Tomographic images have been used to simulate RO measurements. This example is a north-south slice at a longitude of 350°E, measured on 28 March, 1998 at 0742UT (top panel). At this time the planetary index k_p was 1.7, the sun spot number was 56 and the value of the solar flux was 103.6 x 10^-22 Wm^-2Hz^-1. Because the image only covers a limited geographic region it has not been possible to simulate the whole of the RO geometry. Instead, 55 rays have been traced from a transmitter moving vertically at 46°N from 90 km to 414 km to a receiver at a fixed altitude of 450 km moving from a latitude of 64°N to 54°N. This allows a simulation of typical ray paths on one side of an occultation tangent point.

A best linear unbiased estimator (BLUE) has been run in order to modify the output of the Parameterised Ionospheric Model (PIM) (middle panel) for this time and these geophysical conditions. The electron density grid from the BLUE is shown in the bottom panel.

Click on images to enlarge

Tomographic image

PIM electron density grid

Output from Best Linear Unbiased Estimator

RO measurements have been simulated using 71 tomographic images. In each case, the errors in the total electron content along each ray from the transmitter to the receiver (slant TEC) have been calculated for both the PIM electron density grid and for the output of the BLUE. The results show the increase in accuracy provided by the BLUE.

Similarly, the electron density errors have been calculated for a vertical column situated at a latitude of 50°N. Again, the reduction in the errors exhibited by the BLUE output can be seen.

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