# L23 Pre-flight **Block 3: IR EW and Signature Management — Lesson 23: IR Seekers, IRST, and FLIR** *Work this before L23. 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 - L22 wrap-up (five signature components, in-band intensity ranking rule, aspect and thermal crossover) - The Jupyter Book Reading page for L23 — the seeker / IRST / FLIR division of labor, reticle vs imaging seekers, why IRST is a passive radar with a ranging problem, and the passive detection range rule. --- ## Quiz questions (5 items, ~5 minutes) **Q1.** (Multiple choice) A **reticle seeker** tracks a target by: - [ ] (a) Forming a full image and matching the target's shape frame to frame - [ ] (b) Chopping the target's energy with a spinning patterned disk and reading the modulation - [ ] (c) Transmitting a laser pulse and timing the return - [ ] (d) Comparing the target's radar and IR returns --- **Q2.** (Multiple choice) Why did **imaging (FPA) seekers** fundamentally change the countermeasure game compared with reticle seekers? - [ ] (a) They see a shape with spatial, spectral, and temporal structure, which a flare struggles to fake - [ ] (b) They detect at longer wavelengths where flares do not radiate at all - [ ] (c) They are active sensors, so decoys cannot blind them - [ ] (d) They have a wider field of view than any reticle seeker --- **Q3.** (Multiple choice) An IRST is often called a "passive radar." Which pairing correctly gives its biggest **operational advantage** and its biggest **limitation**? - [ ] (a) Advantage: high-resolution imagery; limitation: needs a human interpreter - [ ] (b) Advantage: emits nothing for the target's RWR to detect; limitation: angles come easy but range does not - [ ] (c) Advantage: unaffected by weather; limitation: rear-aspect only - [ ] (d) Advantage: longer wavelength than radar; limitation: cannot track more than one target --- **Q4.** (Short answer) In one or two sentences: using the rule $R_{\max} \propto \sqrt{J\,\tau/\text{NEI}}$ and radar's $R_{\max} \propto \sigma^{1/4}$, explain why IRST systems are attractive against **low-observable (stealth)** aircraft. --- **Q5.** (Multiple choice) Early IR missiles could only be fired from the target's **rear hemisphere**, while later ones became **all-aspect**. What made the difference? - [ ] (a) Faster rocket motors that could catch a crossing target - [ ] (b) Larger warheads that removed the need for precise aim - [ ] (c) Cooled MWIR detectors that could see the exhaust plume, not just hot metal - [ ] (d) Radar mid-course guidance added to the missile