Temperature measurement apparatus and temperature measurement method

A temperature measurement method of measuring a temperature of a steel sheet, the temperature measurement method comprising:

• a luminance acquisition step of acquiring radiation luminance of the steel sheet at a plurality of wavelengths at each position on a surface of the steel sheet in a field of view, by using an imaging unit that is a hyperspectral camera taking, as the field of view, a range including at least a part of the steel sheet in a sheet width direction;
• and
• a temperature calculation step of, by using an arithmetic processing unit, selecting two wavelengths from wavelength range at which the radiation luminance of the steel sheet is acquired by the imaging unit and calculating a temperature at each position on the surface of the steel sheet by two-color radiation temperature measurement, by using the radiation luminance of the steel sheet acquired by the imaging unit at the two selected wavelengths,
• wherein the arithmetic processing unit:
• holds at least two or more sets of wavelengths, consisting of two wavelengths, within wavelength range at which the radiation luminance of the steel sheet is acquired by the imaging unit, and
• wherein the temperature calculation step includes:
• increasing an exposure amount of the imaging unit in a case in which the radiation luminance of the steel sheet acquired in a set of wavelengths including the longest wavelength among the plurality of sets of wavelengths held by the arithmetic processing unit falls below a lower limit threshold value set in advance,
• reducing the exposure amount of the imaging unit in a case in which the radiation luminance of the steel sheet acquired in a set of wavelengths including the shortest wavelength among the plurality of sets of wavelengths held by the arithmetic processing unit exceeds an upper limit threshold value set in advance, and
• adjusting the exposure amount so that at least one set of wavelengths is able to detect the radiation luminance from a luminance lower limit value to a luminance upper limit value at any position in the sheet width direction within a measurement target range.