Scientists develop a new tool that cleans satellite trails from Hubble images

The telescope is constantly being photobombed by satellites.
Loukia Papadopoulos
A Hubble image with some streaks.jpg
A Hubble image with some streaks.


The Hubble Space Telescope is in a low-Earth orbit which means its snapshots are constantly photobombed by artificial satellites.

This is according to a press release published Thursday by researchers at Baltimore's Space Telescope Science Institute (STScI).

Now, the scientists plan to do something about it.

"We developed a new tool to identify satellite trails that is an improvement over the previous satellite software because it is much more sensitive. So we think it will be better for identifying and removing satellite trails in Hubble images," said Dave Stark of STScI.

The new tool is based on the image analysis technique known as the Radon Transform. It identifies satellite trails across Hubble's camera with the widest field of view: the Advanced Camera for Surveys (ACS).

"To date, these satellite trails have not had a significant impact on research with Hubble," said Tom Brown, Head of STScI's Hubble Mission Office. "The cosmic rays that strike the telescope's detectors are a bigger nuisance."

Messy streaks

Radiation from space and artificial satellites hits the ACS electronic detectors on every exposure, leaving behind streaks that mess with the resulting image’s clarity. Luckily these streaks are easy to remove.

"The average width I measured for satellites was 5 to 10 pixels. The ACS' widest view is 4,000 pixels across, so a typical trail will affect less than 0.5% of a single exposure. So not only can we flag them, but they don't impact the majority of pixels in individual Hubble images. Even as the number of satellites increases, our tools for cleaning the pictures will still be relevant," said Stark.

Typically, Hubble assembles a series of multiple exposures on the same celestial target which means a satellite streaking across the sky can appear in one frame and not the next consecutive one. Stark and his team, therefore, engineered a masking routine that identifies where the bad pixels are and the extent to which they affect the image and then flags them.

 '"When we flag them, we should be able to recover the full field of view without a problem, after combining the data from all exposures," said Stark.

The Radon Transform software tool Stark used is perfect for identifying and characterizing linear features in an image because it sums up all the light along every possible straight path across an image.

The new software is also up to ten times more sensitive than prior software developed by STScI to detect satellite trials. It can identify roughly twice as many trails as other studies.

"We have a toolbox of things that people use to clean Hubble data and calibrate it. And our new application is another tool that will help us make the best out of every Hubble exposure," said Stark in the statement.

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