What Factors Affect the Image Quality of a SWIR Camera?
In the electromagnetic spectrum, infrared lies between visible light and microwaves. Infrared wavelengths range from 750 nm to 14,000 nm. It is usually divided into near-infrared (NIR), short wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR). Although infrared radiation in the SWIR band is invisible to the human eye, it interacts with objects in a similar way to visible wavelengths.
Most SWIR camera sensors are based on InGaAs materials, which work in the same way as silicon-based CCD or CMOS sensors by converting photons into electrons - hence the name quantum detectors. The InGaAs sensor consists of indium, gallium, and arsenide photodiode and a silicon-based readout integrated circuit (ROIC). The following introduces the specific factors that affect the image quality of SWIR cameras.
The effect of dark current on image quality
In the absence of light exposure, the current that flows in the sensor is called dark current (eg produces a signal). It is caused by the thermal excitation effect of electrons in the InGaAs material. The absolute value of dark current can vary widely between sensors. The higher the sensor temperature, the higher the dark current. As a rule of thumb, it doubles in absolute value for every 9°C rises in temperature.
For example, by taking the same photo with the same camera at 20°C and 45°C sensor temperature, the histograms will show very different results. At 45°C sensor temperature, the minimum value is higher (0 is black, 255 is white), as is the average. At 20°C, there are no saturated pixels (max 254), while at 45°C there are quite a few saturated pixels.
The effect of temperature on spectral sensitivity
Sensor temperature also has a large impact on the spectral sensitivity of SWIR cameras. When the sensor temperature is reduced by 40°C (from 25°C to -15°C), it causes a shift of spectral sensitivity to lower wavelengths by about 25 nm. This may be critical for applications operating at the low or high end of the sensitivity curve. When sensitivity higher than 1.700 nm is required, the sensor temperature should not be too low (below 20°C). While the dark current (and noise) increases with temperature, signals at the high end of the spectrum may be better.
Sensor temperature control is critical
Temperature levels affect spectral sensitivity and dark current. Dark current has a big impact on image quality (black level and noise). Temperature control is critical for applications where image quality is critical and when operating at the low or high end of the sensitivity curve.
To accurately monitor and control temperature, SWIR cameras manufactured by JAVOL VISION are equipped with three temperature sensors at the following locations:
1. Inside the InGaAs sensor housing
2. Sensor board
3. Motherboard
In addition, JAVOL VISION's SWIR cameras offer advanced features to correct and minimize these effects (such as advanced background correction).
With excellent production technology and thoughtful service, we have become one of the leading manufacturers of infrared thermal imaging systems. Our professional production team and complete management system can meet the diverse needs of customers. We will continue to adjust and optimize new solutions according to customer needs and can provide customers with thoughtful one-stop service. If you want to buy our SWIR camera, please contact us immediately!