Proceedings with Extended Abstracts (single PDF file) - Radio ...

Figure 2: A 45 MHz reference sky temperature map (solid line) and the calibrated radar temperature(dashed line).The beam direction was also estimated by performing a cross-correlation between the skymap data and radar data (i.e. between the two curves in Fig. 2). This produced a lag of146 s 120 s, which is much greater than any of the previous methods. This deviation maybe due to differences observed on the edges of the galactic equator, where the two curves rise¡at slightly different rates.4 Verification using vertical velocityThe pointing direction of the beam can also be estimated by analysing the long-term mean ofvertical wind velocities measured using the radar. At mid-latitudes, the mean vertical velocityover a period of three or four months should be near zero 1 . This will not be the case, however,if the radar antenna beam is tilted off-vertical, as a component of the horizontal wind, which issignificantly stronger than the vertical wind, will be measured along with the vertical wind.Figure 3a contains the mean horizontal wind from September 1 to December 28, 2002,obtained from the NCEP/NCAR reanalysis dataset and shows a westerly flow which reachesa maximum velocity at just above 10 km. The magnitude of the vertical bias, ∆w, producedby a horizontal wind, v, for an off-vertical beam is given by ∆w vsinθ, where θ is the angleoff vertical in the direction of v. The mean vertical velocity as measured by the radar fromSeptember 1 to December 28, 2002, is shown in Fig. 3b (solid line). Also included is theexpected bias caused by the horizontal wind (dashed line) and its uncertainty (dotted line).There is clearly a significant downward vertical velocity in the radar profile, but the features ofthe vertical velocity profile do not match those of the expected bias, in fact, the peaks are inquite different locations. This suggests that the non-zero mean vertical velocity is unlikely tobe caused by horizontal wind contamination.5 ConclusionThis paper has described experiments that were performed to verify the beam pattern of theCUSTAR antenna array. A technique which involved measuring the variation of sky noise over1 Most long-term means measured using existing VHF radars have, however, shown a typical downward verticalvelocity of a few cm s ¡ 1 [e.g. Nastrom and VanZandt, 1994].393