It depends on what substance/object you are trying to determine the intensity.
lux meter or light meter
The intensity of a note refers to its volume or loudness. It is the measure of how strong or soft a sound is produced by a musical instrument or voice. Intensity is influenced by factors such as the force with which a note is played or sung, and the instrument being used.
A seismogragh and/or seismometer.
There is no particular instrument used for measuring tornado intensity. Ratings are based primarily on damage assessment. Occasionally doppler radar has measure wind speeds inside a tornado, but such measurements are rare.
A seismometer is used to measure the intensity of an earthquake by detecting and recording the ground motion caused by seismic waves. It provides data on the amplitude and frequency of the seismic waves, which helps in determining the earthquake's magnitude and duration.
In most cases the intensity of a tornado is never actually measured. Tornadoes are rated based on the severity of the damage they cause. Mobile Doppler radar can measure wind speeds in a tornado, but since such radar cannot measure ground-level winds the measurements are not used in ratings.
Yes. A photometer is an instrument that measures the intensity of the incoming light and quantifies it into numerical data. A photometer is a light sensitive device and measure the power of light.
No. The instrument used to measure wind speed is an anemometer.
The instrument which is used to measure snowfall is called a snow gauge.
Seismometer
A thermometer
A pyranometer is the instrument used for measuring the intensity of sunlight. It measures the total solar radiation flux density in watts per square meter.