The  radar  interprets  velocity  and  spectrum  width returns from beyond the ambiguous range as occurring within the range. Range dealiasing software has been implemented in the Radar Data Acquisition (RDA) component  preprocessor.  The  purpose  is  to  attempt  to replace  range-folded  doppler  data  to  its  proper  range. This  software  compares  radar  power  returns  from  the possible ranges of doppler velocity and spectrum width data, If the power at one possible range is more than the power at the other ranges, the data are assigned to that range and the doppler data from the other ranges are considered  ambiguous.  If  the  power  from  the  different cringes is within 10 dB, the doppler data at all those ranges   are   considered   unambiguous.   Ambiguous doppler data are flagged as range folded, treated as missing by all algorithms, and are displayed as purple (adaptable)  at  the  principal  user  processor  (PUP). Recognition  of  Range-Folded  Data Range-folded data should be easily recognized in a Reflectivity  product.  Range-folded  data  have  a  “spiky” appearance  in  the  radials  where  they  appear.  In addition, the reflectivity values where the data are folded  will  not  be  similar  to  those  surrounding  them. Range-folded data are detectable by comparing Reflectivity  and  Mean  Radial  Velocity  products,  as  well as  comparing  current  displays  with  previous  products for time and space continuity. Range  folding  may  occur  under  conditions  of anomalous  propagation  where  the  radar  beam  is constrained to follow a path close to the Earth’s surface, or when strong convection occurs beyond the first trip (250 nmi). When  possible,  the  range  dealiasing  software  will place the doppler velocity and spectrum width data at the proper range. When this software cannot determine the proper range, the data will be flagged and displayed as  range  folded. Assessing the Impact of Range-Folded Data Range-folded   data   can   impact   products   and algorithms   that   use   reflectivity   data.   When range-folded  data  are  present,  corrupted  data  are displayed with valid data. Products using multiple reflectivity scans may be affected as well. The impact of doppler velocity and spectrum width range   folding   is   significant,   both   in   the   radar’s unambiguous  range  limits  and  in  areas  of  significant velocity data lost due to ambiguous returns. In addition, range ambiguous values are treated as missing by the velocity-based algorithms and can, therefore, seriously impact  those  algorithms. Assessing Impacts of Range-Folded Data on Velocity Products The presence of range-folded (overlaid) data on Mean  Radial  Velocity  products  is  inevitable.  The inability  to  determine  velocity  estimates  for  the  sample volumes results from the inability of the range unfolding algorithm  to  distinguish  between  power  returns  from two  or  more  sample  volumes  at  the  same  relative location  within  different  trips.  Therefore,  valid  velocity estimates can be derived for only one corresponding sample   volume   along   each   radial,   The   ring   of range-folded (overlaid) data at the beginning of the second and subsequent trips is caused by the first trip ground clutter and is a common result of this range unfolding  limitation. NON-METEOROLOGICAL  RADAR ECHOES This  section  will  briefly  describe  methods  of identifying  and  assessing  the  impacts  of  ground  clutter, anomalous propagation, sidelobes, and solar effects. Ground Clutter Prior  to  calculation  of  reflectivity,  velocity,  or spectrum width, return signals from ranges within the radar’s normal ground clutter pattern are processed to remove most of the signal returned from targets that are stationary (part B of the FMH-11). The portion of signal not removed, called residual clutter, will remain as part of many of the products. RECOGNITION   OF   RESIDUAL   GROUND CLUTTER.—  A  low-elevation  Reflectivity  product will  show  ground  clutter  close  to  the  radar  or  distant mountainous terrain, It will normally appear as a cluster of points (having a speckled nature) or as a large area of contiguous returns. Errors are recognizable as wedges having  sharp  radial  discontinuities  from  adjacent regions  and  whose  predominant  colors  differ  markedly. Errors may also appear as radial spikes several volume samples in length, whose velocities are shifted toward high  positive  or  negative  values.  A  time  lapse  of Reflectivity  products  will  show  no  movement  of  these returns.  With  increasing  antenna  elevations,  ground clutter   returns   will   disappear.   Generally,   mean velocities will be near zero and spectrum widths will be very narrow. 12-6