ECE 495 — Electromagnetic Warfare and Survivability

Block 3: IR EW and Signature Management
Lesson 24: IR Countermeasures

Juan Jurado, Col, USAF, Ph.D.
Permanent Professor and Head
Electrical and Computer Engineering
Fall 2026

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Block 3 · Lesson 24 · Where We Left Off

Where We Left Off

L23 introduced the hunters: reticle seekers that track a chopped point of energy, imaging seekers that track a shape, and the passive sensors that cue them.

Today we fight back. How do you beat a sensor that emits nothing?

Today

A duel: every countermeasure we play, the seeker answers. We end where the duel stands today — imaging seekers versus lasers.

Block 3 · Lesson 24 · Objectives

Lesson Objectives

By the end of this lesson, you will be able to:

Classify IRCM by the four ways to attack the optical track: starve it, clutter it, deceive it, damage it
Explain flare seduction with the J contest and the tracking-gate timeline
Describe the IRCCM cues — trajectory, spectral, intensity — that kill flares
Argue why modern seekers pushed IRCM toward DIRCM and suppression

Block 3 · Lesson 24 · Part One

Our Move

Four ways to attack an optical track, and the one the flare plays.

Block 3 · Lesson 24 · The Four Moves

Four Ways to Attack the Optical Track

Every IRCM in this lesson is one of four moves against the seeker's information:

Move	What it does to the track
Starve it	Reduce the signature $J$ so the track never starts (suppression)
Clutter it	Add competing sources so the right one is unclear (flares, decoys)
Deceive it	Inject false information into the tracker (seduction, DIRCM)
Damage it	Overload or destroy the detector with directed energy

The target is not the missile — it is the missile's information.

Block 3 · Lesson 24 · The Flare

Our Move: the Flare

A flare offers the reticle seeker a better point of energy — and the seeker takes it.

Pyrotechnic (MTV) or special-material decoys, burning hotter in-band
Seduction: dispensed after lock, the flare drags the gate off the target
Smart dispensers sequence size, timing, and direction per threat

The contest

$$\frac{J_\text{flare}}{J_\text{tgt}} > 1$$

The flare wins while that holds with margin — and only inside the gate.

Block 3 · Lesson 24 · Flare Tactics

Playing Flares Before the Lock

Seduction assumes the missile is already tracking. Pre-emptive tactics attack earlier:

Distraction — decoys out before the seeker locks: it acquires a flare, not the aircraft
Dilution — many credible targets at once: the shooter must engage them all
Pre-emptive flaring burns the magazine fast — magazine depth is a KPP

Rise time, peak intensity, burn time, and spectral match fill out the scorecard.

Block 3 · Lesson 24 · Part Two

The Seeker Answers

A move this old has a mature counter. A flare is a lie, and lies have tells.

Block 3 · Lesson 24 · IRCCM

The Seeker's Answer: Three Cues That Kill a Flare

A flare is a lie, and lies have tells. Modern seekers check three of them:

Trajectory — the flare decelerates and falls away; aircraft do not fly like that
Spectral — at $\sim$2000 K the flare is hotter than any tailpipe; a two-color ratio flags it
Intensity — the flare's signature jumps in a fraction of a second; real ones do not

JET

GATE ON THE FLARE

Any tell trips the logic: freeze the gate on the original track and ignore the newcomer.

Block 3 · Lesson 24 · Band IV

Check: the Imaging Seeker Ends the Flare Era

Against a modern Band IV threat, the duel tilts hard:

An imaging seeker sees two objects separate — and keeps tracking the one shaped like an aircraft
Two-color and kinematic logic reject conventional flares even without a full image
Flares still earn their ride against the huge inventory of legacy reticle threats
But against the newest MANPADS, expendables alone are a losing hand

JET

FLARE REJECTED — LOCK HOLDS

You cannot out-shout a seeker that can see shapes.

Block 3 · Lesson 24 · DIRCM

Our Answer: DIRCM

If the seeker ignores decoys, attack the seeker itself — with light:

MWSlaunch detected

→

Turretslews to the seeker

→

Modulated laserinto its optics

→

Break lockgate driven off

A modulated laser feeds the seeker false tracking error — the goal is optical break lock: drive the gate off the aircraft, and keep it off
Earlier lamp jammers radiated blindly; lasers add power, precision, tailoring

Block 3 · Lesson 24 · Suppression

The Quiet Move: Suppress the Signature

The duel's cheapest victory is the one that never starts — attack $J$ at the design table:

Plume — mix exhaust with cool bypass air; shape nozzles to shred the hot core
Hot parts — bury the engines, mask line-of-sight to the nozzle, avoid afterburner
Skin — low-emissivity finishes push the L22 skin term down

L23 prices it

$$R_{\max} \propto \sqrt{J}$$

For the B-21, this is not a pod on a pylon — it is the airframe itself.

Block 3 · Lesson 24 · Looking Ahead

Where This Is Headed: the Other Signature

Block 3 now pivots from the IR signature to its RF twin:

Everything we did to $J$ — rank, aspect, suppress — has a radar-side analog in RCS
L25 builds it: RCS as geometric cross section $\times$ reflectivity $\times$ directivity
The same duel logic returns: the radar's $\sigma^{1/4}$ is the RF version of our $\sqrt{J}$
By L28 we fuse them: a survivable aircraft manages every signature at once

Block 3 · Lesson 24 · Quick Exercise

Quick Exercise / Type-along: Race the Gate

Type this with me — today's flare model, run at two rise times.

t     = linspace(0,4,4001);      % s since dispense
J_tgt = 800;                     % target, stern MWIR [W/sr]
J_pk  = 4000;                    % flare peak scale [W/sr]
tau_b = 2.0;                     % flare burn-down [s]
gate  = 2000*deg2rad(1.5);       % gate half-width [m]
sep   = 200*(t - 0.75*(1-exp(-t/0.75)));   % flare drops aft
tc    = t(find(sep > gate, 1));  % pair splits the gate
for tau_r = [0.1 1.0]
    J  = J_pk*(1-exp(-t/tau_r)).*exp(-t/tau_b);
    to = t(find(J > J_tgt, 1));  % flare wins the contest
    fprintf('tau_r %.1f s: win %.2f s window %.2f s peak %.0f\n', ...
            tau_r, to, tc - to, max(J));
end
fprintf('gate %.0f m   split %.2f s\n', gate, tc);

Two numbers moved and one could not. Which one is stuck, and why?

Both flares are 4000 W/sr on the label. Why is the slow one only 1540?

Block 3 · Lesson 24 · Quick Problem

Quick Problem: Is the Window Open?

A notional aircraft dispenses one flare against a reticle seeker locked on its stern.

Target: $J_\text{tgt} = 400$ W/sr
Flare: $J_\text{pk} = 2500$ W/sr, $\tau_r = 0.25$ s, $\tau_b = 2.5$ s
Aircraft speed $v_\text{ac} = 240$ m/s; flare drag constant $\tau_d = 0.5$ s
Gate half-angle 1.0° at $R = 2.5$ km, so $g = R\,\theta_{1/2} = 43.6$ m

(a) The flare's intensity at $t = 0.2$ s. Has it won the J contest?
(b) The flare–target separation at $t = 0.2$ s. Is the seduction window open?
(c) The separation at $t = 0.6$ s. Is the window still open?

(a) 1270 W/sr, 3.18× the target: won · (b) 8.4 m, inside 43.6 m: open · (c) 60.1 m, past 43.6 m: shut

Two to three minutes, calculators or a MATLAB console; then click. Worked path, pure substitution into the reading's two curves. (a) J at 0.2 s is 2500 times 1 minus e to the minus 0.8, 0.5507, times e to the minus 0.08, 0.9231: 1270 W/sr, 3.18 times the 400 W/sr target — the contest is won, with margin. (b) s at 0.2 s is 240 times 0.2 minus 0.5 times 1 minus e to the minus 0.4, which is 0.3297, so 240 times 0.0352, 8.4 m — well inside the 43.6 m gate. Both conditions hold: the window is open and the seeker is being seduced. (c) s at 0.6 s is 240 times 0.6 minus 0.5 times 1 minus e to the minus 1.2, 0.6988, so 240 times 0.2506, 60.1 m — past the gate, the pair has split, the window is shut. The flare did not fade: at 0.6 s it is at 1790 W/sr, still 4.5 times the target. The so-what: geometry, not brightness, shut the window — the pair split the gate just before 0.5 s while the flare was still climbing — so every tenth of a second a slow rise spends climbing comes straight out of a window less than half a second long.

Today's Interactive Demo: the Seduction Window

Companion script: L24_FlareSeduction.m

Live demo

Seeker Bench

usafa-ece.github.io/ece-495-ew

Block 3 · Lesson 24 · Wrap-Up

Wrap-Up

Key ideas

IRCM is four moves on the seeker's information: starve, clutter, deceive, damage
A flare wins while $J_\text{flare}/J_\text{tgt} > 1$ inside the gate — rise time and geometry set the window
IRCCM tells — trajectory, spectral, intensity — ended the flare's easy era
The modern duel is DIRCM vs imaging seekers, atop signatures suppressed by design

Next lesson

L25: RCS Physics — geometric cross section, reflectivity, and directivity
Work the L25 pre-flight before class — you could be the one up front