Lecture 6 - Law Enforcement Flashcards
Describe the operation of radio detection and ranging (RADAR) systems.
Operates in the Radio wave band of frequencies of the Electromagnetic spectrum. A radio wave is transmitted towards area of interest at time t=0 (through an antenna)
− The radio wave arrives at an object at time t
travel
− The radio wave is scattered in all directions,
− A proportion of the original wave travels back and is
received by the antenna at time t
return
− The total round trip time for the radio wave is t total = t travel + return
R = (ct total)/2
Explain their key operational parameters of range, range resolution and bandwidth.
Range - Range is the maximum distance that a radar can detect objects.
Range resolution - Range resolution is the smallest distance between two objects that can be detected by a radar.
Bandwidth - Range of frequencies that a radar can transmit and receive.
How are different types of radar systems more/less suited for various police operational scenarios
Real-world: Waves are complex and composed of many frequencies. So you must see which mechanism is more suited towards a certain technology
Explain the workings and technical challenges of ground-penetrating radar
A GPR system transmits a pulse of electromagnetic energy into the ground. The pulse of energy travels through the ground and encounters objects or changes in the ground’s composition. When the pulse encounters an object, it is reflected and returned to the receiver. The reflected signals are used to create an image of the subsurface.
Challenges: Ground-penetrating radar can be affected by the presence of moisture, which can distort the radar signals. The depth of penetration of GPR is limited by the frequency of the electromagnetic waves. Not able to penetrate very deep into the ground, only a few meters.
Explain the workings and technical challenges of through-the-wall radar.
It is a type of radar that uses electromagnetic waves to detect objects behind walls. It works by transmitting a signal through the wall and then receiving the echoes that bounce back from objects on the other side. The reflections can be processed to create a detailed image of the objects in the room.
Technical challenges include propagation through the walls, making it difficult to detect objects far away, and RFI, where interference from another present electronic device may impact the signal.
Convey the arguments which civil rights activists have put forward in opposition to the police’s use of through the wall radar
December 2014 case; US Marshals Service tracked fugitive Steven Denson to a house in Wichita. Argued an invasion of privacy for detecting possession of illegal firearms.
“The idea that the government can send signals through the wall of your house to figure out what’s
inside is problematic“
The waves used in radar systems fall into which band(s) of the Electromagnetic Spectrum?
(Tick 1 box)
Millimeter-Waves
Infra-Red and Microwaves
Radio and Microwaves
Radio waves
X-Rays
mm waves and radio waves
State the formula which describes the Range Resolution [ΔR] of a radar system
Delta R = C/2B where c is the speed of light = 3x10*8 ms-1 and B is the signal bandwidth
Tick the statement from the list below which most accurately describes the attenuation and
imaging characteristics of electromagnetic (EM) waves employed in a through-the-wall radar
system:
High frequency EM waves will experience less attenuation by a wall and generate
poorer/less accurate images than low frequency EM waves
High frequency EM waves will experience more attenuation by a wall and generate
better/more accurate images than low frequency EM waves
Low frequency EM waves will experience more attenuation by a wall and generate
poorer/less accurate images than high frequency EM waves
Low frequency EM waves will experience less attenuation by a wall and generate
better/more accurate images than high frequency EM waves
(2) High frequency EM waves will experience more attenuation by a wall and generate
better/more accurate images than low frequency EM waves
In a hostage situation (illustrated in the diagram below), a hostage taker is negotiating with
the police using a landline phone located in room 2. The victim is tied up in room1.
The police know that the phone is in room 2 but do not know where it is located, and
therefore cannot infer the hostage takers approximate position. However, they are planning
to use a through-the-wall radar to determine the position of the hostage taker in room 2.
The through-the-wall radar operates at 5.8 GHz and has a bandwidth of 100 MHz. It detects
the hostage taker and measures a round-trip time [ttotal] of the transmitted radar wave to be
1.6x10-7 seconds to the hostage taker’s position.
[a] What is the range of the hostage taker to the radar?
[b] State the accuracy (range resolution) of the range measurement.
(a) 24 meters
(b) 1.5 meters
State Ohms law in words, and derive the relationship between current (I) and voltage (V).
The current (I) going through a conductor is proportional to the voltage. The constant of
proportionality is the Resistance (R) of the conductor which is inversely proportional to
the resistance
A security company is developing a new Taser gun. In their initial design their stun gun
design delivers 32 electronic pulses per second, with each pulse carrying a charge of 650
micro-coulombs.
[a] Calculate the current will be delivered to a person every second. Give your answer to 1
decimal place.
[b] Explain why the initial design will, or will not pass safety checks
(a) 20.8 milliamps
(b) No, it will not be approved. Though the PRF is well below the dangerous tetanus region,
the current still falls is into an unsafe region. Effects of 20.8 mA current on a human
include sustained muscular contraction, extreme pain, and respiratory arrest. Death is
also a possible consequence.
State the element which fuel cells typically use to convert its chemical potential energy into
electrical energy
Hydrogen
(Oxygen will also be accepted as an answer)
Bob has had a few drinks at a pub which has resulted in his blood alcohol concentration
(BAC) being 120mg/100ml. He decides to drive home and gets stopped by the police for
suspected drinking and driving. The police administer a roadside screening breathalyser
test.
[a] What will be the reading given by the breathalyser device? Give your answer in
micrograms per 100 milliliters (μg/100ml) and to 2 decimal places
[b] State whether Bob is above or below the UK drink driving limit.
120mg /100ml = 120x10-3g/100ml
Breath = 120x10-3g/2100 = 5.714x10*-5g
Breath = 57.14 ug/100ml
Describe how a stun gun works as a weapon of compliance in terms of
electrostatics and human physiology
A stun gun delivers a powerful electric shock to the target, causing involuntary muscle contractions and temporary incapacitation.
The electric shock disrupts the nervous system, causing the muscles to contract and the body to release endorphins, which can lead to a feeling of pain and dizziness.
The effects of a stun gun are temporary and usually wear off within a few minutes.
