1i.atcorr(1)                 GRASS GIS User's Manual                i.atcorr(1)
2
3
4

NAME

6       i.atcorr  - Performs atmospheric correction using the 6S algorithm.
7       6S - Second Simulation of Satellite Signal in the Solar Spectrum.
8

KEYWORDS

10       imagery,  atmospheric  correction,  radiometric  conversion,  radiance,
11       reflectance, satellite
12

SYNOPSIS

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

DESCRIPTION

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

6S CODE PARAMETER CHOICES

104   A. Geometrical conditions
105       Code                                                         Description                                                  Details
106
107       1                                                            meteosat observation                                         enter   month,day,decimal   hour   (universal   time-hh.ddd)
108                                                                                                                                                       n.  of  column,n.
109                                                                                                                                 of line. (full scale 5000*2500) 
110
111       2                                                            goes east observation                                        enter   month,day,decimal   hour   (universal   time-hh.ddd)
112                                                                                                                                                       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                                                                                                                                                       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                                                                                                                                                         n.   of    col‐
121                                                                                                                                 umn(1-2048),xlonan,hna
122                                                                                                                                                        give  long.(xlo‐
123                                                                                                                                 nan)       and       overpass       hour       (hna)      at
124                                                                                                                                                         the   ascendant
125                                                                                                                                 node at equator
126
127       5                                                            avhrr (AM noaa)                                              enter   month,day,decimal   hour   (universal   time-hh.ddd)
128                                                                                                                                                         n.   of    col‐
129                                                                                                                                 umn(1-2048),xlonan,hna
130                                                                                                                                                        give  long.(xlo‐
131                                                                                                                                 nan)       and       overpass       hour       (hna)      at
132                                                                                                                                                         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                                                   
229
230       1                                                            continental model                                             
231
232       2                                                            maritime model                                                
233
234       3                                                            urban model                                                   
235
236       4                                                            shettle model for background desert aerosol                   
237
238       5                                                            biomass burning                                               
239
240       6                                                            stratospheric model                                           
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

EXAMPLES

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

REMAINING DOCUMENTATION ISSUES

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

SEE ALSO

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

REFERENCES

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

AUTHORS

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

SOURCE CODE

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       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
1078
1079
1080
1081GRASS 7.8.5                                                        i.atcorr(1)
Impressum