Radar shows U.S. border security gaps WASHINGTON - A sophisticated airborne radar system developed to track Taliban fighters planting roadside bombs in Operated from a Predator surveillance drone, the radar system has collected evidence that Border Patrol agents apprehended fewer than half of the foreign migrants and smugglers who had illegally crossed into a 150-square-mile stretch of southern Arizona. The number of "gotaways," as the Border Patrol calls those who escape apprehension, is both more precise and higher than official estimates. According to internal reports, Border Patrol agents used the airborne radar to help find and detain 1,874 people in the Sonora Desert between Oct. 1 and Jan. 17. But the radar system spotted an additional 1,962 people in the same area who evaded arrest and disappeared into the United States. In contrast, the Government Accountability Office, the investigative arm of Congress, estimated in January that the Border Patrol had caught 64% of those who illegally crossed into the Tucson sector in 2011. The new tally of unlawful border crossings could complicate White House efforts to pass comprehensive immigration reform after Congress returns from recess next week. The Obama administration contends America's borders are more strictly policed than ever, with nearly 365,000 apprehensions last year. Republicans have demanded more guards, drones, fencing and other security measures before legal status is granted to the estimated 11 million people believed to have entered America illegally or overstayed their visas. President Obama is scheduled to visit Mexico in early May, and efforts to maintain rigorous border security - to stop economic migrants moving north and American-made weapons flowing south - are likely to be among his priorities in discussions with Mexico's newly elected president, Enrique Peña Nieto. The new system is called Vader, for Vehicle Dismount and Exploitation Radar. It was borrowed from the Army's Aberdeen Proving Ground in Maryland and has been deployed in Arizona since March 2012. Michael Friel, a spokesman for U.S. Customs and Border Protection, said the Vader remained in a "preliminary testing phase." He also said the method used in the agency's internal reports to compare apprehensions to arrests was flawed because it didn't include people who were detained after the airborne radar had left the area. Officials warn that the radar would not work well near border towns and areas where migrants and smugglers can quickly load into a car and blend into highway traffic. "There is no silver bullet in border technology," Friel said. The tests have gone well enough that the agency has asked Congress to allocate money to purchase two more Vader systems. Each system costs about $5 million per year to maintain and operate. The Pentagon's internal research and development group, the Defense Advanced Research Projects Agency, helped design the Vader to aid U.S. forces in spotting insurgents burying improvised explosive devices in Afghanistan. Two of the systems are in use there. The radar is sharp enough to detect and track individuals on foot from a Predator five miles overhead. It uses a synthetic aperture radar to collect high-contrast black-and-white images and to follow scores of moving targets in real time. The processed signals are transmitted from the drone to a ground station, where the figures are displayed as moving dots on a detailed map. "It's a match made in heaven for border security," said a former U.S. law enforcement official. He said the radar had helped Border Patrol agents watch migrants and smugglers gathering on the Mexican side of the border before they start trekking north. But not all of the agents are happy to get a precise head count for the first time of how many people they are missing. "The rank-and-file guys are afraid it will make them look bad," the official said. He spoke on condition of anonymity because details of the program are not public. The system is being tested along with military-grade camera towers and surveillance blimps developed for use in Iraq and Afghanistan in an effort to provide more accurate coverage of remote border areas. Most of the Vader flights have focused on a stretch of border flanked by desert and the craggy Baboquivari Mountains west of Nogales, Ariz. The radar is used three or four days a week, for eight to 12 hours a day. "That is the kind of technology we would like to see all across the border," Rep. Michael McCaul (R-Texas), who chairs the House Committee on Homeland Security, said in a telephone interview. McCaul said he was briefed on the Vader during a visit to the border in Arizona on Feb. 18. He is writing a bill that would compel the Department of Homeland Security to write a national strategy that accurately measures the effectiveness of border security efforts. "You can't measure what you can't see," he said. There is an awful lot we're not seeing. Marshall Fitz, director of immigration policy for the Center for American Progress, a liberal think tank in Washington with close ties to the White House, said linking immigration policy to illegal border crossings is a "political gimmick" designed to delay any real reforms. No matter how many border agents or high-tech systems are deployed on the border, Fitz said, "you are never going to get to the point where you can raise the 'Mission accomplished' banner."