This information can be found in the Tau Product Specification, pages 40-41. The Product Spec is available for download online at the FLIR >> Cores >> Resources web page.

The `Full` version of Radiometry includes Isotherm (3.3.3.1) and Spot Meter (3.3.3.2) features. Advanced Radiometry includes the Full features, as well as those detailed in 3.3.3.3 (note the `high-volume` requirement.)

3.3.3 Radiometric Features
Note: In the Tau 2.0 release, only the 324 configurations provided the radiometric features defined in the following sub-paragraphs. In the Tau 2.1 release and later releases, all configurations provide this capability.

3.3.3.1 Isotherm
The Tau 2 core performance configuration provides an “isotherm” feature in which portions of the scene exceeding a user- selectable threshold are mapped to different portions of the palette. The isotherm feature is most useful for palettes in which the bottom half is composed of gray shades and the upper half is composed of color shades (for example, yellow to orange to red). Three user-specified thresholds are applicable to the isotherm mode, with the option for a fourth threshold in Tau 2.7 and later releases. If the four isotherm mode is enabled, the fourth value represents the saturation threshold (specified in either degrees Celsius or in percentage of full- scale of the temperature symbol bar) above which pixels will be mapped to the top shade of the palette (255). The third is the upper threshold above which pixels will be mapped to the top shades of the palette (224 to 255). The second is the middle threshold; pixels with value between the middle and upper threshold are mapped to shades 176 to 223. The first is the lower threshold; pixels with value between the lower and middle threshold are mapped to shades 128 to 175.

3.3.3.2 Spot Meter
The Tau 2 core performance configuration provides temperature-measurement capability via a spot meter in the central 4x4 area. Accuracy of the spot meter is +20 Co in high-gain state (see 3.3.2.2) and the greater of +20% or +20C in low-gain state. (Typical performance is on the order of +10 Co in high-gain state.)

The spot meter value is readable via command. Additionally, two user-selectable options for on- screen display of spot-meter data are provided: a numeric value and/or a thermometer-style gauge. The numeric indicator and gauge can be shown in degrees Celsius or Fahrenheit.

3.3.3.3 Advanced Radiometry and TLinear
For high-volume OEM customers, the Tau 2 core provides the option of the following advanced radiometric features:

• Improved accuracy: typical performance on the order of +5 Co or 5% in high-gain state (varies slightly across the full operating temperature range)
• Moveable / resizable spot-meter: coordinates user-selectable to any arbitrary location on the array
• Additional spot-meter data: spot-meter reports average, standard deviation, minimum, and maximum value
• TLinear: digital data linear in scene temperature, i.e. in real-time operation, the pixel values in the 14-bit digital data correspond to the temperature of the scene.

In normal mode with TLinear disabled, the Tau camera outputs digital data linear in radiometric flux. In TLinear mode, the Tau camera outputs digital data linear in scene temperature. The TLinear feature applies to the 14-bit CMOS and LVDS channels and is user selectable. Two resolution modes are available and user selectable: high resolution (0.04 Kelvin/count) and low resolution (0.4 Kelvin/count).