Question

Discuss in rich details how the signal is manipulated in a SONAR/RADAR and detailly analyze how the signal can be utilized for detection of any physical device.

Answer 1

Solution.

First some basic about SONAR and RADAR

Both radar and sonar locate objects from the echo of a signal that is bounced off the object. The only difference in RADAR (radio waves) and SONAR (sound waves) is

Sonar requires a medium to move through, most notably water. Whereas Radar sends out radio waves which are part of the electromagnetic spectrum (just as light is, only a different frequency). Electromagnetic waves need no medium to pass through and thus can work even in space.

Now, we will discuss the working of a SONAR that is signal signal manipulation and its use for detection of any physical device:

There are two types of sonar sets: active and passive.

An active sonar set sends out sound pulses called pings, then receives the returning sound echo. Whereas the passive sonar sets receive sound echoes without transmitting their own sound signals.

In an active sonar sets, the sound signals are very powerful compared with ordinary sounds. Most sonar sets send out sounds that are millions of times more powerful than a shout. Each ping lasts a fraction of a second. Some sonar sets emit sounds you can hear. Other sonar signals are pitched so high that the human ear cannot hear them. These signals are called ultrasonic waves. The sonar sets has a special receiver which can pick up the returning echoes. The location of underwater objects can then be determined by the length of time that elapses between sending the signal and hearing the returning echo.

The working written above is the basic of how Sonar works but if I discuss in rich details then there are many method of detection of physical device using Sonar many people found different techniques to detect the position and trace the object using Sonar. One of the technique to detect the physical object involves following steps :

1. SONAR IMAGE PRE-PROCESSING METHODS

This algorithm is a combination of four different filters each of which aims to revise a special defect. To eliminate the defects of non-uniformity of illumination, the Homomorphic filtering is used. Sonar image is decomposed into the reflectance factor and the illumination intensity using the following equation: g(x,y)=i(x,y).r(x,y) where g(x,y) is the sonar image, i(x, y) is the multiplication factor of illumination and r(x, y) is the reflectance function.

Applied Homomorphic filtering algorithm is summed up in the following steps:

• Separation of the components of illumination and reflectance using the log of the image in: g(x, y) = In[f(x, y)] = In[i(x, y). r(x, y)] = In(i(x, y) ) + In(r(x, y))
• Evaluation of Fourier transform of the log-image. The resulting equation is as follows : ?(??,??) = ?(??,??)+ ?(??, ??)
• High-pass filtering of the Fourier transform: use of the H modified Gaussian filter : G(??,??) = H(??,??).I(??,??) + H(??,??). R(??,??).
• Evaluations of inverse Fourier transform to return in the spatial domain.
• Application of the exponential function to get the filtered image.

2. SONAR IMAGES TEXTURAL ANALYSIS.

The analysis of textured images plays an important role in image processing, pattern recognition and particularly in sonar images classification.

3. SONAR IMAGE SEGMENTATION AND CLASSIFICATION METHODS

Many segmentation methods are based on statistical model using first and second order statistics.

After the segmentation and classification we can detect the physical object we wanted.

Now, we will discuss the working of a RADAR that is signal signal manipulation and its use for detection of any physical device:

Radar sets, also called radar systems have four main parts -- a transmitter, an antenna, a receiver, and an indicator (display screen).

The transmitter produces the radio waves. When a radio wave strikes an object such as an airplane, part of the wave is reflected back to the radar set. The signal is detected by the antenna as a radio echo. The returning echo is sent to the receiver, where its strength is increased, or amplified. The echo is usually displayed as an image that can be seen on the indicator. The usual type of indicator is the plan position indicator, or PPI.

A common type of radar is called pulse radar. This type of radar sends out radio waves in short bursts, or pulses. The distance to a object is determined by the time it takes the signal to reach the target and the echo to return.

For example: Radio signals travel at a known speed -- about 186,000 miles per second, the speed of light. If the radio signal comes back in 1/1,000 second, then the round trip is 186 miles. The target must be half that far, or 93 miles away.

The location of the object in relation to the radar set is found in a different way. The radar antenna sends out radio pulses in a narrow beam, much like the beam of a flashlight. The antenna and its beam are rotated slowly through all possible directions, searching the entire horizon for objects. An echo is reflected from a ship or other object only if the narrow beam happens to strike it. The returning echoes are amplified by the receiver, then go to the indicator, which displays the range and direction of the target.