Does anyone know if it is possible to stitch aerial thermal imagery without losing radiometric temperature data? I am looking to generate a thermal orthomosaic.

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Hello Benjamin; not sure it's too late to reply to your post, but I just signed up to DIY Drones  :-)

I've been working on this subject for some time now (I'm also a Certified Level 2 thermography operator) conducting UAV surveys on landfills, crops and Photo-voltaic installations.

Based on my experience it is possible to get radiometric thermal orthomosaics, but not so immediate.

Some of the things to take into account:

- Sensor resolution (the higher the better, obviously); the low resolution of thermal sensors (640 x 480 can be considered 'high-end' for the average guy like me) plays a big part in the overall scenario as a big limiting factor, requiring careful selection of flight altitude (bound to gsd as well) , flight speed, flight-path, over-&side-lap;

- Type of media captured: video vs image sequence; typically thermal imagers easily acquire (radiometric) videos (in proprietary format); this implies that still images need to extracted from the video (depending on the surveyed area extension this might take quite some time); captured (or sampled from video) images are radiometric only when viewed with 'thermal infrared' software (typically from the imager manufacturer who know their sensors and related constants), and, at least to my knowledge, these tools are not good at mosaicing (at least not the number of images collected by UAVs - several hundreds to thousands).

So, basically you have radiometric jpegs or tiffs, but per-pixel temperature data is only available with the tools I mentioned above, outside of those you have Digital Numbers (0-255 for 8 bit; 0- 65535 for 16 bit).

Over time I have tested different flight parameters and tools (both open and closed source), and based on the results obtained, I have implemented different workflows and image processing routines.

I do not know your setup and specs, so I cannot be more specific; however you can try with PIX4D (I'm not affiliated with them by any means): to my experience, among the UAV commercial tools, it literally is the 'Swiss army knife' of multi-spectral and radiometric processing - you can get a fully functional demo license for a limited time which allows you to do the thermal index map process (some instructions: https://support.pix4d.com/hc/en-us/articles/202755349-Can-Pix4Dmapp...https://support.pix4d.com/hc/en-us/articles/210140893#gsc.tab=0https://support.pix4d.com/hc/en-us/articles/208592186#gsc.tab=0). I'm also attaching a sample draft snapshot from PIX4D of a thermal map of a cultivated field - it's not finalized yet, and it's low-res, but it's just to give you a rough and basic idea of the 'potentials'.

Please let me know if this helps (or at least steers towards your direction): I'm most interested in and actively involved with this subject.

Best Regards

Giovanni

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Hi Giovanni,

i just made an account so i could let you know that was a very helpful answer which helped me a lot thank you


Giovanni - iGV said:

Hello Benjamin; not sure it's too late to reply to your post, but I just signed up to DIY Drones  :-)

I've been working on this subject for some time now (I'm also a Certified Level 2 thermography operator) conducting UAV surveys on landfills, crops and Photo-voltaic installations.

Based on my experience it is possible to get radiometric thermal orthomosaics, but not so immediate.

Some of the things to take into account:

- Sensor resolution (the higher the better, obviously); the low resolution of thermal sensors (640 x 480 can be considered 'high-end' for the average guy like me) plays a big part in the overall scenario as a big limiting factor, requiring careful selection of flight altitude (bound to gsd as well) , flight speed, flight-path, over-&side-lap;

- Type of media captured: video vs image sequence; typically thermal imagers easily acquire (radiometric) videos (in proprietary format); this implies that still images need to extracted from the video (depending on the surveyed area extension this might take quite some time); captured (or sampled from video) images are radiometric only when viewed with 'thermal infrared' software (typically from the imager manufacturer who know their sensors and related constants), and, at least to my knowledge, these tools are not good at mosaicing (at least not the number of images collected by UAVs - several hundreds to thousands).

So, basically you have radiometric jpegs or tiffs, but per-pixel temperature data is only available with the tools I mentioned above, outside of those you have Digital Numbers (0-255 for 8 bit; 0- 65535 for 16 bit).

Over time I have tested different flight parameters and tools (both open and closed source), and based on the results obtained, I have implemented different workflows and image processing routines.

I do not know your setup and specs, so I cannot be more specific; however you can try with PIX4D (I'm not affiliated with them by any means): to my experience, among the UAV commercial tools, it literally is the 'Swiss army knife' of multi-spectral and radiometric processing - you can get a fully functional demo license for a limited time which allows you to do the thermal index map process (some instructions: https://support.pix4d.com/hc/en-us/articles/202755349-Can-Pix4Dmapp...https://support.pix4d.com/hc/en-us/articles/210140893#gsc.tab=0https://support.pix4d.com/hc/en-us/articles/208592186#gsc.tab=0). I'm also attaching a sample draft snapshot from PIX4D of a thermal map of a cultivated field - it's not finalized yet, and it's low-res, but it's just to give you a rough and basic idea of the 'potentials'.

Please let me know if this helps (or at least steers towards your direction): I'm most interested in and actively involved with this subject.

Best Regards

Giovanni

Hi Futurwise Aerial,

I'd almost forgotten about this post...   ;-)

Thanks for taking the time to read it and letting me know.

 

Futurewise Aerial said:

Hi Giovanni,

i just made an account so i could let you know that was a very helpful answer which helped me a lot thank you


Giovanni - iGV said:

Hello Benjamin; not sure it's too late to reply to your post, but I just signed up to DIY Drones  :-)

I've been working on this subject for some time now (I'm also a Certified Level 2 thermography operator) conducting UAV surveys on landfills, crops and Photo-voltaic installations.

Based on my experience it is possible to get radiometric thermal orthomosaics, but not so immediate.

Some of the things to take into account:

- Sensor resolution (the higher the better, obviously); the low resolution of thermal sensors (640 x 480 can be considered 'high-end' for the average guy like me) plays a big part in the overall scenario as a big limiting factor, requiring careful selection of flight altitude (bound to gsd as well) , flight speed, flight-path, over-&side-lap;

- Type of media captured: video vs image sequence; typically thermal imagers easily acquire (radiometric) videos (in proprietary format); this implies that still images need to extracted from the video (depending on the surveyed area extension this might take quite some time); captured (or sampled from video) images are radiometric only when viewed with 'thermal infrared' software (typically from the imager manufacturer who know their sensors and related constants), and, at least to my knowledge, these tools are not good at mosaicing (at least not the number of images collected by UAVs - several hundreds to thousands).

So, basically you have radiometric jpegs or tiffs, but per-pixel temperature data is only available with the tools I mentioned above, outside of those you have Digital Numbers (0-255 for 8 bit; 0- 65535 for 16 bit).

Over time I have tested different flight parameters and tools (both open and closed source), and based on the results obtained, I have implemented different workflows and image processing routines.

I do not know your setup and specs, so I cannot be more specific; however you can try with PIX4D (I'm not affiliated with them by any means): to my experience, among the UAV commercial tools, it literally is the 'Swiss army knife' of multi-spectral and radiometric processing - you can get a fully functional demo license for a limited time which allows you to do the thermal index map process (some instructions: https://support.pix4d.com/hc/en-us/articles/202755349-Can-Pix4Dmapp...https://support.pix4d.com/hc/en-us/articles/210140893#gsc.tab=0https://support.pix4d.com/hc/en-us/articles/208592186#gsc.tab=0). I'm also attaching a sample draft snapshot from PIX4D of a thermal map of a cultivated field - it's not finalized yet, and it's low-res, but it's just to give you a rough and basic idea of the 'potentials'.

Please let me know if this helps (or at least steers towards your direction): I'm most interested in and actively involved with this subject.

Best Regards

Giovanni

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