基于地形匹配的直升机低空飞行前视告警方法

为解决直升机低空飞行时的防撞告警问题，提出一种利用地形匹配来修正直升机与地形之间相对位置误差的前视告警方法。首先，利用直升机飞行动力学模型预测逃逸轨迹，在此基础上生成告警边界。然后，将机载地形数据库与雷达探测的高程数据从空域变换到频域，通过基于互功率谱算法的地形匹配方法计算得到直升机与地形的相对位置误差，以获取二者之间的准确相对位置。由于地形匹配效果受地形起伏程度影响，采用地形熵选择匹配区域方法在进行地形匹配前筛除地形起伏较小的匹配区域，以此提高匹配准确度。最后，基于UH-60直升机飞行动力学模型设置了1 000组对照算例进行告警方法仿真测试。仿真结果表明:采用所提告警方法的测试组相比于常规告警方法，虚警率降低约16%，告警成功率提高近30%。说明所提的前视告警方法能够有效实现直升机低空飞行防撞告警。 

Helicopter forward looking alert method for low-altitude flight based on terrain matching

In order to solve the problem of terrain awareness when helicopters fly at low altitudes, a forward looking terrain avoidance method is presented using terrain matching, which can correct the relative position error between helicopter and terrain. First, the recovery trajectory of a helicopter is predicted by the helicopter flight dynamics model, based on which the alert envelope is generated. The elevation data of terrain database and radar detection are transformed from airspace to frequency domain. Then, by using the terrain matching method, which is based on cross power spectrum algorithm, the relative position error between the helicopter and the terrain is calculated to obtain the accurate relative position. As the effect of terrain matching can be influenced by topographic relief amplitude, the terrain entropy selection method is adopted to remove the matching area with less topographic relief before terrain matching. Then the matching accuracy is improved. Finally, based on the flight dynamics model of the UH-60 helicopter, 1 000 sets of control case simulation are conducted to verify the alert method. According to the results, the proposed alarm method can significantly reduce the nuisance alert rate by about 16% and increase the successful alert rate greatly by nearly 30%, compared with conventional alert methods. It is shown that the forward looking alert method proposed in this paper can effectively achieve the helicopter collision avoidance alert at low altitude.