What is meant by LFM (Linear Frequency Modulation) waveform?
An LFM pulse is one in which the "instantaneous frequency" changes linearly over the duration of the pulse.  By "instantaneous frequency" I mean the rate of change of phase.  Over its $\tau=500\mu s$ duration, a pulse with "bandwidth" $B=50 kHz$ and center frequency $f_c=150 kHz$ would be defined by

$f(t)=A\cos(\theta(t))=A\cos(2\pi(f_c-B/2)t+\pi(B/\tau)t^2+\theta_0)$ 

Taking the derivative of phase with respect to time, we have

$\partial\theta(t)/\partial{t}=2\pi(f_c-B/2)+2\pi(B/\tau)t $

We can see that this sweeps from $2\pi(f_c-B/2)$ to $2\pi(f_c+B/2)$ over the duration of the pulse.

An LFM pulse provides better range resolution than an unmodulated pulse of the same duration.