Thermal imaging allows us to see variations in temperature. Infrared energy is emitted by objects at normal temperatures, but the hotter the object, the more infrared energy it emits. Thermal imagers use a microbolometer as the sensor array to detect infrared energy. A special germanium lens focuses infrared energy on this sensor. Microbolometers consists of a resistive vanadium oxide or amorphous silicon film that detect electrical resistance changes related to temperature. These changes in the temperature are converted into a very detailed temperature pattern of electrical signals called a thermogram.
The sensor’s resolution is the number of individual detector elements found on the sensor array. Resolution is measured in horizontal and vertical dimensions such as 160×120, 384×288, and 640×480. The sensor’s resolution is an important factor in determining a thermal unit’s ability to generate a high-quality image. The higher resolution of a thermal sensor, the more surface area for energy to be gathered and more detail produced in the image. Using thermal with a high-resolution sensor assists in identifying suspects at closer ranges while also detecting targets at longer distances. A higher resolution sensor will be able to recognize physical attributes better than lower resolution sensors.
Pixel pitch is another important factor in thermal performance. Pixel pitch is the distance from the center of one pixel to the next. Pixel pitch is measured in micrometers or microns. In general, the lower the pixel pitch, the more compact the sensor, but also the more pixels used to capture light improving resolution and viewing distance. The lower the pixel pitch, the better the thermal device will be able to maintain clarity when digitally zoomed. This is an important factor to consider between two units. If all attributes, such as lens diameter, sensors and display resolution are the same but one unit has a lower pixel pitch, it can be assumed the unit with the lower pixel pitch will have better image quality, especially when using digital zoom.
Frame rate is the frequency at which an imaging device produces consecutive images. Frame rate describes both the speed of recording and the speed of playback. In thermal, frame rate refers to the unit’s speed of recording. Frame rate is depicted in hertz (Hz) which is one cycle per second. The higher the frame rate, the more motion is captured and smoother the imaging will appear to the human eye. Thermal is generally produced in 9 Hz, 30 Hz, 50hz/60 Hz frame rates. Frame rates below 25 Hz, such as 9 Hz cameras, will produce a stuttering motion of objects. 50 and 60 Hz will produce the most fluid motion of objects. Generally, the human eye will not detect a significant difference in frame rate above 30 Hz. Higher frame rates, however, will enhance the details and clarity of fast-moving targets. If a suspect or game is running and needs to be identified, the higher frame rate will provide a clear view of the target while lower frame rates will have some minor motion blur and loss of detail.
Range of Observation, Detection, and Identification
For thermal, the “Johnson Criteria” defines the device’s ability to detect, recognize, and identify. The Johnson Criteria assumes that the critical dimension (head and torso) for a human being is 0.75 meters. Therefore to meet the requirements of Detection, Recognition, and Identification (DRI) there needs to be 1.5 pixels, 6 pixels, and 12 pixels respectively across 0.75 meters in the image. Depending on the specific application, it is important to select a thermal unit with the proper detection range. If the unit is unable to detect targets as far as you need, you will be literally left in the dark.
1.5pixels/.75m = 2 pixels per meter
6 pixels/.75m – 8 pixels per meter
12 pixels/.75m = 16pixels per meter
Detection – In order to detect an object its dimension needs to be covered by 1.5 or more pixels. The object would not be recognizable or identifiable. You would only see that an object is present.
Recognition – This is defined as seeing what type of object it is, but not identifiable. It means being able to make the distinction between a person, dog, car or truck. In order to recognize an object, it’s dimension needs to be covered by at least 6 pixels across.
Identification – This is defined as seeing if a person is a friend or foe by distinguishing if the person is holding a rifle or a shovel. The object’s critical dimension needs to be covered by at least 12 pixels.
Organic Light-Emitting Diode (OLED)
OLED is a light-emitting diode that uses a series of organic thin films between two conductors. When electrical current is applied to the conductors, a bright light is emitted. OLEDs do not require a backlight like LCD and are more efficient. OLED has numerous benefits over LCD—it offers lower power consumption, faster refresh rates, better contrast, and higher brightness levels. OLED is also tolerant to hot and cold temperatures without affecting the display performance. Pulsar thermal vision units use Active Matrix Organic Light-Emitting Diodes (AMOLED) which offer the additional features of increased response times and a further reduction in power consumption.
Display resolution is the resolution of the display or image seen by the user and is not to be confused with the thermal sensor resolution. Resolution refers to the number of pixels in the display. These numbers refer to the total number of pixels along the width and height of the display. A resolution of 800×600 means the display has 800 pixels across its width and is 600 pixels high. Generally the higher the number, the more details the image will provide; however, thermal imaging is only as good as its sensor resolution. This means a 640×480 thermal image will appear no better on an 800×600 display compared to a 640×480 display.
In contrast to traditional night vision, thermal vision allows for more user adjustments and functions to be implemented via the display. For example, brightness adjustment, image contrast, image color, time, battery level, etc. can be shown as icons on the display’s image. Other features such as digital zoom and temporary display deactivation are unique features of thermal devices that traditional night vision devices do not have.
Digital Zoom and Picture In Picture
Digital zoom is increasing the perceived magnification of the thermal device. Digital zoom is an electronic adjustment and is not an adjustment of the device’s optical lenses. As digital zoom is applied, the central image is cropped and increased to match the same aspect ratio as the original image. The result is a zoomed-in view of the image, but with a sacrifice in image quality. Higher resolution sensors will be able to achieve higher digital zoom ranges without significant loss of image quality.
Picture-in-Picture is a proprietary Pulsar feature that incorporates a zoomed image of the target within the main or native image. Viewing both low and high magnification simultaneously has many useful applications such as identifying suspects while also providing situational awareness of the main environment. As shown in the image below, the magnified image is displayed at the top of the image, and zoom can be increased to enhance details of the object. The main image is the optical magnification and provides a wide field of view for tracking moving objects easier.
Color modes change the colors of the image associated with hot and cold. While black and white imaging provides the best resolution out of all color modes, other modes may have a better fit for specific applications. For example, when detecting targets in a forest, or where the environment is primarily cool, using red hot color mode will help the user spot heat sources more easily. In this mode, only the hottest objects are shown in red. e. This creates a clear contrast between a possible suspect and a tree or other object. Rainbow is ideally used for fire rescue and targeting hot spots. Sepia is best for long-term surveillance as it lowers eye fatigue.
A unique advantage to thermal devices is recording capability. Most thermal units will be equipped with a video output port. Video output refers to the unit’s ability to output a video signal. The device can be plugged into an external digital video recorder to record the images seen through the device. Pulsar’s Helion thermal monoculars are equipped with 8 GB of built-in recording. Pulsar Helions can take pictures and video. The images and video can be later saved to a PC, tablet, or phone.
Pulsar Stream Vision app allows devices to be operated and viewed remotely via a tablet or smartphone. The thermal imaging can be wirelessly viewed on a smart device in real time. This feature enhances surveillance abilities as devices can be set up and viewed through a smart device while away from the device.
Thermal devices are power hungry and as technology integration expands, the demand for power will only increase. Pulsar designs thermal devices with power management as a top priority. Instead of using internal rechargeable batteries, Pulsar uses swappable battery compartments effectively eliminating downtime in the field. While competitors’ products require an eight-hour recharge, Pulsar thermal imagers require a quick swap for a fresh battery pack to keep you on the job.
Pulsar Quantum thermal monoculars utilize a quick-access battery compartment. The battery compartment takes four AA batteries and conveniently can be quickly removed if needing to be replaced by a spare battery compartment with fresh batteries for six and a half hours of operating time.
Pulsar Helion thermal monoculars use a quick-release rechargeable battery pack called B-Packs. The included IPS 5 B-Pack provides eight hours of operating time. Extra B-Packs can be purchased separately, such as the IPS10 which provides up to 20 hours of operating time or the BPS 3xAA battery holder for backup.
All Pulsar thermal devices can be powered by an external battery power. Pulsar Helion thermal monoculars can be powered via USB, so while on a stakeout or glassing, the device can be powered by a vehicle instead of the battery pack.