What are the center wavelength and bandwidth for the Thermal Band?
Below are the values for the wavelength and bandwidth of the Thermal (LWIR) Band:
|LWIR||11 μm||6 μm|
For more information on center wavelengths and bandwidths for other bands, see What is the center wavelength and bandwidth of each filter on RedEdge?
There is a small gap in my thermal heatmap. Why is that?
The thermal camera needs to recalibrate every 5 minutes or 2°C change in internal temperature. The method of recalibration is called a non-uniformity correction (NUC). This process lasts ~3 seconds and will prevent any captures from all bands during this time. This can result in small gaps between captures. If you have additional concerns, feel free to contact support.
Can I control when the recalibration occurs?
By using the HTTP API, you may use the thermal_nuc endpoint to manually trigger a NUC. This endpoint also contains the property "elapsed_seconds_since_nuc," which can be used in determining if a NUC is necessary.
Using the Serial (MAVLink) API, you may use the thermalNucTime and thermalNucTemp for similar purposes. Note that using these commands will cause automatic NUCing to become disabled, and all further NUCs will need to be commanded until the camera has been power cycled.
What is the accuracy and sensitivity of the thermal band?
|Thermal Accuracy||Thermal Sensitivity|
|+/- 5 K||< 50 mK|
Thermal Accuracy is the accuracy we can expect with the assumption that the object being measured has an emissivity of 1.0. Measurements of objects with very low emissivity (such as a mirror) are subject to a much greater error. Plants tend to have emissivities around 0.97, while the soil is usually in the range of 0.92-0.95, depending on moisture content. Because plant and soil emissivity values are not too far from 1.0, you can expect temperature values to have accuracy close to the published accuracy.
Thermal Sensitivity is the difference in temperature that the Thermal Band can detect. Please note that a sensitivity of 50 mK (or 0.05 K) is equivalent to a sensitivity of 0.05°C.
My Thermal degrees after processing seem wrong. How can I fix this?
When processing your thermal data in Pix4D and Agisoft, you may notice that your thermal (LWIR) band output has much higher than expected values. This is because the output units are centi-Kelvin. In order to convert the temperature values from centi-Kelvin to a unit that is easier to interpret, you will need to divide the output by 100 (which gives you Kelvin) and then subtract 273.15 to convert to Celsius.
My Thermal pixel values seem too low in snow and cold temperatures
The thermal sensors in the Altum and Altum-PT make certain assumptions about the object being imaged. One of these assumptions is that the emissivity of the target object is 1.0. However, the emissivity of snow is approximately 0.8 - 0.9, meaning up to 20% of the temperature reading is a reflection of the sky. The temperature reading can also be significantly impacted by the temperature of the thermal window in front of the imager, especially at extreme temperatures.
The following articles from FLIR may be helpful:
How can I preview thermal images on my computer?
Standard photo viewers such as Windows Photo Viewer or Preview will not be able to open thermal images from Altum or Altum-PT. To do so, you will need a more dynamic image processing program, such as Fiji.