Collect the data with 20% overlap.
Use the IsoThermal settings to keep the coloration consistent.
With the M300/H20T you can set the upper and lower thresholds for the IsoThermal. Set the lower to 20 C below the water temp and the upper to 20-40 C above the ambient air temp.
Water doesn't do super well with thermal sensors because it will pick up a bit of a reflection.
You will need a Pro subscription to process the data.