L21 Pre-flight

L21 Pre-flight#

Block 3: IR EW and Signature Management — Lesson 21: IR/EO Fundamentals Work this before L21. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.

Assumed pre-class reading#

  • L20 wrap-up (Project 2 results and Block 2 synthesis)

  • The Jupyter Book Reading page for L21 — why warm objects radiate and how temperature sets the peak wavelength, the MWIR and LWIR atmospheric windows, reflective vs emissive sensing, and photon vs thermal detectors.

Quiz questions (5 items, ~5 minutes)#

Q1. (Multiple choice) A jet’s exhaust plume (~1000 K) and the aircraft’s skin (~325 K) both radiate. Compared with the skin, the hotter plume:

  • [ ] (a) peaks at a longer wavelength and radiates less total power

  • [ ] (b) peaks at a shorter wavelength and radiates more total power

  • [ ] (c) peaks at a shorter wavelength but radiates less total power overall

  • [ ] (d) peaks at a longer wavelength and radiates far more total power

Q2. (Multiple choice) Which pair are the two infrared atmospheric windows that military thermal systems are built around?

  • [ ] (a) 0.4–0.7 µm (visible) and 1–2 µm (near IR)

  • [ ] (b) 3–5 µm (MWIR) and 8–12 µm (LWIR)

  • [ ] (c) 5–8 µm (the CO₂ window) and 14–20 µm (very long wave)

  • [ ] (d) 8–12 µm (LWIR) and 20–40 µm

Q3. (Multiple choice) A thermal (LWIR) imager can form a useful image on a moonless night with no illumination because it:

  • [ ] (a) amplifies faint starlight, like a night-vision tube

  • [ ] (b) emits its own infrared to illuminate the scene

  • [ ] (c) senses the heat that objects radiate on their own

  • [ ] (d) requires a laser designator to function

Q4. (Short answer) In one sentence, why must a high-performance (photon) IR detector be cooled, often to around 77 K?

Q5. (Multiple choice) An early spin-scan “reticle” heat-seeking missile steers toward the brightest hot spot in its field of view. The classic countermeasure that exploits this weakness is to:

  • [ ] (a) jam the missile’s guidance radar with barrage noise from a pod

  • [ ] (b) release a flare that presents a brighter infrared source

  • [ ] (c) dispense chaff so the seeker tracks a cloud of false returns

  • [ ] (d) switch off the aircraft’s transponder and radios

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