A clever way to map the Moon’s surface using shadows
The team tested their approach on an area centered on the Mare Ingenii, a region on the far side of the moon. They fed the algorithm with the angles of incoming sunlight from photographs containing shadows taken by NASA’s Lunar Reconnaissance Orbiter (LRO) – a satellite that constantly orbits the moon, capturing information – as well only elevation data collected by its laser altimeter. The resulting high-resolution terrain model matched shaded photographs with a high degree of accuracy and dramatically improved elevation resolution. Elevation data collected by the LRO’s laser altimeter has a resolution of 60 meters per pixel; the final terrain model of the new method had a resolution of 0.9 meters per pixel. This meant that craters as small as three meters in diameter became identifiable. “It’s a different approach to understanding the moon’s topography that could help prepare for future human and robotic exploration,” says Noah Petro, a planetary geologist at NASA’s Goddard Space Flight Center who was not involved in the research. .
The LRO has been orbiting the moon since 2009, collecting data that has been used to create a digital terrain model that covers 98% of the moon’s surface. This is the base map on which all higher resolution terrain models, such as the one in the new study, are placed. Together, these high-resolution maps form the basis for planning surface voyages. Landing sites should be flat and free of rocks. Ideally, the travel routes to and from the craters should not be steep, so that they can be traveled by rovers.
High resolution lunar landscape maps can also be used to model lighting conditions. Predicting when and where to expect shadows and sunlight is crucial for planning future missions, says Paul Hayne, a planetary scientist at the University of Colorado Boulder’s Atmospheric and Space Physics Laboratory. Potential landing sites will need to receive solar radiation for at least part of the day to recharge instruments and rovers. Sunny areas directly adjacent to craters could also be useful, as exploring shady regions can take time, meaning rovers may need to be recharged as soon as they come out of a crater.
A more detailed understanding of the terrain can also help NASA decide which permanently shadowed regions to target when searching for water ice. For example, the slope of the crater walls can provide insight into how long the crater formed and whether shadows and temperatures might have persisted long enough for water ice to be present. “We often need very accurate terrain models to turn a snapshot into a time story, to find the cold traps where the ice might be stable for long periods of time,” says Hayne.
And on top of all that, the new imaging approach should also help with navigation. Rovers must be able to travel along precisely calculated routes. On-board motion sensors can help rovers navigate, but sensor and estimation errors can accumulate over large distances, causing vehicles to drift. One way to overcome this is to have rovers use on-board cameras to create high-resolution terrain models themselves, then pinpoint their location relative to known features and adjust their trajectory accordingly, says Martin Schuster. , robotics scientist at the German Aerospace Center. Institute of Robotics and Mechatronics. “Matching local terrain models with externally created high-resolution models, like the one produced in the new study, can help rovers locate themselves,” he says. If the resolution of previously created terrain maps is too low, it may be more difficult to stay on the path.
The moon is a quarter of a million miles from Earth. It is difficult to get there and if the astronauts encounter unexpected problems on the surface, they will be limited in their reaction. Anticipating the terrain features that explorers and rovers will encounter is therefore extremely important and could even save lives. Finding the best and most accurate ways to map the moon’s surface is an integral part of mission preparation. “We want to use all the data available to tell us everything we can about the places we want to explore,” Petro says.