1i.atcorr(1) Grass User's Manual i.atcorr(1)
2
3
4
6 i.atcorr - Performs atmospheric correction using the 6S algorithm.
7 6S - Second Simulation of Satellite Signal in the Solar Spectrum.
8
10 imagery, atmospheric correction, radiometric conversion, radiance,
11 reflectance, satellite
12
14 i.atcorr
15 i.atcorr --help
16 i.atcorr [-irab] input=name [range=min,max] [elevation=name] [vis‐
17 ibility=name] parameters=name output=name [rescale=min,max]
18 [--overwrite] [--help] [--verbose] [--quiet] [--ui]
19
20 Flags:
21 -i
22 Output raster map as integer
23
24 -r
25 Input raster map converted to reflectance (default is radiance)
26
27 -a
28 Input from ETM+ image taken after July 1, 2000
29
30 -b
31 Input from ETM+ image taken before July 1, 2000
32
33 --overwrite
34 Allow output files to overwrite existing files
35
36 --help
37 Print usage summary
38
39 --verbose
40 Verbose module output
41
42 --quiet
43 Quiet module output
44
45 --ui
46 Force launching GUI dialog
47
48 Parameters:
49 input=name [required]
50 Name of input raster map
51
52 range=min,max
53 Input range
54 Default: 0,255
55
56 elevation=name
57 Name of input elevation raster map (in m)
58
59 visibility=name
60 Name of input visibility raster map (in km)
61
62 parameters=name [required]
63 Name of input text file with 6S parameters
64
65 output=name [required]
66 Name for output raster map
67
68 rescale=min,max
69 Rescale output raster map
70 Default: 0,255
71
73 i.atcorr performs atmospheric correction on the input raster map using
74 the 6S algorithm (Second Simulation of Satellite Signal in the Solar
75 Spectrum). A detailed algorithm description is available at the Land
76 Surface Reflectance Science Computing Facility website.
77
78 Important: Current region settings are ignored! The region is adjusted
79 to cover the input raster map before the atmospheric correction is per‐
80 formed. The previous settings are restored afterwards.
81
82 If the -r flag is used, the input raster map is treated as reflectance.
83 Otherwise, the input raster map is treated as radiance values and it is
84 converted to reflectance at the i.atcorr runtime. The output data are
85 always reflectance.
86
87 The satellite overpass time has to be specified in Greenwich Mean Time
88 (GMT).
89
90 An example of the 6S parameters could be:
91 8 - geometrical conditions=Landsat ETM+
92 2 19 13.00 -47.410 -20.234 - month day hh.ddd longitude latitude ("hh.ddd" is in decimal hours GMT)
93 1 - atmospheric model=tropical
94 1 - aerosols model=continental
95 15 - visibility [km] (aerosol model concentration)
96 -0.600 - mean target elevation above sea level [km] (here 600 m asl)
97 -1000 - sensor height (here, sensor on board a satellite)
98 64 - 4th band of ETM+ Landsat 7
99 If the position is not available in longitude-latitude (WGS84), the
100 m.proj conversion module can be used to reproject from a different ref‐
101 erence system.
102
104 A. Geometrical conditions
105 Code Description Details
106
107 1 meteosat observation enter month,day,decimal hour (universal time-hh.ddd)
108 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â n. of column,n.
109 of line. (full scale 5000*2500)Â
110
111 2 goes east observation enter month,day,decimal hour (universal time-hh.ddd)
112 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â n. of column,n.
113 of line. (full scale 17000*12000)c
114
115 3 goes west observation enter month,day,decimal hour (universal time-hh.ddd)
116 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â n. of column,n.
117 of line. (full scale 17000*12000)
118
119 4 avhrr (PM noaa) enter month,day,decimal hour (universal time-hh.ddd)
120 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â n. of col‐
121 umn(1-2048),xlonan,hna
122 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â give long.(xlo‐
123 nan) and overpass hour (hna) at
124 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â the ascendant
125 node at equator
126
127 5 avhrr (AM noaa) enter month,day,decimal hour (universal time-hh.ddd)
128 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â n. of col‐
129 umn(1-2048),xlonan,hna
130 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â give long.(xlo‐
131 nan) and overpass hour (hna) at
132 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â the ascendant
133 node at equator
134
135
136 6 hrv (spot) enter month,day,hh.ddd,long.,lat. *
137
138 7 tm (landsat) enter month,day,hh.ddd,long.,lat. *
139
140 8 etm+ (landsat7) enter month,day,hh.ddd,long.,lat. *
141
142 9 liss (IRS 1C) enter month,day,hh.ddd,long.,lat. *
143
144 10 aster enter month,day,hh.ddd,long.,lat. *
145
146 11 avnir enter month,day,hh.ddd,long.,lat. *
147
148 12 ikonos enter month,day,hh.ddd,long.,lat. *
149
150 13 RapidEye enter month,day,hh.ddd,long.,lat. *
151
152 14 VGT1 (SPOT4) enter month,day,hh.ddd,long.,lat. *
153
154 15 VGT2 (SPOT5) enter month,day,hh.ddd,long.,lat. *
155
156 16 WorldView 2 enter month,day,hh.ddd,long.,lat. *
157
158 17 QuickBird enter month,day,hh.ddd,long.,lat. *
159
160 18 LandSat 8 enter month,day,hh.ddd,long.,lat. *
161
162 19 Geoeye 1 enter month,day,hh.ddd,long.,lat. *
163
164 20 Spot6 enter month,day,hh.ddd,long.,lat. *
165
166 21 Spot7 enter month,day,hh.ddd,long.,lat. *
167
168 22 Pleiades1A enter month,day,hh.ddd,long.,lat. *
169
170 23 Pleiades1B enter month,day,hh.ddd,long.,lat. *
171
172 24 Worldview3 enter month,day,hh.ddd,long.,lat. *
173
174 25 Sentinel-2A enter month,day,hh.ddd,long.,lat. *
175
176 26 Sentinel-2B enter month,day,hh.ddd,long.,lat. *
177
178 27 PlanetScope 0c 0d enter month,day,hh.ddd,long.,lat. *
179
180 28 PlanetScope 0e enter month,day,hh.ddd,long.,lat. *
181
182 29 PlanetScope 0f 10 enter month,day,hh.ddd,long.,lat. *
183
184 30 Worldview4 enter month,day,hh.ddd,long.,lat. *
185
186
187 NOTE: for HRV, TM, ETM+, LISS and ASTER experiments, longitude and lat‐
188 itude are the coordinates of the scene center. Latitude must be > 0 for
189 northern hemisphere and < 0 for southern. Longitude must be > 0 for
190 eastern hemisphere and < 0 for western.
191
192 B. Atmospheric model
193 Code Meaning
194
195 0 no gaseous absorption
196
197 1 tropical
198
199 2 midlatitude summer
200
201
202
203 3 midlatitude winter
204
205 4 subarctic summer
206
207 5 subarctic winter
208
209 6 us standard 62
210
211 7 Define your own atmospheric model as a set of the following
212 5 parameters per each measurement: altitude [km] pressure
213 [mb] temperature [k] h2o density [g/m3] o3 density [g/m3]
214 For example: there is one radiosonde measurement for each
215 altitude of 0-25km at a step of 1km, one measurment for each
216 altitude of 25-50km at a step of 5km, and two single mea‐
217 surements for altitudes 70km and 100km. This makes 34 mea‐
218 surments. In that case, there are 34*5 values to input.
219
220 8 Define your own atmospheric model providing values of the
221 water vapor and ozone content: uw [g/cm2] uo3 [cm-atm] The
222 profile is taken from us62.
223
224
225 C. Aerosols model
226 Code Meaning Details
227
228 0 no aerosols Â
229
230 1 continental model Â
231
232 2 maritime model Â
233
234 3 urban model Â
235
236 4 shettle model for background desert aerosol Â
237
238 5 biomass burning Â
239
240 6 stratospheric model Â
241
242 7 define your own model Enter the volumic percentage of each component: c(1) = volu‐
243 mic % of dust-like c(2) = volumic % of water-soluble c(3) =
244 volumic % of oceanic c(4) = volumic % of soot All values
245 should be between 0 and 1.
246
247 8 define your own model Size distribution function: Multimodal Log Normal (up to 4
248 modes).
249
250 9 define your own model Size distribution function: Modified gamma.
251
252 10 define your own model Size distribution function: Junge Power-Law.
253
254 11 define your own model Sun-photometer measurements, 50 values max, entered as: r
255 and d V / d (logr) where r is the radius [micron], V is the
256 volume, d V / d (logr) [cm3/cm2/micron]. Followed by: nr
257 and ni for each wavelength where nr and ni are respectively
258 the real and imaginary part of the refractive index.
259
260
261 D. Aerosol concentration model (visibility)
262 If you have an estimate of the meteorological parameter visibility v,
263 enter directly the value of v [km] (the aerosol optical depth (AOD)
264 will be computed from a standard aerosol profile).
265
266 If you have an estimate of aerosol optical depth, enter 0 for the visi‐
267 bility and in a following line enter the aerosol optical depth at 550nm
268 (iaer means ’i’ for input and ’aer’ for aerosol), for example:
269 0 - visibility
270 0.112 - aerosol optical depth at 550 nm
271
272 NOTE: if iaer is 0, enter -1 for visibility.
273
274 NOTE: if a visibility map is provided, these parameters are ignored.
275
276 E. Target altitude (xps), sensor platform (xpp)
277 Target altitude (xps, in negative [km]): xps >= 0 means the target is
278 at the sea level.
279 otherwise xps expresses the altitude of the target (e.g., mean eleva‐
280 tion) in [km], given as negative value
281 Sensor platform (xpp, in negative [km] or -1000):
282 xpp = -1000 means that the sensor is on board a satellite.
283 xpp = 0 means that the sensor is at the ground level.
284 -100 < xpp < 0 defines the altitude of the sensor expressed in [km];
285 this altitude is given relative to the target altitude as negative
286 value.
287
288 For aircraft simulations only (xpp is neither equal to 0 nor equal to
289 -1000): puw,po3 (water vapor content,ozone content between the aircraft
290 and the surface)
291 taerp (the aerosol optical thickness at 550nm between the aircraft and
292 the surface)
293
294 If these data are not available, enter negative values for all of them.
295 puw,po3 will then be interpolated from the us62 standard profile
296 according to the values at the ground level; taerp will be computed
297 according to a 2 km exponential profile for aerosol.
298
299 F. Sensor band
300 There are two possibilities: either define your own spectral conditions
301 (codes -2, -1, 0, or 1) or choose a code indicating the band of one of
302 the pre-defined satellites.
303
304 Define your own spectral conditions:
305
306 Code Meaning
307
308 -2 Enter wlinf, wlsup. The filter function will be equal to 1
309 over the whole band (as iwave=0) but step by step output
310 will be printed.
311
312 -1 Enter wl (monochr. cond, gaseous absorption is included).
313
314 0 Enter wlinf, wlsup. The filter function will be equal to 1
315 over the whole band.
316
317 1 Enter wlinf, wlsup and user’s filter function s (lambda) by
318 step of 0.0025 micrometer.
319
320
321 Pre-defined satellite bands:
322
323 Code Band name (peak response)
324
325 2 meteosat vis band (0.350-1.110)
326
327 3 goes east band vis (0.490-0.900)
328
329 4 goes west band vis (0.490-0.900)
330
331 5 avhrr (noaa6) band 1 (0.550-0.750)
332
333 6 avhrr (noaa6) band 2 (0.690-1.120)
334
335
336
337 7 avhrr (noaa7) band 1 (0.500-0.800)
338
339 8 avhrr (noaa7) band 2 (0.640-1.170)
340
341 9 avhrr (noaa8) band 1 (0.540-1.010)
342
343 10 avhrr (noaa8) band 2 (0.680-1.120)
344
345 11 avhrr (noaa9) band 1 (0.530-0.810)
346
347 12 avhrr (noaa9) band 1 (0.680-1.170)
348
349 13 avhrr (noaa10) band 1 (0.530-0.780)
350
351 14 avhrr (noaa10) band 2 (0.600-1.190)
352
353 15 avhrr (noaa11) band 1 (0.540-0.820)
354
355 16 avhrr (noaa11) band 2 (0.600-1.120)
356
357 17 hrv1 (spot1) band 1 (0.470-0.650)
358
359 18 hrv1 (spot1) band 2 (0.600-0.720)
360
361 19 hrv1 (spot1) band 3 (0.730-0.930)
362
363 20 hrv1 (spot1) band pan (0.470-0.790)
364
365 21 hrv2 (spot1) band 1 (0.470-0.650)
366
367 22 hrv2 (spot1) band 2 (0.590-0.730)
368
369 23 hrv2 (spot1) band 3 (0.740-0.940)
370
371 24 hrv2 (spot1) band pan (0.470-0.790)
372
373 25 tm (landsat5) band 1 (0.430-0.560)
374
375 26 tm (landsat5) band 2 (0.500-0.650)
376
377 27 tm (landsat5) band 3 (0.580-0.740)
378
379 28 tm (landsat5) band 4 (0.730-0.950)
380
381 29 tm (landsat5) band 5 (1.5025-1.890)
382
383 30 tm (landsat5) band 7 (1.950-2.410)
384
385 31 mss (landsat5) band 1 (0.475-0.640)
386
387 32 mss (landsat5) band 2 (0.580-0.750)
388
389 33 mss (landsat5) band 3 (0.655-0.855)
390
391 34 mss (landsat5) band 4 (0.785-1.100)
392
393 35 MAS (ER2) band 1 (0.5025-0.5875)
394
395 36 MAS (ER2) band 2 (0.6075-0.7000)
396
397 37 MAS (ER2) band 3 (0.8300-0.9125)
398
399 38 MAS (ER2) band 4 (0.9000-0.9975)
400
401 39 MAS (ER2) band 5 (1.8200-1.9575)
402
403
404 40 MAS (ER2) band 6 (2.0950-2.1925)
405
406 41 MAS (ER2) band 7 (3.5800-3.8700)
407
408 42 MODIS band 1 (0.6100-0.6850)
409
410 43 MODIS band 2 (0.8200-0.9025)
411
412 44 MODIS band 3 (0.4500-0.4825)
413
414 45 MODIS band 4 (0.5400-0.5700)
415
416 46 MODIS band 5 (1.2150-1.2700)
417
418 47 MODIS band 6 (1.6000-1.6650)
419
420 48 MODIS band 7 (2.0575-2.1825)
421
422 49 avhrr (noaa12) band 1 (0.500-1.000)
423
424 50 avhrr (noaa12) band 2 (0.650-1.120)
425
426 51 avhrr (noaa14) band 1 (0.500-1.110)
427
428 52 avhrr (noaa14) band 2 (0.680-1.100)
429
430 53 POLDER band 1 (0.4125-0.4775)
431
432 54 POLDER band 2 (non polar) (0.4100-0.5225)
433
434 55 POLDER band 3 (non polar) (0.5325-0.5950)
435
436 56 POLDER band 4 P1 (0.6300-0.7025)
437
438 57 POLDER band 5 (non polar) (0.7450-0.7800)
439
440 58 POLDER band 6 (non polar) (0.7000-0.8300)
441
442 59 POLDER band 7 P1 (0.8100-0.9200)
443
444 60 POLDER band 8 (non polar) (0.8650-0.9400)
445
446 61 etm+ (landsat7) band 1 blue (435nm - 517nm)
447
448 62 etm+ (landsat7) band 2 green (508nm - 617nm)
449
450 63 etm+ (landsat7) band 3 red (625nm - 702nm)
451
452 64 etm+ (landsat7) band 4 NIR (753nm - 910nm)
453
454 65 etm+ (landsat7) band 5 SWIR (1520nm - 1785nm)
455
456 66 etm+ (landsat7) band 7 SWIR (2028nm - 2375nm)
457
458 67 etm+ (landsat7) band 8 PAN (505nm - 917nm)
459
460 68 liss (IRC 1C) band 2 (0.502-0.620)
461
462 69 liss (IRC 1C) band 3 (0.612-0.700)
463
464 70 liss (IRC 1C) band 4 (0.752-0.880)
465
466 71 liss (IRC 1C) band 5 (1.452-1.760)
467
468 72 aster band 1 (0.480-0.645)
469
470
471 73 aster band 2 (0.588-0.733)
472
473 74 aster band 3N (0.723-0.913)
474
475 75 aster band 4 (1.530-1.750)
476
477 76 aster band 5 (2.103-2.285)
478
479 77 aster band 6 (2.105-2.298)
480
481 78 aster band 7 (2.200-2.393)
482
483 79 aster band 8 (2.248-2.475)
484
485 80 aster band 9 (2.295-2.538)
486
487 81 avnir band 1 (408nm - 517nm)
488
489 82 avnir band 2 (503nm - 612nm)
490
491 83 avnir band 3 (583nm - 717nm)
492
493 84 avnir band 4 (735nm - 922nm)
494
495 85 Ikonos Green band (408nm - 642nm)
496
497 86 Ikonos Red band (448nm - 715nm)
498
499 87 Ikonos NIR band (575nm - 787nm)
500
501 88 RapidEye Blue band (440nm - 512nm)
502
503 89 RapidEye Green band (515nm - 592nm)
504
505 90 RapidEye Red band (628nm - 687nm)
506
507 91 RapidEye Red edge band (685nm - 735nm)
508
509 92 RapidEye NIR band (750nm - 860nm)
510
511 93 VGT1 (SPOT4) band 0 (420nm - 497nm)
512
513 94 VGT1 (SPOT4) band 2 (603nm - 747nm)
514
515 95 VGT1 (SPOT4) band 3 (740nm - 942nm)
516
517 96 VGT1 (SPOT4) MIR band (1540nm - 1777nm)
518
519 97 VGT2 (SPOT5) band 0 (423nm - 492nm)
520
521 98 VGT2 (SPOT5) band 2 (600nm - 737nm)
522
523 99 VGT2 (SPOT5) band 3 (745nm - 945nm)
524
525 100 VGT2 (SPOT5) MIR band (1523nm - 1757nm)
526
527 101 WorldView2 Panchromatic band (448nm - 812nm)
528
529 102 WorldView2 Coastal Blue band (395nm - 457nm)
530
531 103 WorldView2 Blue band (440nm - 517nm)
532
533 104 WorldView2 Green band (503nm - 587nm)
534
535 105 WorldView2 Yellow band (583nm - 632nm)
536
537
538 106 WorldView2 Red band (623nm - 695nm)
539
540 107 WorldView2 Red edge band (698nm - 750nm)
541
542 108 WorldView2 NIR1 band (760nm - 905nm)
543
544 109 WorldView2 NIR2 band (853nm - 1047nm)
545
546 110 QuickBird Panchromatic band (385nm - 1060nm)
547
548 111 QuickBird Blue band (420nm - 585nm)
549
550 112 QuickBird Green band (448nm - 682nm)
551
552 113 QuickBird Red band (560nm - 747nm)
553
554 114 QuickBird NIR1 band (650nm - 935nm)
555
556 115 Landsat 8 Coastal aerosol band (433nm - 455nm)
557
558 116 Landsat 8 Blue band (448nm - 515nm)
559
560 117 Landsat 8 Green band (525nm - 595nm)
561
562 118 Landsat 8 Red band (633nm - 677nm)
563
564 119 Landsat 8 Panchromatic band (498nm - 682nm)
565
566 120 Landsat 8 NIR band (845nm - 885nm)
567
568 121 Landsat 8 Cirrus band (1355nm - 1390nm)
569
570 122 Landsat 8 SWIR1 band (1540nm - 1672nm)
571
572 123 Landsat 8 SWIR2 band (2073nm - 2322nm)
573
574 124 GeoEye 1 Panchromatic band (448nm - 812nm)
575
576 125 GeoEye 1 Blue band (443nm - 525nm)
577
578 126 GeoEye 1 Green band (503nm - 587nm)
579
580 127 GeoEye 1 Red band (653nm - 697nm)
581
582 128 GeoEye 1 NIR band (770nm - 932nm)
583
584 129 Spot6 Blue band (440nm - 532nm)
585
586 130 Spot6 Green band (515nm - 600nm)
587
588 131 Spot6 Red band (610nm - 710nm)
589
590 132 Spot6 NIR band (738nm - 897nm)
591
592 133 Spot6 Pan band (438nm - 760nm)
593
594 134 Spot7 Blue band (445nm - 532nm)
595
596 135 Spot7 Green band (525nm - 607nm)
597
598 136 Spot7 Red band (610nm - 727nm)
599
600 137 Spot7 NIR band (745nm - 902nm)
601
602 138 Spot7 Pan band (443nm - 760nm)
603
604
605 139 Pleiades1A Blue band (433nm - 560nm)
606
607 140 Pleiades1A Green band (500nm - 617nm)
608
609 141 Pleiades1A Red band (590nm - 722nm)
610
611 142 Pleiades1A NIR band (740nm - 945nm)
612
613 143 Pleiades1A Pan band (460nm - 845nm)
614
615 144 Pleiades1B Blue band 438nm - 560nm)
616
617 145 Pleiades1B Green band (498nm - 615nm)
618
619 146 Pleiades1B Red band (608nm - 727nm)
620
621 147 Pleiades1B NIR band (750nm - 945nm)
622
623 148 Pleiades1B Pan band (460nm - 845nm)
624
625 149 Worldview3 Pan band (445nm - 812nm)
626
627 150 Worldview3 Coastal blue band (395nm - 455nm)
628
629 151 Worldview3 Blue band (443nm - 517nm)
630
631 152 Worldview3 Green band (508nm - 587nm)
632
633 153 Worldview3 Yellow band (580nm - 630nm)
634
635 154 Worldview3 Red band (625nm - 697nm)
636
637 155 Worldview3 Red edge band (698nm - 752nm)
638
639 156 Worldview3 NIR1 band (760nm - 902nm)
640
641 157 Worldview3 NIR2 band (855nm - 1042nm)
642
643 158 Worldview3 SWIR1 band (1178nm - 1242nm)
644
645 159 Worldview3 SWIR2 band (1545nm - 1600nm)
646
647 160 Worldview3 SWIR3 band (1633nm - 1687nm)
648
649 161 Worldview3 SWIR4 band (1698nm - 1762nm)
650
651 162 Worldview3 SWIR5 band (2133nm - 2195nm)
652
653 163 Worldview3 SWIR6 band (2170nm - 2235nm)
654
655 164 Worldview3 SWIR7 band (2225nm - 2295nm)
656
657 165 Worldview3 SWIR8 band (2283nm - 2377nm)
658
659 166 Sentinel2A Coastal blue band B1 (430nm - 455nm)
660
661 167 Sentinel2A Blue band B2 (440nm - 530nm)
662
663 168 Sentinel2A Green band B3 (540nm - 580nm)
664
665 169 Sentinel2A Red band B4 (648nm - 682nm)
666
667 170 Sentinel2A Red edge band B5 (695nm - 712nm)
668
669 171 Sentinel2A Red edge band B6 (733nm - 747nm)
670
671
672 172 Sentinel2A Red edge band B7 (770nm - 795nm)
673
674 173 Sentinel2A NIR band B8 (775nm - 905nm)
675
676 174 Sentinel2A Red edge band B8A (850nm - 880nm)
677
678 175 Sentinel2A Water vapour band B9 (933nm - 957nm)
679
680 176 Sentinel2A SWIR Cirrus band B10 (1355nm - 1392nm)
681
682 177 Sentinel2A SWIR band B11 (1558nm - 1667nm)
683
684 178 Sentinel2A SWIR band B12 (2088nm - 2315nm)
685
686 179 Sentinel2B Coastal blue band B1 (430nm - 455nm)
687
688 180 Sentinel2B Blue band B2 (440nm - 530nm)
689
690 181 Sentinel2B Green band B3 (538nm - 580nm)
691
692 182 Sentinel2B Red band B4 (648nm - 682nm)
693
694 183 Sentinel2B Red edge band B5 (695nm - 712nm)
695
696 184 Sentinel2B Red edge band B6 (730nm - 747nm)
697
698 185 Sentinel2B Red edge band B7 (768nm - 792nm)
699
700 186 Sentinel2B NIR band B8 (778nm - 905nm)
701
702 187 Sentinel2B Red edge band B8A (850nm - 877nm)
703
704 188 Sentinel2B Water vapour band B9 (930nm - 955nm)
705
706 189 Sentinel2B SWIR Cirrus band B10 (1358nm - 1397nm)
707
708 190 Sentinel2B SWIR band B11 (1555nm - 1667nm)
709
710 191 Sentinel2B SWIR band B12 (2075nm - 2300nm)
711
712 192 PlanetScope 0c 0d Blue band B1 (440nm - 570nm)
713
714 193 PlanetScope 0c 0d Green band B2 (450nm - 690nm)
715
716 194 PlanetScope 0c 0d Red band B3 (460nm - 700nm)
717
718 195 PlanetScope 0c 0d NIR band B4 (770nm - 880nm)
719
720 196 PlanetScope 0e Blue band B1 (430nm - 700nm)
721
722 197 PlanetScope 0e Green band B2 (450nm - 700nm)
723
724 198 PlanetScope 0e Red band B3 (460nm - 700nm)
725
726 199 PlanetScope 0e NIR band B4 (760nm - 880nm)
727
728 200 PlanetScope 0f 10 Blue band B1 (450nm - 680nm)
729
730 201 PlanetScope 0f 10 Green band B2 (450nm - 680nm)
731
732 202 PlanetScope 0f 10 Red band B3 (450nm - 680nm)
733
734 203 PlanetScope 0f 10 NIR band B4 (760nm - 870nm)
735
736 204 Worldview4 Pan band (424nm - 842nm)
737
738
739 205 Worldview4 Blue band (416nm - 567nm)
740
741 206 Worldview4 Green band (488nm - 626nm)
742
743 207 Worldview4 Red band (639nm - 711nm)
744
745 208 Worldview4 NIR1 band (732nm - 962nm)
746
747
749 Atmospheric correction of a Sentinel-2 band
750 This example illustrates how to perform atmospheric correction of a
751 Sentinel-2 scene in the North Carolina location.
752
753 Let’s assume that the Sentinel-2 L1C scene
754 S2A_OPER_PRD_MSIL1C_PDMC_20161029T092602_R054_V20161028T155402_20161028T155402
755 was downloaded and imported with region cropping (see r.import) into
756 the PERMANENT mapset of the North Carolina location. The computational
757 region was set to the extent of the elevation map in the North Carolina
758 dataset. Now, we have 13 individual bands (B01-B12) that we want to
759 apply the atmospheric correction to. The following steps are applied
760 to each band separately.
761
762 Create the parameters file for i.atcorr
763
764 In the first step we create a file containing the 6S parameters for a
765 particular scene and band. To create a 6S file, we need to obtain the
766 following information:
767
768 · geometrical conditions,
769
770 · moth, day, decimal hours in GMT, decimal longitude and latitude
771 of measurement,
772
773 · atmospheric model,
774
775 · aerosol model,
776
777 · visibility or aerosol optical depth,
778
779 · mean target elevation above sea level,
780
781 · sensor height and,
782
783 · sensor band.
784
785 1 Geometrical conditions
786
787 For Sentinel-2A, the geometrical conditions take the value 25 and for
788 Sentinel-2B, the geometrical conditions value is 26 (See table A). Our
789 scene comes from the Sentinel-2A mission (the file name begins with
790 S2A_...).
791
792 2 Day, time, longitude and latitude of measurement
793
794 Day and time of the measurement are hidden in the filename (i.e., the
795 second datum in the file name with format YYYYMMDDTHHMMSS), and are
796 also noted in the metadata file, which is included in the downloaded
797 scene (file with .xml extension). Our sample scene was taken on October
798 28th (20161028) at 15:54:02 (155402). Note that the time has to be
799 specified in decimal hours in Greenwich Mean Time (GMT). Luckily, the
800 time in the scene name is in GMT and we can convert it to decimal hours
801 as follows: 15 + 54/60 + 2/3600 = 15.901.
802
803 Longitude and latitude refer to the centre of the computational region
804 (which can be smaller than the scene), and must be in WGS84 decimal
805 coordinates. To obtain the coordinates of the centre, we can run:
806 g.region -bg
807
808 The longitude and latitude of the centre are stored in ll_clon and
809 ll_clat. In our case, ll_clon=-78.691 and ll_clat=35.749.
810
811 3 Atmospheric model
812
813 We can choose between various atmospheric models as defined at the
814 beginning of this manual. For North Carolina, we can choose 2 - midlat‐
815 itude summer.
816
817 4 Aerosol model
818
819 We can also choose between various aerosol models as defined at the
820 beginning of this manual. For North Carolina, we can choose 1 - conti‐
821 nental model.
822
823 5 Visibility or Aerosol Optical Depth
824
825 For Sentinel-2 scenes, the visibility is not measured, and therefore we
826 have to estimate the aerosol optical depth instead, e.g. from AERONET.
827 With a bit of luck, you can find a station nearby your location, which
828 measured the Aerosol Optical Depth at 500 nm at the same time as the
829 scene was taken. In our case, on 28th October 2016, the EPA-Res_Trian‐
830 gle_Pk station measured AOD = 0.07 (approximately).
831
832 6 Mean target elevation above sea level
833
834 Mean target elevation above sea level refers to the mean elevation of
835 the computational region. You can estimate it from the digital eleva‐
836 tion model, e.g. by running:
837 r.univar -g elevation
838
839 The mean elevation is stored in mean. In our case, mean=110. In the 6S
840 file it will be displayed in [-km], i.e., -0.110.
841
842 7 Sensor height
843
844 Since the sensor is on board a satellite, the sensor height will be set
845 to -1000.
846
847 8 Sensor band
848
849 The overview of satellite bands can be found in table F (see above).
850 For Sentinel-2A, the band numbers span from 166 to 178, and for Sen‐
851 tinel-2B, from 179 to 191.
852
853 Finally, here is what the 6S file would look like for Band 02 of our
854 scene. In order to use it in the i.atcorr module, we can save it in a
855 text file, for example params_B02.txt.
856 25
857 10 28 15.901 -78.691 35.749
858 2
859 1
860 0
861 0.07
862 -0.110
863 -1000
864 167
865
866 Compute atmospheric correction
867
868 In the next step we run i.atcorr for the selected band B02 of our Sen‐
869 tinel 2 scene. We have to specify the following parameters:
870
871 · input = raster band to be processed,
872
873 · parameters = path to 6S file created in the previous step (we
874 could also enter the values directly),
875
876 · output = name for the output corrected raster band,
877
878 · range = from 1 to the QUANTIFICATION_VALUE stored in the meta‐
879 data file. It is 10000 for both Sentinel-2A and Sentinel-2B.
880
881 · rescale = the output range of values for the corrected bands.
882 This is up to the user to choose, for example: 0-255, 0-1,
883 1-10000.
884
885 If the data is available, the following parameters can be specified as
886 well:
887
888 · elevation = raster of digital elevation model,
889
890 · visibility = raster of visibility model.
891
892 Finally, this is how the command would look like to apply atmospheric
893 correction to band B02:
894 i.atcorr input=B02 parameters=params_B02.txt output=B02.atcorr range=1,10000 rescale=0,255 elevation=elevation
895
896 To apply atmospheric correction to the remaining bands, only the last
897 line in the 6S parameters file (i.e., the sensor band) needs to be
898 changed. The other parameters will remain the same.
899 Figure: Sentinel-2A Band 02 with applied atmospheric correction (his‐
900 togram equalization grayscale color scheme)
901
902 Atmospheric correction of a Landsat-7 band
903 This example is also based on the North Carolina sample dataset (GMT -5
904 hours). First we set the computational region to the satellite map,
905 e.g. band 4:
906 g.region raster=lsat7_2002_40 -p
907
908 It is important to verify the available metadata for the sun position
909 which has to be defined for the atmospheric correction. An option is to
910 check the satellite overpass time with sun position as reported in the
911 metadata file (file copy; North Carolina sample dataset). In the case
912 of the North Carolina sample dataset, these values have been stored for
913 each channel and can be retrieved with:
914 r.info lsat7_2002_40
915 In this case, we have: SUN_AZIMUTH = 120.8810347, SUN_ELEVATION =
916 64.7730999.
917
918 If the sun position metadata are unavailable, we can also calculate
919 them from the overpass time as follows (r.sunmask uses SOLPOS):
920 r.sunmask -s elev=elevation out=dummy year=2002 month=5 day=24 hour=10 min=42 sec=7 timezone=-5
921 # .. reports: sun azimuth: 121.342461, sun angle above horz.(refraction corrected): 65.396652
922 If the overpass time is unknown, use the NASA LaRC Satellite Overpass
923 Predictor.
924
925 Convert digital numbers (DN) to radiance at top-of-atmosphere (TOA)
926 For Landsat and ASTER, the conversion can be conveniently done with
927 i.landsat.toar or i.aster.toar, respectively.
928
929 In case of different satellites, the conversion of DN (digital number =
930 pixel values) to radiance at top-of-atmosphere (TOA) can also be done
931 manually, using e.g. the formula:
932 # formula depends on satellite sensor, see respective metadata
933 Lλ = ((LMAXλ - LMINλ)/(QCALMAX-QCALMIN)) * (QCAL-QCALMIN) + LMINλ
934 where,
935
936 · Lλ = Spectral Radiance at the sensor’s aperture in Watt/(meter
937 squared * ster * µm), the apparent radiance as seen by the
938 satellite sensor;
939
940 · QCAL = the quantized calibrated pixel value in DN;
941
942 · LMINλ = the spectral radiance that is scaled to QCALMIN in
943 watts/(meter squared * ster * µm);
944
945 · LMAXλ = the spectral radiance that is scaled to QCALMAX in
946 watts/(meter squared * ster * µm);
947
948 · QCALMIN = the minimum quantized calibrated pixel value (corre‐
949 sponding to LMINλ) in DN;
950
951 · QCALMAX = the maximum quantized calibrated pixel value (corre‐
952 sponding to LMAXλ) in DN=255.
953 LMINλ and LMAXλ are the radiances related to the minimal and maximal
954 DN value, and they are reported in the metadata file of each image.
955 High gain or low gain is also reported in the metadata file of each
956 satellite image. For Landsat ETM+, the minimal DN value (QCALMIN) is 1
957 (see Landsat handbook, chapter 11), and the maximal DN value (QCALMAX)
958 is 255. QCAL is the DN value for every separate pixel in the Landsat
959 image.
960
961 We extract the coefficients and apply them in order to obtain the radi‐
962 ance map:
963 CHAN=4
964 r.info lsat7_2002_${CHAN}0 -h | tr ’\n’ ’ ’ | sed ’s+ ++g’ | tr ’:’ ’\n’ | grep "LMIN_BAND${CHAN}\|LMAX_BAND${CHAN}"
965 LMAX_BAND4=241.100,p016r035_7x20020524.met
966 LMIN_BAND4=-5.100,p016r035_7x20020524.met
967 QCALMAX_BAND4=255.0,p016r035_7x20020524.met
968 QCALMIN_BAND4=1.0,p016r035_7x20020524.met
969 Conversion to radiance (this calculation is done for band 4, for the
970 other bands, the numbers will need to be replaced with their related
971 values):
972 r.mapcalc "lsat7_2002_40_rad = ((241.1 - (-5.1)) / (255.0 - 1.0)) * (lsat7_2002_40 - 1.0) + (-5.1)"
973 Again, the r.mapcalc calculation is only needed when working with
974 satellite data other than Landsat or ASTER.
975
976 Create the parameters file for i.atcorr
977 The underlying 6S model is parametrized through a control file, indi‐
978 cated with the parameters option. This is a text file defining geomet‐
979 rical and atmospherical conditions of the satellite overpass. Here we
980 create a control file icnd_lsat4.txt for band 4 (NIR), based on meta‐
981 data. For the overpass time, we need to define decimal hours: 10:42:07
982 NC local time = 10.70 decimal hours (decimal minutes: 42 * 100 / 60)
983 which is 15.70 GMT.
984 8 - geometrical conditions=Landsat ETM+
985 5 24 15.70 -78.691 35.749 - month day hh.ddd longitude latitude ("hh.ddd" is in GMT decimal hours)
986 2 - atmospheric model=midlatitude summer
987 1 - aerosols model=continental
988 50 - visibility [km] (aerosol model concentration)
989 -0.110 - mean target elevation above sea level [km]
990 -1000 - sensor on board a satellite
991 64 - 4th band of ETM+ Landsat 7
992 Finally, run the atmospheric correction (-r for reflectance input map;
993 -a for date > July 2000):
994 i.atcorr -r -a lsat7_2002_40_rad elevation=elevation parameters=icnd_lsat4.txt output=lsat7_2002_40_atcorr
995 Note that the altitude value from ’icnd_lsat4.txt’ file is read at the
996 beginning to compute the initial transform. Therefore, it is necessary
997 to provide a value that might be the mean value of the elevation model
998 (r.univar elevation). For the atmospheric correction per se, the eleva‐
999 tion values from the raster map are used.
1000
1001 Note that the process is computationally intensive. Note also, that
1002 i.atcorr reports solar elevation angle above horizon rather than solar
1003 zenith angle.
1004
1006 The influence and importance of the visibility value or map should be
1007 explained, also how to obtain an estimate for either visibility or
1008 aerosol optical depth at 550nm.
1009
1011 GRASS Wiki page about Atmospheric correction
1012
1013 i.aster.toar, i.colors.enhance, i.landsat.toar, r.info, r.mapcalc,
1014 r.univar
1015
1017 · Vermote, E.F., Tanre, D., Deuze, J.L., Herman, M., and Mor‐
1018 crette, J.J., 1997, Second simulation of the satellite signal
1019 in the solar spectrum, 6S: An overview., IEEE Trans. Geosc. and
1020 Remote Sens. 35(3):675-686.
1021
1022 · 6S Manual: PDF1, PDF2, and PDF3
1023
1024 · RapidEye sensors have been provided by RapidEye AG, Germany
1025
1026 · Barsi, J.A., Markham, B.L. and Pedelty, J.A., 2011, The opera‐
1027 tional land imager: spectral response and spectral uniformity.,
1028 Proc. SPIE 8153, 81530G; doi:10.1117/12.895438
1029
1031 Original version of the program for GRASS 5:
1032 Christo Zietsman, 13422863(at)sun.ac.za
1033
1034 Code clean-up and port to GRASS 6.3, 15.12.2006:
1035 Yann Chemin, ychemin(at)gmail.com
1036
1037 Documentation clean-up + IRS LISS sensor addition 5/2009:
1038 Markus Neteler, FEM, Italy
1039
1040 ASTER sensor addition 7/2009:
1041 Michael Perdue, Canada
1042
1043 AVNIR, IKONOS sensors addition 7/2010:
1044 Daniel Victoria, Anne Ghisla
1045
1046 RapidEye sensors addition 11/2010:
1047 Peter Löwe, Anne Ghisla
1048
1049 VGT1 and VGT2 sensors addition from 6SV-1.1 sources, addition 07/2011:
1050 Alfredo Alessandrini, Anne Ghisla
1051
1052 Added Landsat 8 from NASA sources, addition 05/2014:
1053 Nikolaos Ves
1054
1055 Geoeye1 addition 7/2015:
1056 Marco Vizzari
1057
1058 Worldview3 addition 8/2016:
1059 Markus Neteler, mundialis.de, Germany
1060
1061 Sentinel-2A addition 12/2016:
1062 Markus Neteler, mundialis.de, Germany
1063
1064 Sentinel-2B addition 1/2018:
1065 Stefan Blumentrath, Zofie Cimburova, Norwegian Institute for Nature
1066 Research, NINA, Oslo, Norway
1067
1068 Worldview4 addition 12/2018:
1069 Markus Neteler, mundialis.de, Germany
1070
1072 Available at: i.atcorr source code (history)
1073
1074 Main index | Imagery index | Topics index | Keywords index | Graphical
1075 index | Full index
1076
1077 © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
1078
1079
1080
1081GRASS 7.8.2 i.atcorr(1)