Communications: directive radio wave systems and devices (e.g. – Radar for meteorological use
Reexamination Certificate
1999-07-06
2001-05-22
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar for meteorological use
C342S074000, C342S075000
Reexamination Certificate
active
06236351
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to airborne radars and more particularly to controllers for airborne radars. Radar is often sequenced through various scans, with each scan or set of scans dedicated to a particular one of the tasks performed by the radar. The scan sequence and the time allotted for each scan type limits the type and number of data gathering tasks the radar can support. In present airborne radars, the radar alternates between windshear and weather detection scans at low altitude. In one commercially available radar, one scan gathers weather data and three scans detect windshear. Even at these current rates, the amount of weather data gathering capability is marginal. Additional data gathering tasks cannot, therefore be added to the radar scan schedule of existing radars without compromising weather radar performance.
Present day airborne radar systems also require that the pilot manually control the tilt angle of the radar antenna in order to scan for the desired data usually weather. An example of manually setting tilt is described in “RDR-4B Forward Looking Windshear/Weather Avoidance Radar System Pilot's Manual with Radar Operating Guidelines,” by AlliedSignal Aerospace Commercial Avionics Systems, ACS-5082, Rev 1, July '96, the entire contents of which are incorporated herein by reference.
The pilot manual describes the procedure for selecting the antenna tilt to scan for weather. This procedure requires the pilot to adjust manually the tilt of the antenna for each range scale until “a sprinkle of ground return” is visible at the far edge of the display. At the larger range scales (>80 nm) the ground returns may not be visible making an optimal antenna tilt decision difficult due to the lack of terrain returns. At these ranges, it is difficult for the pilot to make a distinction between weather returns and strong ground clutter returns without continually adjusting the antenna tilt to see if the returns disappear as the antenna beam is adjusted upward. As the altitude of the aircraft changes with respect to target height, the antenna tilt angle must be adjusted to maintain the proper positioning of the radar beam with respect to the target. This requirement increases pilot workload, and presents possible difficulties in maximizing the effectiveness and utility of the radar system. Furthermore, pilots must also make periodic adjustments to the weather radar tilt to maintain an optimal weather viewing tilt angle.
There are two different automatic tilt capabilities on general aviation radars:
Automatic tilt based on barometric altitude and range selection.
Automatic tilt angle compensation based on altitude changes.
In the first implementation, the radar receives the barometric altitude from the air-data computer and calculates a tilt angle to have the radar beam hit the ground at the selected display range. Since the automatic tilt angle calculation is based on the barometric altitude, not absolute altitude above the ground, this method can result in different levels of ground clutter in the display depending on the local pressure conditions as well as the factual terrain altitude. Pilot acceptance of this method of automatic tilt has been limited at best. It is definitely not suitable for air transport flight crews.
With the second implementation, the pilot is allowed to make an initial setting of the tilt angle. This eliminates problems associated with the first method. Then, if the automatic tilt control is activated, the system automatically compensates for the required tilt changes as the aircraft altitude changes. It is basically an automatic altitude change compensator. This method, however, unrealistically assumes that the terrain ahead of the aircraft is flat or otherwise unknown. This method is thus still subject to variations in the ground clutter when the aircraft flies over different terrain altitudes.
Accordingly, improvements to existing tilt control systems are needed in the industry.
SUMMARY OF THE INVENTION
The present invention describes a method for automatically determining an optimal antenna tilt angle for all weather display ranges as well as for other radar data gathering functions such as, for example, terrain, turbulence detection, autoland, and/or position validation scans. According to one embodiment of the present invention, the radar tilt control is managed as a function of flight phase and altitude. In another embodiment of the invention, a digital terrain database is used to automatically determine tilt angle. According to one aspect of the invention, the tilt management function is automated by a computer and the weather radar through the use of the aircraft's position and a terrain database.
In one embodiment of the present invention, the automatic tilt control system uses the radar range, aircraft position (latitude, longitude, altitude, and heading); radar specific parameters (radar beam width and sweep limit) and a terrain database (digital elevation model) to compute tilt angle settings for the radar. The tilt angles are automatically updated when the aircraft changes altitudes, turns or the underlying terrain requires a different tilt angle. The system will still allow the pilot to override and set a tilt angle manually.
One aspect of the invention is the use of a terrain database to compensate for terrain height variations ahead of the aircraft in different directions. When setting the tilt value via segmented tilt that allows the radar to be tilt managed over multiple segments of its sweep. In the weather radar mode, the use of segments improves the radar's ability to minimize ground clutter facilitating better storm cell detection.
One embodiment of the present invention is an automatic radar tilt system based on using the terrain altitude information in the Enhanced Ground Proximity Warning System (EGPWS). EGPWS type systems are also known by other acronyms, e.g. TAWS for terrain awareness systems, GOCAT and GCAS for ground collision avoidance system. The inventions described herein are not limited to any particular type of ground proximity warning system used in conjunction with a terrain data base and the terms “EGPWS”, EGPWC” and “terrain based collision avoidance systems”, or other previously listed acronyms, refer collectively to any and all such systems. In embodiments of the present invention using such systems, based on the aircraft altitude above the terrain and terrain conditions in the area, the EGPWS determines the tilt angle to intercept terrain. This information is used by the radar to determine the tilt angle settings. The automatic tilt angle settings result in minimum ground clutter on the display while maintaining the optimum weather detection capability when I the weather detection mode and permits more efficient use of the radar when in modes that require collection of terrain data.
The present invention solves several additional problems of the prior art. The present invention reduces the need for the pilot to distinguish ground returns from weather returns at all range scales. The present invention reduces the need for the pilot to adjust the antenna tilt angle to compensate for mountainous terrain in all range scales. The present invention minimizes the need for the pilot to manually adjust the tilt angle while trying to fly the aircraft and navigate around hazardous terrain and weather. Instead, the pilot can spend more time analyzing storm patterns on the weather display. Furthermore, the present invention eliminates the need to adjust tilt while on the ground by minimizing ground clutter in proximity to the aircraft.
Automating the tilt control as taught by the present invention improves the efficiency of each data gathering scan since the probability of having the radar beam appropriately targeted is greatly enhanced. This increase in the data gathering efficiency further enables the use of a single radar to perform multiple types of data gathering scans without appearing to detract from the weather updates rates to which pilots have become a
Conner Kevin J
Hammack Stephen D.
Joyce Jim
Kuntman Daryal
Morici Martin M.
Allied-Signal Inc.
Sotomayor John B.
LandOfFree
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