Logo: University of Southern California

Mars Pictures Coded by USC

January 30, 2004 —

Data streaming from the Mars rovers to earth is packaged in special concentrated form – communications packages directly based on research by University professor Solomon W. Golomb.

The millions of miles between the red planet and earth-based antennas, and the limited power of the transmitters aboard Spirit and Opportunity mean that every bit in the message has to count, says Golomb,

To accomplish this, the images and other information acquired by the vehicles is processed in onboard computers using coding techniques that enable the messages sent home to be far smaller -- contain far fewer symbols -- than the original raw data.

One of the systems the Rovers use to do this is called the "Low Complexity Lossless Compression for Images" system, or LOCO-I, developed by a three-man team of engineers working at Hewlett-Packard Laboratories in Palo Alto.

The mathematical heart of LOCO-I are what are known as Golomb codes, building on research published in 1966 by Golomb, who had then been at USC three years. He now holds the Andrew and Erna Viterbi Chair in Communications in the USC School of Engineering's department of Electrical Engineering/Systems.

"The coding scheme I invented is called 'universal' " Golomb said, “because it doesn't depend on knowing in advance the precise statistics of what will be encountered; and 'lossless,' because although it reduces the amount of data that has to be sent, it doesn't actually lose any of the information."

Golomb's name occurs more than 34 times in the original 2000 paper describing the LOCO-1. In an e-mail message to Golomb, Gadiel Seroussi, a member of the H-P. Team, wrote: "Obviously, Golomb codes have had a very long reach."

The Mars images are not the first interplanetary milestone for Golomb. In 1961, a radar signal encoded using another Golomb-pioneered signal technology was bounced off Venus, and successfully detected by Golomb's team at Jet Propulsion Laboratory.

"Reliable communication over interplanetary distances has had a remarkable history. “ said Golomb. “Until about sixty years ago many people doubted that it was possible at all. By the time of the Apollo Moon landings we could get radio signals to and from the Moon, about 250,000 miles away. Now we can get television pictures from a planet more than 100 million miles away."