Debris population estimation is an important task in statistical characterization of space debris environment, and is of great significance for validation of space debris environment models, assessment of impact risk to spacecrafts and prediction of the long-term growth potential of the number of debris. A method of estimating the confidence interval for debris population using radar in beam-park mode with the beam pointed due east and due south with any elevation is given. This method is also applied to the vertical staring radar, which is a special case when the beam elevation is 90 º. In the beam-park mode, the antenna beam is parked at fixed azimuth and elevation angles for a long time, usually longer than 24 hours. Debris objects crossing the beam randomly would be detected, and measurements for detected target would be obtained. No attempt is made to track debris objects passing through the observation volume. In this operating mode, the random event that a debris object in a given altitude bin, which may cross the beam, i.e. has large enough radar cross section and inclination relative to the latitude of the radar site, is actually observed is modeled as a (0-1) distribution. Using debris altitude and inclination data collected, the average probability of crossing the beam for all debris objects in the given altitude bin is obtained. The confidence interval for space debris population is estimated by the Central Limitation Theorem. Simulation results show the effectiveness of the method.
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