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<br />gage locations so the Ze values over the gages were both uncluttered and uncontaminated by <br />clutter suppression. One deliberate exception (Mt. Evans in table 3) provided data with <br />which to evaluate the WSR-88Ds ability to detect snowfall over rugged mountains. <br /> <br />Table 3. - Locations of six snow observing sites in the Denver area. The three sites located nearest <br />the radar had both Belfort gages and hourly snowboard readings. Latitudes and longitudes were <br />measured by GPS, and elevations were estimated from a USGS (U.S. Geological Survey) data base or <br />large-scale maps. <br /> <br /> m.s.I. Distance! Azimuth <br />Gage Location Gage Latitude Longitude Elevation from Radar <br />(Operator) No. (0_') (0_') (m) (kmjO)* <br />SE Aurora 1 39-38.217 104-46.206 1758 25/229 <br />(M. Bedell) <br />NE Aurora 2 39-45.609 104-49.322 1631 24/263 <br />(R. Kissinger) <br />Lakewood 3 39-41.272 105-06.282 1703 49/257 <br />(A. Super) <br />Pine Valley 4 39-24.400 105-20.843 2100 81/239 <br />(S. Becker) <br />Mt. Evans 5 39-39.316 105-35.642 3265 91/261 <br />(M. Jones) <br />Black Forest 6 39-01.720 105-40.908 2295 85/188 <br />(J. Bishop) (no data until late January) <br /> <br />Clutter bypass maps were obtained from the three radars in question and plotted on <br />1:500,000 scale topographic maps of each area. A clutter bypass map shows where ground <br />clutter was detected by the radar during the particular few hours of special observation. The <br />map is attempted to be made under well-mixed atmospheric conditions with no precipitation <br />present. The bypass map is expected to approximate the clutter pattern during standard <br />refraction. Actually, two maps are generated, one for the two lowest antenna tilts (0.5 and <br />1.50) and the other for all higher scan angles. All future references will be to the former map <br />because Ze values from only the lower tilt were used in the analysis to be discussed. <br /> <br />Unfortunately, clutter bypass maps are not generated to the same 10 by 1-km resolution as <br />Ze data but are generated on a coarser 256-radial by 3600 pixel grid. In addition to the <br />problem of the mismatch in Ze and clutter bypass map coordinates, the bypass map tends to <br />"smear" potentially cluttered regions. Much clutter is "point-target" echo (Paul Smith:. <br />personal communication), which is probably over-emphasized by the bypass map pixel scale. <br /> <br />The Denver bypass map, generated in October 1995 and used throughout the 1995-96 winter, <br />showed few continuous uncluttered areas within 30 km of the radar. The uncluttered areas <br />were located to the east and southeast where prairie exists with almost no tree cover or <br />housing developments to provide protection for snow measurements. <br /> <br />The extent of bypass map clutter at moderate ranges west of the Denver radar was surprising <br />because a minor ridge about 12 km distant for azimuths between about 250 and 2800 (all <br />azimuths are given in degrees [0] true in this report) reaches the bottom of the 0.50 tilt beam <br />(the beam is 0.950 wide). This ridge would be expected to absorb any sidelobe energy under <br />the lowest elevation angle beams for which the lower clutter map is generated. Elevations <br />decrease beyond the near ridge until about the 40-km range (South Platte River) and then <br /> <br />8 <br />