Extraction Of Information From Complicated Clutters By HF Surface Wave Radar

High frequency ground wave radar is a kind of over-the-horizon radar. Due to its vertical-polar electromagnetic waves reaching out of the horizon along the surface of the sea, it is applied to detect flying targets hedgehopping or ship targets. However, there are lots of clutters in the backscatter signals, which affect the radar detection ability deeply, especially the ionospheric clutter. So it is important to detect and extract the ionospheric clutter. Referring to the ratio between ionospheric clutter’s power and noise’s power, the Radar Frequency-Selected System can reduce the power of the ionospheric clutter, which will weaken the impact on detecting targets. Besides, HF radio waves’ interaction with the rough sea surface leads to sea echo. So the sea echo brings some information of the sea surface. Therefore, the high frequency ground wave radar has much value in the remote sensing of sea state. There are some advantages using HF ground radar to extract wave parameters. For example, it covers wider region and works for a whole day. It also don’t suffer the effect with the bad weather conditions.The content this paper present is all about the detection and extraction of ionospheric clutter and the reversion of wave parameters. The main contents are as follows:As for the detection and extraction of ionospheric clutter, this paper firstly introduces the main different clutters in the radar echo. This part mainly describes the structure of the ionosphere and the propagation of HF radio waves in the ionosphere, according to which we can obtain some properties of ionospheric clutters. They are the theoretical basis of the detection and extraction of ionospheric clutters. Then, by using the two-dimensional Otsu image segmentation algorithm and the area-feature recognition algorithm, we detect and abstract ionospheric clutters on the basis of their properties on amplitude and expanding patterns in RDP. After these work, this paper makes a further calculation of the ratio of ionospheric clutters and the noise, which will be a parameter to be input into the Radar Frequency-Selected System.As for the reversion of sea surface information, this paper introduces some wave theories associated with this paper at the beginning. They include the formation mechanism of waves, their classification and expressions of them. People often use statistic method and spectrum method to express waves respectively. Then the paper develops scatter models of the first-order and the second-order sea echo. The models connect sea echo’s power to wave spectrum directly, which are the theoretical foundation of the reversion of wave parameters. Finally, based on the models, the RMS wave height can be obtained from the power density of second-order sea echo scaled by the first-order sea echo. An index model on wind speed and significant wave height is proposed based on their directly positive correlation. Using the model, we can calculate the wind speed. As for wind direction, because a relationship between wind direction and the ratio of positive and negative Bragg resonance power is got from the first-order RCS, it can be got from the Bragg resonance power. The multiple beam least square method can eliminate wind direction blur.