What is the difference between base reflectivity and composite reflectivity in terms of weather radar?

Answer 1

From NOAA website:http://weather.noaa.gov/radar/radinfo/radinfo.htmlBase ReflectivityThis is a display of echo intensity (reflectivity) measured in dBZ (decibels of Z, where Z represents the energy reflected back to the radar). "Reflectivity" is the amount of transmitted power returned to the radar receiver. Base Reflectivity images are available at several different elevation angles (tilts) of the antenna and are used to detect precipitation, evaluate storm structure, locate atmospheric boundaries and determine hail potential.

The base reflectivity image currently available on this website is from the lowest "tilt" angle (0.5°). This means the radar's antenna is tilted 0.5° above the horizon.

The maximum range of the "short range" (S Rng) base reflectivity product is 124 nm (about 143 miles) from the radar location. This view will not display echoes that are more distant than 124 nm, even though precipitation may be occurring at greater distances. To determine if precipitation is occurring at greater distances, select the "long range" (L Rng) view (out to 248 nm/286 mi), select an adjacent radar, or link to the National Reflectivity Mosaic.Composite ReflectivityThis display is of maximum echo intensity (reflectivity) from any elevation angle at every range from the radar. This product is used to reveal the highest reflectivity in all echoes. When compared with Base Reflectivity, the Composite Reflectivity can reveal important storm structure features and intensity trends of storms.

The maximum range of the "long range" (L Rng) composite reflectivity product is 248 nm (about 286 miles) from the radar location. The "blocky" appearance of this product is due to its lower spatial resolution on a 2.2 * 2.2 nm grid. It has one-fourth the resolution of the Base Reflectivity and one-half the resolution of the Precipitation products.

Although the Composite Reflectivity product is able to display maximum echo intensities 248 nm from the radar, the beam of the radar at this distance is at a very high altitude in the atmosphere. Thus, only the most intense convective storms and tropical systems will be detected at the longer distances.

Because of this fact, special care must be taken interpreting this product. While the radar image may not indicate precipitation it's quite possible that the radar beam is overshooting precipitation at lower levels, especially at greater distances. To determine if precipitation is occurring at greater distances link to an adjacent radar or link to the National Reflectivity Mosaic.

For a higher resolution (1.1 * 1.1 nm grid) composite reflectivity image, select the short range (S Rng) view. The image is less "blocky" as compared to the long range image. However, the maximum range is reduced to 124 nm (about 143 miles) from the radar location.

Answer 2

Base reflectivity shows the reflectivity at a single elevation angle, providing information about precipitation intensity and location. Composite reflectivity combines reflectivity data from multiple elevation angles to create a 3D representation of the radar echoes within a storm, giving a more complete picture of the storm's structure and intensity.