JP3493074B2 - Ground surface identification device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground surface identification device for determining the properties of the ground surface on an aircraft, for example.

[0002]

2. Description of the Related Art When inferring what kind of surface the ground surface immediately below an aircraft is at night or from above clouds,
Conventionally, the intensity of the reflected wave is measured by using a radio altimeter mounted on an aircraft or the like, and the property of the ground surface is judged by the intensity. This method uses, for example, the property that reflected waves are strong on the surface of the sea or lakes and weak on the forest areas.

However, the intensity of the reflected wave from the ground surface varies greatly even on the same ground surface under various conditions. In addition, ground surfaces having different properties often have almost the same reflection coefficient. Therefore, it is difficult to accurately identify the ground surface only from the strength of the reflected wave, and it is necessary to improve the identification degree of the ground surface identification by using some other information (parameter).

[0004]

As described above, in the conventional ground surface identification device, the radio altimeter is used for identification by using only the reflection intensity of the radio wave, but the ground surface is accurately identified only by the intensity of the reflected wave. There was a problem that it was difficult to do.

The present invention has been made in order to solve such a problem, and provides a ground surface identification device for improving the identification degree of the ground surface identification by utilizing other information (parameter) in addition to the reflection intensity of radio waves. It is intended to be provided.

[0006]

A ground surface identification device according to the present invention is a fructu-of the reflection intensity of a radio wave from the ground surface.
ation (fluctuation) dispersion
It is characterized in that the type of the ground surface is identified by measuring the fact that it is different depending on the nature of the ground surface.

[0007]

The operation principle of the present invention will be described below.
FIG. 1 is a diagram showing a variation of the received signal strength of the reflected wave with respect to time, and the value of the received signal strength I sampled at the sampling period of Δt is shown by a black dot. I between Δt
The absolute value Z _j = | I _{j + 1} −I _j |
N pieces of measurement data are obtained in the measurement period of t. This N Z
_{If the number of j} whose size is Z or more is n, then n / N = P (≧ Z) is the probability of occurrence that the size of Z _j is Z or more.

When Z = 0, P (≧ Z) = 1 (100%)
When Z is sufficiently large, P (≧ Z) = 0. Calculate each P (≧ Z) for a given Z stage. It is known that there is a relationship of P (≧ Z) ∝Z ^−D (1) between Z and P (≧ Z), and the value of D is determined by the properties of the ground surface. In the present invention, D is calculated to determine the nature of the ground surface. Here, if the logarithm of both sides of the above equation (1) is taken, log {P (≧ Z)} ∝−DlogZ ...
It becomes (2). FIG. 2 is a diagram showing the relationship of the equation (2), and the slope of the straight line shows the value of D.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing an embodiment of the present invention.
Is a radio altimeter, 2 is a radio altimeter altitude output, 3 is a radio altimeter received intensity output, 4 is an analog-digital converter (A / D), 5 is a first memory, 6 is a second memory, 7
Is an arithmetic circuit, 8 is a discrimination circuit, and 9 is a determination result output.

Next, the operation of the apparatus shown in FIG. 1 will be described. The A / D 4 converts the reception intensity output 3 into a digital signal at a sampling cycle of Δt. Let that value be I ₁ , I
₂ , I ₃ , ..., I _j , I _{j + 1} , ... I _N (see FIG. 1). In the arithmetic circuit 7, Z _j = | I _{j + 1} −I _j
| Is calculated and Z _j is temporarily stored in the memory 5. After the predetermined number N of data is stored, the number n of data of Z or more of N data is calculated, and n / N = P
Let (≧ Z) be the existence probability of Z or more in the data. P (≧ Z) is calculated for each type of Z, and the relationship between Z and P (≧ Z) is displayed on the logarithmic-logarithmic coordinate axis as shown in FIG. The value of D for the ground surface is determined from the slope of the straight line in FIG.

The memory 6 stores the value of D measured for various known ground surfaces, and the value of D calculated by the arithmetic circuit 7 is compared with the value of D stored in the memory 6. hand,
The ground surface corresponding to the value of D measured this time is identified and output as the determination result output 9. Although the radio altimeter is used in the embodiment shown in FIG. 3, a dedicated transceiver and antenna for identifying the type of ground surface may be provided. It goes without saying that a device for identifying the ground surface can be used in combination with a conventional device that utilizes the reflection coefficient of the ground surface.

[0012]

As described above, according to the present invention, the displacing of the flux-ion of the radio wave reflection on the ground surface.
Since the type of ground surface is identified from the fractal dimension analysis by using the ersion, it is possible to reliably determine the type of ground surface without considering the change in reflected wave intensity due to the difference in output of the transmitter or the difference in altitude of the aircraft. Can be determined.
Further, there is an effect that the device of the present invention and the conventional device utilizing the reflection coefficient of the ground surface can be used in combination to provide a device having an improved degree of distinction.

[Brief description of drawings]

FIG. 1 Fluctuat of the intensity of reflected waves from the ground surface
It is a figure which shows ion.

2 is a display of the fluctuation shown in FIG.
It is a graph which displayed ersion on a logarithmic-logarithmic coordinate axis.

FIG. 3 is a block diagram showing an embodiment of the present invention.

[Explanation of symbols] 1 Radio altimeter 2 Altitude output 3 Received strength output 4 analog-digital converter 5 First memory 6 Second memory 7 arithmetic circuit 8 Discrimination circuit 9 Judgment result output

Claims (3)

(57) [Claims] 1. A transmitter that emits a radio wave substantially perpendicular to the ground surface (including the water surface), a receiver that receives a reflected wave in which the radio wave emitted from this transmitter is reflected from the ground surface, and this receiver. Output for each predetermined sampling cycle, the absolute value of the difference from the previous measured value is calculated for one sampling cycle, and the first memory that stores the calculated absolute value is the first memory for the same ground surface. When the total number of the absolute values stored in the memory of reaches a predetermined number N,
When there are n of the above N pieces whose absolute value is Z or more, the probability P (≧ Z) is calculated by n / N, and the probability P (≧ Z
Z) and the probability calculation means for calculating the relationship between Z and P (≧ Z) ∝Z ^−D , and the relationship between Z calculated by the above probability calculation means and the probability P (≧ Z) Fractal dimension determining means for determining a value, the value of D determined by the fractal dimension determining means is collated with the contents of a second memory for storing the value of D previously determined for a known ground surface, A ground surface identification device comprising: collation means for identifying a surface. 2. The ground surface identification according to claim 1, further comprising an identification means for identifying the ground surface by utilizing the reflection coefficient of the ground surface using the intensity of the reflected wave received by the receiver. apparatus. 3. The ground surface identification device according to claim 1, wherein the transmitter and the receiver are the transmitter and the receiver of an altimeter mounted on an aircraft or the like.