Sensors 9-10

Question 1

What are the 3 EO spectrum category?

Answer 1

UV, Visible and Infrared (IR) radiation

Question 2

EO radiation sources?

Answer 2

1. Self emissions: from the vibration and rotation of the atoms and molecules within any material whose temperature is above 0 K (-273C)
2. External sources: EM energy that has been REFLECTED from an external source (sunlight, LASER)

Question 3

What is the relationship between reflectivity and emissivity?

Answer 3

Above 3.5 microns, emissivity dominates. Above 3.5 microns, these wavelength belongs to IR (middle, far, extreme)
Below 3.5 microns, reflectivity dominates

Question 4

What are the 2 effects that are responsible for the attenuation of IR radiation as it passes through the earth’s atmosphere?

Answer 4

Absorption + Scattering
ABSORPTION: Certain frequency are absorbed by the molecules in the air with the matching vibration or rotation. (Resonant absorption). Water vapour is the greatest source of attenuation and account for 60% of IR radiation absorption, next in importance is CO2

SCATTERING: Caused by particles such as dust/water drop in the atmosphere. It depends on weather. More scattering at lower altitude and shorter wavelength.

Haze: severely scatters visible energy but doesn’t affect IR
In light fog: IR is affected but remains still better than visible energy
Rain+Cloud: IR detection has no advantage over visual detection.

Question 5

What LASER stands for?

Answer 5

Light Amplification by Stimulated Emission of Radiation

Question 6

Give a definition of LASER

Answer 6

Excited electron drops to a lower energy state by releasing a photon with equal energy to that lost; This stimulates another electron to release a photon

Question 7

What are the required elements to develop a LASER

Answer 7

1. LASER medium (material with an intrinsic metastable state)
2. Energy Source (to develop the population inversion)
3. LASER cavity (to develop + amplify the LASER
   signal)
4. a ‘‘Stimulating’’ photon to initiate the appropriate decay level

Question 8

What are the LASER Properties (Characteristics)?

Answer 8

a. Monochromatic (emits energy at one specific freq) (One colour because no interference with other wavelength)
b. Coherent (propagating in phase with each other)
c. Highly directional (Photons travel very nearly parallel and little spreading of the beam occurs)
d. High Intensity (the nature of a LASER allows it to be pulsed at extremely high power)

Question 9

In a general sense, all Electro-Optic systems contain 3 fundamental components..what are they?

Answer 9

1. Optical element = to collect, filter, focus incoming energy
2. Detector element = sense the wavelength of the collected energy and convert the energy into an electrical signal
3. Processing component = to process the electrical signal into a usable image

Question 10

What are the 2 basic ways in which IR systems can be categorized?

Answer 10

1. Passive(Overt)= sensor system uses existing environmental conditions to detect, track, etc
2. Active(covert) = sensor system emits some form of EM energy in the EO spectrum as part of their prime function.

Question 11

What roles EO systems generally serve?

Answer 11

a. Surveillance (Visible + IR) wavelength of 380-760 nm of range
b. Detection + Tracking (IR)
c. Weapon Guidance (IR)