Real Aperture Image Generation and Correlation Study
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REAL APERTURE IMAGE GENERATION AND CORRELATION STUDYExternal Guide Professor Dr G. Jagadeesh Internal Guide Ms Roopa K (Sr. Lecturer)
Karthik G.S : 1MV08TE020 Karthik K.S : 1MV08TE021 Kishore K : 1MV08TE023
Real aperture image Generation and correlation studyAIM: To generate radar images as obtained from a missile onboard seeker and use them to apply correlation technique with respect to digitally stored image data for extended target detection. The study involves generating missile onboard seeker radar image based on simplified geometry and radar parameters as function of different Grazing angles and positions in a missile trajectory.
Then the generated images are digitally correlated with stored image data to obtain 2D intensity plot of correlation.The correlation plots provide the angular errors developed over the flight time of the approaching missile which is then used to correct the flight path during terminal guidance. This work is to be done using visualization and computation application software with image processing tools (MATLAB).It is software intensive work with application to missile terminal guidance.
PHASES OF WORK COVERED
Development of radar image simulation tool Implementation of algorithm for image intensity Results for Test case involving runway /city landscape
RADAR RADAR is an abbreviation for RAdio Detection And Ranging. Uses modulated waveforms and directive antennas to transmit electromagnetic energy into a specific volume in space to search for targets. Objects (targets) within a search volume will reflect portions of this energy (radar returns or echoes) back to the radar. Echoes are then processed by the radar receiver to extract target information such as range, velocity, angular position, and other target identifying characteristics. 2 operational types of Radar: Passive Radar Active Radar
Types of RADARS Considering the waveforms used, RADARS can be classified as Continuous-wave Radars (CW) Pulsed-Radars (PR) CW radars are those that continuously emit electromagnetic energy, and use separate transmit and receive antennas. Target range information cannot be extracted without utilizing some form of modulation. Pulsed radars use a train of pulsed waveforms (mainly with modulation). In this category, radar systems can be classified on the basis of the Pulse Repetition Frequency (PRF), as low PRF, medium PRF, and high PRF radars. Low PRF radars are primarily used for ranging where target velocity (Doppler shift) is not of interest.
During each PRI the radar radiates energy only for seconds and listens for target returns for the rest of the PRI.
Imaging RADARS Imaging radar produces an image in which the digital number(intensity) at each pixel position is determined by the strength of the radar signal reflected from the corresponding location in the scene. Imaging radars can be divided in 2 main categories, depending on the imaging technique used:
Real Aperture Radar(RAR) Synthetic Aperture Radar(SAR).
Real Aperture Radars Real-aperture radar (RAR) is a form of radar usually implemented by mounting, on a moving platform These are non-coherent which are controlled by the physical length of the antenna It is an active radar because it emits little pulses of energy transmitted from the radar antenna to the piece of terrain which we want to obtain the image Aperture means the opening used to collect the reflected energy that is used to form an image In the case of radar imaging, this is the antenna. For RAR systems, only the amplitude of each echo return is measured and processed
Synthetic Aperture Radars SAR or coherent radars generates high resolution images. The target is illuminated several times from different locations generating numerous echoes that are recorded coherently (i.e., amplitude and phase as a function of time) and subsequently combined to synthesize a linear array. SAR systems can be either airborne or space borne and are much more complex than the RAR systems
Missiles and its types A Missile is a self-propelled guided weapon system Missile guidance refers to a variety of methods of guiding a missile to its intended target Missiles come in types adapted for different purposes: surface-to-surface, air-to-surface (ballistic, cruise, anti-ship, anti-tank), surface-to-air (anti-aircraft and anti-ballistic), air-to-air, and anti-satellite missiles Surface to surface missile is considered in the study
Surface to surface missile
Seeker in MissilesWhy seeker in missile? Because there is uncertainty in the flight path or target location that makes it impossible to achieve the desired accuracy without a seeker. The active radar seeker, from a radar engineer's view, may be defined as an application-specific compact missile-borne pulse tracking radar whose antenna is mounted ,such that the antenna is isolated from the body movement of the missile.
Active radar seekers are the most popular in all the current missile programs owing to their flexibility of design and implementation to suit almost every mission requirement apart from all weather capability.
Active Radar seeker
Radar Cross Section The size and ability of a target to reflect radar energy can be summarized into a single term, , known as the radar crosssection(RCS), which has units of m Assume the power density of a wave incident on a target located at range R away from the radar is PDI . The amount of reflected power from the target is: where denotes the target cross section RCS forms a strong function of viewing aspect in 3-D
Parameters affecting RCS
Detection of targets located on the ground, generally poses more serious challenges because of the randomness of the terrain and the presence of strongly scattering features on the ground which decreases the SNR of the backscattered signal, now called clutter.
Radar scattering depends on: Dielectric properties (terrain property) Conductivity(terrain property) Surface roughness/ volume properties (terrain property) Incidence angle /Elevation angle(geometric property)
Furthermore dependence on:
Frequency (radar property) Moisture(terrain property)
Polarization (radar property)Motion (geometry/ trajectory)
Parameters affecting RCSDifferent surface features exhibit different scattering characteristics: Urban areas: very strong backscatter Forest: intermediate backscatter Calm water: smooth surface, low backscatter
Rough sea: increased backscatter due to wind and current effects
More wavelength, more penetration
There are two types of Radar Target: Point targets - Point targets are those targets whose size is smaller than the beam width.
Backscattering Point Target
Higher facilitates point target detection.Extended targets Extended targets are those targets whose size is larger than the beam width, complete beam filling.
POINT TARGET DETECTION
High facilitates point target detection
EXTENDED TARGET DETECTION
Detection based on
RAR SEEKER IMAGE SYNTHESIS
RAR SEEKER IMAGE SYNTHESIS The input includes extended target boundaries, location, nature of target or surroundings and approaching trajectory data. The Geometry and Projection block gives the azimuth and elevation angles subtended by the On-board radar with respect to the distributed target of interest, which contributes the Trajectory related information. Experimentally obtained database of radar backscatter strength as a function of frequency, polarization, target type and grazing/depression angle are stored and this is used by 0 computation block as a lookup corresponding to the input data to calculate 0.
The Blurring module generates the boundary areas separating the regions of varying backscatter.The image generation plot (intensity plot) finally generates the whole frame by weighted averaging method.
Image Generation Procedure A test image is constructed based on the geometry of the Landscape and its structures. For example, if a runway is situated in a thickly wooded area, a geometric shape of the runway is drawn with a defined boundary. This test image is then dynamically filled with gray scale intensity corresponding to the backscatter strength of the runway and the surroundings. For the purpose of generating radar image the rectangular boundaries around distributed target of interest should be specified. Based on this scanning area is marked .
The scanning interval is the time between two samples taken for processing to generate an image. This time includes the beam acceleration period, uniform scan period and beam deceleration period. The radial and azimuthal extent of the surface area that is illuminated by the airborne radar is called as the Radar Footprint.
Common Search patterns used are: Raster Spiral Helical and Nodding (Sinusoidal) The intensity pixels in the images are generated by averaging the backscatter intensities over the area illuminated by the beam (foot print area) The scan angular rate has to be increased as the onboard radar approaches towards target since as beam footprint shrinks more time is needed to generate the complete frame covering the same area of interest.
Raster Scanning in RAR Raster Scanning has been employed in this study. Raster scanning is a technique for generating or recording a video image by means of a line-by-line sweep, tantamount to a data mapping scheme between one and two dimensional spaces.
In raster scanning, the beam sweeps horizontally left-to-right at a steady rate, then blanks and rapidly moves back to the left, where it turns back on and sweeps out the next line.
Search Radar Scan 3D Geometry
Antenna beam footprint s