L22 Pre-flight

L22 Pre-flight#

Block 3: IR EW and Signature Management — Lesson 22: IR Emitters Work this before L22. 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#

  • L21 wrap-up (blackbody, MWIR/LWIR windows, reflective vs emissive sensing)

  • The Jupyter Book Reading page for L22 — the five IR signature components, the in-band intensity rule used to rank them, how aspect and look-geometry shift the dominant component, and thermal crossover.

Quiz questions (5 items, ~5 minutes)#

Q1. (Multiple choice) Viewed from dead astern at night, which component dominates an aircraft’s IR signature, and in which band?

  • [ ] (a) Airframe skin; LWIR

  • [ ] (b) Hot parts and exhaust plume; MWIR

  • [ ] (c) Reflected sunlight; MWIR

  • [ ] (d) Reflected earthshine; LWIR

Q2. (Multiple choice) In the ranking rule \(I_{\text{band}} \propto \varepsilon \cdot A \cdot f_{\text{band}}(T) \cdot \sigma T^4\), which single factor best explains why a small, very hot nozzle can outshine the large, cool airframe skin per unit area?

  • [ ] (a) The emissivity \(\varepsilon\)

  • [ ] (b) The projected area \(A\)

  • [ ] (c) The \(\sigma T^4\) (temperature) term

  • [ ] (d) The band fraction \(f_{\text{band}}\) at fixed temperature

Q3. (Multiple choice) Reflected sunlight is a meaningful part of an aircraft’s signature in which band, and when?

  • [ ] (a) LWIR, at night

  • [ ] (b) MWIR, during the day

  • [ ] (c) LWIR, during the day

  • [ ] (d) It never contributes meaningfully

Q4. (Short answer) In one sentence, what is thermal crossover, and why does it matter to a penetrating aircraft trying to stay hidden in the LWIR?

Q5. (Multiple choice) Why can an aircraft present a strong MWIR signature from the rear but a much weaker one from the beam?

  • [ ] (a) The skin is physically hotter near the tail

  • [ ] (b) From astern the sensor sees the hot nozzle and plume directly, which are masked at the beam

  • [ ] (c) Reflected sunlight only reaches the tail

  • [ ] (d) The atmosphere only transmits MWIR toward the rear

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