EO

Question 1

Which three parts of the EM spectrum does EO cover?

Answer 1

1. Ultraviolet (UV): From 10 nm up to 400 nm
2. Visible Spectrum: Between 400 and 700 nm
3. Infrared (IR): Up to approximately 1 mm wavelength

Question 2

Which four factors affect the general detection problem?

Answer 2

1. Scene illumination and illuminance
2. Target and background contrast
3. Atmospheric conditions
4. Detector quality

Question 3

What can be used as visual cues in optical systems?

Answer 3

McTEC

1. Movement
2. Contrast
3. Texture
4. Edges and outlines
5. Colour (relevant only in daylight)

Question 4

What are the atmospheric transmission windows for IR radiation?

Answer 4

2. Short-wavelength infrared (SWIR): 3 µm to 5 µm
3. Mid-wavelength infrared (MWIR): 8 µm to 14 µm.

Question 5

Explain atmospheric absorption and scattering.

Answer 5

• Atmospheric Absorption: Gases like water vapour and carbon dioxide absorb IR radiation, reducing target contrast.

• Scattering: Caused by aerosols and particles, it leads to diffraction, absorption, and reflection of radiation.

Question 6

What was the name of the first-generation image intensifier? What were its limitations?

Answer 6

Cascade Intensifier.

Converted photons to electrons, amplifying them, and converting them back to visible light.

Its limitations included large power requirements, bulky/heavy size and low resolution.

Question 7

What is the technology associated with modern (second/third gen) II systems? What are its major advantages?

Answer 7

Modern image intensification - To amplify light more efficiently.

Significant advantages include higher resolution, better sensitivity, and reduced size and weight.

Question 8

Explain what is meant by blackbody, grey-body, and selective radiators.

Answer 8

• Blackbody: An idealised object that absorbs all incident radiation and re-emits it perfectly.

• Grey-body: A real object that does not absorb all incident radiation but emits a fraction of it based on its emissivity.

• Selective Radiator: Emits radiation at specific wavelengths or bands, typically gases at high temperatures emitting line spectra.

Question 9

What type of materials are sources of the above types of radiation?

Answer 9

• Blackbody: The idealised theoretical model in which no perfect blackbody exists, but stars are close approximations.

• Grey-body: Most real-world objects, such as earth surfaces, buildings, and vehicles.

• Selective Radiator: Gases like those in jet engine exhaust or gas-discharge lamps.

Question 10

Briefly compare thermal and photon detectors, stating the advantages and disadvantages of each. If designing a horizon surveillance system, which detector would you use and why?

Answer 10

• Thermal Detectors: Measure temperature changes, typically slower response times, and no cooling required.
Advantage: Good sensitivity over a wide range of wavelengths.
Disadvantage: Slower response.

• Photon Detectors: Measure individual photon events, faster response times, often require cooling. Advantage: Higher sensitivity and quicker response.
Disadvantage: Requires cooling. Photon detectors would be preferred for horizon surveillance due to their higher sensitivity and faster response times.

Question 11

What are the 2 types of cooling available for photon detectors, which is most appropriate for a missile IR seeker, and why? What temperature do these coolers operate at typically?

Answer 11

• Thermoelectric Cooling: Suitable for less demanding applications.
• Cryogenic Cooling: Most appropriate for missile IR seekers due to the need for high sensitivity and low noise. These coolers typically operate at around 77 K (liquid nitrogen) or lower temperatures.

77K!!!!!!

Question 12

Compare and contrast serial scan, parallel scan, and fully staring arrays. What is a SPRITE detector, and how does it work?

Answer 12

• Serial Scan: Sequentially scans the scene, typically slower.
• Parallel Scan: Scans multiple lines simultaneously, faster than serial.
• Fully Staring Arrays: The entire scene is imaged simultaneously, with no moving parts, the fastest.
• SPRITE Detector: (Signal PRocessing In The Element) uses a continuous strip of photodetector material to improve signal processing within each detector element, enhancing sensitivity and resolution.

Question 13

What is spontaneous emission?

Answer 13

Spontaneous emission is when an excited electron spontaneously falls to a lower energy state, emitting a photon without external stimulation.

Question 14

What is stimulated emission?

Answer 14

Stimulated emission occurs when an incoming photon causes an excited electron to fall to a lower energy state, emitting a photon coherent with the stimulating photon.