(CNN) Dozens of searchers set off into the rugged Nevada backcountry Saturday after analysts scanning radar and satellite images spotted what may be clues to the whereabouts of missing adventurer Steve Fossett .
Fossett has been missing since his plane went down 27 days ago.
The formal aerial search by the Civil Air Patrol and Nevada National Guard helicopters ended September 19 after pilots spent more than two weeks scouring an area twice the size of New Jersey.
A new Air Force analysis of radar and satellite images led to this weekend's ground search, plus with three Civil Air Patrol planes flying over the mountainous area.
Volunteers on the ground planned to search during the day Saturday and Sunday, said Gary Derks , the state Department of Public Safety official in charge of the search.
"We have about 50 people on ATVs, horseback, walking -- anything they can find to get them into the canyon," said Derks .
"If he's there, he's going to be hard to see. That's why we're sending in the ground search-and-rescue crews, too," Derks added.