Vapour-pressure deficit temperature, the relative humidity and, if possible, the canopy air temperature. We must then compute the saturation pressure. Saturation pressure can be looked up in a psychrometric chart or derived from the Arrhenius equation, a way to compute it directly from temperature is where: To convert between Rankine and degrees Fahrenheit: formula_10 We compute this pressure for both the ambient and canopy temperatures. We then can compute the actual partial pressure of the water vapour in the air by multiplying by the relative humidity [%]: and finally VPD using formula_12 or formula_13 when the canopy temperature is known. Vapour-pressure deficit
Tissue-to-air ratio Tissue-to-air ratio Tissue-to-air ratio (TAR) is a term used in radiotherapy treatment planning to help calculate absorbed dose to water in conditions other than those directly measured. The TAR at a point in a water phantom irradiated by a photon beam is taken to be the ratio of the total absorbed dose at that point to the absorbed dose at the same point in a minimal-scatter phantom with just-sufficient build-up. Tissue-air ratio is defined as the ratio of the dose to water at a given depth to the dose in air measured with a buildup cap: formula_1 where D(f,z) is