Robust M-Periodogram Is Used For the Analysis of Signals With Heavy-Tailed Distribution Noise. It Is Also Used For the Non-Stationary Signals In the Form of Robust Spectrogram. Robust Spectrogram Is Also Used to Estimate the Instantaneous Frequency (If) of the Signal. In This Paper, We Are Introducing a Robust Spectrogram Estimator Based on Welch Periodogram For Estimating the Instantaneous Frequency of the Signal With a Time Varying Window Length.