High-speed rail safety is a concern: Five elements of video surveillance system architecture

When constructing a railway video surveillance system, it is necessary to consider special factors other than conventional surveillance application systems based on the application characteristics of the line and the particularity of the environment, such as the following aspects:

Natural phenomena such as wind, rain, thunder and lightning

Wind, rain, thunder and lightning pose great challenges to outdoor cameras. Rain, snow, high temperature, low temperature, lightning strikes, strong winds, etc., each damaging link may cause a sharp increase in system maintenance costs. The characteristics of railway projects are large spans, often long distances and high mountains, and sometimes high-altitude operations. Once the system is put into operation, there will be many restrictions when applying for operations, resulting in increased costs. Therefore, the selection, installation, wiring and high quality of outdoor cameras are particularly important.

Long-distance camera problem

High-speed rail monitoring is mainly divided into indoor machine rooms, indoor waiting halls, ticket offices, outdoor squares, platforms, etc. There is nothing special about the deployment of cameras in these locations, but another application with more points is along the railway. The long railway is the absolute place for long-distance cameras. Long-distance cameras may need to monitor tens of meters, hundreds of meters or even several kilometers, which means that long-distance cameras may need to have a vision effect of several kilometers. The vision camera is not a simple camera with a long focal length lens. Simply put, when the focal length is pulled to a certain length, it is difficult to locate a target far away by manual keyboard control. In other words, the micro-step control function of the camera is very important. In addition, for high-altitude vision cameras, anti-shake, night vision lighting and other issues need to be considered.

Preset position accuracy

In high-speed rail monitoring, in order to quickly locate the scene or respond to the alarm, customers usually set multiple preset positions for quick application in the future. The number of preset positions is usually not a problem. Currently, most cameras support 128 or even 256 preset positions, and actual projects will not use so many. However, the accuracy of the preset position is an important indicator for evaluating PTZ cameras. For example, when the user sets a preset position, some camera preset positions will usually be offset when they are called later, so manual fine-tuning has to be performed again, which loses the meaning of the preset position itself and affects its use.

Encoder and DVR selection

In high-speed rail projects, encoders and DVRs are usually deployed in the computer rooms of various stations. Therefore, encoders and DVRs need to have ultra-stable performance (embedded encoders and embedded DVRs are preferred), good networking capabilities, remote management and upgrade capabilities. Due to the complex network system architecture, large span, and multiple routes, the encoder equipment needs to have a local cache function to avoid video loss in the case of temporary network termination, and to be able to supplement the video to the NVR storage once the network is restored. In addition, image clarity, dual-stream support, two-way audio support, and the number of alarm inputs and outputs are all indicators that need to be considered.

Coding Standards

At present, the railway projects mainly use MPEG-4 encoding technology and H.264 encoding technology. In the future, AVS encoding may be deployed, which uses a combination of intra-frame compression and inter-frame compression to remove the temporal and spatial redundant information of video information. The encoding device delay should be no more than 300ms, the forwarding delay at each level should be no more than 500ms, the decoding device delay should be no more than 300ms, the PTZ response delay should be no more than 500ms, and the system front-end acquisition device to the user monitoring terminal delay should be no more than 3s.