Last week at the BCT Big Bat Skills Event, I listened to Dr K Fawcett Williams who discussed the use of thermal imaging.
Thermal imaging is the acquisition and analysis of thermal information from non-contact thermal imaging devices.
Thermal imaging picks up electromagnetic radiation in the infrared part of the spectrum. IR is given off by everything. In this blog, we discover the benefits of thermal imaging, applications, equipment, expertise, and limitations.
The best things about thermal imaging:
- Non-invasive: TI is very non-invasive due to its ability to detect animals tens to hundreds of metres away. The tech doesn't emit light generally and therefore it doesn't disturb animals in night settings.
- Accurate: The use of TI can indicate where roosts are in trees and structures, as well as entry and exit points. TI is less likely to give false negatives which often lead to a stop in work later on down the line due to a discovery of a species. Equally, it is less likely to lead to false positives and the cost implications of mitigation for a species that is not necessarily there. TI does not suffer from visibility bias where detection levels are reduced with reducing light levels.
- 24-hour use: TI can be used in the day and also at night. It is therefore good for interdisciplinary consultants.
- Savings: Some cameras can do the equivalent of six surveyors.
- Health & Safety: TI use means there are fewer people doing long nights and helps prevent fatigue.
- Bridges and large structures
- Towers and tall structures
- Tunnels and underground
- Around waterways and water bodies
- Roads, railways, bike paths - linear structures
- Looking at landscape level activity
- Trees (emergence studies)
Thermal imaging can be used as a survey aid or as a method. It allows you to collect data in the field, in the form of thermal video files and then analyse the data later on. Thermal video files can be radiometric or non-radiometric. The former contains spatial information and the temperature measurements within the survey space, and is more accurate than the latter.
Generally, you would use thermal imaging alongside static detectors. You should make sure that the times on all equipment is synchronised and also note that thermal imaging picks up data more readily than a detector. Also, note that the distance at which a thermal imager picks up a target species will be different to what a detector can pick up.
Thermal imaging is not suitable for hibernation inspection surveys.
Dr K Fawcett Williams uses this equipment:
- FLIR T1030sc
- FLIR A65
- FLIR T540
There are a lot more choices out there though and Kayleigh has compiled a list of the top 11 pieces of equipment out there that you can access for free. Choosing the right equipment in relation to what you need it for is vital.
- long-wave spectral range for bat surveys
- optimal device temp range of -40℃ to +120℃
- video capability if you want to refer back later on
- >30Hz video frame rates for identifying bats in flight
- uncooled devices run quieter than uncooled, therefore are less disturbing, and are more affordable! They do lose out in terms of image quality, however, weighed against potentially disturbing an animal, that is something worth working around.
- go for a device with a low Noise Equivalent Temperature Difference - ideally 20–50 mK.
- try and go for a high resolution (high number of pixels). More detailed guidance is here and here.
- wide-angle lenses are ideal for close-up emergence and re-entry surveys, whilst narrow-angle lenses are great long-distance activity surveys.
You do not need to be a certified thermographer to use thermal imaging however you do need experience. You can get thermography and bat specific training, however, such as the Level 1/2/3 Thermography Certification. If you need expert advice head on over to KFW Scientific and Creative.
There are various limitations:
- Detection distances - plan and calculate your distances and field of view. Account for blindspots.
- Analysis - Bats, birds, moths and other species are all out there. Build experience so that you know how to look at the data to pull out the information that you need.
- It is hard to find animals within things - this is because everything emits IR. Note that you may be able to find bats under really thin bark plates.
- You cannot use thermal imaging to identify bats to a species level. It allows you detect and recognise them. This is why using a bat detector alongside a thermal imager allows you to paint a more detailed picture. Likewise, you can use a bioacoustic recorder if you are looking at non-bat species.
- Think about the ingress rating (IP), especially if you work in weather conditions or environments in which water is a problem.
- Consider your devices tolerance to temperature changes.
Thermal Imaging: Bat Survey Guidelines are available to read.
- Changing Technology In Ecological Surveys: The Role Of Thermal Imaging And Infra-Red Cameras - BSG Ecology
- Thermal imaging in plant and ecosystem ecology: applications and challenges - ESA Journals
- Thermal imaging for wildlife surveys - Inside Ecology
- Thermal Imaging Basics - BCT
- Kayleigh Fawcett Williams YouTube