IDL & ENVI Aid in Martian Discoveries

“I don’t think there is another processing package that has the breadth and depth of spectral tools. IDL and ENVI allow you to plug in additional capabilities to customize your data analysis.” Bill Farrand, Mars Exploration Rover Team

In January 2004 two rovers, launched by NASA, landed on opposite sides of Mars. The goal of the Mars exploration mission was to answer questions posed for generations: what is the history of water on Mars, and what is the potential that life could, or ever did, exist on the planet?

The twin rovers are operated by the Jet Propulsion Laboratory in Pasadena, California, and are dubbed Spirit and Opportunity. They each carry onboard a suite of sophisticated data collection instruments, including a robotic arm and several cameras. They were originally expected to travel only about 600 meters over their entire lifespan, but they have far surpassed that objective, to the delight of the Mars Exploration Rover (MER) mission team – a team of experts from around the country who manage each intricate detail of the operation. The rovers’ agility in navigating the cratered surface has provided researchers on Earth with more substantive discoveries than they ever expected, such as proof of the existence of evaporites, or rocks formed when lake or sea water evaporates.

Exploring New Geologic Possibilities

Thanks to the rovers, and advanced imaging software technology like IDL and ENVI, scientists now can better understand the geochemical and mineralogical make up of Mars. Geologist William Farrand, a research scientist with the Space Science Institute (SSI) of Boulder, Colorado who joined the MER team in 2002, uses both IDL and ENVI to manage, analyze and present the image data from the rovers. He explains that, “There are so many things that we’re discovering about the nature of rocks and soils on the Martian surface and how, in some cases, they’ve been altered by the action of water. We’re learning about the climate’s history and past environmental condition on Mars by examining clues in rocks and soil samples – some of which are 3 billion years old.”

To gather data for eventual analysis with IDL and ENVI, Farrand and other researchers on the team plan the rovers’ daily activities by identifying areas of interest on the Martian landscape and directing them to those regions. Spectacular high resolution imaging is achieved using a pair of multispectral Panoramic Cameras, or Pancams, one mounted on each rover, which provide stereo imagery, as well as a full panoramic, three-dimensional view of the surface around each rover.

Scientists Manage and Analyze Data with IDL

A set of IDL routines, developed by scientists and engineers at Cornell University, helps analysts and scientists work with the specific types of imagery returned by the rovers. The set of programs called “MERtools” by the team, is used for monitoring camera health, data tracking, and data analysis. The data are gathered each Martian day, compressed on-board and sent to Earth in both direct-to-Earth transmissions and transmissions relayed by the orbiting Mars Odyssey spacecraft.

IDL’s role in the mission doesn’t end with managing the cameras and their data. Understanding the enormous amount of data sent from Spirit and Opportunity each day is a complex task. Farrand, who works extensively with the downloads of Pancam data, uses IDL and ENVI to sort, manage, examine and create files from each data product. Analyzing extraordinary amounts of data each day can be tedious, but Farrand says that the ease and convenience of the IDL environment saves him time. “I don’t think there is another processing package that has the breadth and depth of spectral tools. IDL and ENVI allow you to plug in additional capabilities to customize your data analysis.”

An ENVI routine was customized with IDL to create a composite of fraction images derived from linear spectral image analysis. Two subtly different rock types are assigned to the red and green channels, while a soil fraction image is assigned to the blue channel.

Customized IDL and ENVI Routines

Once Farrand has verified the data with IDL, he uses IDL and ENVI routines he developed to get an idea of what kinds of spectrally distinct rocks and soils exist on the red planet. IDL’s functionality provides him with a set of powerful image processing tools from which to build a customized version of the linear spectral mixture analysis and matched filter routines. Using ENVI’s suite of spectral tools, he also performs classifications of, and information extraction from the multispectral Pancam images.

Farrand also uses ENVI’s integral spectral library to relate the broadband spectra of materials on the surface of Mars to those of laboratory-measured minerals on Earth. One ENVI routine which Farrand uses repeatedly in his research is the decorrelation stretch tool which enhances subtle color difference in Martian rocks and soils.

Discoveries about the Martian environment continue each day. Although robots will never take the place of human intuition and experience, and many of the pieces of the Mars mystery have yet to be solved, Farrand says that Opportunity and Spirit have been very successful in uncovering a wealth of information about the planet’s geologic condition, and software tools from CREASO have been essential to this success.