SYMBOLS AND ACRONYMS ......................................... xiii
1. INTRODUCTION ................................................. 1
1.1. Imaging system nomenclature ............................. 3
1.2. System modeling ......................................... 5
1.3. Sensitivity and resolution limits ....................... 8
1.4. Infrared imaging systems ............................... 11
1.5. Infrared imaging system modeling ....................... 13
1.6. Model inputs ........................................... 14
1.7. References ............................................. 15
2. IR IMAGING SYSTEM EVOLUTION ................................. 17
2.1. Optics ................................................. 18
2.2. Scanners ............................................... 19
2.3. Detectors and coolers .................................. 22
2.3.1. Detector classification ......................... 22
2.3.2. Specific detectors .............................. 24
2.3.3. Detector operation .............................. 25
2.4. Specific systems ....................................... 26
2.4.1. Line scanners ................................... 26
2.4.2. Common module systems ........................... 27
2.4.3. EOMUX systems ................................... 30
2.4.4. EMUX systems .................................... 30
2.4.5. Second-generation systems ....................... 32
2.4.6. Staring array systems ........................... 33
2.4.7. Third-generation systems ........................ 34
2.5. Field of view .......................................... 34
2.5.1. Fill factor ..................................... 34
2.5.2. Staring arrays .................................. 35
2.5.3. Scanning arrays ................................. 36
2.6. References ............................................. 39
3.RADIOMETRY ................................................... 40
3.1. Radiative transfer ..................................... 41
3.2. Planck's blackbody law ................................. 42
3.3. Camera formula ......................................... 45
3.3.1. Scanning arrays ................................. 50
3.3.2. Staring arrays .................................. 50
3.4. Point source ........................................... 51
3.5. Photometry ............................................. 57
3.6. Normalization .......................................... 57
3.7. References ............................................. 61
4. MTF THEORY .................................................. 62
4.1. MTF definition ......................................... 63
4.2. Spatial frequency ...................................... 65
4.3. Linear filter theory ................................... 67
4.3.1. The EO system as a linear system ................ 68
4.3.2. Cascading MTFs .................................. 70
4.4. Superposition applied to optical systems ............... 71
4.5. Phase shifts ........................................... 74
4.6. References ............................................. 75
5. COMMON MODULE SYSTEMS ....................................... 76
5.1. Optics OTF ............................................. 78
5.1.1. Diffraction-limited OTF ......................... 78
5.1.2. Central obscuration ............................. 81
5.1.3. Non-circular apertures .......................... 83
5.1.4. Anamorphic optics ............................... 83
5.1.5. Aberrations ..................................... 84
5.1.5.1. Theoretical approximation .............. 84
5.1.5.2. Gaussian approximation ................. 85
5.1.5.3. Aberration parameter ................... 86
5.1.6. Defocused optics ................................ 87
5.2. Detectors .............................................. 89
5.3. Motion ................................................. 90
5.3.1. Linear motion ................................... 91
5.3.2. Sinusoidal motion ............................... 95
5.3.3. Random motion (jitter) .......................... 96
5.3.4. Nonlinear scan mirror movement .................. 99
5.3.5. Low-frequency motion ............................ 99
5.4. Electronic MTF ........................................ 100
5.4.1. Conversion: Electrical frequency to spatial
frequency ...................................... 100
5.4.2. Detector time constant ......................... 105
5.4.3. Amplifiers ..................................... 105
5.4.4. Electrical filters ............................. 105
5.5. LEDs .................................................. 108
5.6. Visual optics ......................................... 108
5.7. Eye response .......................................... 109
5.7.1. Conversion: Eye spatial frequency to spatial
frequency ...................................... 109
5.7.2. Eye MTF ........................................ 110
5.7.3. Eye contrast threshold function (CTF) .......... 115
5.8. Optical zoom .......................................... 116
5.9. System design example: Random motion .................. 117
5.10.References ............................................ 120
6. EOMUX SYSTEMS .............................................. 122
6.1. Vidicon ............................................... 122
6.1.1. Conversion: Vidicon lines to spatial
frequency ...................................... 123
6.1.2. Vidicon MTF .................................... 123
6.2. Video amplifiers and filters .......................... 124
6.2.1. Conversion: Video frequency to spatial
frequency ...................................... 125
6.2.2. Boost circuitry ................................ 125
6.2.3. Video amplifiers ............................... 127
6.3. CRT monitors .......................................... 127
6.4. References ............................................ 130
7. EMUX SYSTEMS ............................................... 131
7.1. Detector .............................................. 132
7.1.1. TD1 ............................................ 133
7.1.2. SPRITE detector ................................ 135
7.1.3. Uncooled detectors ............................. 137
7.2. Conversion: Sampling frequency to spatial
frequency ............................................. 138
7.3. Conversion: Video sampling frequency to spatial
frequency ............................................. 139
7.4. Digital to analog data ................................ 139
7.4.1. Sample-and-hold ................................ 140
7.4.2. Post-reconstruction filter ..................... 140
7.5. References ............................................ 144
8. STARING ARRAY SYSTEMS ...................................... 145
8.1. Transfer efficiency ................................... 145
8.2. Flat-panel displays ................................... 147
9. LINE SCANNERS .............................................. 148
9.1. Rectangular aperture .................................. 152
9.1.1. Diffraction-limited OTF ........................ 153
9.1.2. DefocusOTF ..................................... 154
9.1.3. Ground coverage ................................ 157
9.2. Scanner ............................................... 158
9.3. Motion ................................................ 158
9.4. Electronic MTF ........................................ 158
9.5. AN/AAD-5 CRT MTF ...................................... 159
9.6. AN/AAD-5 film ......................................... 160
9.6.1. Conversion: Film response to spatial
frequency ...................................... 160
9.6.2. Film MTF ....................................... 160
9.7. References ............................................ 161
10.TWO-DIMENSIONAL MTF ........................................ 162
10.1.Optics ................................................ 162
10.2.Motion ................................................ 164
10.2.1.Linear motion .................................. 164
10.2.2.Sinusoidal motion .............................. 166
10.2.3.Random motion .................................. 167
10.3.Detector .............................................. 167
10.4.Electronics ........................................... 167
10.5.Digital processing .................................... 167
10.6.Visual optics ......................................... 168
10.7.Vidicon ............................................... 168
10.8.Displays .............................................. 168
10.9.The eye ............................................... 168
10.10.References ........................................... 168
11.SAMPLING ................................................... 169
11.1.Sampling theory ....................................... 172
11.2.Horizontal sampling frequency ......................... 175
11.2.1.Scanning systems ............................... 175
11.2.2.Staring arrays ................................. 177
11.3.Vertical sampling frequency ........................... 178
11.3.1.Scanning systems ............................... 178
11.3.2.Staring arrays ................................. 181
11.4.Reconstruction ........................................ 182
11.4.1.CRT monitor .................................... 182
11.4.2.Flat-panel display ............................. 183
11.5.Fλ/d .................................................. 185
11.6.Microscan ............................................. 189
11.7.Super resolution reconstruction ....................... 194
11.8.Sample-scene phase .................................... 195
11.9.Spurious response ..................................... 197
11.9.1.Schade's approach .............................. 198
11.9.2.MTF squeeze .................................... 200
11.9.3.Resolved cycle contraction ..................... 204
11.10.References ........................................... 204
12.IMAGING PROCESSING ......................................... 207
12.1.z-transform ........................................... 207
12.2.Digital filters ....................................... 208
12.2.1.Boost filter ................................... 211
12.2.2.Averaging filter ............................... 212
12.3.Electronic zoom (interpolation) ....................... 214
12.3.1.Ideal interpolator ............................. 215
12.3.2.Lanczos interpolator ........................... 215
12.3.3.Pixel replication .............................. 217
12.3.4.Linear interpolation ........................... 218
12.3.5.Bilinear interpolation ......................... 219
12.3.6.Image quality .................................. 220
12.4.Line-to-line interpolation ............................ 221
12.5.Noise reduction algorithms ............................ 223
12.6.Image restoration ..................................... 225
12.7.References ............................................ 225
13.RESOLUTION ................................................. 227
13.1.Analog metrics ........................................ 229
13.2.NIIRS ................................................. 231
13.3.Sampled data systems .................................. 234
13.4.Schade's equivalent resolution ........................ 237
13.4.1.Analog systems ................................. 237
13.4.2.Sampled data systems ........................... 244
13.5.References ............................................ 246
14.IMAGE QUALITY .............................................. 247
14.1.Mathematical metrics .................................. 248
14.2.MTF ................................................... 249
14.3.Perceived resolution .................................. 251
14.4.Subjective quality factor ............................. 252
14.5.MTF A ................................................. 255
14.6.Square-root integral .................................. 255
14.7.Targeting task performance ............................ 256
14.8.Resolution versus perceivable detail .................. 257
14.9.References ............................................ 258
15.ATMOSPHERIC TRANSMITTANCE .................................. 259
15.1.Atmospheric constituents .............................. 262
15.1.1.Water vapor .................................... 263
15.1.2.Aerosols ....................................... 266
15.2.Visibility ............................................ 268
15.2.1.Meteorological range ........................... 269
15.2.2.Contrast transmittance ......................... 270
15.3.LOWTRAN, MODTRAN, and HITRAN .......................... 271
15.4.Spectrally averaged atmospheric transmittance ......... 275
15.5.Weather conditions .................................... 278
15.5.1.Average conditions ............................. 278
15.5.2.Probability of occurrence ...................... 279
15.5.3.Navy model ..................................... 281
15.5.4.Land-based systems, horizontal path ............ 284
15.5.5.Land-based systems, slant path ................. 285
15.6.MWIR versus LWIR ...................................... 286
15.7.Sun glints ............................................ 293
15.8.Solar scattering ...................................... 295
15.9.Battlefield obscurants ................................ 295
15.10.References ........................................... 297
16.ATMOSPHERIC MTF ............................................ 299
16.1.CN2 ................................................... 301
16.2.Fried's coherence diameter ............................ 304
16.2.1.Horizontal path length ......................... 304
16.2.2.Slant path ..................................... 306
16.3.Turbulence MTF ........................................ 309
16.4.Aerosol MTF ........................................... 312
16.5.References ............................................ 314
17.TARGET SIGNATURES .......................................... 316
17.1.What is ΔТ? ........................................... 318
17.2.300K models ........................................... 320
17.3.Area-weighted ΔT ...................................... 321
17.4.Thermal structure metrics ............................. 323
17.5.Diurnal variations .................................... 324
17.5.1.Solar heating .................................. 325
17.5.2.ΔТ cumulative probability ...................... 327
17.5.3.Environmental modifiers ........................ 328
17.6.Active targets ........................................ 329
17.6.1.Fuel combustion ................................ 329
17.6.2.Frictional heat ................................ 330
17.7.Typical ΔTs ........................................... 330
17.8.Target signature modeling ............................. 330
17.9.Sky background ........................................ 331
17.10.Target signatures in the visible ..................... 332
17.11.Path radiance ........................................ 333
17.11.1.Infrared path radiance ........................ 334
17.11.2.Visible path radiance ......................... 335
17.12.References ........................................... 337
18.SENSITIVITY AND NOISE ...................................... 339
18.1.Noise equivalent bandwidth ............................ 340
18.2.Scanning arrays (analog system) ....................... 342
18.2.1.Photon noise ................................... 343
18.2.2.Johnson noise .................................. 343
18.2.3.Amplifier noise ................................ 344
18.3.Staring arrays ........................................ 344
18.3.1.Shot noise ..................................... 344
18.3.2.Dark current ................................... 344
18.3.3.Fixed pattern noise ............................ 346
18.3.4.Multiplexer noise .............................. 348
18.3.5.Quantization noise ............................. 348
18.4.Detector responsivity ................................. 349
18.4.1.Classical semiconductors ....................... 350
18.4.2.Novel semiconductors ........................... 351
18.4.3.Thermal detectors .............................. 351
18.5.Specific detectivity .................................. 352
18.5.1.BLIP ........................................... 352
18.5.2.Johnson noise limited .......................... 354
18.5.3.D*BB to D*p conversion ......................... 354
18.5.4.D*300 .......................................... 355
18.5.5.Focal ratio .................................... 356
18.6.System SNR ............................................ 357
18.7.NEDT .................................................. 358
18.7.1.Scanning systems ............................... 358
18.7.2.Staring arrays ................................. 359
18.7.3.Uncooled systems ............................... 359
18.7.4.Background temperature ......................... 360
18.7.5.Variable integration time ...................... 361
18.8.Real systems .......................................... 362
18.8.1.Three-dimensional noise model .................. 362
18.8.2.Fixed pattern noise ............................ 367
18.8.3.Noise figure ................................... 370
18.8.4.Non-scene photons .............................. 370
18.9.Signal-to-noise optimization .......................... 374
18.10.300K models .......................................... 378
18.11.NEI .................................................. 378
18.12.References ........................................... 380
19.SYSTEM PERFORMANCE MODELS .................................. 382
19.1.1975 NVL model ........................................ 384
19.2.FLIR92 ................................................ 386
19.2.1.FL1R92 theory .................................. 387
19.2.2.Moderate aspect ratio targets .................. 390
19.2.3.SNRTH and tE ................................... 392
19.2.4.Frame integration .............................. 393
19.2.5.Head movement .................................. 394
19.2.6.Embedded 1975 NVL model ........................ 394
19.2.7.Two-dimensional MRT ............................ 395
19.2.8.The brick wall ................................. 396
19.3.NVTherm Sept 2002 ..................................... 396
19.4.NVThermIP ............................................. 400
19.5.TRM3 .................................................. 404
19.6.Triangle orientation discrimination ................... 405
19.7.Model Comparisons ..................................... 406
19.8.References ............................................ 408
20.TARGET DISCRIMINATION ...................................... 410
20.1.One-dimensional target acquisition .................... 412
20.1.1.Johnson criterion .............................. 413
20.1.2.Extended discrimination ........................ 415
20.1.3.Target transfer probability function ........... 418
20.2.Two-dimensional discrimination ........................ 423
20.2.1.Discrimination requirements .................... 423
20.2.2.Two-dimensional TTPF ........................... 425
20.2.3.Targeting task performance ..................... 426
20.3.Current definitions ................................... 431
20.4.Current N50/ V50 values ................................ 433
20.5.Hot spot detection .................................... 438
20.6.Clutter ............................................... 439
20.7.References ............................................ 442
21.RANGE PREDICTIONS .......................................... 445
21.1.ACQUIRE ............................................... 447
21.1.1.Range prediction methodology ................... 448
21.1.2.Range performance probability .................. 450
21.1.3.Two fields of view ............................. 451
21.2.Trade-off analyses .................................... 452
21.2.1.Line-of-sight stabilization .................... 452
21.2.2.Resolution versus sensitivity .................. 453
21.2.3.STADIUM FLIR ................................... 456
21.3.NVThermIP ............................................. 457
21.3.1.Viewing distance ............................... 458
21.3.2.Electric zoom .................................. 460
21.3.3.Scene contrast ................................. 460
21.3.4.Frame averaging ................................ 461
21.3.5.Image enhancement .............................. 462
21.3.6.Super-resolution reconstruction ................ 463
21.4.Simplified range predictions .......................... 465
21.4.1.Trade-off analyses ............................. 468
21.4.2.Detector-limited systems ....................... 474
21.5.Pixels versus cycles .................................. 475
21.6.Pixels on target ...................................... 476
21.7.300K models ........................................... 481
21.8.Search ................................................ 482
21.9.GIQE/NIIRS ............................................ 483
21.10.References ........................................... 487
APPENDIX 1 (Focal ratio) ...................................... 490
APPENDIX 2 (CosineNθ) ......................................... 492
APPENDIX 3 (Central limit theorem) ............................ 494
INDEX ......................................................... 495
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