How Far Can I See?

Target Detection

The resolution required for the detection of an object is determined by the obtained pixels. The Johnson Criteria, which are used worldwide, apply here. These criteria were established in the 1950s.

Criterion:

The 50% probability detects the pixels that objects of various sizes will occupy for a temperature difference of 20C. The criterion consists of 3 main parts. These;

Detection: Indicates that an object exists.
Recognition: Indicates what an object is. (like truck, human)
Identification: Indicates how an object is. (Man with gun, like F16)

Factors in Target Detection

Detector Resolution
Field of View (Field of View)
Optical Zoom
Heat Sensitivity
Fog, Rain and Snow

As the detector resolution increases, the target data increases, making identification easier.

Field of View (FoV)

As the angle of view increases, it is necessary to decrease the distance in order to see the same image. Therefore, smaller viewing angles allow for more remote detection.

With the same optical lens (2000 mm), the pixels occupied by the object at different distances in the detector are reduced. Therefore, diagnosis becomes difficult. In order to improve this, the optical lens should be enlarged further, that is, the angle of view should be narrowed.

OPTICAL ZOOMING

Optical zooming is actually changing the angle of view by changing the distance between the lens used and the detector. In this way, the amount of data falling on the detector changes without any manipulation on the original image. In this way, target identification becomes easier. While wide area scanning can be performed thanks to optical zoom, a detected target becomes detectable by optical zoom.

DIGITAL ZOOMING

When digital zooming is applied over optical zoom, the image is enlarged by a factor of two.

Target and Range

Heat Sensitivity

As the distance increases, the temperature differences between the objects decrease due to meteorological conditions. Therefore, there is a need to detect small temperature changes over long distances. Cameras with high heat sensitivity can detect these differences and create more sensitive and clear images.

Fog

Normal Camera Thermal Camera

The heat is absorbed by the water molecules in the air and therefore the temperature value decreases over long distances. In cases such as fog, the water molecules in the air are less against situations such as rain, so heat permeability is high. In this way, thermal cameras can provide images.

Snow

Due to low temperature differences in snowy weather, it is difficult to detect the environment in particular. However, the detection of objects can be achieved thanks to the temperature differences between the objects and the background. Although it is a factor in range, it does not prevent target detection.

COMPARISON

In the examples above, the effect of the number of detector pixels on the detection distance can be seen. The number of pixels covered by a 2.3 x 2.3 m target at 300 m distance, with all conditions the same, was calculated at different detector resolutions.

In the examples above, the effect of the field of view (FOV) on the detection distance can be seen. The number of pixels covered in different fields of view by a 2.3 x 2.3 m target at 300 m distance, with all conditions the same, was calculated.

How Far Can I See?

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