BALTIMORE (AP) — Starting Friday, the roughly 600,000 people living in Baltimore will be constantly recorded whenever they step out under the open sky.

Marvin L. Cheatham Sr., for one, knows he could be watched as he goes to a doctor’s appointment or visits friends. He’ll be spied upon in his back yard, and as he steps into his car, and when he drives around the city, his entire trip will be recorded, too.

All his movements will be captured, and he’s OK with this — even though police will have no search warrant, and the overwhelming majority of Baltimore’s citizens will have committed no crimes — because the city is so besieged by violence.

“I am so upset and angry about all these people that have died, I’m willing to give up some of my rights, as bad as that sounds, and I’m a staunch civil rights person,” said Cheatham, who led his local NAACP chapter in the 1990s. “I had 19 homicides two years ago in my neighborhood.”

For the next six months, up to three airplanes outfitted with wide-angle cameras will sweep over Baltimore in daytime flights designed to capture movements across about 90 percent of the city. Software will stitch together photos taken once each second, creating a continuous visual record to support the street-level cameras, license plate readers and gunfire sound detectors police already use to try to solve crimes.

Analysts alerted to a crime will be able to zoom in from the city-wide image and move backward and forward in time to identify the movements of potential suspects and witnesses, telling officers within hours just where to look for people who traveled to and from the scene.

Police Commissioner Michael Harrison has promised that this system will only be used to investigate homicides, non-fatal shootings, armed robberies and carjackings. He said he doesn't know whether the pilot program will be effective.

“I have no expectation of what it would do or what it will not do because it has not been done in the United States before,” he told The Associated Press. “What I’ve been shown shows me that it’s a potential tool that could be used by detectives in the crime fight.”

As for concerns about violating the people's rights across an entire city, Harrison said the Supreme Court has ruled that “there is no expectation of privacy in a public place.”

The American Civil Liberties Union of Maryland argues that this continuous aerial surveillance infringes upon reasonable expectations of privacy regarding movement, results in indiscriminate searches without a warrant and impedes the right to gather freely.

It's the technological equivalent of a police officer following every resident, wherever they go, whenever they leave their home, senior ACLU attorney David Rocah said.

“If that happened in real life, I think everyone would very clearly and viscerally understand the privacy implications, but because this is being done remotely with sophisticated video technology from an airplane, we don’t experience the invasion in the same way,” Rocah said.

A federal judge denied the ACLU's request for a preliminary injunction, saying far more intrusive surveillance has been found constitutional. The plaintiffs are appealing.

Ohio-based Persistent Surveillance Systems will capture the images and provide the analysis to police, funded with roughly $3.7 million from Texas billionaires Laura and John Arnold.

PSS President Ross McNutt initially developed the technology to help the Air Force identify people leaving improvised explosive devices that were killing troops in Iraq. McNutt says that resolution of the images aren't sharp enough to identify faces, ethnicity, gender and clothing, nor vehicles’ color, make, model and license plate.

Police say they won't be using this to monitor people outside the context of a serious crime that has already happened. The city's agreement specifies that PSS analysts will study movements “only when an egregious violent crime is already known to have occurred.”

But the ACLU's plaintiffs — community activists and political organizers — said simply knowing that their movements are being recorded makes people reluctant to participate in events and protests.

The contractor already secretly tested this surveillance in Baltimore in 2016, as crime soared after the death in police custody of a young black man, Freddie Gray. But that effort was cut short once exposed, and violent crime has flourished since then, along with mistrust of police, and some of Baltimore's leaders are now publicly committed to testing mass aerial surveillance.

This deeply segregated seaport city has now suffered more than 300 homicides annually for five years straight, setting a per-capita U.S. record with 348 killings in 2019. Eighty-nine people have been killed so far in 2020, just three fewer than last year’s pace. Lesser crimes are down sharply as people shelter inside during the coronavirus pandemic, however, with 177 non-fatal shootings, compared to 212 last year.

Third-party researchers from three universities and the RAND Corp. will evaluate whether the program leads to arrests and case closures, earns public support and ultimately has a deterrent effect.

Andrew Ferguson, a law professor who writes on policing using big data, said police chiefs see technology as a solution when they're backed to the wall by violence in their communities.

“It doesn’t matter what that something is. They just have to respond because ‘Chief what are you doing about crime?’” Ferguson said. “The real answers are ‘Well, I need better schools. I need more jobs. I need some hope and opportunity in these cities, better housing.’ But that’s not available. He doesn’t have that.”