MODIS - Revision history

Neteler: /* Introduction */ MODIS Tile Calculator

2018-05-10T16:51:59Z

Introduction: MODIS Tile Calculator

← Older revision		Revision as of 16:51, 10 May 2018
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	MODIS (MODerate resolution Imaging Spectroradiometer) is a whiskbroom multi-spectral sensor (across track scanner) on board the satellites Terra and Aqua that measures 36 spectral frequencies of light. Its swath is 2330 km (across track) by 10° of latitude (along track at nadir). Their circular, sun-synchronous, near polar orbit takes about 99 min. which means that the same region is acquired several times during daylight. However, at nadir observations of the same region are taken every 16 days. A complete earth scan is achieved every 1.2 days. Due to its large swath geometric distortions occur at the scan edges. The pixel size grows with the scan angle, by a factor of 8 at the edge of scan, making the shape of each scan-stripe look like a bow-tie. Successively, the scan-stripes being wider at the edges of the scan, overlap each other. This overlap creates a double-vision effect on the edges of the scan, as each point of the Earth’s surface appears in two adjacent scans. This distortion emphasises the line where scan-stripes meet and, thus, magnifies small differences between the sides of the scan mirror.		MODIS (MODerate resolution Imaging Spectroradiometer) is a whiskbroom multi-spectral sensor (across track scanner) on board the satellites Terra and Aqua that measures 36 spectral frequencies of light. Its swath is 2330 km (across track) by 10° of latitude (along track at nadir). Their circular, sun-synchronous, near polar orbit takes about 99 min. which means that the same region is acquired several times during daylight. However, at nadir observations of the same region are taken every 16 days. A complete earth scan is achieved every 1.2 days. Due to its large swath geometric distortions occur at the scan edges. The pixel size grows with the scan angle, by a factor of 8 at the edge of scan, making the shape of each scan-stripe look like a bow-tie. Successively, the scan-stripes being wider at the edges of the scan, overlap each other. This overlap creates a double-vision effect on the edges of the scan, as each point of the Earth’s surface appears in two adjacent scans. This distortion emphasises the line where scan-stripes meet and, thus, magnifies small differences between the sides of the scan mirror.

	MODIS ~~Sinusoidal Grid SHAPE files can be downloaded [http~~://~~gis~~.~~cri~~.~~fmach~~.it/~~modis~~-~~sinusoidal-gis-files~~/ ~~here]~~		MODIS Tile Calculator: https://landweb.modaps.eosdis.nasa.gov/cgi-bin/developer/tilemap.cgi

	== MODIS Land ==		== MODIS Land ==

Neteler: /* Download of MODIS tiles: i.modis.download */

2018-05-10T16:30:18Z

Download of MODIS tiles: i.modis.download

← Older revision		Revision as of 16:30, 10 May 2018
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	# store NASA username and password in two lines		# store NASA username and password in two lines
	echo "myusername		echo "myusername
	xxxxxx" > ~/.~~rmodis~~		xxxxxx" > ~/.imodis

	# create new space-time cube		# create new space-time cube

Neteler: MODIS data download: expanded

2018-05-10T16:15:41Z

MODIS data download: expanded

← Older revision		Revision as of 16:15, 10 May 2018
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	Now {{AddonCmd\|i.modis}}, {{AddonCmd\|i.modis.download}}, and {{AddonCmd\|i.modis.import}} are locally installed.		Now {{AddonCmd\|i.modis}}, {{AddonCmd\|i.modis.download}}, and {{AddonCmd\|i.modis.import}} are locally installed.

			==== Download of MODIS tiles: i.modis.download ====

			For obtaining the needed NASA credentials, see [http://www.pymodis.org/info.html#requirements here].

			Example: download of Global MODIS Vegetation Index, sixteen days Global 0.05Deg CMG (Terra/Aqua):

			<source lang="bash">
			##### preparation: first time only
			# store NASA username and password in two lines
			echo "myusername
			xxxxxx" > ~/.rmodis

			# create new space-time cube
			t.create type=strds temporaltype=absolute output=ndvi_16_5600m title="Global NDVI 16 days MOD13C1" \
			description="MOD13C1 Global NDVI 16 days" semantictype=mean
			##### END first time only

			MODIS_TMPFOLDER=/path/to/modis/ndvi_MOD13C1.006/

			# fetch list of available MODIS data up to today
			i.modis.download settings=~/.imodis product=ndvi_terra_sixteen_5600 \
			startday=2015-01-01 endday=`date +"%Y-%m-%d"` folder=$MODIS_TMPFOLDER
			</source>

			The downloaded HDF files can then be imported with {{AddonCmd\|i.modis.download}}.

			==== Download of MODIS tiles: modis_download.py ====

			As an alternative to {{AddonCmd\|i.modis.download}} the pyModis' tool [http://www.pymodis.org/scripts/modis_download.html modis_download.py] can be used directly. Be sure to have created the needed <tt>.netrc</tt> file with your NASA credentials (see [http://www.pymodis.org/info.html#requirements here] for details):

			<source lang="bash">
			# example: Global MODIS Vegetation Index, sixteen days Global 0.05Deg CMG (Terra/Aqua)
			mkdir -p ndvi_MOD13C1.006

			modis_download.py -e 2015-10-01 -f 2016-01-31 --product=MOD13C1.006 ndvi_MOD13C1.006/
			</source>

			The downloaded HDF files can then be imported with {{AddonCmd\|i.modis.download}}.

	=== MODIS Land Products Quality Control ===		=== MODIS Land Products Quality Control ===

Neteler: expanded

2018-05-10T15:51:14Z

expanded

@@ Line 25: / Line 25: @@
 See [http://modis-land.gsfc.nasa.gov/ MODIS Land Team Home Page]
-=== MODIS data download ===
+=== MODIS data download: installation of convenient GRASS GIS addon i.modis ===
-For a convenient download addon, see {{AddonCmd|i.modis}}, a tToolset for downloading and processing of MODIS products using pyModis.
+For a convenient download addon, see {{AddonCmd|i.modis}}, a toolset for downloading and processing of MODIS products using pyModis.
 === MODIS Land Products Quality Control ===

Neteler: + MODIS data download

2018-05-10T15:22:08Z

+ MODIS data download

← Older revision		Revision as of 15:22, 10 May 2018
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	See [http://modis-land.gsfc.nasa.gov/ MODIS Land Team Home Page]		See [http://modis-land.gsfc.nasa.gov/ MODIS Land Team Home Page]

			=== MODIS data download ===

			For a convenient download addon, see {{AddonCmd\|i.modis}}, a tToolset for downloading and processing of MODIS products using pyModis.

	=== MODIS Land Products Quality Control ===		=== MODIS Land Products Quality Control ===

⚠️Mmetz: MOD09A1/MYD09A1 version 6: no bitshift needed for qa

2016-10-28T13:54:09Z

MOD09A1/MYD09A1 version 6: no bitshift needed for qa

← Older revision		Revision as of 13:54, 28 October 2016
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	Here, the quality subdataset is of type unsigned int 32 bit, therefore you need to use '>>>' instead of '>>' in r.mapcalc expressions. For example, to extract the MODLAND QA bits, use		Here, the quality subdataset is of type unsigned int 32 bit, therefore you need to use '>>>' instead of '>>' in r.mapcalc expressions. For example, to extract the MODLAND QA bits, use

	qa = (quality ~~>>> 0)~~ & 3		qa = quality & 3

	~~The shift by 0 bits is used here to force r.mapcalc to cast quality to unsigned int 32 bit, otherwise the result might not be correct (implementation-defined).~~

	To extract the quality of band 2, use		To extract the quality of band 2, use

⚠️Mmetz: MOD09A1/MYD09A1 version 6: use both MODLAND QA and band data quality

2016-10-28T12:50:33Z

MOD09A1/MYD09A1 version 6: use both MODLAND QA and band data quality

← Older revision		Revision as of 12:50, 28 October 2016
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	* bit 31: adjacency correction performed		* bit 31: adjacency correction performed

	Here, the quality subdataset is of type unsigned int 32 bit, therefore you need to use '>>>' instead of '>>' in r.mapcalc expressions. For example, to extract the quality of band 2, use		Here, the quality subdataset is of type unsigned int 32 bit, therefore you need to use '>>>' instead of '>>' in r.mapcalc expressions. For example, to extract the MODLAND QA bits, use

			qa = (quality >>> 0) & 3

			The shift by 0 bits is used here to force r.mapcalc to cast quality to unsigned int 32 bit, otherwise the result might not be correct (implementation-defined).

			To extract the quality of band 2, use

	band2_quality = (quality >>> 6) & 15		band2_quality = (quality >>> 6) & 15
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	* See the user guide at https://lpdaac.usgs.gov/sites/default/files/public/product_documentation/mod09_user_guide_v1.4.pdf		* See the user guide at https://lpdaac.usgs.gov/sites/default/files/public/product_documentation/mod09_user_guide_v1.4.pdf

	The band quality might indicate lower quality (7 = noisy detector or 8 = dead detector), even though the MODLAND QA bits indicate ideal quality on all bands. ~~If in doubt~~, ~~the~~ MODLAND QA bits ~~are right and~~ the band quality ~~bits are wrong~~. That means if ~~the MODLAND QA bits indicate ideal quality, the band values are most probably useful even if a given band quality indicates less than ideal band quality: discard a band value if~~ MODLAND QA > 1 and if band quality > 8 (maybe band quality > 12 for high tolerance).		The band quality might indicate lower quality (7 = noisy detector or 8 = dead detector), even though the MODLAND QA bits indicate ideal quality on all bands. On the other hand, MODLAND QA bits sometimes indicate pixel "... not produced for other reasons, some or all bands ...". In this case, the band-specific data quality needs to be checked. That means pixels should only be discarded if both MODLAND QA > 1 and band quality > 8 (maybe band quality > 12 for high tolerance).

	==== MOD11A1/MYD11A1 version 6 ====		==== MOD11A1/MYD11A1 version 6 ====

⚠️Mmetz: MOD13Q1/MYD13Q1 version 6: update quality filtering

2016-10-27T20:01:27Z

MOD13Q1/MYD13Q1 version 6: update quality filtering

← Older revision		Revision as of 20:01, 27 October 2016
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	* bit 15: Possible shadow		* bit 15: Possible shadow

	The ~~MODLAND QA~~ bits are sometimes indicating ~~low quality or pixel~~ not ~~produced~~, even for a reasonable VI value and ~~usefulness~~ indicating good quality. Therefore the ~~MODLAND QA bits~~ should be used with care, or not at all. The ~~VI usefulness~~ extracted with		The VI usefulness bits are sometimes indicating 1111 = "Not useful for any other reason/not processed", even for a reasonable VI value and MODLAND QA bits indicating good quality. Therefore the VI usefulness should be used with care, or not at all. The MODLAND QA bits extracted with

	~~usefulness~~ = (quality ~~>> 2)~~ & 15		qa = quality & 3

	is sufficient to filter out bad quality pixels.		is sufficient to filter out bad quality pixels with qa > 1.

	=== Advanced MODIS LST time series reconstruction ===		=== Advanced MODIS LST time series reconstruction ===

⚠️Mmetz: MOD11A1/MYD11A1 version 6: handle QC fill value

2016-10-26T20:21:35Z

MOD11A1/MYD11A1 version 6: handle QC fill value

← Older revision		Revision as of 20:21, 26 October 2016
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	* bits 4 - 5: Emissivity error flag		* bits 4 - 5: Emissivity error flag
	* bits 6 - 7: LST error flag		* bits 6 - 7: LST error flag

			The nodata (NULL) value is set to 0 (zero) which is not mentioned in the documentation, but set in the hdf file and recognized by GDAL. Unfortunately, the value 0 (zero) also indicates highest quality pixels. In order to preserve pixels with value 0 (zero), the nodata value needs to be changed with "gdalbuildvrt -srcnodata 255 -vrtnodata 255" or with "gdal_translate -a_nodata 255" or after import into GRASS with "r.null null=255". After that, pixels with a QC value of 0 and a valid LST value are of highest quality, while pixels with a QC value of 0 and an invalid LST value can be set to NULL.

	The most useful bit fields are the "Mandatory QA flag", extracted with		The most useful bit fields are the "Mandatory QA flag", extracted with
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	and the "LST error flag", extracted with		and the "LST error flag", extracted with

	lst_error = (quality >> 6) & 3		lst_error = (quality >> 6) & 3

	==== MOD13Q1/MYD13Q1 version 6 ====		==== MOD13Q1/MYD13Q1 version 6 ====

⚠️Mmetz: MOD11A1/MYD11A1 version 6 change qc data type

2016-10-26T12:22:17Z

MOD11A1/MYD11A1 version 6 change qc data type

← Older revision		Revision as of 12:22, 26 October 2016
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	Land Surface Temperature (LST) at 1 km resolution, daily		Land Surface Temperature (LST) at 1 km resolution, daily

	The name of the quality control subdatasets are "QC_Day" and "QC_Night". The type is unsigned int 16 bit, and the contents are		The name of the quality control subdatasets are "QC_Day" and "QC_Night". The type is unsigned int 8 bit, and the contents are
	* bits 0 - 1: Mandatory QA flag		* bits 0 - 1: Mandatory QA flag
	* bits 2 - 3: Data quality flag		* bits 2 - 3: Data quality flag