Radar Altimeter Inertial Vertical Loop for Precise Landing Guidance
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Solution Overview
Problem
Unmanned aircraft systems (UAS) and Urban Air Mobility (UAM) applications face challenging navigation requirements during landing, particularly in non-certified pilot scenarios, requiring precise vertical position and velocity estimation that current GPS-aided inertial navigation systems cannot reliably provide without ground-based assistance, which is costly and vulnerable to jamming.
Innovation Solution
A radar altimeter inertial vertical loop (RIVL) filter is integrated into navigation systems, incorporating ground maps and sensors like GPS and barometers to estimate vehicle vertical position and velocity, accounting for sensor and map errors, and using a switching mechanism to ensure consistent input data for improved navigation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS-aided inertial navigation systems are used for landing, then navigation coverage is extended, but vertical position and velocity precision is insufficient without ground-based differential GPS systems
Solution Approach 1:
The patent introduces a radar altimeter as an intermediary sensor to measure vertical position directly, bridging the gap between GPS horizontal positioning and the need for precise vertical navigation. The radar altimeter provides direct range measurements to the ground surface, enabling accurate vertical position estimation without requiring complex ground-based differential GPS infrastructure.
Solution Approach 2:
The patent merges GPS horizontal position data with radar altimeter vertical range data and inertial measurement unit vertical velocity data into a unified navigation solution. This combination allows the system to achieve precise three-dimensional position and velocity estimation by integrating measurements from multiple sensors, each contributing their strength to the overall navigation accuracy.
2Measurement precision
If barometer with dedicated vertical loop is used, then vertical navigation is provided, but estimation errors and sensor measurement errors are not utilized, failing to satisfy vertical position requirements
Solution Approach 1:
The patent implements a feedback mechanism where the navigation filter continuously estimates vertical position and velocity, compares these estimates with direct measurements from the radar altimeter and barometer, and uses the differences (innovation sequences) to update and refine the state estimates. This feedback loop enables the system to actively correct estimation errors and adapt to changing conditions, significantly improving vertical position accuracy.
Solution Approach 2:
The patent changes the approach from using barometric pressure alone to a multi-parameter estimation system that incorporates radar altimeter range measurements, barometric pressure data, and inertial measurement unit vertical velocity. By utilizing multiple parameters and their relationships, the system achieves more accurate vertical position estimation while accounting for individual sensor errors through statistical filtering.
3Measurement precision
If ground-based differential GPS systems are deployed, then vertical position requirements are met, but power consumption increases and landing zone maintenance personnel are required
Solution Approach 1:
The patent enables the navigation system to be self-sufficient by using onboard sensors (radar altimeter, barometer, inertial measurement unit) that do not require external ground-based infrastructure. The system performs its own vertical navigation functions using measurements taken directly from the vehicle environment, eliminating the need for ground-based differential GPS systems and associated maintenance personnel.
4Measurement precision
If ground-based differential GPS systems are used, then navigation precision is improved, but vulnerability to jamming and power system requirements increase
Solution Approach 1:
The patent extracts the vertical navigation function from the vulnerable ground-based differential GPS system by implementing an independent onboard measurement system. The radar altimeter, barometer, and inertial measurement unit provide vertical navigation capabilities that are self-contained and not dependent on external ground infrastructure, thereby eliminating the vulnerability to jamming associated with ground-based systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RIVL filter enhances navigation systems' ability to meet demanding landing zone requirements for UAS and UAM vehicles, providing precise vertical position and velocity estimates even in complex environments, enabling safe and reliable landings in various landing zones.
Implementation Method 1
A radar altimeter is incorporated into a navigation system using a vertical loop mechanism
Data Source
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AI summary
A system to provide navigation solutions for vehicle landing guidance comprises onboard aiding sensors, an IMU, a radar altimeter, a map database, and a navigation system including a navigation filter that outputs estimated kinematic state statistics for the vehicle. An onboard processor inputs horizontal and vertical position statistics from the navigation filter into the map database, and computes an estimated ground/object height, ground/object velocity, ground/object acceleration, and error statistics thereof, based on terrain and object map data. The processer includes a radar altimeter inertial vertical loop (RIVL) filter that determines relative vertical acceleration based on a difference between vehicle vertical acceleration and ground/obj ect vertical acceleration; determines relative vertical velocity based on a difference between vehicle vertical velocity and ground/object vertical velocity; performs consistency checks on the relative vertical acceleration and relative vertical velocity; and outputs estimated vehicle vertical position and vertical velocity statistics for compensation of the navigation filter outputs.