may see quality issues similar to those below. Users are encouraged to submit examples of image-quality issues to uso@asf.alaska.edu.

Browse images affected by map projection

When an image granule is located above 65° latitude, the browse image can appear to be oriented and shaped differently than its outline in Vertex. The browse image is a geocoded JPEG displayed in a polar stereo map projection at latitudes above 65° in either hemisphere. The Vertex map always displays a granule in a Mercator projection. The examples show a Vertex map outline of a granule in the Arctic Ocean and an associated browse image. The browse image also is an example of stepped ends.

granule-map
ascending-browse-image-1

Images from data close to the noise floor

Images that contain a great deal of noise have often been processed close to the noise floor (the data closest to the point where it is too noisy to be useful). The noise can look like repeating lines across an image, something like horizontal window blinds, as in the left image below. Those repeating lines are not the same as the bright spots in these images, which appear in the image below and to the right as a line of repeated bright spots or bursts. Those bright bursts are image anomalies that are not yet well understood. Also visible in these images are beam seams (see the next section).

noisy-image-repeating-lines
noisy-image-bright-bursts

Beam seams

When one image is made up of several beams, the seams can show, particularly in dark data. Beam seams are visible in many of the images on this page, including the one to the right.

Offsets between channels

Beams that seem to have noisy or missing data at one end, such as the dark blue edge at the top of the image, have been processed in one channel more than another (such as the HV or VH channels).

Stepped edges

Stepped ends, as in this image, are an artifact of the multi-beam scanning technology of TOPSAR and the way that ESA “slices” a data take into discrete, manageable units. 

Bright burst

Bright bursts are processing anomalies that are not well understood. Bright bursts are in the upper left corner of the image below at left and in the light stripe across the image below right. Also visible in the image on the left are noise (window-blind effect), beam seams, and a bit of blue on the far left that may indicate an offset between channels.