**5. Terrain following radar**

Terrain-following radar is an aviation innovation that permits an extremely low-flying airplane to keep up a moderately constant height over the ground level. It dependent on TAWS and called as ground-hugging or terrain-hugging flight. It is like a GPWS.-Record the general objectives of a TFR system in two classifications. The first of these would be to minimize detection by the opponent; subsequently, it is a vital factor or else the mission will fall flat if the aircraft identified. TFR provides active radar avoidance by increasing the terrain mask, lowering the altitude, lowering the RF signature, escaping or reducing the time in threat coverage and operation at night and adverse weather condition [4, 8, 9].

Minimizing detection is of no use if the flight crash inbound or outbound on the mission. Therefore, the other primary goal of a TFR is to offer maximum flight safety. Flight safety maximization achieved by maintaining safe altitude from terrain, avoiding unpredicted obstacles, consistent performance of the system, high availability/reliability [4, 8, 9].

The major goals of terrain following radar represented in **Figure 2**, the risk vs. terrain average clearance plottedin the graphical form. It helps us to determine the total risk value. This total

**Figure 2.** Terrain following radar vs. risk [4].

**Figure 3.** Terrain following radar scan.

risk obtained by the ground hitting probability and the probability of kill by the weapons, which varies in the order with risk and terrain clearance plot [4, 8, 9].

#### **5.1. Scanning of terrain following radar**

Terrain following radar scans the air gap in front of aircraft with a vertical scan. It produces a wedge of information in vertical, horizontal and azimuth direction. TFR scan the plane by referring horizon as the middle and provide the wedge above, below, left side, right side facet. All wedge patterns ware interpreted and analyzed. An antenna scan pattern to produce this wedge illustrated in **Figure 3**.

#### **5.2. Algorithm of terrain following radar-**

There have been several approaches to the terrain-following algorithms. The typical algorithm of terrain following radar is shown in **Figure 4a–d** which represents the following algorithms. They are,


**Figure 4.** (a, b, c, and d) Terrain following radar computation approaches.
