EW300 Final Study Guide

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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


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