# 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