EW300 Final Study Guide
Regarding an infrared imager, select the TRUE statement(s):
-Atmospheric conditions affect maximum ranges to target achieved. -Emitted energy must be within detector's bandwidth
When dealing with a Basic Pulse RADAR, the Duty Cycle (DC) is equal to which of the following
-Average Power divided by the Peak Power -Pulse Width divided by the Pulse Repetition Frequency -Pulse Width divided by the Pulse Repetition Time
Select advantages Electro Optics have over RADAR:
-Covert (passive) -Precision imaging (ID possible)
Which of the following must be true to resolve a single target from a group?
-Cross range resolution (azimuth and elevation) must be less than actual distance between targets at the same range. -Range resolution must be less than distance between actual targets at the same bearing and altitude.
Which of the following are true regarding Track While Scan (TWS) systems compared to Servo Tracking Systems?
-Has a reduced track update rate compared to Servo Tracking Systems -Creates a track file for individual targets -Some systems employ beam splitting to enhance angular resolution. -The system is able to lead the problem by calculating where the contact will be in the future.
Which of the following can possibly impact maximum detection range for a RADAR system?
-Height of our antenna -pulse width and rest time -Transmission frequency -Shape of the target
What change in variables would result in a decreased cross range resolution for an ISAR system?
-Increase in frequency -Increase in integration time
If unambiguous RADAR range is dictating maximum detection range for a specific target, which of the following actions could an operator perform to optimize radar performance in detecting that target?
-Increase the Threshold Level to filter noise -Decrease PRF to Increase Runamb
Relative to mechanically steered arrays, select advantages of electronically steered arrays.
-Instantaneous beam positioning -Less moving parts -Can adjust beamwidth to cater towards search of fire control desires
Which of the following are true regarding military laser use?
-Lasers are used to mark targets for both pilots as well as for laser guided bomb homing. -Lasers are used to approximate distance to target -Lasers can be used to illuminate targets in both the IR and visual spectrum -Lasers are used to induce material failure on a target
Select the two types of antenna polarization:
-Linear (Verticle & Horizontal) -Circular
Which of the following changes would result in a decrease in a maximum radar range (Rmax)?
-Reduced RADAR cross section of target -Widening beamwidth (azimuth or elevation)
Regarding SAR and ISAR, which of the following is true?
-SAR uses the motion of the transmitter/receiver to create the large aperture. -ISAR uses the motion of the target to create a synthetic aperture. -SAR is used to provide a high-resolution image of large non-moving targets. -ISAR is extremely effective in imaging surface contacts.
When deriving the infrared range equation, what assumptions do we make?
-Scattering & Absorption are present -Transmittance (tao) is a provided, environmental value. -Spherical spreading from point target -Graybody
Which statements are true about threshold levels?
-Threshold level can be adjusted manually -decreasing the threshold level is likely to display more false returns -The power level of a received signal must be greater than the threshold level in order to be displayed on the RADAR screen
Which ranges do we attempt to maximize through system design, location, and operation to achieve the greatest distance our RADAR can detect (and correctly display) a target?
-Unambiguous RADAR Range -Over the Horizon RADAR Range -Simplified Max RADAR Range
Which equations must be compared to determine maximum IR detection range?
-Visual line of sight range -Infrared maximum range
Beamforming can be achieved by which two means?
-antenna array -quasi-optical reflectors
Which of the following result in enhanced cross range resolution?
-decrease range to target -increase antenna size -increase frequency
Given the three assumptions we use in this course (see below), select all statements that are true about Graybodies: -Constant temperature -Opaque object, τ = 0 -For graybodies, α ρ ε are NOT a function of wavelength (constant)
-emissivity + reflectivity = 1 -reflectivity > 0 -absorptivity = emissivity
Which of the following are true regarding laser fluence?
-solved by multiplying laser irradiance by the time the laser dwells on the target -incorporates scattering into approximating laser beam attenuation
Put the following "gates" in the order used by a track-while-scan radar during a normal tracking sequence:
1. Acquisition 2. Tracking 3. Turn
Order, from ocean surface to ocean floor, the layers of the common ocean Sound Velocity Profile.
1. Surface layer 2. seasonal thermocline layer 3. main thermocline layer 4. deep isothermal layer
While evaluating a recent Sound Velocity Profile, you note that the sound velocity increases from the surface to a depth of 75 meters. From that point, the sound velocity decreases until water depth reaches 200 meters. What is your recommended depth (Best Depth) if your mission requires you to avoid detection from a destroyer?
135
Which of the following are true regarding phased array antennas ?
A 2-D array is required to focus a beam in both azimuth and elevation
Thermal Resolution
Ability to detect small variations in temperature differences
Electromagnetic wave energy is attenuated due to __________, __________, and __________ .
Absorption Spreading Scattering
What type of interference occurs when EM waves interact with one another and the resultant wave increases in amplitude?
Constructive
Depth excess is a term associated with this sound propagation path.
Convergence zone
Barrage Jamming
Covers a wide band of frequencies simultaneously
Two waves that are exactly 180 degrees out of phase will achieve ___________ interference.
Destructive
Basic Pulse Radar
Detects bearing and range to target using a single antenna
Basic Continuous Wave RADAR
Detects bearing and relative velocity of target using 2 antennas.
Pulse Doppler RADAR
Detects bearing, range, and relative velocity of a target using a mixer and 1 antenna.
Frequency Modulated Continuous Wave RADAR
Determines target bearing, relative velocity, and range with 2 anttenas and changing frequency over a given time period.
Refraction
EM wave passes into a medium with a different speed of propagation and the wave bends.
__________ converts ideal exitance into actual material exitance by accounting for differences in blackbody vs graybody properties.
Emissivity
Radiant Power
Energy per time propagating from a radiating source (W)
255 is a reasonable value of bandwidth factor.
False
A SAR antenna needs the antenna to be stationary and the target to be moving.
False
Smin must be greater than the received signal power at the antenna in order for detection.
False
The nominal speed of sound in water is 343 m/s.
False
The temperature of the environment is vital information needed to solve for bandwidth factor.
False
Fast Time Constant (FTC)
Filters away atmospheric noise based on rate of change of return signals.
Sensitivity Time Control (STC)
Filters away surface-based environmental noise near the RADAR system.
Spatial Resolution
Imaging system's ability to distinguish separate objects
In the radio wave portion of the Electromagnetic spectrum, absorption generally _____________ as frequency ________?
Increases;Increases
Which of the following statements are true about refraction?
Index of refraction determines the extent of refraction which will occur in a medium.
Background Limited
Lack of contrast between target and background
A low level light vision system requires:
Light reflected off the object
RADAR cross section is dependent on which factors?
Material Size Aspect Angle Shape
Moving Target Indicator (MTI)
Measures changes in return signal phase to filter out stationary targets
Radiant Exitance
Power per unit area emitted from surface (W/m^2)
Irradiance
Power per unit area incident to the surface of an optic aperture (W/m^2)
Electronic Protection (EP) is best described as:
Protecting friendly assets from unwanted effects of EM spectrum use
_____ is a signal processing technique in which the receiver is able to separate two or more targets with overlapping returns on the basis of the frequency, thus reducing the RADAR's range resolution.
Pulse Compression
Which of the following make up a basic continuous wave (CW) RADAR system?
Receiver Transmitter Mixer Two Antennas
Electronic Support (ES) is best described as:
Search for, intercept, ID, and localize sources of EM energy.
Noise Limited
Sensor's internal heat masks signature of target
blackbody radiator
Substance that absorbs all incident energy and emits all absorbed energy
Select all the FUNCTIONS of a weapon system:
Target Detection Neutralization Localization Classification Weapon Selection Tracking
Pulse integration
The process of summing successive pulses along the same bearing in order to detect a target.
Interference
The property by which EM waves superimpose and their energies combine when overlapping.
Diffraction
The tendency of EM waves to spread out, or bend around objects
Which of the following statements about Light Amplification (LLL) systems is true?
They can become saturated if too much light is present
In comparison to the radio spectrum, the electro-optic spectrum consists of higher frequencies and shorter wavelengths
True
One of the fundamental differences between Basic Continuous Wave (CW) and Basic Pulsed RADAR is that Basic Pulsed displays the contact's range.
True
bandpass filter
Used by Doppler RADARs to filter contacts based on speed.
Electronic Attack (EA) is best described as:
Using EM energy to degrade, destroy, or neutralize enemy combat capabilities.
What is thermal crossover?
When the environmental heating cycle causes target temperature = environment temperature (no contrast)
Duty Cycle
a ratio that represents the time that the transmitter is on to one complete cycle of operation.
Directive Gain
antenna's ability to concentrate energy in the beam
What variable accounts for the detector's sensitivity to specific wavelengths of emitted energy?
bandwidth factor
Threshold Level
chosen signal level above which a contact is displayed
PRF
determines max unambiguous range
Pulse Width
determines range resolution and min range
Antenna Aperture
effective area of RADAR's transmitter/receiver of energy
Noise
generated internally and externally, creating false returns
Beamwidth
half power (and greater) width of antenna beam
Scan Rate
how fast the antenna is rotated
Servo-controlled tracking systems require an error signal as feedback to adjust the radar position. Because of this, servo trackers will always:
lag the target
Peak Power
max power transmitted by a RADAR
Average Power
mean power transmitted over the entire cycle
What unit of measure is most commonly used to describe the Electro-Optical Spectrum:
microns
Swept Spot Jamming
moves energy over bandwidth range from small to large
A difference in starting point between two EM waves is a difference in:
phase angle
Deception Jamming
spoofing/synthesized radar
The infrared maximum range equation accounts for what forms of attenuation?
spreading scattering absorption
RADAR Cross Section
target's effective area that reflects RADAR energy
Pulse Width
the active transmit time or duration of the electromagnetic pulse.
Cross Range Resolution (RCROSS)
the minimum angular separation between two targets at the same range that the RADAR system is able to distinguish as two separate targets.
Range Resolution
the minimum range between two targets on the same bearing that the RADAR system is able to distinguish as two separate targets.
Rest Time (RT)
the non-transmit time or the interval between electromagnetic pulses.
Pulse Repetition Frequency (PRF)
the number of pulses transmitted per second
Spot Jamming
the power output of the jammer is concentrated in a very narrow bandwidth
Burn-through
the range at which the strength of the target's RADAR return becomes equal to or greater than the Electronic Attack (EA) signal.
Pulse Repetition Time
the total time for one transmission cycle.
A Synthetic Aperture Radar (SAR) achieves a large effective aperture by:
using motion of the transmitter/receiver.
Smin
weakest possible signal that could still yield a valid return
Reflection
when an EM wave strikes a surface and bounces off it
