# 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 (~900 K) and the aircraft's skin (~300 K) both radiate. Compared with the skin, the hotter plume's peak emission sits at a ____ wavelength and carries ____ total power: - [ ] (a) longer; less - [ ] (b) shorter; more - [ ] (c) shorter; less - [ ] (d) longer; more --- **Q2.** (Multiple choice) Which pair are the two infrared atmospheric windows that military thermal systems are built around? - [ ] (a) 0.4–0.7 µm and 1–2 µm - [ ] (b) 3–5 µm (MWIR) and 8–12 µm (LWIR) - [ ] (c) 5–8 µm and 14–20 µm - [ ] (d) 8–12 µm 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 radar frequency with noise - [ ] (b) release a flare that presents a brighter infrared source - [ ] (c) deploy chaff to create false radar returns - [ ] (d) switch off the aircraft's transponder