Radar sends out a certain wavelength of electromagnetic radiation. This electromagnetic radiation is of the longwave variety and therefore will not damage the environment. The energy emitted from the radar travels at about the speed of light as does all electromagnetic radiation. The speed of light is 299,800,000 m/s. With this speed, radar can sample hydrometeors during one pulse in a small fraction of a second. Radar can typically send and receive radiation between 200 and 3,000 times in one second. The number of pulses radar sends out is called the Pulse Repetition Frequency. Radar sends out electromagnetic radiation that strikes hydrometeors in the atmosphere. Some of this radiation reflects back directly toward the radar set. This energy that is reflected directly back is called backscattered radiation. The amount of energy the radar receives (compared to the amount it sends out) is very small. An example of this is to think about the amount of light reflected off Mars and seen on Earth compared to the total energy emitted from the Sun. The Earth only receives a very small amount of the total energy that the sun gives off that is reflected off Mars and toward the Earth. The amount of backscattered radiation the radar receives depends on the number of hydrometeors, the size of hydrometeors and absorption qualities of the hydrometeors such as density, shape and other unique properties. An object with a higher density, a larger surface area facing perpendicular to the radar's energy and composition of a more reflective material will send relatively more backscattered energy to the radar set. Radar is an active remote sensor. It sends out as well as receives electromagnetic radiation. The backscattered energy it receives is processed by the computer and put into a graphical form for the radar user. Higher amounts of backscattered energy correlate with higher VIP values on the graphical display. Because electromagnetic radiation travels at a known speed and the radar can process the time between radiation being emitted and received, a known distance to the hydrometeors can be calculated. Velocity (m/s) * Time (s) = Distance (meters). With the information of distance and amount of backscattered radiation, the data can be plotted on a graph showing intensity of precipitation and the direction / distance the precipitation is from the radar set. |