# How to calculate the interannual variability and Seasonal Amplitude?

I have a time series of remote sensing observables. For example, the observed brightness from 2007 to 2019. And we have 2 datapoints per day. How can I calculate the interannual variability of this variable? and the seasonal amplitude? and how to define them? I want to study the relationship between interannual variability and seasonal amplitude of this variable. It's better to do a scatter plot with X-axis as interannual variability and Y-axis as seasonal amplitude. But I have no idea about the definition and the calculation of inter annual variability and seasonal amplitude (and also seasonal variability). I am a beginner, is there anyone who can help me? thanks a lot!