Suppose a Stock follows an Itô process with instantaneous volatility σ(S(t),t)\sigma(S(t),t). Precisely dS(t)=μS(t)dt+σ(S(t),t)S(t)dW(t)dS(t)=\mu S(t)dt+\sigma(S(t),t)S(t)dW(t) I have a historical data for the values of S(t)S(t).How can I estimate the instantaneous volatilities σ(S(t),t)\sigma(S(t),t) that took place on each day in this historical daily data series?