Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
1999-07-02
2001-04-24
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S042000, C342S046000, C342S059000, C342S118000, C342S120000, C342S450000, C342S463000, C342S465000
Reexamination Certificate
active
06222487
ABSTRACT:
BACKGROUND
The present invention relates generally to a method of and a system for altimetry, especially passive distant altimetry of an object.
The method used to measure the height of an object above, for example, ground or sea level will depend on, among other things, the spatial relationship the measurement means has with the object whose height is to be measured. If the measurement means is located at the object, i.e. is airborne, then the height can be measured passively by an air pressure gage or actively by radar means, for example an altimetry radar. On the other hand, if the measurement means is located on, for example, the ground separated from the object, then the height to the object can be measured actively by a simple altimetry radar if located directly underneath the object or if not, by a more complex altimetry radar, as both the distance and elevation to the object of interest has to be measured.
The present invention concerns the measurement of the height from, for example, the ground to an object by measurement means located, for example, arbitrarily on the ground. Such altimetry measurements, as previously mentioned, usually require expensive and complicated equipment such as altimetry radar equipment. An altimetry radar is an active device that transmits radar pulses, which is not always a desirable feature.
SUMMARY
An object of the invention is to define a method for providing a cost effective manner of measuring the altitude of an object passively.
Another object of the invention is to define a cost effective system for passively measuring the altitude of an object.
The above-mentioned objects are achieved in accordance with the invention by a method and a system for determining an altitude of an object of interest. The object of interest can, for example, be an airplane that transmits electromagnetic radiation in the form of radar signals. A number of sub-units that can detect the radar signals are spread out in an area, preferably in a large geographical area, where the radar signals of the airplane/object is possible to detect. The sub-units are associated with at least one information centre with which they can communicate. The sub-units communicate to the at least one information centre when they are able to detect the radar signals. The at least one information centre determines the altitude of the airplane based on the airplanes line of sight, i.e. its radar horizon, and thus which sub-units can detect the radar signals. By ranking the sub-units as to what altitude the airplane would have if the sub-units just barely can detect the radar signals, the at least one information centre determines the airplanes altitude by determining which sub-unit with the maximum line of sight altitude can detect the radar signals and by determining which sub-unit that cannot detect the radar signals have the lowest line of sight altitude.
The aforementioned objects are also achieved according to the invention by a method of determining an altitude, in relation to a predetermined altitude reference level, of an object that emits electromagnetic radiation. The predetermine altitude reference level can advantageously be the sea level. The method involves at least one information centre being in communication with a plurality of sub-units. The sub-units comprises passive electromagnetic radiation sensors. According to the invention the method comprises a number of steps in each sub-unit. A first step of sensing electromagnetic radiation by means of the passive electromagnetic radiation sensors. A second step of determining if electromagnetic radiation is sensed. And, if it is determined that electromagnetic radiation is sensed, then in a third step communicating to the at least one information centre that electromagnetic radiation has been sensed. According to the invention the method further comprises a number of steps in the at least one information centre. A first step of determining the spatial coordinates of the sub-units. A second step of receiving communication from sub-units that they have sensed electromagnetic radiation. A third step of determining the surface coordinates of the object. And a fourth step which in dependence on which sub-units have communicated that they have sensed electromagnetic radiation, determines in relation of a predetermined level an altitude of the object.
Suitably the method advantageously also in the at least one information centre, further comprises the step of determining the line of sight horizon altitudes, in relation to the determined surface coordinates of the object, of each sub-unit, based on the respective determined spatial coordinates of each sub-unit. And also comprises further the step of ranking the sub-units according to the determined line of sight horizon altitudes, which ranking is consequently used in the step of determining the altitude of the object.
Preferably in the method in the at least one information centre the step of determining an altitude of the object comprises the step of determining a minimum altitude of the object. This is accomplished by determining which sub-unit or sub-units that have sensed electromagnetic radiation are just within the line of sight horizon of the object.
Advantageously the method in the at least one information centre further comprises the step of rejecting sub-units at determined spatial coordinates that are unsuitable for the object in question at the determined surface coordinates in question. The reason for rejection can, for example, be due to the local terrain. The rejected sub-units are not to be taken into any further consideration for the object in question at the determined surface coordinates in question.
Each sub-unit can further also suitably comprise the step of classifying sensed electromagnetic radiation according to one or more of either the frequencies, pulse modulation, pulse repetition frequency, pulse length, or sensed level. This will imply that in the step of communicating to the at least one information centre the classification of the sensed electromagnetic radiation is also communicated, and in that in the at least one information centre that the step of determining an altitude of an object is only done in dependence on sub-units that have communicated that they have sensed electromagnetic radiation with at least substantially the same classification.
Suitably the method in the at least one information centre further comprises the step of determining a maximum altitude of the object by determining which sub-unit or sub-units within a sector that the object emits electromagnetic radiation are beyond the line of sight horizon of the object. It will then be advantageous if the method in the at least one information centre further comprises the step of determining the sector that the object emits electromagnetic radiation in by setting limits of the sector in view of which sub-units have communicated that they have sensed electromagnetic radiation.
In some versions each sub-unit suitably further comprises the step of measuring sensed electromagnetic radiation for the purpose of determining the surface coordinates of the object. Typically the time of arrival (TOA) of the sensed electromagnetic radiation is measured. The step of communicating to the at least one information centre, will then also communicate the result of measuring sensed electromagnetic radiation for the purpose of determining the surface coordinates of the object as measured values. The method in the at least one information centre then suitably also comprises, in the step of determining the surface coordinates of the object, using the communicated measured values from the sub-units in combination with the determined spatial coordinates of the sub-units for determining the surface coordinates of the object.
The aforementioned objects are also achieved by a system of determining an altitude, in relation to a predetermined altitude reference level, of an object that emits electromagnetic radiation. The system comprises at least one information centre and a plurality of sub-units associat
Ahlbom Sten
Andersson Bengt
Arvidsson Ragner
Burns, Daone, Swecker & Mathis, L.L.P.
Gregory Bernarr E.
Telefonaktiebolaget LM Ericsson (Publ)
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