Dear Tom,
The National Weather Service website provides two short-range radar images: base and composite reflectivity. What is the difference?
Dave Makarski, Arlington Heights
Dear Dave,
Radars transmit a beam of energy, some of which is reflected back to the radar site when the beam strikes an object (such as a raindrop). Reflectivity, a measure of the amount of energy that returns to the radar, is greatest when raindrops and cloud particles are both large and numerous.
The radar beam is first transmitted at 0.5 degree above the horizontal, making a full circular sweep, followed by additional sweeps at progressively greater tilt angles. Base reflectivity refers to reflectivity when the beam is elevated 0.5 degree; its data indicate rain reaching the ground. Composite reflectivity displays in a single picture the highest reflectivity values from all beam tilt angles; it describes the storm's total water content.
The National Weather Service website provides two short-range radar images: base and composite reflectivity. What is the difference?
Dave Makarski, Arlington Heights
Dear Dave,
Radars transmit a beam of energy, some of which is reflected back to the radar site when the beam strikes an object (such as a raindrop). Reflectivity, a measure of the amount of energy that returns to the radar, is greatest when raindrops and cloud particles are both large and numerous.
The radar beam is first transmitted at 0.5 degree above the horizontal, making a full circular sweep, followed by additional sweeps at progressively greater tilt angles. Base reflectivity refers to reflectivity when the beam is elevated 0.5 degree; its data indicate rain reaching the ground. Composite reflectivity displays in a single picture the highest reflectivity values from all beam tilt angles; it describes the storm's total water content.
