Storing surveillance

How to strike a balance between security and privacy in public surveillance is one of the big questions with which our society is currently wrestling. But for frontline CCTV operators like Dave Tucker at Nottingham City Transport (NCT), there are more pressing questions, such as how to store the staggering amount of footage collected by 324 buses each carrying between five and eight internal and external cameras.

While the primary purpose of the CCTV cameras on NCT’s buses is to aid in insurance investigation, they also serve as public surveillance cameras and Tucker’s department is frequently called on to provide evidence for the police.

“About 5% of what we do relates to ‘off-bus’ crime,” he explains. “We have two cameras facing outside the bus, and very often we have been involved in serious cases where we been able to put offenders in area where a crime occurred. A few are now serving time because of that information. This year there have been year three off-bus rapes where we have been able to help police.”

Storing all that footage securely is quite a challenge. Even at four frames a second, 30 minutes of Nottingham bus footage requires 2GB of storage space, and buses operate for up to 16 hours a day. Furthermore, footage can only be cached on the bus’s internal hard drive for a certain amount of time.

Trickier still is storing the footage of significant incidents, of which NCT experiences 15 to 20 a day. This footage must be kept for up to six years or, if the incident involves a child, until the child turns 18 plus an additional three years.

With an archive growing at a rate of 2.5 terabytes each year, backing up to hard drive was becoming unsustainable.

“We also had one or two problems where we lost data backing up to hard drives,” explains Tucker. “It was very difficult and hard to manage.”

One year ago, NCT found a novel solution in a technology more commonly associated with home cinema: Blu-ray.

The ‘write once read many’ attribute of the media fitted the requirements for an unalterable record and legal authenticity, as did the 50-year life span of the format.

The organisation deployed a QStar DISC 1000 Blu-ray library along with hierarchical storage management (HSM) software – that prioritises storage media according to the importance of the data and cost – to automate the archiving process.

The QStar Blu-ray system, Tucker says, is “worth its weight in gold”, while the introduction of HSM means NCT can now upgrade the quality and longevity of its CCTV.

“At the moment we’re reliant on receiving requests within seven days or the footage overwrites,” says Tucker. “Technology has moved on quite a bit and in the very near future we’ll be able to record for a 30 day period at 12.5 frames a second compared to four frames currently.”

Tucker’s greatest headache to date has been moving the archives to the new format: “It’s taken me eight months to review [the footage from] 2008, and I’ve used 15 50GB Blu-ray discs in the process,” he says.

Eight months of staring at the inside of a bus might sound tedious, but it has had its moments, says Tucker.

“I’ve captured someone chasing a go-cart that’s run into one of our buses, and I’ve seen two people fighting fall out the window as the bus went around a corner. They fell out together. It sounds horrific but they still got up and ran off,” he recalls.

“[Some incidents] can be quite entertaining but unfortunately I’m not allowed to send them to YouTube because of the Data Protection Act,” he adds.

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