# PET formulas (Heat Overlay)

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The physiological equivalent temperature PET is calculated for two possible options based on the situation:

- A cell is in the shade or it is night at time t: PET
_{shade, night}; - A cell is in the sun during the day: PET
_{sun};

## PET Sun formula

The PET sun formula is as followed:

where,

- is the calculated atmospheric temperature at time t;
- is the hourly radiation at time t;
- is the calculated wind speed at 1.2 meters above ground time t;
- is the calculated wet-bulb temperature at time t;
- is the sun altitude at time t;
- is the bowen ratio at time t;
- is the calculated sky view factor.
- Constant values are sourced from the DPRA Heat stress report;

## PET Shade and Night formula

The PET shade and night formula is as followed:

where,

- is the calculated atmospheric temperature at time t;
- is the calculated wind speed at 1.2 meters above ground time t;
- is the calculated wet-bulb temperature at time t;
- is the calculated sky view factor;
- is the calculated diffusive radiation at time t;
- is the Stefan Boltzmann constant, which is .
- Constant values are sourced from the DPRA Heat stress report;