Atmospheric correction - Revision history

Neteler: +Atmospheric correction for multiple bands

2024-09-25T21:11:10Z

+Atmospheric correction for multiple bands

← Older revision		Revision as of 21:11, 25 September 2024
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	This file is then used in the {{cmd\|i.atcorr}} module:		This file is then used in the {{cmd\|i.atcorr}} module:

	~~{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a -o iimg=lsat7_2002_10_rad ialt=elev_int icnd=icdn_lsat1.txt oimg=lsat7_2002_10_atcorr</source>~~

	~~or, using GRASS 7.x:~~

	{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a input=lsat7_2002_10_rad elevation=elev_int parameters=icdn_lsat1.txt output=lsat7_2002_10_atcorr</source>		{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a input=lsat7_2002_10_rad elevation=elev_int parameters=icdn_lsat1.txt output=lsat7_2002_10_atcorr</source>
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	Where:		Where:
	* <tt>'''-a'''</tt> refers to a Landsat image taken after July 2000		* <tt>'''-a'''</tt> refers to a Landsat image taken after July 2000
	* <tt>'''~~-o'''</tt> activates the cache acceleration (GRASS 6.x only)~~		* <tt>'''input'''</tt> is the image to be corrected
	* <tt>'''iimg/input'''</tt> is the image to be corrected		* <tt>'''elevation'''</tt> is the altitude map which overrides the initialization value of 110 meters
	* <tt>'''~~ialt/~~elevation'''</tt> is the altitude map which overrides the initialization value of 110 meters		* <tt>'''parameters'''</tt> is the path to the icnd.txt file
	* <tt>'''~~icnd/~~parameters'''</tt> is the path to the icnd.txt file		* <tt>'''output'''</tt> is the name of the output image
	* <tt>'''~~oimg/~~output'''</tt> is the name of the output image

	Detailed information can be found in {{cmd\|i.atcorr}}'s manual.		Detailed information can be found in {{cmd\|i.atcorr}}'s manual.

	'''Note,''' {{cmd\|i.atcorr}} wont complain if the defined elevation model (parameter <code>elevation=</code>) does not cover the extent of the Landsat scene that is the subject of the process -- it will result in NaN's. ''[Maybe this can be requested as an enhancement?]''		'''Note,''' {{cmd\|i.atcorr}} wont complain if the defined elevation model (parameter <code>elevation=</code>) does not cover the extent of the Landsat scene that is the subject of the process -- it will result in NaN's. ''[Maybe this can be requested as an enhancement?]''

			== Atmospheric correction for multiple bands ==

			To run {{cmd\|i.atcorr}} in GRASS GIS on multiple bands, you will need to execute the module for each band individually since i.atcorr is designed to handle a single band at a time. However, you can automate this process using a script (Bash, or Python) to apply the atmospheric correction to multiple bands sequentially. Here's an example of how to run {{cmd\|i.atcorr}} for multiple bands using a Bash script:

			<source lang=bash>
			#!/bin/bash

			# List of bands to process
			bands=("10" "20" "30" "40" "50")

			# Loop through each band and apply i.atcorr
			for band in "${bands[@]}"
			do
			echo "Processing $band..."
			# Run i.atcorr for each band, modify parameters as needed
			g.region raster=$band
			i.atcorr -a input=lsat7_2002_${band}_rad elevation=elev_int parameters=icdn_lsat1.txt output=lsat7_2002_${band}_atcorr
			done

			echo "Atmospheric correction done for all bands!"
			</source>

	== Sources for aerosol optical depth (AOD) estimations ==		== Sources for aerosol optical depth (AOD) estimations ==

Neteler: /* Spectral radiance/reflectance */

2020-04-08T13:14:11Z

Spectral radiance/reflectance

← Older revision		Revision as of 13:14, 8 April 2020
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	* (1) http://landsathandbook.gsfc.nasa.gov/handbook/handbook_htmls/chapter11/chapter11.html		* (1) http://landsathandbook.gsfc.nasa.gov/handbook/handbook_htmls/chapter11/chapter11.html
	* (2) http://landsat.usgs.gov/documents/L5TM_postcal_v11.pdf		* (2) http://landsat.usgs.gov/documents/L5TM_postcal_v11.pdf
			* WorldView: https://dg-cms-uploads-production.s3.amazonaws.com/uploads/document/file/209/ABSRADCAL_FLEET_2016v0_Rel20170606.pdf

	=== Whitepapers ===		=== Whitepapers ===

Neteler: +WorldView

2020-04-08T13:12:53Z

+WorldView

← Older revision		Revision as of 13:12, 8 April 2020
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	# Converting '''Digital Numbers''' (DN) to '''Top-of-Atmosphere Radiances''' (ToAR)		# Converting '''Digital Numbers''' (DN) to '''Top-of-Atmosphere Radiances''' (ToAR)
	~~#* for Landsat imagery, apply the equation below or use the {{cmd\|i.landsat.toar}} module~~
	#* DNs -- which are actually the pixel values -- are the result of the quantified amount of energy observed and measured at the sensor		#* DNs -- which are actually the pixel values -- are the result of the quantified amount of energy observed and measured at the sensor
	#* the {{cmd\|i.landsat.toar}} module supports all Landsat sensors ~~icluding~~ MSS, TM and ETM+		#* for '''Landsat''' imagery, apply the equation below or use the {{cmd\|i.landsat.toar}} module
			#* the {{cmd\|i.landsat.toar}} module supports all Landsat sensors including MSS, TM and ETM+
			#* for '''WorldView''' imagery, apply this equation with {{cmd\|r.mapcalc}}:<br> <tt>L = Gain * DN * (abscalfactor/effective bandwidth) + Offset</tt><br> with the band specific "abscalfactor" and "effectiveBandwidth" being delivered with the imagery in the metadata file and the Gain and Offset are the absolute radiometric calibration band-dependent adjustment factors that are given in e.g. [https://dg-cms-uploads-production.s3.amazonaws.com/uploads/document/file/209/ABSRADCAL_FLEET_2016v0_Rel20170606.pdf this DigitalGlobe document]. Note that these are not necessarily stagnant values and they are revisited annually.
	# Converting '''ToA Radiances''' to '''Top-of-Canopy Reflectances''' (ToCR) → use the {{cmd\|i.atcorr}} module		# Converting '''ToA Radiances''' to '''Top-of-Canopy Reflectances''' (ToCR) → use the {{cmd\|i.atcorr}} module
	#* the conversion to ''Reflectances'' attempts to assess for and remove atmospheric effects, a process known as ''atmospheric correction''		#* the conversion to ''Reflectances'' attempts to assess for and remove atmospheric effects, a process known as ''atmospheric correction''

Neteler: + See also: i.topo.corr

2018-02-16T13:06:43Z

+ See also: i.topo.corr

← Older revision		Revision as of 13:06, 16 February 2018
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	[[Category: Tutorial]]		[[Category: Tutorial]]
	[[Category: Image processing]]		[[Category: Image processing]]

			== See also ==

			* Terrain correction: {{cmd\|i.topo.corr}}

Neteler: +Landsat Atmospheric Correction Parameter Calculator

2016-12-15T12:16:42Z

+Landsat Atmospheric Correction Parameter Calculator

← Older revision		Revision as of 12:16, 15 December 2016
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	=== TοDο ===		=== TοDο ===
			* Cross-check with [http://atmcorr.gsfc.nasa.gov Landsat Atmospheric Correction Parameter Calculator]
	* understand if the [http://modis.gsfc.nasa.gov/data/dataprod/dataproducts.php?MOD_NUMBER=04 MODIS Aerosol Product (MOD04)] could be useful to estimate the visibility for the aerosol model.		* understand if the [http://modis.gsfc.nasa.gov/data/dataprod/dataproducts.php?MOD_NUMBER=04 MODIS Aerosol Product (MOD04)] could be useful to estimate the visibility for the aerosol model.
	* provide an example on using [http://modis.gsfc.nasa.gov/data/dataprod/dataproducts.php?MOD_NUMBER=08 MODIS Gridded Atmospheric Product (MOD08)].		* provide an example on using [http://modis.gsfc.nasa.gov/data/dataprod/dataproducts.php?MOD_NUMBER=08 MODIS Gridded Atmospheric Product (MOD08)].

Neteler at 14:09, 12 August 2016

2016-08-12T14:09:44Z

← Older revision		Revision as of 14:09, 12 August 2016
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	== Atmospheric correction ==		== Atmospheric correction ==

	Radiance values can be converted to reflectance values in undergoing an atmospheric correction by applying the <math>6S</math> algorithm. The algorithm will transform the Top-of-Atmosphere radiance values to Top-of-Canopy reflectance values using predefined information on the aerosol content and atmospheric composition of the time the image was taken. What follows describes the method to use this algorithm in GRASS GIS. Again, only calculations for band 1 are demonstrated here, and the number(s) to be changed for indicating other spectral bands, are <span style="color:#FF0000">red</span>. The <code>icnd_lsat1.txt</code> control file consists of the following parameters, and is written with a text editor:		Radiance values can be converted to reflectance values in undergoing an atmospheric correction by applying the <math>6S</math> algorithm available in {{cmd\|i.atcorr}}. The algorithm will transform the Top-of-Atmosphere radiance values to Top-of-Canopy reflectance values using predefined information on the aerosol content and atmospheric composition of the time the image was taken. What follows describes the method to use this algorithm in GRASS GIS. Again, only calculations for band 1 are demonstrated here, and the number(s) to be changed for indicating other spectral bands, are <span style="color:#FF0000">red</span>. The <code>icnd_lsat1.txt</code> control file consists of the following parameters, and is written with a text editor:

	8 # indicates that it is an ETM+ image		8 # indicates that it is an ETM+ image

Neteler: +example

2016-03-04T11:19:02Z

+example

← Older revision		Revision as of 11:19, 4 March 2016
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	# ''Optional:'' select "Day" or "Night" to restrict computation to (local) day/night overpass of the satellite		# ''Optional:'' select "Day" or "Night" to restrict computation to (local) day/night overpass of the satellite

			''Example:'' Calculation for NC Landsat scenes: see [http://www.grassbook.org/wp-content/uploads/ncexternal/landsat/landsat_overpass_time_list_NC.txt here]

	--- For LANDSAT only ---		--- For LANDSAT only ---

⚠️Andbal: added grass7.x code

2016-01-19T11:37:39Z

added grass7.x code

← Older revision		Revision as of 11:37, 19 January 2016
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	# Insert the date of acquisition		# Insert the date of acquisition
	# ''Optional:'' select "Day" or "Night" to restrict computation to (local) day/night overpass of the satellite		# ''Optional:'' select "Day" or "Night" to restrict computation to (local) day/night overpass of the satellite


			--- For LANDSAT only ---

			USGS provide the [http://landsat.usgs.gov/consumer.php Landsat Bulk Metadata Service] web page where is possible to extract metadata (included overpass time) for all the Landsat missions.

	== Atmospheric correction ==		== Atmospheric correction ==
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	{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a -o iimg=lsat7_2002_10_rad ialt=elev_int icnd=icdn_lsat1.txt oimg=lsat7_2002_10_atcorr</source>		{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a -o iimg=lsat7_2002_10_rad ialt=elev_int icnd=icdn_lsat1.txt oimg=lsat7_2002_10_atcorr</source>

			or, using GRASS 7.x:

			{{cmd\|i.atcorr}} <source lang="bash" enclose=none>-a input=lsat7_2002_10_rad elevation=elev_int parameters=icdn_lsat1.txt output=lsat7_2002_10_atcorr</source>

	Where:		Where:
	* <tt>'''-a'''</tt> refers to a Landsat image taken after July 2000		* <tt>'''-a'''</tt> refers to a Landsat image taken after July 2000
	* <tt>'''-o'''</tt> activates the cache acceleration		* <tt>'''-o'''</tt> activates the cache acceleration (GRASS 6.x only)
	* <tt>'''iimg'''</tt> is the image to be corrected		* <tt>'''iimg/input'''</tt> is the image to be corrected
	* <tt>'''ialt'''</tt> is the altitude map which overrides the initialization value of 110 meters		* <tt>'''ialt/elevation'''</tt> is the altitude map which overrides the initialization value of 110 meters
	* <tt>'''icnd'''</tt> is the path to the icnd.txt file		* <tt>'''icnd/parameters'''</tt> is the path to the icnd.txt file
	* <tt>'''oimg'''</tt> is the name of the output image		* <tt>'''oimg/output'''</tt> is the name of the output image

	Detailed information can be found in {{cmd\|i.atcorr}}'s manual.		Detailed information can be found in {{cmd\|i.atcorr}}'s manual.
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	* [http://cloudsgate2.larc.nasa.gov/cgi-bin/predict/predict.cgi NASA LaRC Satellite Overpass Predictor]		* [http://cloudsgate2.larc.nasa.gov/cgi-bin/predict/predict.cgi NASA LaRC Satellite Overpass Predictor]
			* [http://landsat.usgs.gov/consumer.php Landsat Bulk Metadata Service]
	* NASA's [http://atmcorr.gsfc.nasa.gov/ Atmospheric Correction Parameter Calculator]		* NASA's [http://atmcorr.gsfc.nasa.gov/ Atmospheric Correction Parameter Calculator]

⚠️Andbal: Corrected link and update of overpass time sub-section

2015-12-11T10:43:17Z

Corrected link and update of overpass time sub-section

← Older revision		Revision as of 10:43, 11 December 2015
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	# Converting '''Digital Numbers''' (DN) to '''Top-of-Atmosphere Radiances''' (ToAR)		# Converting '''Digital Numbers''' (DN) to '''Top-of-Atmosphere Radiances''' (ToAR)
	#* for Landsat imagery, apply the equation below or use the {{cmd\|i.landsat.toar~~\|version=65~~}} module		#* for Landsat imagery, apply the equation below or use the {{cmd\|i.landsat.toar}} module
	#* DNs -- which are actually the pixel values -- are the result of the quantified amount of energy observed and measured at the sensor		#* DNs -- which are actually the pixel values -- are the result of the quantified amount of energy observed and measured at the sensor
	#* the {{cmd\|i.landsat.toar~~\|version=65~~}} module supports all Landsat sensors icluding MSS, TM and ETM+		#* the {{cmd\|i.landsat.toar}} module supports all Landsat sensors icluding MSS, TM and ETM+
	# Converting '''ToA Radiances''' to '''Top-of-Canopy Reflectances''' (ToCR) → use the {{cmd\|i.atcorr}} module		# Converting '''ToA Radiances''' to '''Top-of-Canopy Reflectances''' (ToCR) → use the {{cmd\|i.atcorr}} module
	#* the conversion to ''Reflectances'' attempts to assess for and remove atmospheric effects, a process known as ''atmospheric correction''		#* the conversion to ''Reflectances'' attempts to assess for and remove atmospheric effects, a process known as ''atmospheric correction''
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	* GRASS 6.4.0 or higher		* GRASS 6.4.0 or higher
	* North Carolina sample dataset (location): ~~http~~://grass.osgeo.org/download/data~~.php~~		* North Carolina sample dataset (location): https://grass.osgeo.org/download/sample-data/

	After downloading of the North Carolina dataset, it must be unzipped into your GIS database. When starting GRASS GIS, select this GIS database, open the ‘nc_spm_08’ dataset as LOCATION, and ‘PERMANENT’ as MAPSET.		After downloading of the North Carolina dataset, it must be unzipped into your GIS database. When starting GRASS GIS, select this GIS database, open the ‘nc_spm_08’ dataset as LOCATION, and ‘PERMANENT’ as MAPSET.
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	== Calculating radiance values ==		== Calculating radiance values ==

	The NC data set mapset contains, amongst others, a Landsat ETM+ image of 24th of May 2002. Every pixel of this image contains a DN or grey value. In order to be able to make calculations with satellite imagery, or compare values amongst different sensors, these values have to be converted to radiances or reflectances. The formulas to do this conversion are described here for Landsat images (or use ~~[[GRASS_AddOns#i.landsat.toar~~\|i.landsat.toar]]).		The NC data set mapset contains, amongst others, a Landsat ETM+ image of 24th of May 2002. Every pixel of this image contains a DN or grey value. In order to be able to make calculations with satellite imagery, or compare values amongst different sensors, these values have to be converted to radiances or reflectances. The formulas to do this conversion are described here for Landsat images (or use {{cmd\|i.landsat.toar}}).


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	{{cmd\|r.univar}} <source lang="bash" enclose=none>elev_int</source>		{{cmd\|r.univar}} <source lang="bash" enclose=none>elev_int</source>

	== Estimating the overpass time ~~from~~ the sun position ==		== Estimating the overpass time ==
			This value is needed for the control file. For details, refer to Wikipedia's entry on [http://en.wikipedia.org/wiki/Decimal_time#Scientific_decimal_time Scientific decimal time].
			In case this parameter is not reported in the metadata file, we have two ways to obtain it.

			=== From sun position ===

	The satellite overpass time can be estimated rather precisely from the sun position reported in metadata using {{cmd\|r.sunmask}}.		The satellite overpass time can be estimated rather precisely from the sun position reported in metadata using {{cmd\|r.sunmask}}.
	The [~~ftp~~://~~ftp~~.~~glcf~~.~~umiacs.umd.edu~~/~~glcf~~/~~Landsat~~/~~WRS2~~/~~p016~~/~~r035~~/p016r035_7x20020524.~~ETM-EarthSat-Orthorectified/p016r035_7x20020524~~.~~met~~ metadata file] for the following example contains: <source lang="bash" enclose="none">SUN_AZIMUTH = 120.8810347, SUN_ELEVATION = 64.7730999</source>.		The [http://www.grassbook.org/wp-content/uploads/ncexternal/landsat/2002/p016r035_7x20020524.met.gz metadata file] for the following example contains: <source lang="bash" enclose="none">SUN_AZIMUTH = 120.8810347, SUN_ELEVATION = 64.7730999</source>.

	# iteratively change hour and minutes to obtain a good result, timezone needs to be correct of course		# iteratively change hour and minutes to obtain a good result, timezone needs to be correct of course
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	Solar position: sun azimuth: 121.342461, sun angle above horz.(refraction corrected): 65.396652		Solar position: sun azimuth: 121.342461, sun angle above horz.(refraction corrected): 65.396652

	The resulting overpass local time <code>10:42:07</code> corresponds to <code>15:42</code> in GMT which corresponds to <code>15.70</code> in decimal GMT hours (decimal minutes: <math>42 * 100 / 60</math>). ~~This value is needed for the control file~~. ~~For details, refer to Wikipedia~~'~~s entry on~~ [http://en.~~wikipedia~~.org/~~wiki~~/~~Decimal_time~~#~~Scientific_decimal_time Scientific~~ decimal ~~time].~~		The resulting overpass local time <code>10:42:07</code> corresponds to <code>15:42</code> in GMT which corresponds to <code>15.70</code> in decimal GMT hours (decimal minutes: <math>42 * 100 / 60</math>).

			=== From NASA web tool ===

			The [http://cloudsgate2.larc.nasa.gov/cgi-bin/predict/predict.cgi NASA LaRC Satellite Overpass Predictor] can compute satellite overpass time from d''ate of acquisition'' and ''scene center coordinates''. The [http://www.grassbook.org/wp-content/uploads/ncexternal/landsat/2002/p016r035_7x20020524.met.gz metadata file] for the following example contains: <source lang="bash" enclose="none">ACQUISITION_DATE = 2002-05-24, SCENE_CENTER_LAT = +36.0512847, SCENE_CENTER_LON = -79.3280820</source>.

			# Select the World zone in the bottom-right side of the page and click <code>Go >></code>
			# Insert Lat/Long coordinates (decimal degrees, without ''plus'' sign but with ''minus'' sign)
			# Select the proper satellite
			# Insert the date of acquisition
			# ''Optional:'' select "Day" or "Night" to restrict computation to (local) day/night overpass of the satellite

	== Atmospheric correction ==		== Atmospheric correction ==
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	=== Related on-line tools ===		=== Related on-line tools ===

	* [http://~~www-air~~.larc.nasa.gov/~~tools~~/predict.~~htm~~ NASA LaRC Satellite Overpass Predictor]		* [http://cloudsgate2.larc.nasa.gov/cgi-bin/predict/predict.cgi NASA LaRC Satellite Overpass Predictor]
	* NASA's [http://atmcorr.gsfc.nasa.gov/ Atmospheric Correction Parameter Calculator]		* NASA's [http://atmcorr.gsfc.nasa.gov/ Atmospheric Correction Parameter Calculator]

Neteler: How to estimate Aerosol Optical Thickness URL

2015-11-24T22:13:39Z

How to estimate Aerosol Optical Thickness URL

← Older revision		Revision as of 22:13, 24 November 2015
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	** File and layer specifications are available, for example, at [http://www.atmos.washington.edu/~robwood/modis/filespecs/MOD08_D3.CDL.fs MODIS HDF File Specification MOD08_D3: MODIS Level 3 Daily Atmosphere Gridded Product]		** File and layer specifications are available, for example, at [http://www.atmos.washington.edu/~robwood/modis/filespecs/MOD08_D3.CDL.fs MODIS HDF File Specification MOD08_D3: MODIS Level 3 Daily Atmosphere Gridded Product]
	** The layer '''Optical_Depth_Land_And_Ocean_Mean''', described as ''Aerosol Optical Thickness at 0.55 microns for both Ocean (best) and Land (corrected): Mean'', can be probably used as an input for {{cmd\|i.atcorr}}. '''Note,''' the layer's values have to be scaled by using the scaling factor ''Optical_Depth_Land_And_Ocean_Mean:scale_factor ='' '''0.001d''' as reported in the specifications.		** The layer '''Optical_Depth_Land_And_Ocean_Mean''', described as ''Aerosol Optical Thickness at 0.55 microns for both Ocean (best) and Land (corrected): Mean'', can be probably used as an input for {{cmd\|i.atcorr}}. '''Note,''' the layer's values have to be scaled by using the scaling factor ''Optical_Depth_Land_And_Ocean_Mean:scale_factor ='' '''0.001d''' as reported in the specifications.
			* [http://www.cesbio.ups-tlse.fr/multitemp/?p=1710 How to estimate Aerosol Optical Thickness]

	=== TοDο ===		=== TοDο ===