QUALITY CONTROL OF DATA
Signal Continuity Modelling:
Before embarking on the calculation of the spectral moments, the average noise in the spectral frame for each range bin is estimated by using the Hildebrand/Sekhov(3) algorithm as is the standard practice in profiler work. The atmospheric signal in each spectral frame (corresponding to radial velocities) is then identified by using a multiple peak detection scheme in conjunction with a suitable check on the continuity of the signal between consecutive range bins. The continuity scheme, at present uses a spectral window of width equal to 1/5th of the Nyquist frequency (the unambiguous velocity) centered around a well defined peak at a lower range bin where the signal to noise ratio is sufficiently large.The scheme thus picks the maxima in the spectrum in successive range bins consistent with this model restriction.
Consensus Averaging:
Each of the three spectral frames corresponding to the three beams are normally obtained in 4 to 6 minutes depending on the number of coherent integrations, incoherent integration and the number of FFT points used in the observations. Thus in a span of about one hour of observation period a total of at least ten sets of Doppler profilers are available. Moments of each of these sets are estimated to calculate the power, radial velocities and the spectral width for all the observed range/height bins. The radial velocity values for each beam obtained, for a given range bin are utilized to calculate the u,v for every six minute set of observation. These u and v values are then passed through a process of consensus averaging which helps to eliminate to a large extent the effects of transient interfering signals, outliers and random spiky, noise. The consensus averaged radial velocities are then used to calculate the zonal, meridional and vertical wind velocities representative of the mean wind in the hour of the observation. The equations are
u = vre cos θ + w sin θ,v = vrn cos θ + w sin θ, w = vz
Where vre, vrn and vz are the radial velocities, along east, north and zenith respectively. u, v, w are zonal, meridional and vertical velocities and θ is the elevation angle of the tilted beams. The mean horizontal wind speed and direction are calculated as
ws
= √ u2 + v2, wd
= tan-1(u/v)
(u,v are
consensusly averaged values)
Availability of Data
Data Validation