Topography: The surface of the moon and rocky planets, Mars in particular, is of great interest to anyone attempting to explore our solar system. The surface must be known in as much detail as possible, for missions to land safely, or for any robotic craft to traverse the surface. But so far, methods for analyzing images from, for example, orbiting spacecraft have involved enormous workloads and computing power, with limited results. A project by a former PhD student at the Niels Bohr Institute at the University of Copenhagen, Iris Fernandes, has changed the situation. By studying the Stevns Klint limestone formation in Denmark, she developed a method to interpret shadows in images, so that the exact topography could be extracted. The method is even faster and less labor intensive. The result is now published Planetary and space sciences 218.
Human space exploration involves high levels of safety – so accurate images of the terrain are adamant
The topography of any surface will create shade when sunlight hits it. We can clearly see the nuances in images of the Moon, for example, but we don’t know the elevation of the terrain. So we see the topography change, but not to what extent! Being able to see even very small features is necessary to ensure safe landing or movement of, for example, a rover. Not to mention the safety of astronauts.
If a rover can’t see detail, it could get stuck in sandy surfaces or hit rocks – and being able to see interesting geologic formations to find rich geologic environments for research purposes is also a big help. importance.
The old limitations of surveying topography have now been largely eradicated
When satellites orbit a planet, they can take pictures of the surface with reasonable quality. But to establish an interpretation of the exact topography sufficient to land extremely expensive equipment or perhaps even astronauts, a lot of ad hoc information still needs to be processed.
The method of using shades existed before, but it was computationally inefficient and still had to rely on assumptions. The new method uses a much more direct and precise calculation, it does not rely on a whole set of parameters to be fed into the computer, and it can even calculate uncertainties and precision.
“This method is fast, accurate and does not rely on any assumptions. Previously,” says Iris Fernandes, “if you asked the question: how accurate is the topography assessment — there really wasn’t a satisfying answer.
Now the precise topography is revealed, and we can even quantify the uncertainties. »
Scientific curiosity can take you to surprising places
“I was involved in a project where we wanted to use images from Stevns Klint to model patterns on the surface. I even presented this method at a conference in Los Angeles. But the nuances presented a challenge, because the algorithm “saw” the nuances as geological. Features.
This created a bias in the model. We had to find ways to remove nuance, in order to remove bias.
I have always been interested in planets and knew that the surface of the moon was studied. There aren’t many disturbing features on the Moon, so this was ideal for eliminating bias.
When we filtered the shades, we could see what they were ‘hiding’, so to speak – the surface shapes”, explains Iris Fernandes.
Resolving existing images presented a new problem — and a new approach
When work on the Moon began, the discrepancy between the different resolutions of the images and the topographic data turned out to be enormous. A new problem has arisen, in other words. “How could we combine different data sources in different resolutions?
This presented a huge mathematical problem – and that’s really what the study is about.
This is where the old research had stopped. What we did differently from previous attempts to solve this problem is that we focused on the math and reduced it to a difficult mathematical equation. Basically, to see if this equation could solve the problem.
And he did it,” smiles Iris Fernandes. “You could say that we, my supervisor, Professor Klaus Mosegaard and I, have found the mathematical key to a door that had remained closed for many years.
The path to follow
The focus is now on improving the method even more. Wherever data is available on rock formation in the solar system, such as the Moon, Mars, asteroids or others, the method can be applied to extract precise topographic details.
The images used for this task could be images of satellites or even of the rovers themselves, currently on the ground on Mars – or of any mobile robot in the future.
The objectives for carrying out a correct topographical analysis can be different, it can be the safety of the equipment or the astronauts or the search for geologically interesting sites.
In other words, there is a wide range of possible applications. “It’s a kind of computer vision,” says Iris Fernandes: “When, for example, a robot has some form of machinery to interact with the environment, the method can help with navigation or ” hand-eye coordination”, because it is less “heavy” in calculation and therefore faster.
I’m only speculating now, but an interesting feature might be to assess the roundness of small rocks, in order to find the former presence of water.
The method shows data for us as humans in a way that we intuitively understand – like images of the roundness of stones, which is very easy to interpret. »