Question

VLF Radio Data Revisited. Download the file HW9Problem3.mat that we worked with for HW9 and load it into MATLAB. Remember that this file contains 30 seconds of electromagnetic wave data

sampled at100 kHz recorded in eastern Colorado. Create a time domain plot of the data. Create a spectrogram of the data using the following code with the following parameters.spectrogram(data,WINDOW,NOVERLAP,NFFT,Fs,'yaxis'); Make the window a Hanning window of length 1024, make the overlap 50%, and the ftt length the same as the window length. Change the color scale of the spectrogram using caxis ([-30 0]); colorbar; Just after 16.3 seconds, in the time domain plot from part (a) there is an impulsive spike in the data.How does this spike appear in the spectrogram? Why? The spectrogram is an image with a pixel for each time and frequency pair. Based on the spectrogram parameters you input in part (b), what is the freqeuncy resolution Af and time resolution At of the spectrogram? Hint: calculate the frequency resolution of the fft's that make up the spectrogram and think about how the window length and overlap affect the time resolutions Zoom in to your spectrogram using the magnifying glass until you see individual pixels to validate your answer to part(e).

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