3D position determination of small coherent meteor targets with EISCAT UHF

Kero, J.1, Szasz, C.1, Wannberg, G.2, Pellinen-Wannberg, A.1 and Westman, A.2

1 Swedish Institute of Space Physics, Kiruna, Sweden
2 EISCAT Scientific Association, Kiruna, Sweden

The target cross section of the ionized region created by a meteoroid passing through the common volume of the EISCAT UHF receivers can be determined and investigated as a function of scatter angle from the received power at each site. However, since the observed target sizes have proven to be very small, the received power strongly depends on which part of the common volume the target passes through. The true position of the target can be estimated geometrically. We consider each remote receiver as located in one foci of an ellipsoidal surface with the Tromsø transmitter in the other. The Tromsø receiver is located at the focus of a sphere. The range measured in Tromsø gives the radius of the spherical surface and the ranges measured at the remote receivers can in combination with the Tromsø range reveal the geometries of the ellipsoids. The target’s location is found by calculating the point where the three geometrical shapes intersect. The accuracy of the position determination is limited by the range resolution of the measurements, which is about 100 m for each receiver and a single radar pulse but considerably smaller when taking into account that most of our events comprise several measurement points that may be combined with least-squares. We have been able to correct the measured ranges for systematic biases by statistically comparing the profiles of the received power of a large number of events with the theoretical beam shapes. The biases are probably caused by group delay in the transmission lines and remote station clock offset. The biases are of the order of one to a few microseconds and may be insignificant for incoherent measurements but of vital importance for the position determination of small coherent targets.