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Navigation—A General Overview

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Two types of approaches are used for landing purpose. They are non-precision

approach and precision approach. Only horizontal guidance is provided by non-

precision approach. Precision approach provides both horizontal and vertical guid-

ance for landing. Nowadays for precision approach the Instrument Landing System

(ILS), Microwave Landing System (MLS) and Differential GPS (both Local and

Wide Area) are used.

The ILS is an instrument based technique to guide the airplane for safe landing

in precision approach method. It uses two directional radio frequency (RF) beams

to provide both horizontal and vertical guidance to the pilot during an approach to

landing.ThemaincomponentsinILSarelocalizer,glidepathandmarkers.RFsignals

or are used to provide the horizontal guidance called the localizer (108–112 MHz)

and vertical guidance called glide path (329.15–335 MHz) and the track position

fixed by the markers. The Distance Measuring Equipment (DME) also installed in

some ILS to provide the slant distance to the airplane with respect to ground touch

point. Generally the DME is accompanied with the glide path antenna. The localizer

antenna array is placed about 1000 ft off the stop end of the runway. It radiates

two signals one is at 90 Hz with AM modulated, and other is at 150 Hz. For vertical

guidance also, a signal is generated as similar to the horizontal guidance but it rotates

at 90°.

The frequency of the signal is in the range of 300 MHz. The glide path antenna

array is mounted vertically. The height of this antenna array would be too great to be

installed safely near a runway (usually about 1000 ft. from the threshold and 400–500

ft. from the edge of the runway).

Microwave Landing System (MLS) is a precision landing approach. It installed in

large airports to provide landing maneuvers in all weather conditions. MLS provides

three dimensional navigation guidance; azimuth, elevation and distance for exact

decent and alignment of airplane. ILS and MLS will be very much useful during the

visibility problem due to fog, rain and aerosol.

Vision and LIDAR Based Navigation

Nowadays vision based navigation is playing a key role in autonomous navigation.

In this system, input is taken from the optical sensors like cameras and it is processed

in Deep Neural Network (DNN) based systems and produces the control signals to

the vehicle. The main role of DNN systems are detection and classification of objects

such as estimation of road curvature, obstacle and traffic signs etc. All these tasks

are done with very high speed. Then only the autonomous navigation system will

take the decision in time.

Light Detection and Ranging (LIDAR) measures the distance and relative angle of

target by computing the time of flight with illumination of laser beams. Basic compo-

nents of LIDAR are laser, scanner and a GNSS receiver. It is extremely suitable for

3D mapping of surrounding environments. Vision and LIDAR working together will

detect the surroundings fully and gather the contextual information of surroundings