1i.landsat.toar(1) GRASS GIS User's Manual i.landsat.toar(1)
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6 i.landsat.toar - Calculates top-of-atmosphere radiance or reflectance
7 and temperature for Landsat MSS/TM/ETM+/OLI
8
10 imagery, radiometric conversion, radiance, reflectance, brightness tem‐
11 perature, atmospheric correction, satellite, Landsat
12
14 i.landsat.toar
15 i.landsat.toar --help
16 i.landsat.toar [-rnp] input=basename output=basename [metfile=name]
17 [sensor=string] [method=string] [date=yyyy-mm-dd] [sun_eleva‐
18 tion=float] [product_date=yyyy-mm-dd] [gain=string] [per‐
19 cent=float] [pixel=integer] [rayleigh=float] [lsat‐
20 met=string[,string,...]] [scale=float] [--overwrite] [--help]
21 [--verbose] [--quiet] [--ui]
22 Flags:
24 -r
25 Output at-sensor radiance instead of reflectance for all bands
26 -n
28 Input raster maps use as extension the number of the band instead
29 the code
30 -p
32 Print output metadata info
33 --overwrite
35 Allow output files to overwrite existing files
36 --help
38 Print usage summary
39 --verbose
41 Verbose module output
42 --quiet
44 Quiet module output
45 --ui
47 Force launching GUI dialog
48 Parameters:
50 input=basename [required]
51 Base name of input raster bands
52 Example: ’B.’ for B.1, B.2, ...
53 output=basename [required]
55 Prefix for output raster maps
56 Example: ’B.toar.’ generates B.toar.1, B.toar.2, ...
57 metfile=name
59 Name of Landsat metadata file (.met or MTL.txt)
60 sensor=string
62 Spacecraft sensor
63 Required only if ’metfile’ not given (recommended for sanity)
64 Options: mss1, mss2, mss3, mss4, mss5, tm4, tm5, tm7, oli8
65 mss1: Landsat-1 MSS
66 mss2: Landsat-2 MSS
67 mss3: Landsat-3 MSS
68 mss4: Landsat-4 MSS
69 mss5: Landsat-5 MSS
70 tm4: Landsat-4 TM
71 tm5: Landsat-5 TM
72 tm7: Landsat-7 ETM+
73 oli8: Landsat_8 OLI/TIRS
74 method=string
76 Atmospheric correction method
77 Options: uncorrected, dos1, dos2, dos2b, dos3, dos4
78 Default: uncorrected
79 date=yyyy-mm-dd
81 Image acquisition date (yyyy-mm-dd)
82 Required only if ’metfile’ not given
83 sun_elevation=float
85 Sun elevation in degrees
86 Required only if ’metfile’ not given
87 product_date=yyyy-mm-dd
89 Image creation date (yyyy-mm-dd)
90 Required only if ’metfile’ not given
91 gain=string
93 Gain (H/L) of all Landsat ETM+ bands (1-5,61,62,7,8)
94 Required only if ’metfile’ not given
95 percent=float
97 Percent of solar radiance in path radiance
98 Required only if ’method’ is any DOS
99 Default: 0.01
100 pixel=integer
102 Minimum pixels to consider digital number as dark object
103 Required only if ’method’ is any DOS
104 Default: 1000
105 rayleigh=float
107 Rayleigh atmosphere (diffuse sky irradiance)
108 Required only if ’method’ is DOS3
109 Default: 0.0
110 lsatmet=string[,string,...]
112 return value stored for a given metadata
113 Required only if ’metfile’ and -p given
114 Options: number, creation, date, sun_elev, sensor, bands, sunaz,
115 time
116 number: Landsat Number
117 creation: Creation timestamp
118 date: Date
119 sun_elev: Sun Elevation
120 sensor: Sensor
121 bands: Bands count
122 sunaz: Sun Azimuth Angle
123 time: Time
124 scale=float
126 Scale factor for output
127 Default: 1.0
128
130 i.landsat.toar is used to transform the calibrated digital number of
131 Landsat imagery products to top-of-atmosphere radiance or top-of-atmos‐
132 phere reflectance and temperature (band 6 of the sensors TM and ETM+).
133 Optionally, it can be used to calculate the at-surface radiance or
134 reflectance with atmospheric correction (DOS method).
135 Usually, to do so the production date, the acquisition date, and the
137 solar elevation are needed. Moreover, for Landsat-7 ETM+ it is also
138 needed the gain (high or low) of the nine respective bands.
139 Optionally (recommended), the data can be read from metadata file (.met
141 or MTL.txt) for all Landsat MSS, TM, ETM+ and OLI/TIRS. However, if the
142 solar elevation is given the value of the metadata file is overwritten.
143 This is necessary when the data in the .met file is incorrect or not
144 accurate. Also, if acquisition or production dates are not found in the
145 metadata file then the command line values are used.
146 Attention: Any null value or smaller than QCALmin in the input raster
148 is set to null in the output raster and it is not included in the equa‐
149 tions.
150
152 The standard geometric and radiometric corrections result in a cali‐
153 brated digital number (QCAL = DN) images. To further standardize the
154 impact of illumination geometry, the QCAL images are first converted
155 first to at-sensor radiance and then to at-sensor reflectance. The
156 thermal band is first converted from QCAL to at-sensor radiance, and
157 then to effective at-sensor temperature in Kelvin degrees.
158 Radiometric calibration converts QCAL to at-sensor radiance, a radio‐
160 metric quantity measured in W/(m² * sr * µm) using the equations:
161 · gain = (Lmax - Lmin) / (QCALmax - QCALmin)
163 · bias = Lmin - gain * QCALmin
165 · radiance = gain * QCAL + bias
167 where, Lmax and Lmin are the calibration constants, and QCALmax and
168 QCALmin are the highest and the lowest points of the range of rescaled
169 radiance in QCAL.
170 Then, to calculate at-sensor reflectance the equations are:
172 · sun_radiance = [Esun * sin(e)] / (PI * d^2)
174 · reflectance = radiance / sun_radiance
176 where, d is the earth-sun distance in astronomical units, e is the
177 solar elevation angle, and Esun is the mean solar exoatmospheric irra‐
178 diance in W/(m² * µm).
179
181 Atmospheric correction and reflectance calibration remove the path
182 radiance, i.e. the stray light from the atmosphere, and the spectral
183 effect of solar illumination. To output these simple at-surface radi‐
184 ance and at-surface reflectance, the equations are (not for thermal
185 bands):
186 · sun_radiance = TAUv * [Esun * sin(e) * TAUz + Esky] / (PI *
188 d^2)
189 · radiance_path = radiance_dark - percent * sun_radiance
191 · radiance = (at-sensor_radiance - radiance_path)
193 · reflectance = radiance / sun_radiance
195 where, percent is a value between 0.0 and 1.0 (usually 0.01), Esky is
196 the diffuse sky irradiance, TAUz is the atmospheric transmittance along
197 the path from the sun to the ground surface, and TAUv is the atmo‐
198 spheric transmittance along the path from the ground surface to the
199 sensor. radiance_dark is the at-sensor radiance calculated from the
200 darkest object, i.e. DN with a least ’dark_parameter’ (usually 1000)
201 pixels for the entire image. The values are,
202 · DOS1: TAUv = 1.0, TAUz = 1.0 and Esky = 0.0
204 · DOS2: TAUv = 1.0, Esky = 0.0, and TAUz = sin(e) for all bands
206 with maximum wave length less than 1. (i.e. bands 4-6 MSS, 1-4
207 TM, and 1-4 ETM+) other bands TAUz = 1.0
208 · DOS3: TAUv = exp[-t/cos(sat_zenith)], TAUz = exp[-t/sin(e)],
210 Esky = rayleigh
211 · DOS4: TAUv = exp[-t/cos(sat_zenith)], TAUz = exp[-t/sin(e)],
213 Esky = PI * radiance_dark
214 Attention: Output radiance remain untouched (i.e. no set to 0.0 when it
215 is negative) then they are possible negative values. However, output
216 reflectance is set to 0.0 when is obtained a negative value.
217
219 The output raster cell values can be rescaled with the scale parameter
220 (e.g., with 100 in case of using reflectance output in i.gensigset).
221 On Landsat-8 metadata file
223 NASA reports a structure of the L1G Metadata file (LDCM-DFCB-004.pdf)
224 for Landsat Data Continuity Mission (i.e. Landsat-8).
225 NASA retains in MIN_MAX_RADIANCE group the necessary information to
227 transform Digital Numbers (DN) in radiance values. Then, i.landsat.toar
228 replaces the possible standard values with the metadata values. The
229 results match with the values reported by the metada file in RADIOMET‐
230 RIC_RESCALING group.
231 Also, NASA reports the same values of reflectance for all bands in
233 max-min values and in gain-bias values. This is strange that all bands
234 have the same range of reflectance. Also, they wrote in the web page as
235 to calculate reflectance directly from DN, first with RADIOMET‐
236 RIC_RESCALING values and second divided by sin(sun_elevation).
237 This is a simple rescaling
239 · reflectance = radiance / sun_radiance = (DN * RADIANCE_MULT +
241 RADIANCE_ADD) / sun_radiance
242 · now reflectance = DN * REFLECTANCE_MULT + REFLECTANCE_ADD
244 · then REFLECTANCE_MULT = RADIANCE_MULT / sun_radiance
246 · and REFLECTANCE_ADD = RADIANCE_ADD / sun_radiance
248 The problem arises when we need ESUN values (not provided) to compute
250 sun_radiance and DOS. We assume that REFLECTANCE_MAXIMUM corresponds to
251 the RADIANCE_MAXIMUM, then
252 · REFLECTANCE_MAXIMUM / sin(e) = RADIANCE_MAXIMUM / sun_radiance
254 · Esun = (PI * d^2) * RADIANCE_MAXIMUM / REFLECTANCE_MAXIMUM
256 where d is the earth-sun distance provided by metadata file or computed
257 inside the program.
258 The i.landsat.toar reverts back the NASA rescaling to continue using
260 Lmax, Lmin, and Esun values to compute the constant to convert DN to
261 radiance and radiance to reflectance with the "traditional" equations
262 and simple atmospheric corrections. Attention: When MAXIMUM values are
263 not provided, i.landsat.toar tries to calculate Lmax, Lmin, and Esun
264 from RADIOMETRIC_RESCALING (in tests the results were the same).
265 Calibration constants
267 In verbose mode (flag --verbose), the program write basic satellite
268 data and the parameters used in the transformations.
269 Production date is not an exact value but it is necessary to apply cor‐
271 rect calibration constants, which were changed in the dates:
272 · Landsat-1 MSS: never
274 · Landsat-2 MSS: July 16, 1975
276 · Landsat-3 MSS: June 1, 1978
278 · Landsat-4 MSS: August 26, 1982 and April 1, 1983
280 · Landsat-4 TM: August 1, 1983 and January 15, 1984
282 · Landsat-5 MSS: April 6, 1984 and November 9, 1984
284 · Landsat-5 TM: May 4, 2003 and April, 2 2007
286 · Landsat-7 ETM+: July 1, 2000
288 · Landsat-8 OLI/TIRS: launched in 2013
290
292 Metadata file examples
293 Transform digital numbers of Landsat-7 ETM+ in band rasters 203_30.1,
294 203_30.2 [...] to uncorrected at-sensor reflectance in output files
295 203_30.1_toar, 203_30.2_toar [...] and at-sensor temperature in output
296 files 293_39.61_toar and 293_39.62_toar:
297 i.landsat.toar input=203_30. output=_toar \
298 metfile=p203r030_7x20010620.met
299 or
300 i.landsat.toar input=L5121060_06020060714. \
301 output=L5121060_06020060714_toar \
302 metfile=L5121060_06020060714_MTL.txt
303 or
304 i.landsat.toar input=LC80160352013134LGN03_B output=toar \
305 metfile=LC80160352013134LGN03_MTL.txt sensor=oli8 date=2013-05-14
306 DOS1 example
308 DN to reflectance using DOS1:
309 # rename channels or make a copy to match i.landsat.toar’s input scheme:
310 g.copy raster=lsat7_2002_10,lsat7_2002.1
311 g.copy raster=lsat7_2002_20,lsat7_2002.2
312 g.copy raster=lsat7_2002_30,lsat7_2002.3
313 g.copy raster=lsat7_2002_40,lsat7_2002.4
314 g.copy raster=lsat7_2002_50,lsat7_2002.5
315 g.copy raster=lsat7_2002_61,lsat7_2002.61
316 g.copy raster=lsat7_2002_62,lsat7_2002.62
317 g.copy raster=lsat7_2002_70,lsat7_2002.7
318 g.copy raster=lsat7_2002_80,lsat7_2002.8
319 Calculation of reflectance values from DN using DOS1 (metadata obtained
320 from p016r035_7x20020524.met.gz):
321 i.landsat.toar input=lsat7_2002. output=lsat7_2002_toar. sensor=tm7 \
322 method=dos1 date=2002-05-24 sun_elevation=64.7730999 \
323 product_date=2004-02-12 gain=HHHLHLHHL
324 The resulting Landsat channels are named lsat7_2002_toar.1 ..
325 lsat7_2002_toar.8.
326
328 · Chander G., B.L. Markham and D.L. Helder, 2009: Remote Sensing
329 of Environment, vol. 113
330 · Chander G.H. and B. Markham, 2003: IEEE Transactions On Geo‐
332 science And Remote Sensing, vol. 41, no. 11.
333 · Chavez P.S., jr. 1996: Image-based atmospheric corrections -
335 Revisited and Improved. Photogrammetric Engineering and Remote
336 Sensing 62(9): 1025-1036.
337 · Huang et al: At-Satellite Reflectance, 2002: A First Order Nor‐
339 malization Of Landsat 7 ETM+ Images.
340 · R. Irish: Landsat 7. Science Data Users Handbook. February 17,
342 2007; 15 May 2011.
343 · Markham B.L. and J.L. Barker, 1986: Landsat MSS and TM
345 Post-Calibration Dynamic Ranges, Exoatmospheric Reflectances
346 and At-Satellite Temperatures. EOSAT Landsat Technical Notes,
347 No. 1.
348 · Moran M.S., R.D. Jackson, P.N. Slater and P.M. Teillet, 1992:
350 Remote Sensing of Environment, vol. 41.
351 · Song et al, 2001: Classification and Change Detection Using
353 Landsat TM Data, When and How to Correct Atmospheric Effects?
354 Remote Sensing of Environment, vol. 75.
355
357 i.atcorr, i.colors.enhance, r.mapcalc, r.in.gdal
358 Landsat Data Dictionary by USGS
360
362 E. Jorge Tizado (ej.tizado unileon es), Dept. Biodiversity and Envi‐
363 ronmental Management, University of León, Spain
364
366 Available at: i.landsat.toar source code (history)
367 Main index | Imagery index | Topics index | Keywords index | Graphical
369 index | Full index
370 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
372GRASS 7.8.5 i.landsat.toar(1)