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

Where the notations carry same meaning as in Farley et al. (1981). The magnitude orcoherence⏐S 12 (ω)⏐in (1) represents the measure of the localization of the targets in theechoing region, while the phase ∆φ 12 (ω) of S 12 (ω) is the averaged phase difference of theradar echoes received by the separated antenna modulus 1 and 2. In the similar waycoherence and phase can be obtained from other module pairs 2 and 3 & 3 and 1 also.The complex normalized cross spectrum is computed in accordance with (1), isensemble averaged over 50 times (around 20 sec) to obtain coherence and phase. For thereliability of the estimate, the data were selected if the coherence is greater than 0.8. In orderto apply radar interferometry, let z represents local zenith direction with the origin of thereference of coordinate system at the phase center of array 2. With this definition, y is toward17 degree north by west and x is the axis normal to y and z. From the cross spectra computedfrom three antenna arrays, we can estimate the azimuth and elevation of the backscatter ineach range gate. With the help of observed phase differences ∆φ 12 (ω) and ∆φ 23 (ω), theelevation angle θ(ω) and azimuth angle φ(ω) of target can be derived as following (Wang andChu, 2001):−1d12∆φ23( ω)+ 2πm+ ∆Ψ23φ(ω)= tan [tan β + ()] − β , (2)d23cosβ ∆φ12( ω)+ 2πn+ ∆Ψ12− 1 ∆φ23( ω)+ 2πm+ ∆Ψ23θ ( ω)= cos [] , (3)kd23sinφwhere k=2π/λ is the wave number, λ is the radar wave length), m and n are, respectively, theinterferometry lobe numbers in vertical and azimuth directions resulting from grating lobeeffect of interferometer, and ∆ψ 12 (ω) and ∆ψ 23 (ω) represent the system phase biases forantenna pairs 2-3 and 2-1. β is the angle difference between antenna pairs from right angletriangle. From simple geometry, we have x = r cosθ sinφ, y = r cosθ cosφ, z = r sinθ, wherer indicate range, the elevation angle θ and azimuth angle φ that can be obtained fromformulas (2) and (3).Figure 1 shows the RTI plot obtained from backscattered signals detected with array 1.The results presented here are selected from 1820 to 1833 LT. Multiplicity of QP echoes, withup to four echoes being visible with in the scattering volume at a time. The simultaneouspresence of multiple of QP echoes up to 8 to 9 striations are also reported else where( Tsunoda et al.,1999; Hysell and Burcham, 2000).Figure 1. RTI plot at 1820-1833 LT on July, 2000. The numbers indicate QP echoes occur in the 13 minutes.From the figure 1 it is clear that echoes varying with time for different striations, withnegative slope representing the propagation is towards the radar. Interferometry data containsinformation about the spatial structure of the irregularities underlying the QP echoes. Thishelps to derive the 3-dimensional information of the backscatter in each range gate and thetime history about the spatial variation of the QP echoes.In Figure 2 we presented the eighth striation such that the conclusive results are therepresentative case of the observations of Chung-Li VHF radar. The first two panels are range95