Thermal imaging cameras add new layers of information to wildlife surveys, especially when it comes to monitoring nocturnal species such as bats, as thermal imagers enable surveyors to see in the dark.
Thermal imaging technology is developing rapidly. With so many options of thermal imaging cameras available, your choice of thermal imager will depend on your specific survey requirements and budget. In this article, we break down the key specifications and features to consider and how they may relate to your bat surveying needs. We also recommend several models that we’ve put to the test in the field.
Don’t worry, we’ve got you covered! Before reading on, check out Everything You Need to Know: Thermal Imaging and Bat Surveys, covering; how thermal imaging cameras work, the benefits and challenges of using them for bat surveys and other FAQs.
Thermal video of a pipistrelle bat in flight
There are several thermal imager specifications that define image clarity and the performance of a thermal imager at different distances. These are the essential specifications to understand to help inform your choice of thermal imager. Below, we outline the key specifications to take into account, as well as the recommended minimum specifications described in ‘Thermal Imaging: Bat Survey Guidelines‘.
Thermal sensitivity is quantified as the Noise Equivalent Temperature Difference (NETD) and is measured in millikelvin (mK). A lower NETD value indicates a more sensitive thermal sensor capable of detecting smaller temperature variations. A thermal imager with a lower NETD value will yield higher-quality images even in challenging weather conditions, such as high humidity, rain, and fog. For bat surveys, it is recommended to have an NETD/sensitivity value of <50 mK.
Sensor resolution, also known as detector resolution, determines the level of detail in the captured images. A higher resolution results in more intricate and detailed images. For bat surveys, the minimum viable sensor resolution is 320 x 240 pixels, although this resolution is more suitable for close-range applications. For greater versatility, it is advisable to consider an imager with a resolution of 640 x 480 pixels or higher. A higher resolution will produce significantly more detailed images and work more effectively beyond close range.
It is important to note that, separate to sensor resolution, manufacturers may also provide information on display resolution (the resolution of the screen inside the imager) and recording resolution (the resolution of the video files, which may be lower during video playback). If intending to review the recorded footage after a survey, choose an imager with an adequate recording resolution. The best way to assess this is by reviewing sample footage online to gain a sense of image clarity.
A frame rate of at least 30 Hz is required to observe the fast movement of bats.
The majority of thermal imagers are equipped with a fixed lens, which means that the field of view is predetermined. The choice of lens is a consideration that should align with your survey needs. A wider field of view is more suitable for close-range applications, such as observing bat emergence and re-entry. Conversely, a narrower field of view is often better suited for longer-range applications, such as surveying structures, trees, and other features.
Manufacturers often provide a detection distance for thermal imagers, but it should be noted that this is dependent on factors such as animal size and weather conditions. In the following section, we outline some approximate detection ranges for pipistrelle bats with several popular thermal imagers.
Thermal imagers typically have a base magnification ranging from 1x to 5x. Lower magnification is more suitable for close-range use, while higher magnification is preferable for long-range observations. However, it is important to note that higher magnifications often come at the cost of a narrower field of view, which is generally not advantageous for bat surveys. Opting for magnifications in the 2x to 3x range provides a good compromise for versatility.
It is common for thermal imaging cameras to incorporate digital zoom rather than optical zoom. Although digital zoom may sound appealing, its utility is limited as the image quality does not typically improve in proportion to the zoom level. This can result in larger but pixelated images, unless explicitly stated otherwise by the manufacturer.
A bat box showing a clear thermal signal (bright white) at the top of the box
In addition to ensuring the image clarity and range specifications meet your surveying needs, there are several other features to consider that can prove useful in the field.
Useful for reviewing footage later, observing behaviours and providing evidence. Can be used alongside acoustic recordings to provide a visual element.
Look for a thermal imager that can hold up to the elements. The IP (ingress protection) rating describes a thermal imagers’ weatherproofing capability.
It is essential to consider the duration of thermal imager usage during a survey. Most thermal imagers operate using a rechargeable battery pack, and manufacturers typically provide information about the usage time on a single charge. Additionally, it is advisable to choose a model that offers the option of a replaceable battery, providing a backup power source when needed.
Having a tripod mount on the thermal imager is particularly advantageous for emergence/re-entry surveys or when securing the imager in a fixed location. This feature allows you to set the imager on a tripod and record video (if compatible) from a stationary position. By setting the thermal imager to record, you can engage in other tasks without being tethered to the imager throughout the survey.
Pulsar thermal imaging binoculars mounted on a tripod
We offer a curated selection of thermal imagers in our NatureSpy shop that meet the minimum required thermal imager specifications for bat surveys.
The Pulsar Axion XM30F serves as Pulsar’s entry-level thermal monocular. As with all models in the current Pulsar range, it is quick and responsive and can take photos and record video. It also offers compatibility with Pulsar’s Stream Vision mobile app, enabling control of the thermal imager through a smartphone. The device includes a rechargeable battery pack (Pulsar APS 3), capable of lasting up to 5 hours on a single charge.
While the Pulsar Axion XM30F meets the recommended specifications for bat surveys, it has some limitations to be aware of. Its thermal sensitivity, with an NETD of <50 mK, is adequate for detecting bats. However, the limiting factor lies in its 320 x 240 sensor size, resulting in a relatively small field of view with less detailed imagery compared to other Pulsar thermal imagers. Under favourable atmospheric conditions, the Pulsar Axion XM30F can detect a pipistrelle bat up to a distance of approximately 25m.
Overall, we recommend this model for lighter or more casual use, as well as for closer-range bat surveying. For clearer images, greater versatility and frequent usage, we suggest considering the thermal imagers below.
The Pulsar Axion 2 XG35 is positioned in the middle of Pulsar’s range of thermal monoculars. It has a good level of thermal sensitivity (<40 mK), a sizeable sensor (640 x 480), and a moderately wide 35mm lens (12.5° horizontal x 9.4° vertical / 16.4° at 100m). With a rechargeable battery pack (Pulsar APS 5), it can operate for up to 7 hours on a single charge.
Under favourable atmospheric conditions, the Pulsar Axion 2 XG35 can detect a pipistrelle bat up to a distance of approximately 30m. Due to its moderately wide field of view, combined with a sensitive and large thermal sensor, the Axion 2 XG35 is a popular choice for emergence/re-entry surveys, complementing conventional techniques such as acoustic monitoring.
Pulsar’s flagship thermal monocular, the Pulsar Helion 2 XP50 Pro, stands out with a high level of thermal sensitivity measuring <25 mK. This exceptional sensitivity allows the XP50 Pro to perform well even in less-than-ideal atmospheric conditions, delivering clearer imagery over longer distances. Equipped with a 50mm lens and a large 640 x 480 thermal sensor, this thermal imager excels in bat emergence/re-entry surveys. The Pulsar IPS7 rechargeable battery pack delivers a battery life of up to 8 hours on a single charge.
The Pulsar Helion 2 XP50 Pro can detect a pipistrelle bat up to a distance of approximately 35m. When compared to the Pulsar Axion 2 XG35, the Helion 2 XP50 Pro takes the lead in terms of thermal sensitivity, with superior performance in sub-optimal atmospheric conditions and achieving slightly longer detection ranges. However, the Axion 2 XG35 features a slightly wider lens, which is often desirable for closer range survey work, such as bat emergence/re-entry surveys.
Due for release in 2023, the Pulsar Telos XP50 builds on the success of the Pulsar Helion 2 XP50 Pro with two significant changes: even greater thermal sensitivity (<18 mK NETD) and upgradeable hardware, allowing for future upgrades such as new optics and higher resolutions sensors (due to be available in 2024). This means the Telos XP50 will perform even better than the Helion 2 XP50 Pro in sub-optimal weather conditions and is designed to be future-proofed and customisable by integrating new technology.
The Pulsar Telos XP50 is capable of detecting a pipistrelle bat up to approximately 35m away. We will update this article once we have more information on the Telos XP50 and have tested it in the field.
Learn more about thermal imaging camera specifications in our standalone guide, covering topics that include: detection, recognition and identification range, sensor resolution, thermal sensitivity, pixel pitch and more.
Thermal image of a pipistrelle bat in flight
The most crucial specifications to consider are those that ensure clear and detailed images at the distances you typically work within. It is recommended to select a thermal imaging camera with high thermal sensitivity (e.g., <50 mK NETD), a large thermal sensor (e.g., 640 x 480 pixels), and a fast frame rate (30 Hz or faster). Additionally, the choice of lens is important, with wider lenses being more suitable for closer range tasks like emergence/re-entry surveys, while narrower lenses tend to perform better for longer range work. Other features to consider include the ability to record video and battery life.
A thermal imaging camera must be sensitive enough to reliably detect bats for the type of survey work you conduct, so the most suitable thermal imaging camera is subject to your survey requirements. We detail the main thermal imager specifications to consider above. For a deeper dive, we recommend reading Thermal Imaging: Bat Survey Guidelines.
We think that Pulsar thermal imaging cameras are excellent for bat survey work due to their high quality images, useful features, reliability and rugged design.
At NatureSpy, we stock a curated range of thermal imaging cameras that we’ve put to the test in the field. As a conservation social enterprise, profits from our online shop go straight back into wildlife conservation projects.
