Need help with spectrogram? Pls help

[brano]

I have plotted the spectrogram of linear FM signal using TFTB toolbox in Matlab. Here is the code:
y=fmlin(128,0.1,0.3);
h=tftb_window(21,'Hamming');
tfrsp(y,1:128,128,h,1);

My questions are:
How to find peak values of the spectrogram for every time instant (when you have mesh plot)?
How to plot a graph for a constant frequency, that will show at what time instants is that frequency present?

Thank you in advance...

 

[hmsheng]

max() function can do for your first question.
I can't understand your second question.