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Issues with thermal_ir (ThermoMAP camera) temperature results

Hello,

Over the passt couple weeks I’ve been trying to produce a thermal model using a SenseFly DuetT camera. I have collected a few datasets with decent quality in different conditions to try out a few things in order to produce better results. I’ve been trying to process these images using the workflow described here : https://support.pix4d.com/hc/en-us/articles/360000173463-Processing-thermal-images and I’ve tried to play around with the model type (Thermal Camera instead of ThermoMap, single paramteres etc.) but to no avail… The processing runs fairly smoothly and everything, which is great, but the results obtained are mostly unreasonnable (such as negative temperatures for unfrozen rivers). I am now left to wonder if this is due to my processing or me missing something or if my camera is completely off track… I didn’t expect extraordinar results yet (I haven’t merged the thermal model with RBG 3D models yet so I was expecting some minor issues with the model quality) but no matter what I try, there always seems to be weird temperature results. You’ll find my latest results below:

Hi Simon, Duet-T gives absolute temperature values in degree C already. Thus you will not need any formula to convert the temperature. thermal_ir is the temperature. Does the max value of 6.74 degree and minimum value of 0 degree C seem reasonable?

Hello Momtanu, temperatures between 0 an 6.74 degrees don’t seem too far off but I measured the temperature at the surface of the river in the middle of the model in several spots and it was between 7.2 and 8.3 degrees overall so it’s not perfectly accurate. I produced a better model over the last few days but I’m left with one problem… I am not sure which of the models produced is supposed to be the temperature model (where each pixels value is the absolute temperature)… Since the duet-t is supposed to show absolute temperatures already, does that mean that the reflectance map (where the values are fairly close to what I would expect the temperatures to be on that day) is the model that shows absolute temperature for each pixel?

IndexMap for thermal_ir band:

You are right the thermal ir map is the temperature map showing absolute temperature value of each pixel. Since you know your area, you know the temperatures that day, the one closer to your values will be more accurate. Also, keep in mind to always look at the quality report for the quality, a good reconstrcution will have accurate values. It is good to know how the reflectance map is getting the values from the raw images: The software will give different weights to each image (with the overlapping pixel) depending on the angle of incidence and distance from the pixel to the camera center mainly.