Radar guidance system

• US 4,698,635 A
• Filed: 03/02/1986
• Issued: 10/06/1987
• Est. Priority Date: 03/02/1986
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Coate, Godfrey T., Hilton, Richard D.
• Primary Examiner(s): Tubbesing, T. H.
• Assistant Examiner(s): GREGORY, BERNARR E
• Application Number:
  US06/855,206
• Time in Patent Office: 583 Days
• Field of Search: 342/61-65, 342/120, 342/123, 342/127, 342/134, 342/135, 342/145, 342/189, 342/195, 342/159-162, 342/202, 364/444, 364/445, 364/447-449, 364/456, 364/457, 364/423, 364/424, 364/427-429, 364/443
• US Class Current: 342/64
• CPC Class Codes: G01C 21/005 with correlation of navigation data from several sources, e.g. map or contour matching G01C21/30 takes precedence
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 13/89 for mapping or imaging

Abstract

Improved radar guidance system for the navigation apparatus of an aircrafts it flies over substantially flat terrain with random and different features. The system is generally made up of an airborne radar altimeter, a video signal processor and a master processor. The altimeter transmits a series of pulses at predetermined time intervals for impacting a plurality of spaced points along the aircraft ground track. The echo signal of each pulse-impacted point processor divides the amplified signal into corresponding signals. A comparator of the signal processor transforms one of the divided signals into a constant output. A track and hold arrangement of the signal processor correlates the delayed leading edge of the comparator output with the other of the divided signals so as to determine a point of intersection therebetween. The intersection point is a quantitized value of the delay sample of a given echo signal that is indicative of the average weighted reflectivity value of a preselected annulus of one or more random and different features about a pulse-impacted track point. The master processor combines a series of delay samples into a sample data array and then compares the sample array with a series of data arrays of a stored data matrix at a given altitude of the aircraft for the purpose of determining the aircraft flight path. Depending on the requirements of the signal processor, a Doppler filter may be used.

Claims

1. A radar guidance system for the navigation apparatus of an airborne vehicle, said system comprising:

radar altimeter means for transmitting a series of pulses for impacting a series of relatively spaced points along the vehicle ground track of substantially flat terrain having random and different features,

video signal processor means connected to the altimeter means for receiving the echo signal from each pulse-impacted point of the series, the echo signal of a given pulse-impacted point being indicative of the average weighted reflectivity of one or more random and different terrain features surrounding the given point, said video signal processor means being comprised of logarithmic amplifier means, comparator means, delay line means, and track-and-hold means, said comparator means and said track-and-hold means being parallel connected to the output of said logarithmic amplifier means, said delay line means being connected to the output of the comparator means, said track and hold means being connected to the output of the delay line means, said track and hold means for receiving and correlating the outputs of the amplifer means and the delay line means in order to determine a point of intersection therebetween that is indicative of a qunatitized value of a delay sample of an annulus made up of one or more random and different terrain features of average-weighted reflectivity of an echo signal about a given pulse-impacted point along the vehicle ground track during system use,

said video signal processor means being provided with further means, said further means being connected to the output of the track and hold means, for transforming the delay sample of each annulus into a digital signal, and

master processor means connected to the output of the further means for combining a series of digital signals of the video signal processor means into an arrayed output and then comparing the arrayed output with a series of stored digital arrays arranged in matrix fashion in order to ascertain which stored digital array of the series thereof is substantially matched by the arrayed output for the purpose of enabling the determination whether the actual ground track of the vehicle corresponds to the intended ground track thereof.

2. A system as set forth in claim 1 wherein said further means is analog-to-digital converter means.

3. A system as set forth in claim 1 wherein each pulse is of compressed duration and of teardrop configuration.

4. A system as set forth in claim 1 wherein said vehicle is a missile.

5. A system as set forth in claim 1 wherein said further means is analog-to-digital converter means.

6. A system as set forth in claim 1 wherein register means and digital-to-analog converter means are series interconnected between said master processor means and said comparator means, said master processor means together with said register means and said digital-to-analog converter means all cooperating to determine a threshold bias level output to the comparator means for the purpose of removing background noise from an echo signal during system use.

7. A system as set forth in claim 1 wherein said video signal processor means includes Doppler filter means.

8. A radar guidance system for the navigation apparatus of an airborne vehicle, said system comprising:

master processor means,

radar altimeter means connected to an output of the processor means and operating in response to the output of the processor means for transmitting a series of pulses for impacting a series of relatively spaced points along the vehicle ground track of substantially flat terrain and further operating to receive an echo signal from each pulse-impacted point of the series of spaced points,

video signal processor means generally made up of logarithmic amplifier means, comparator means, delay line means and track and hold means, said amplifier means being connected to the output of said altimeter means and receiving from the output of the altimeter means the echo signal of each pulse-impacted point, the output of said amplifier means being parallel connected to the positive input of the comparator means and the track and hold means, the track and hold means and the delay line means being series interconnected to the output of the comparator means such that the track and hold means is connected to the output of the delay line means, the delay line means for delaying the leading edge of the output of the comparator means a predetermined amount of time, the track and hold means for correlating the outputs of the amplifier means and the delay line means so as to form a point of intersection between the outputs, such intersection point being quantization of a delay sample of an annulus of the echo signal about a given pulse-impacted point along the vehicle ground track where each delay sample is representative of the reflectivity of an annulus about a pulse-impacted point; and

where the annulus is made up of one or more random and different terrain features,

said video signal processor means being comprised of digital-to-analog converter means and threshold register means, the digital-to-analog converter means and the register means being series interconnected such that the output of the digital-to-analog converter means is connected to the negative bias input of the comparator means and the input of the register means is connected to another output of the master processor means, said register means including feedback means connected to the master processor means, the other output of said master processor means together with the feedback means of said register means causing selective adjustment of the negative bias of said comparator means in order to determine the threshold noise level of each echo signal so as to substantially eliminate noise from the output of the comparator means when a series of amplified echo signals are received by the positive input of the comparator means as the result of a series of pulses being transmitted from said altimeter means for impacting a series of relatively spaced points along the vehicle ground track during system use, and

converter means connected to the output of the track and hold means for transforming the quantization of the delay sample of each echo signal into a digital signal,

said master processor means being connected to the output of the converter means for combining a series of digital signals into an array and comparing the digital signal array with a plurality of digital signal arrays as arranged in a reference matrix in order to ascertain which array of the plurality of matrixed digital arrays is substantially matched by the digital array of the combined series of signals of the delay samples so as to determine whether the actual ground track of the vehicle corresponds to the intended ground track thereof.

9. A system as set forth in claim 8 wherein each pulse transmitted by said altimeter means is of compressed duration and teardrop configuration.

10. A system as set forth in claim 8 wherein said video signal processor means includes Doppler filter means.

11. A method for determining the actual ground track of an airborne vehicle;

said method comprising the steps of;

transmitting a series of electromagnetic pulses from the vehicle in a downward direction for impacting a plurality of preselected relatively spaced points along the vehicle ground track of relatively flat terrain, where each pulse of the series is transmitted at a predetermined time interval and is directed toward its respective point of the plurality of preselected points along the vehicle ground track, and where the terrain has different reflectivity characteristics by virtue of random and different features therealong,

receiving at the vehicle an echo signal from each pulse-impacted point of the series of pulse-impacted and relatively spaced points along the vehicle ground track while at the same time amplifying each received echo signal,

dividing each amplified echo signal,

comparing one of the divided signals of each amplified echo signal with a predetermined negative bias level for the purpose of substantially eliminating background noise therefrom while at the same time transforming the compared signal into a substantial constant output,

delaying the leading edge of the constant output of the compared signal of each amplified echo signal a predetermined amount so that the delayed edge is within the duration of the envelope of its associated divided signal,

correlating the divided signals of each amplified echo signal such that the delayed leading edge of the compared signal is correlated with its associated divided signal so as to determine for each amplified echo signal an intersection point between its compared signal and its associated divided signal, the intersection point of each amplified echo signal representing the quantitized value of a delay sample thereof where any delay sample of a given amplified echo signal that stems from its associated pulse-impacted point along the ground track is indicative of the average weighted aggregate reflectivity of an annulus of one or more random and different terrain features about the associated pulse-impacted point therealong,

transforming the delay sample of each echo signal into a digital format,

combining all of the digital formats of the samples into a data array, and

analytically correlating the data array of the samples with reference matrix data having a series of data arrays for the purpose of substantially matching the data array of the sample with one data array of the series of data arrays of the reference matrix data so as to enable the determination of whether the actual ground track of the vehicle corresponds to the intended ground track thereof.

12. A method as set forth in claim 11 wherein the step of comparing is effected by comparator means.

13. A method as set forth in claim 11 wherein the combined steps of amplifying, dividing, comparing, delaying, correlating and transforming is effected by video signal processor means.

14. A method as set forth in claim 11 wherein the steps of combining and analytically correlating is effected by master processor means.

15. A method as set forth in claim 11 wherein the step of delaying is effected by delay line means.

16. A method as set forth in claim 11 wherein the step of correlating is effected by track and hold means.

17. A method as set forth in claim 11 wherein the step of transforming is effected by analog-to-digital means.

18. A method as set forth in claim 11 wherein the step of amplifying is effected by logarithmic amplifier means.

19. A method as set forth in claim 11 wherein the steps of transmitting and receiving is effected by radar altimeter means.