A Clever Way to Map the Moon’s Surface—Using Shadows

NASA's astronauts will return to the moon early in the 20th century. Humans will return to the moon for the first time in 40 years. The course of lunar exploration could be changed by what they discover there.

They will be looking at areas inside deep craters where the sun doesn't rise above the walls. The permanently shadowed regions may have had trapped water because of the cold. Future explorers could use the ice as a source of fuel and as a source of water.

Before any of this can happen, NASA needs to find a safe landing site with a route that leads to the water deposits. High-resolution models of the lunar surface have been used to draw up a list of places to touch down. There is a tool that can help determine which is best. Increased assurance of the actual terrain that explorers and rovers will encounter is what researchers have developed a new way to create 3D maps of the moon.

The technique of using shadows to reveal the moon's surface has been used for 50 years.

When looking at shadows, it is natural for our eyes to see the shapes and forms of objects. The system of terrain modeling uses multiple shadowed images of an area, data on the incoming angle of the light in each satellite image, and elevation data to build a 3D model of what's casting the shadows in those pictures.

Shadowed images of a crater taken at different times, when sunlight hits the terrain at different angles, can be used to work out, for instance, that the crater's wall must have a 20- degree incline.

Some assumptions need to be made about the terrain in order to use this shadow technique. An initial rough elevation model is created using the technique and continually improved until it matches the shadowed images. It can take a long time for a trial to work out.

The angles of incoming sunlight and the shape of the terrain were related by an equation that was solved by Fernandes and her colleague. This is the first time a model has been created using this equation. The result is that the new approach doesn't require any prior assumptions about the terrain and produces high-resolution terrain maps in one try. It's a big advantage to build terrain models for more than one area.