Abstract: The present invention relates to methods and to arrangements for monitoring an object which emits a rotating or oscillating beam whose angular velocity is unknown. The time points at which the beam passes a predetermined number of measuring positions are determined. An angular velocity start value is generated and a predetermined number of object position determinations (at least two independent determinations) are made on the basis of the determined time points, the measuring positions and the start value. It is determined whether or not the position determinations can be considered to be sufficiently in agreement with one another. When agreement is considered sufficient, the start value is accepted as an approximate value, this value approximating the angular velocity of the beam with an acceptable degree of accuracy. If the position determinations are not found to be sufficiently in agreement, the start value is modified and new position determinations are made.

Abstract: A method and a system for determining an altitude of an object of interest, for example, an airplane that transmits electromagnetic radiation in the form of radar signals. A number of sub-units that can detect the radar signals are spread out in an area, preferably in a large geographical area, where the radar signals of the airplane/object it is possible to detect. The sub-units communicate to the information center when they are able to detect the radar signals. The information center determines the altitude of the airplane based on the airplanes line of sight, i.e., its radar horizon, and thus which sub-units can detect the radar signals.

Abstract: System for determining the position of radar transmitters where the system includes at least one information center with associated cells and means of communication between the information center and the cells with a restricted transfer rate utilising existing infrastructure in the country, such as for example a national telephone network and also mobile telephone networks and their base stations. Each cell includes at least one sensor in order to be able to detect radar signals. Leading edges of pulses in the radar signals are detected and time-marked after which they are sorted according to PRI (Pulse Repetition Interval). The time of arrival for the first pulse in a pulse train is calculated and data reduced by modulo calculation to a value that as a maximum is the propagation time difference for pulses between two cells in a pair of cells/sensors that are used together for calculating the bearing.