height to rise was noted in several sequential groups. Consequently, a plot was made with the minimm height of each group represented by a cross (Fig. 3.19). A possible explanation for the increasing heights was immediately seen. The hypothesis is that the rising sequences of points resulted from regions of relatively intense ionization mov~ (The anten- | ' yas, though designed for vertical radiation and reception, are not. restricted 40 thie direction, and oblique returns are often encount-. ered when horizontal inhomogeneities are present in the ionosphere. — The "height" at which such echoes appear is greater by virtue of the eae path length and is, hence, called “apparent height" in Fig. . 3e19- KM aes ' 57,.+73M 60.+84M 800 600 400 Sh 200 TPES 59.+81M ere KM fs Ol +90M 2) £4. £ eT tee coe te + brs geet ——— SESE t ¢ e . t+ ts TEE aa =, Litt Dol? $6.479M 62.+95M SPER PS eee 800 600 400 200 ~ o 2 3 4 6 8 10 i@ CE 2 3 4 6 8 10 14 Fig. 3.16 = Ionospheric Records at Rongerik Following Shot 4 by 73 to 95 min, Showing Clearly Oblique Echoes and Trend Toward Nornaloy 45 SECRET mC ~ ing horizontally in some direction away from the operating site as part of a radial motion originating above the explosion,