JPH0149909B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention extracts an IF signal and an altitude signal from an FM-CW radio altimeter in an aircraft, etc.
The present invention relates to a ground identification device that identifies ground conditions from these signals.

Aircraft and precision guided missiles generally carry radio altimeters when highly accurate altitude information at low altitudes is required. By the way, even when using a radio altimeter, at extremely low altitudes below 1000ft, the altimeter's readings are influenced by ground factors. This is because the radio altimeter indicates the distance to the reflective surface.
This is because it is affected by changes in the topography of the ground, buildings, forests, etc. From this, for example, the sea, river,
If it is possible to obtain ground information that indicates the distinction between fields, forests, urban areas, etc., it can be effectively used as correction data for the altimeter, allowing for optimal flight according to the conditions at the time.

Additionally, in recent years, the demand for ultra-low-altitude flight has increased. This is because, with advances in radar technology and the development of radar networks, the only way to avoid being detected by radar is to fly at extremely low altitudes or to weave through mountainous areas. For this reason, ground information is essential to maintaining complete, high-speed, and extremely low-altitude flight.

By the way, it is quite difficult to incorporate sufficient specialized equipment into aircraft and precision guided missiles to obtain such ground information. An example of something that uses specialized equipment is the US cruise missile. The missile uses a C-band radar altimeter (Honeywell Inc.) to fly at very low altitudes and accurately reach its target location.
It has a navigation device that calculates the flight route by comparing the altitude difference pattern of the surrounding area with the built-in altitude difference pattern already determined from the flight course map using the APN-194 altimeter). ing. Therefore, the aircraft flies along a predetermined course without the need for radar to detect targets.
Although it is possible to incorporate it as a dedicated device, it cannot be applied to all aircraft and precision-guided missiles, and in general, it is normal to use radar and altimeter separately, taking advantage of their respective characteristics. be. In other words, cruise missile systems are limited to special uses.

The purpose of the present invention is to replace the conventionally commonly used FM-CW radio altimeter without incorporating a new special radar altimeter such as that used in cruise missiles.
An object of the present invention is to provide a ground identification device that can relatively easily obtain ground information by using an IF signal and an altitude signal.

Embodiments of the ground identification device according to the present invention will be described below with reference to the drawings.

In the figure, FM-CW radio altimeter (e.g.
Of the output signals of the French TRT ERT-011 model), input the IF signal to terminal 1 and the altitude signal to terminal 2. The IF signal at terminal 1 is generally called the beat frequency, and is caused by the time difference between the radio altimeter's transmitted and received waves, and this component is a composite of frequencies depending on the distance of the object. . In this case, when the distance is short, the time is short and the frequency is low; conversely, when the distance is long, the time is taken and the frequency is high. Furthermore, radio altimeter antennas are generally used with blunt directivity so that changes in the aircraft (pitch, roll, etc.) have little effect on the antenna. In other words, a wide range of information is included.

The IF signal at terminal 1 is branched and applied to frequency analysis circuit 3 and detection circuit 4. In frequency analysis circuit 3, in order to view the IF signal at the frequency level,
The frequency spectrum of the IF signal is obtained by performing fast Fourier transform or filtering processing-A/D conversion. The selection of this process is determined by the required information content. Fast Fourier transform requires internal calculation processing. Therefore, there is a limit to high-speed processing. On the other hand, filtering process-A/
Since the structure of the D transform is simple, it requires almost no processing time and can be designed compactly, but its accuracy is worse than that of the fast Fourier transform. The processing results performed here indicate the state of the ground, that is, the shape and distribution of the reflective surface on the ground. for example,
Places with relatively flat reflective surfaces, such as oceans, lakes, and plains,
The frequency spectrum does not disperse, but in places where reflective surfaces are irregularly scattered, such as in urban areas and mountains, the spectrum tends to become dispersive. The data processed by the frequency analysis circuit 3 is sent to the storage circuit 8.

The IF signal branched to the other detection circuit 4 is
The A/D conversion circuit 5 detects the signal and converts it into a DC voltage.
is output to. This is done to analyze the IF signal in terms of power level. This output is converted by the A/D conversion circuit 5 and then input to the correction circuit 7. Also, the altitude signal input from terminal 2 is also
It is converted in the D conversion circuit 6 and enters the correction circuit 7. The radio altimeter internally adjusts the output level according to the altitude, but because it is not perfectly adjusted, the IF signal changes somewhat depending on the altitude. Therefore, the correction circuit 7 performs processing to correct the deviation of the IF signal caused by the change in altitude.
Thereby, the power level of the IF signal will be indicative of the reflection coefficient of the object on the ground. Correction circuit 7
The processed signal is sent to the storage circuit 8. The memory circuit 8 is composed of three types: a plurality of register memories 8A, a main memory 8B, and a data memory 8C. Input data is written into the register memory 8A one after another, and old data is erased one after another, so that the latest data always exists in the register memory 8A. The values of the plurality of register memories 8A are then averaged and sequentially input to the main memory 8B. This is to minimize errors due to data variations.
The patterned data in the main memory 8B in the storage circuit 8 is transferred to the identification circuit 9. The identification circuit 9 derives reference data of objects to be identified, such as oceans, rivers, lakes, mountains, fields, cities, etc. stored in the data memory 8C of the storage circuit 8, and compares and discriminates them with the data in the main memory 8B. . This takes advantage of the fact that the spectral distribution has a certain pattern depending on the ground conditions, and that the reflection coefficient varies depending on the material and shape of the reflecting surface. The amount of error is investigated, comparison data with the minimum pattern deviation is selected, and the data is output as the final identification result based on the fact that the reflection coefficient also satisfies the condition. The data on the amount of error obtained here is
This is important because it shows how close it is to the standard data for comparison. The smaller this value is, the closer it is to the reference data. In addition, a change in the amount of error over time indicates that a decrease indicates that the result is closer to the identification result, and an increase can be seen as a sign that the result of the identification is changing to a different state, that is, a change to another state. The identification result thus obtained is output to the output terminal 10 together with the error amount data.

As explained above, by adding this device to a commonly used FM-CW radio altimeter, it is possible to provide ground information. Moreover, there is no need to incorporate a new special radar altimeter like that used in cruise missiles, and the feature is that the conventional altimeter is utilized to the maximum extent possible.

The range of information that can be obtained from this device is not only the ground identification ability, but also the combined effects of the radio altimeter, such as improving the accuracy of the altimeter, detecting ground protrusions, and checking with topographic maps.

Below are some specific examples. First, in the case of helicopters, it is possible to accurately detect altitude and obstacles at night, in dense fog, and in rainy weather, when visual flight is difficult, as well as to read terrain changes and determine flight paths, and for rescue operations at sea. It will be able to judge sea conditions and control altitude, and will also be able to detect obstacles during flight in mountainous areas, read terrain changes, and obtain takeoff and landing information for locations other than airfields.

It is also effective for controlling the altitude and position of general aircraft during takeoff and landing at airports. Among the data needed when an autopilot takes off and lands, it can provide data such as runway detection, road surface condition judgment, and accurate altitude output, thereby improving safety during takeoff and landing. Even in mountainous areas or urban areas where the object reflecting the altitude output is unclear, accurate altitude correction is possible by using the output of this device in combination. chimneys, towers,
If the altitude output does not show any change even with respect to a protrusion on the ground such as a building, a warning can be output by detecting the short-distance component of the spectrum distribution.

As another use, by inputting data on objects that can be identified by this device in advance, the flight path can be determined and corrected by comparing the identification results. For example, since it is possible not only to simply identify the ocean as a sea, but also to obtain data on wave conditions, even on the ocean where there is no altitude change, it can be used for guided missiles equipped with radar for offshore flights. Precision-guided missiles flying above the water surface are required to fly close to the water surface in order to avoid being detected by radar, but by using this device, it is possible to detect the water surface and obtain information on the roughness of the water surface. . In other words, when the water surface is choppy, the radar is also affected by the waves, so there is no need to fly close to the water surface, and when the water surface is calm, the radar will try to fly lower to improve its acquisition level. There is a need. In this way, arbitrary judgments can be made depending on the conditions at the time.

As described above, the present invention analyzes the output signal of the FM-CW radio altimeter, which has been commonly used in the past, to provide ground identification information required during very low-altitude flight (below 1000 ft). , enabling safe and versatile flight.

[Brief explanation of drawings]

The figure is a block diagram showing an embodiment of a ground identification device according to the present invention. 1, 2...Input terminal, 3...Frequency analysis circuit, 4...
Detection circuit, 5, 6... A/D conversion circuit, 7... Correction circuit, 8... Memory circuit, 9... Identification circuit, 10... Output terminal.

Claims (1)

[Claims] 1. An IF signal and an altitude signal are extracted from an FM-CW radio altimeter, the IF signals are applied to a frequency analysis circuit and a detection circuit, respectively, and the IF signal is viewed at a frequency level by the frequency analysis circuit. In addition to determining the frequency spectrum distribution, a detected signal obtained by viewing the IF signal in terms of power level was determined by the detection circuit and added to a correction circuit, and the altitude signal was further added to the correction circuit to correct deviations in the IF signal due to altitude. A signal indicating the reflection coefficient of an object on the ground is obtained, the signal indicating the frequency spectrum distribution and the reflection coefficient is added to a storage circuit, the frequency spectrum distribution is patterned and stored in the storage circuit, and the storage circuit is previously identified. A standard pattern of the spectral distribution of the object is stored, and the frequency spectral distribution patterned and stored is compared with the standard pattern using an identification circuit, and the one with the minimum comparison error is selected. A ground identification device that identifies an object that satisfies the condition of the reflection coefficient. 2. The ground identification device according to claim 1, wherein a change in ground conditions is identified from a change in the comparison error over time.