VOL. 11, NO. 2, JANUARY 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 1285 NAVIGATION SYSTEMS IN NOE FLIGHT SENSORS AND THEIR INTEGRATION N. Tamilselvam, D. Divya Priya, B. Rajeswari and N. Siddika Department of Aeronautical Engineering, Adhiyamaan College of Engineering Hosur, Tamilnadu, India E-Mail: Selva.gte.research@gmail.com ABSTRACT This project presents the optimization method for Nap-of-the-Earth. The Nap of the Earth (NOE) mode is the most exciting, most dangerous, and is typically the slowest. It is used by military aircraft to avoid enemy detection and attack in a high-threat environment. NOE is used to minimize detection by the ground-based radar, targets and the control system. The Radar Altimeter or Terrain-Following Radar system, Terrain Awareness and Warning system is used to detect the obstacles during flying in NOE flights. Here, while the flight is at nap of the earth operation, the speed and the altitude must be slow as already determined. The terrain following radar maintains the altitude from the ground level. So we analyze the problem to increase the performance of the aircraft by ranging the terrain by some modes of the Terrain Avoidance and Warning System which is given by ICAO, UKCA, EASA, and FAA. Further to this, different TAWS modes of operation, explanation of mode selection and advancement in TAWS are explained in detail. In this paper, MATLAB programming is done for some modes of TAWS operation and the simulation of flight path for the excessive terrain. Closure rate from mode 2 operation of flight is also done. Keywords: nap-of-the-earth, radar system, optimization method, high-threat environment, terrain avoidance and warning system. INTRODUCTION Nap-of-the-earth (NOE) is a type of very low- altitude flight course used by military aircraft to avoid enemy detection and attack in a high-threat environment. This mode is the slowest and more exciting. When flying at the nap of the earth, the pilot flies at varying airspeeds and altitudes and stays as close to the earth’s surface as possible. During NOE flight, geographical features are also used. This keeps below enemy radar coverage. NOE is used to minimize detection by hostile aircraft, ground- based radar, or attack targets. Doppler radar has the potential to determine NOE flight, but the aircraft that comes towards has to be within radar range in the first place, and low flight minimizes this possibility due to the effect of terrain masking. The lowest NOE flying is by helicopters because they have lower speeds and more maneuverability than fixed-wing aircraft, mainly in the fast-jets. Only Helicopters can fly at treetop levels or even below the height of surrounding trees where there are clear areas (such as in river gullies), flying under wires (such as electricity cables) over them. Attack helicopters can hide behind trees or buildings, popping up just enough to use their (rotor mast-mounted) radar or other sensors and then minimally exposing themselves to launch weapons. Then the escape can be made by further NOE flying. The Figure-1 represents the nap of the earth operation. In this the high level path and the low level path of the flight is represented. The high level path is identified by the radar system from the base, while the low level flight path used fly under the radar which is called as the NOE flying technique. They have their own flight path which avoids the collision with terrain. Figure-1. Nap of the earth flight. Obstacle Detection and Analysis There are two types of obstacle detection in NOE flights 1.Obstacle Detection Using Passive Sensors and 2.Obstacle Detection Using Active Sensors. Obstacle Detection Using Passive Sensors A passive sensor is a microwave instrument designed to receive and to measure natural emissions produced by constituents of the Earth's surface and its atmosphere. The power measured by passive sensors is a function of the surface composition, physical temperature, surface roughness, and other physical characteristics of the Earth. The Radio Frequency (RF) bands for passive sensor measurements are determined by fixed physical properties (molecular resonance) of the substance being measured. These frequencies do not change and information cannot be duplicated in other frequency bands.