Smugglers are using video cameras and small drones to spot vulnerabilities along the US-Mexico border, and the Department of Homeland Security is struggling to stop them.
Reports of unmanned aircraft flying along the Southwest border have spiked in recent months, with more than three dozen sightings since October, when the current financial year began.
That data point is on a course to quadruple from the previous year, according to US Customs and Border Protection, where officials say they are concerned that criminal groups are using the aircraft for surveillance while seeking paths to traffic drugs and other illicit material into the United States.
"They're probably trying to get eyeballs on agents out in the field and see where soft areas are," said James Thom, acting operations director for CBP's Air and Marine Operations Centre outside Los Angeles. "To date, I don't know that we've successfully been able to detect and track drone activity."
The growing use of off-the-shelf, hard-to-spot drones is a prime example of the relentless cat-and-mouse game between criminals and Border Patrol agents.
Smugglers constantly seek to outsmart US law enforcement. And as part of the Trump Administration's pledge to crack down on the influx of drugs and people entering the country illegally, Homeland Security is scrambling to identify technology and techniques that can thwart them.
When it comes to drones though, the true number flying along the border could be much higher than what's been reported. Such aircraft present a tiny radar cross section. They also give off little-to-no reflection and tend to fly for short periods at very low altitudes, said Jennifer Gabris, a CBP spokeswoman.
"These characteristics make them more difficult to detect using conventional sensor systems," Gabris said.
While most drones are believed to be flying surveillance missions, at least one made it across the US border carrying drugs worth tens of thousands of dollars. In January, a 25-year-old man was sentenced to 12 years in prison for flying a drone over a fence near the bustling checkpoint between San Diego and Tijuana, Mexico. The unmanned aircraft was carrying a plastic bag packed with 6kg of methamphetamine.
Since 2011, traffickers have made at least 562 illicit flights across the US border in ultralight aircraft such as helicopters, single-engine planes or gyrocopters, Gabris said. Those pilots often fly their aircraft just above the tree line in rugged areas, making it difficult for border agents to detect or track them. The aircraft typically carry about 90kg worth of drugs, according to a 2017 Government Accountability Office report warning about the flexible smuggling method.
Pilots "don't even have to land on our side of the border - they'll take off, drop a package that will get picked up and fly back," said Henry Willis, a senior policy researcher at the Rand Corporation. "As a smuggling tactic and tool, it can be attractive for a lot of reasons . . . and another one of the ways our borders can be penetrated."
US President Donald Trump wants to construct a wall along segments of the Southwest border to stop such infiltration. But traffickers typically fly drones and small manned aircraft in remote areas with natural boundaries such as mountain ranges or rivers - places, Trump has said, that would not require a wall.
Expanding and hardening existing barriers along the Southern border could prompt more smugglers to turn to aircraft, said Christopher Wilson, deputy director of the Mexico Institute at the Wilson Centre. "Obviously," he said, "something that flies over a wall does not get stopped by a wall."
As drone flights picked up in recent years, manned ultralight flights have fallen significantly. In 2011, DHS officials tracked 198 ultralight flights into the US, most of which took place in California, Arizona and New Mexico. In 2017, 17 such flights were recorded.
CBP has spent millions on at least three detection systems to stop pilots from making illicit flights into US airspace. Two of those projects were scrapped within a seven-year period after they failed to meet requirements.
In 2010, officials tested a system that Border Patrol agents could carry to remote areas and set up themselves. The project was phased out last year, according to the GAO report, after mixed reviews on functionality.
In 2013, Customs and Border Protection awarded a $100 million contract to a New York-based radar company for a solution called Ultralight Aircraft Detection, or ULAD. That technology also proved to have limited capability and was not pursued, the GAO reported.
Now, CBP has moved on to a modified product created by the Defence Department called LSTAR, an acronym for Lightweight Surveillance Target Acquisition Radar. LSTAR is better at detecting small aircraft that traditional systems do not always pick up, said Tim Snyder, director of plans and programmes at the Air and Marine Operations Centre. The system is in place in Arizona, Snyder said. Three other locations will get it this year.
As border agents get better at tracking such aircraft and intercepting ground pickups in California and Arizona, CBP's Thom said smugglers are adjusting, too, by pushing flights east into Texas.
"It's not where we should be focusing the bulk of border-security resources, but we do need to continue to work on these threats," Wilson said.
"The tough thing is that technology continues to evolve on the side of traffickers - but the good thing is that technology continues to evolve on the side of law enforcement."