Method for determining the temperature of products transported on the conveyor belt of a cryogenic tunnel, comprising the following steps: - a temperature measurement system, for example a pyrometer, fixed in space in a position close to, above or to the side of the conveyor, is implemented in order to carry out a continuous measurement of the surface temperature of products moving along opposite the temperature measurement system; - a distance measurement system such as a laser or an ultrasound system is implemented to measure the thickness of a product whose temperature was measured during the previous step, said thickness measurement being carried out at the very place where the temperature measurement is carried out; - there is provided a computer which then performs the following evaluation: a) when the thickness of the product is between a lower limit and an upper limit, it is then considered that the temperature measured for this product by the temperature measurement system is a reliable value of the temperature of the product; b) when the thickness of the product is greater than the upper limit or well below the lower limit, then the computer takes into account and stores in memory the last product temperature value measured by the system and considered by the computer as a reliable value according to paragraph a) above, and this value is then considered as a good indication of the temperature of the product whose measured thickness is outside the range of limits; c) after a determined period of time, during which the measured thickness is outside said range, the computer concludes that there are no products on the conveyor, and no longer takes into account the temperature measurements provided by the temperature measurement system, measurements considered as "default" values. - a temperature measurement system, for example a pyrometer, fixed in space in a position close to, above or to the side of the conveyor, is implemented in order to carry out a continuous measurement of the surface temperature of products moving along opposite the temperature measurement system; - a distance measurement system such as a laser or an ultrasound system is implemented to measure the thickness of a product whose temperature was measured during the previous step, said thickness measurement being carried out at the very place where the temperature measurement is carried out; - there is provided a computer which then performs the following evaluation: a) when the thickness of the product is between a lower limit and an upper limit, it is then considered that the temperature measured for this product by the temperature measurement system is a reliable value of the temperature of the product; b) when the thickness of the product is greater than the upper limit or well below the lower limit, then the computer takes into account and stores in memory the last product temperature value measured by the system and considered by the computer as a reliable value according to paragraph a) above, and this value is then considered as a good indication of the temperature of the product whose measured thickness is outside the range of limits; c) after a determined period of time, during which the measured thickness is outside said range, the computer concludes that there are no products on the conveyor, and no longer takes into account the temperature measurements provided by the temperature measurement system, measurements considered as "default" values. a) when the thickness of the product is between a lower limit and an upper limit, it is then considered that the temperature measured for this product by the temperature measurement system is a reliable value of the temperature of the product; b) when the thickness of the product is greater than the upper limit or well below the lower limit, then the computer takes into account and stores in memory the last product temperature value measured by the system and considered by the computer as a reliable value according to paragraph a) above, and this value is then considered as a good indication of the temperature of the product whose measured thickness is outside the range of limits; c) after a determined period of time, during which the measured thickness is outside said range, the computer concludes that there are no products on the conveyor, and no longer takes into account the temperature measurements provided by the temperature measurement system, measurements considered as "default" values.