In order to maximise the benefits of your CCTV system it is important to establish some basic criteria as a starting point for the system design. The first of which is to define the problem and consider if CCTV is the most appropriate response. Given that the answer is “yes it is”, it is critical to establish the operational requirements (OR) of the system.
The basic model for an OR is to establish the following information…
- Site Plan – to identify areas of concern.
- Statement of the Problem.
- Stakeholder Liaison.
- Risk Assessment.
- Success Criteria.
- Determine the Technical Solution.
With the OR in place it is then possible to design the most appropriate CCTV solution. The second level of the OR must identify observation category of each camera. I.e. is it to monitor the area, detect a figure or recognise a known individual. There are five surveillance categories.
- Monitor and Control
When this has been established, other factors need to be taken into considerations such as image quality, target speed, lighting and environmental conditions etc.
Finally, the response to CCTV information needs to be considered. Who will monitor it, where from, will they be dedicated to it. What training do they need and are there any legal issues associated with privacy and data protection.
The system design can be broken down into six core elements.
Establish the most appropriate technology to use. Does it need to be wall or ceiling mounted, vandal resistant, static or fully functional? Does it need to work in low light conditions or are there challenging lighting conditions such as high contrast areas?
Dependant on the camera choice a suitable lens needs to be selected. The choices are dependent on the Operational Requirement. What size lens is required to achieve the surveillance category detailed in the OR? Does it need to be IR cut to work with infrared illumination?
A formula can be used to calculate the lens size dependent upon the size of the imaging CCD multiplied by the target distance over the scene height.
Transmission is important to determine which types most suit the Operation Requirement. Fibre Optic for long distance and secure transmission or IP on a LAN for integration?
Lighting is one of the fundamentals of CCTV design. Although with the advent of wide dynamic processing it is possible to get usable images in a range of challenging conditions, it is essential the scene illumination and reflectance is understood to achieve the best possible results. The following is a guide to illumination.
- Direct sunlight = 10,000 to 13,000 fc
- Full daylight = 1,000 to 2,000 fc
- Overcast day = 100 fc
- Dusk = 10 fc
- Twilight = 1 fc
- Deep twilight = 0.1 fc
- Full moon = .01 fc
- Quarter moon = .001 fc
- Moonless night = .0001 fc
- Overcast night = .00001 fc
- Black asphalt = 5%
- Bare earth = 7%
- Gravel surface = 13%
- Trees on grass = 20%
- Red (brick) = 25%
- Old concrete = 25%
- Green (grass) = 40%
- Old white paint = 55%
- New white paint = 75%
The display monitors need to be selected to best display the received images. The size and position needs to be selected to enable the operator to use the system both safely and comfortably.
Finally the recorded evidence needs to be established in terms of image rate, quality of compression, resolution and duration. How is the data to be exported should it be required in a criminal case?