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Raw counts vs object signal
07-24-2013, 05:33 PM
Post: #1
Raw counts vs object signal
Can anyone give me a clear explanation of what the "raw counts" and "object signal" options are that are available in the ResearchIR software (under Options > Units) and how they relate to radiance? I have tried asking FLIR support, but they have not responded to my question which I asked over a week ago!
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07-25-2013, 08:33 AM
Post: #2
ITC RE: Raw counts vs object signal
  • Raw count: The pixel value as delivered by the camera on the digital interface or as saved in radiometric image files. No correction for object parameters is included. Depending on the camera model, drift compensation may also not be included.
  • Object signal: A calibrated value proportional to the radiation from the object. This is the detector signal corrected for drift, gain, and offset, including compensation for object parameters. The correct setting of object parameters (reflected apparent temperature, emissivity, object distance, relative humidity, and atmospheric temperature) is assumed.
  • Temperature: The blackbody temperature of the object when the calibration algorithm based on Planck’s law is applied to the object signal.
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07-25-2013, 12:25 PM
Post: #3
RE: Raw counts vs object signal
Gary, Thanks for the info, which I had already read in the software documentation. If you check the glossary in the ResearchIR documentation, it says Object Signal is a "non-calibrated value". Clearly one of these definitions is wrong.

I need to to know whether either Raw Count or Object Signal is the raw radiation values at the sensor and what the exact units are (e.g., W/m2) as I am trying to extract accurate temperatures for fumaroles on a volcanic lava dome acquired at distances of more than 4 km. At these distances, the algorithms in ResearchIR don't work and numerical modelling of the atmospheric transmissivity is necessary, for which the raw radiation values at the camera are needed. Based on what I have read so far, it would seem like that Raw Count would be the correct parameter. Is this so?

Does anyone know what the relationship between object signal and radiation is?
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07-25-2013, 01:22 PM
Post: #4
RE: Raw counts vs object signal
I believe the definition of object signal stating that is it a calibrated value is correct. You can prove this to yourself by adjusting object parameters and watch the value change.

I would use the object signal values since they are corrected for drift, lens emission, etc. Set the emissivity to 1.0 and the object distance to 0. This will delete any adjustment from those two parameters.

IR detectors respond linearly with the intensity of radiation received. The calibration process links the object signal to blackbody temperature.

To calculate radiance received from target (included emitted and reflected energy)

1. Set emissivity to 1.0
2. Read apparent temperature on object.
3. Integrate Plancks formula using the apparent temperature between the sensitivity wavelengths of the camera.
4. Calculate the area from distance, FOV, and image area data.
5. Calculate Power and intensity from all of the above.

If you are interested in the radiation only from the target excluding reflection from ambient, the temperature in step one must be calculated using emissivity and T amb data as well.

See the attachment.


Attached File(s)
.pdf  ITC Tech Note - Calculating Emissive Power from Temperature.pdf (Size: 346.62 KB / Downloads: 44)
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