The actual length of the pulses shown in is determined by the pulse duration or length of time the radar transmits energy. Pulse duration for the WSR-88D when operating in short pulse mode (VCP 11, 12, 21, 121, 211, 212, 221, or 32) is 1.57 X 10 -6 s and in long pulse mode (VCP 31) is 4.7 X 10 -6 s. Also, since the main beam describes a cone, a cross section perpendicular to the beam centerline is a circle. Another way of describing the power density is power per unit area of a cross section. This is illustrated in where the cross-sectional area of pulse 1 is 4 times larger than the area of pulse 2. Since the transmitted energy is the same for both pulse samples, then pulse 2 has a power density 4 times greater than the power density of pulse 1.
: Example of a pulse volume and power density difference viewed from either end of the pulse sample.