How often do we need to do the “dark correct” or “zero”? We did the “dark correct” when we measured the irradiance in our culture chamber. When we go into the field, we will do it again, but do we need to do it every time we go into the field?
Dark or "zero" corrections should be performed when you first receive the instrument. How frequently a dark correction should be performed depends on many factors including:
The temperature where you are working—the warmer (over 25°C) it gets, the more the dark values will change with changes in temperature.
How close to the noise floor (i.e., the minimum signal measureable by the instrument) you are working. For example, if you are frequently working where the signals are very noisy then you should dark correct daily. A quick check is to make a measurement with the instrument dark and see how close to zero the readings are compared with the signal you want to measure. If the dark is either positive or negative by a substantial factor compared to the signal you are measuring, then it is time to dark correct and repeat the measurement.