Radar in surveillance

What is radar?

Radar is an established detection technology based on radio waves. It is increasingly used in consumer products because modern radar devices can be small and chip based.

Being based on a non-visual technology, radar has a lot to offer in surveillance. Security radar works well in many situations where other surveillance technologies may fail, such as in poor lighting, darkness, and fog. Radar is also stable in many situations where video surveillance with analytics software are likely to create false alarms, for example, when there are moving shadows or lights in the scene, in bad weather, or when there are raindrops or insects on the device. Radar also has the benefit of providing surveillance that maintains privacy because people can't be identified from the radar information.

Security radar can be used on its own. for example in environments where cameras aren't allowed due to privacy concerns, but radar is primarily integrated into a security system with video an audio products.

Radar devices are commonly combined with visual cameras for identification of individuals. This is especially effective with PTZ cameras, which can track and identify persons or vehicles based on their exact geographical position provided by the radar. Radars are also often used together with thermal cameras, where the radar devices' wide area detection combines well with thermal cameras' narrow but long detection area. Radar and audio are also a good combination where visual identification either isn't allowed or isn't prioritised. A deterring audio message may very well stop an intruder detected by the radar.

How does radar work?

A radar device transmits signals consisting of electromagnetic waves in the radio frequency spectrum (radio waves for short). When a radar signal hits an object, the signal is usually reflected and scattered in many directions. A small portion of the signal is reflected back to the radar device, where it will be detected by the radar's receiver. The detected signal provides information that can be used to determine the location, size and velocity of the object that was hit.

While employing the same principle. radars can be constructed to work with either short radio pulses or continuous signals. Their underlying technology may be based on measurements of either the reflected signal's transit time or its frequency shift. Radars may be designed to provide either the distance to a detected object of the velocity of that object, and advanced signal processing can refine the detection process further.

Why use radar in surveillance?

Security radar provides surveillance based on a completely different technology compared to, for example, visual cameras. It can be integrated into a security system with visual cameras, thermal cameras, horn speakers, and PIR motion detectors, or can be used standalone. Standalone use, or when complemented with audio devices, allows a non-visual type of surveillance that may cause less privacy issues than traditional video surveillance.

Reliable in low-visibility conditions

Being blind to visual impressions, a radar device isn't affected by visibility-impairing weather phenomena, for example fog. Radar also works well in difficult or low light, such as intense backlight or even complete darkness. Under such conditions, radar can be a very valuable complement to video surveillance. While thermal cameras with analytics would also do the job, radar provides more object information at a lower cost and enables detection in a wider area.

Low false alarm rate

In surveillance, it's essential to limit the number of false alarms while not missing any real incidents. For instance, with a direct alarm to a security guard, it's important to have a very low rate of false alarms. If there are too many false alarms, the guard might lose faith in the system and end up dismissing a real alarm.

Alarms from different types of motion detectors or video analytics are often set up to trigger video recordings, to trigger pre-recorded audio messages to deter unwanted activity or to directly alert a control room operator. With a high rate of false alarms for video recording, a lot of video will be recorded. This may be problematic, either because there isn't enough storage to keep all the recordings, or, if there is enough storage, a forensic search through all alarm-triggered recordings may require more resources than the system owner can afford. With a high rate of false alarms of pre-recorded audio, you risk to reduce the deterrence significantly.

A security radar can eliminate or minimise false alarms, depending on their causes.:

• Visual effects: Video motion detectors register motion based on a set amount of pixel changes in the surveillance scene. When a high enough number of pixels look different than before, the detector interprets this as motion. However, if you only look at pixel changes, you will get many alarms that are caused by purely visual phenomena. Typical examples are moving shadows or light beams. A security radar will ignore such visual effects due to their lack of a radar cross section, and only detect movement of physical objects.
• Bad weather: Rain and snow can seriously impair the sight of a detector based on video, while radar signals are less affected.
• Tiny objects on the device: With video motion detection, tiny objects can cause false alarms if located very close to the camera. Rain drops and insects on the camera lens are typical examples. Insects may especially be a problem when video surveillance is accompanied by IR lighting for night vision, because insects are drawn to the light. Radars can be designed to ignore objects that are very close to the device, thereby removing this source of false alarm. With video, there is no such possibility.

Surveillance with privacy

Surveillance may be a sensitive matter, and security cameras are often perceived to interfere with personal privacy. Installation of cameras may require permits from authorities or personal consent from everyone caught on video, and in some locations, a camera is not an option. The non-visual detection provided by radar often provides sufficient protection in these cases. This is especially true if the radar device is complemented by, for example, a network speaker which can send out deterring audio messages upon detection.