Terrain, Blockage, and Ground Clutter

S-Pol IHOP_2002, Oklahoma Panhandle
May/Jun 2002

S-Pol was sited on a small rise for IHOP. This was done to allow viewing of ground clutter to as far a range (in all directions) as possible and thereby increase the utility of the Fabry refractive index product. The rise selected was perhaps only 10 meters above the surrounding terrain, but given the flatness of the Oklahoma Panhandle, this was sufficient to view ground targets to as much as 60km in several directions. Note that the refractive index variables were calculated in the radar signal processor from non-clutter filtered source data, but S-Pol ran almost entirely in clutter filter "ON" mode for IHOP; the net effect is that the refractive index information will appear to exist in some areas where there is no apparent ground clutter.

The terrain around S-Pol was flat, with the exception of a depression caused by the Beaver River. This depression ran approximately SW to NE, with the closest center point about 18 km to the NW of S-Pol. The depression was about 8 km broad. This feature is significant in that there was often a lack of refractive index information in that region.

Any blockage of the radar beam tended to be partial blockage, only, and only at the 0.0 ° elevation angle. Typically, blockage affected one or two consecutinve beams, so was considered narrow. Cause of the blockage was likely grain silos located near the radar. There is some variability in time with the occurance of the blockage, possibly due to occassional, small, re-levelling of the antenna pedestal (perhaps by as much as one tenth of a degree), but may more likely be due to changes in the beam path due to atmospheric changes. See blockage.

Clutter images are provided for clear day scans at various elevation angles, both with the clutter filter ON and OFF:

CF Off, 0.0°, (221 kb)

CF On, 0.0°, (214 kb)

CF Off, 0.25° (225 kb)

CF On, 0.25° (218 kb)

CF Off, 0.50° (230 kb)

CF On, 0.50° (115 kb)

CF Off, 0.75° (227 kb)

CF On, 0.75° (221 kb)

CF Off, 1.00° (226 kb)

CF On, 1.00° (218 kb)

--- Bob Rilling --- / NCAR Atmospheric Technology Division
Created: Mon Dec 23 15:12:58 MST 2002
Last modified: