|ECHO HEIGHT ERRORS|
DUE TO SUPERREFRACTION AND SUBREFRACTION
METEOROLOGIST JEFF HABY
A standard radar will assume normal refraction takes place. Radar determines an echo height by
calculating how much the beam changes in elevation with distance from the radar and how the
earth's surface curves under the radar beam.
Errors in the echo height can occur from the beam not refracting normally and land surface elevation changes
at the earth's surface. The land surface elevation change errors can be removed if the radar is given
topographic data of the earth's surface. The refraction errors can be reduced from soundings inputted
into the radar so that the radar determines whether refraction will be more than normal, normal or
less than normal.
If the radar assumes normal refraction, significant echo height errors can occur when
subrefraction take place. Suppose there is a storm that is 100 kilometers from the radar site and the echo
top of the storm in the actual troposphere is 40,000 feet. Suppose superrefraction is taking place and the
radar assumes normal refraction. The radar will not indicate the actual echo top of 40,000 feet since the
beam is not refracting as the radar assumes it is. The radar under superrefraction conditions will
indicate an echo top greater than 40,000 feet in this example. Thus superrefraction overestimates
the echo top height. Using this same line of logic, subrefraction underestimates the echo top height thus
it will indicate a echo top of less than 40,000 feet in this example.