Video Sewer Inspection: Analog vs. Digital Inspection

A major sewer just collapsed, and now it’s up to you to figure out what was the cause (or were there any signs of failure?) After hours or searching through boxes and boxes of VHS tapes, you finally locate the CCTV inspection videotape you are looking for. You put it in the VCR and go through the entire 2 hr+ VHS videotape to locate the section you are looking for. When you finally get to the correct line segment, you discover the video quality is so poor that you can’t determine the existing condition. Sound familiar?

The Apple iPod (digital) has changed the way we store, search and listen to music and videos. We no longer use the Sony Walkman (analog cassette player.) Similarly, the digital era now offers new functions to the CCTV industry. It’s a major reason why so many municipalities have a requirement to inspect their pipes with CCTV digital technology. So what’s the difference between analog and digital?

Let’s break this down into two topics: how the signal gets generated/transmitted, and how it gets stored.

Signal generation/transmission. Like a photocopy, an analog CCTV signal degrades a little bit each time it is reproduced. Furthermore, once the analog signal leaves the camera, it is immediately susceptible to noise and interference while being transmitted over cable. Additional radio and electronic interference can cause a video image to appear noisy, dark, or washed out. These are all the reasons that an analog camera signal from a sewer inspection, transmitted 2000 ft. to the camera truck where specialized electronics are used to digitize the analog signal, does not a digital inspection make.

However, when a digital signal is produced from the digital camera directly, we are transmitting code. Noise and interference can be much more easily filtered out. This also means that a digital signal, much like the digital cable signal than many people now receive for their home television, can be transmitted many miles without any loss of image quality. You get a better picture on the spot, you get a better picture back at your office, and you get the same picture, no matter how many times you copy it.

Storage and retrieval. Magnetic tapes have been used for over 30 years and are quickly dying in favor of easier to store and search digital options. (When was the last time you played with your car’s cassette player?) If you have any doubt, just compare the home videocassette recorder you used to use to the digital video camera you own today – the latter provides a much clearer recording. Furthermore, a pure digital system, which includes both a digital camera and a digital video recorder, provides a tremendous boost in picture quality that will not degrade over time, distance, or with copying. Digital conversion and storage mediums such as frame grabbers, DVDs, hard drives, and flash memory have become common. These simple and precise forms of information storage allow the user to quickly search a video library at the touch of a button – the way you can search your computer hard drive for the name of a document. It is possible to locate the exact minute, second, or frame of information to be reviewed. And digital files can be sent over the Internet – making them that much more portable.

And there’s more. Digital CCTV is a concept that extends way beyond the camera, transmission, and storage media to digital enhancement, digital zoom and digital manipulation. For example, images and video clips can be digitally compressed – the way you zip up your computer files — to greatly reduce storage requirements. Furthermore, you can get down to the pixel level and play with the lighting, thereby improving final image quality, contrast and sharpness.

Digital technology enables us to pull apart the two main inspection technologies: the actual inspection, and the reporting. We don’t need a skilled CATV operator who pans, tilts and zooms on site. Instead, fisheye lenses and hi-resolution digital cameras allow the entire surface of the pipe to be viewed without a human making that decision in real time. The images are simply captured and the data is analyzed at a later time. And it gets better: the digital data can eliminate lens distortion and provide a simple, flat view of the pipe. These methods allow a thorough and rapid off-site review of 100% of the pipe’s surface by qualified personnel — ensuring that your municipality will never miss a defect.

The digital camera has changed the way we take pictures of our children in the school play. Now digital CCTV systems promise to bring the same quality improvements and convenience of use to the sewer industry.

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