Pergamon Adv Space Rcs. Vol. 18, No. 6, pp. (6)217-(6)220,1996 Copyright 0 1995 COSPAR zyxwvutsrqp 0273-l 177(9S)OO927-2 Printed in Great Britain. AU rights reserved 0273-I 177/96 $9.50 + 0.00 zyxwvutsrqpon KRIGING METHOD FOR INSTANTANEOUS MAPPING AT LOW AND EQUATORIAL LATITUDES I. StanisIawska,* G. Juchnikowski* and Lj. R. Gander** * zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Space Research Center, 00-716 W arsaw, ul. Bartyka 18a, Poland ** Geomugnetic~ fnstiture, II306 Grocka, Belgrade. Yggostavia ABSTRACT The Kriging mapping method was applied to measured data from a chain of equatorial and low latitude ionospheric stations. So obtained hourly foF2 maps allow some characteristic features of the F2-layer to be extracted. INTRODUCTION When applied to region-dependent variables the Kriging method /1,2/ has minimum variances. The method has been found to be a useful tool in ionospheric mapping, for example when interpolating foF2 at midlatitudes i3/. In this paper we analyze the spatial variation of foF2 in October in the area 4O”Nto 45’S, 115” to 175” E (See Table 1 for station list). Applying appropriate mathematical transformation methods it is possible to estimate the foF2 values at any area. TABLE 1 The list of the stations STATION AKITA YAMAGAWA CHUNG-LI DARWIN NORFOLK CANBERRA CHRISTCHURCH - LAT 39.7 31.2 24.9 -12.5 -29.0 -35.3 -43.6 LONG STATION LAT 140.1 KOKUBUNJI 35.7 130.6 OKINAWA 26.3 121.2 VANIMO -2.7 131.0 BRISBANE -27.5 168.0 MUNDARING -32.0 149.0 HOBART -42.9 172.8 I LONG 139.5 127.8 141.3 152.9 116.4 147.3 KRIGING METHOD APPLIED TO INTERPOLATION OF foF2 Semivariograms allow to summarize the general form of the variation, its magnitude and spatial scale. The precision of the estimated semi-variances depends on the sample size and on the distribution of the data If the semivariogram is anisotropic a coordinate-dependent scaling factor to the latitudinal distances, SF, must be introduced /4/. A factor of 42 was found for the PRIME area (mid-latitudes). A second scaling factor (also 42) stems from the different correlation distance so that at midlatitudes the total factor needed is around 2. We define an ‘ionospheric distance’ by d = \/ &on(A)-Loti(B + (SF*&-&(A)-Lat(B)))* (1) SF is the scale factor. Data from about 13 ionospheric stations can not be used for constructing the (61217