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I I I I I I I I I I I. I I I I I I I I 4.3 PPIOverlays Plastic overlays were used to record the PPI echo patterns (note that super 8-mm time-lapse photos were also taken of the remote PPI scope). Overlays were usually recorded every 10-15 minutes during the seeding operations. These overlays were used to construct time-space histories of the radar echo patterns. The time histories were then used to construct the estimated areas of effect described in Section 4.1. Alongside the echo time his- tories the seeding locations were also plotted, as was the airborne data concerning liquid water content and updraft speed. These composite charts were then used in the physical interpretation of the precipitation processes in the area of seeding events (natural precipitation cycle for sand events). 4.4 Time-Height Echo Cross Sections During the seeding operations RHI patterns were recorded on plastic overlays along with VID readings (measure- ments of radar reflectivity). The overlays provided data on ithe overall ec ho pattern and the VID readings gave a quantitative measure of the "core" reflectivity values. RHI measurements were planned so as to cover the "core" region of the test cloud as it moved across the target area. Using the "core" region readings at subsequent time intervals, through the time history of the echo, we can construct a time- height echo pattern. Figure 12 is an example of the time-height diagrams constructed. Sections (a), (b), and (c) of Figure 12 are samples of the RHI measurement used. There, numerical values in the "core" regions are the VID readings which were converted to radar reflectivity (dbz). Section (d) of Figure 12 is time-height representative of the VID readings, with contours drawn for levels 37 -~ ~.. ---