USGS EROS Archive - Vegetation Monitoring - eVIIRS Global NDWI
The EROS Visible Infrared Imaging Radiometer Suite (eVIIRS) Global Normalized Difference Water Index (NDWI) collection is based on the Visible Infrared Imaging Radiometer Suite (VIIRS) data acquired by the Joint Polar Satellite System (JPSS), a collaborative program between the National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA). The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites.
The EROS Visible Infrared Imaging Radiometer Suite (eVIIRS) Global Normalized Difference Water Index (NDWI) collection uses the Visible Infrared Imaging Radiometer Suite (VIIRS) collection that is available at NASA’s Land Atmosphere Near-real-time Capability for EOS (LANCE) for the expedited product and Level-1 and Atmosphere Archive & Distribution System (LAADS) for the historical products.
Moderate resolution remote sensing provides a means for operational monitoring communities to develop historical trend information and use near real-time deviations from temporal averages to identify areas of change. High quality, consistent and well-calibrated satellite measurements are needed to detect and monitor changes and trends, especially in vegetation patterns useful for drought, crop yield, phenology and fire potential studies.
The eVIIRS Global NDWI collection is based on the Visible Infrared Imaging Radiometer Suite (VIIRS) data acquired by the National Aeronautics and Space Administration's (NASA) Earth Observing System (EOS). Even though VIIRS data are beneficial in vegetation studies, there have been usability issues encountered with the reprojection, file format and sub-setting. Therefore, eVIIRS was developed to specifically address these issues.
The eVIIRS Global NDWI is a 10-day data composited data set using the VIIRS sensor only. Expedited (near real-time) production runs every ten days for the 10-day products. Because each of the composites are created from a varying number of images, the eVIIRS composites include acquisition files to identify which of the possible inputs were used to populate the final composite. Product generation information can be found in the Open File Report – eVIIRS: A User-Friendly Data Source. The metadata accompanying the data files summarize geographic bounds, projection parameters and product contact information. The data has Global coverage and is available in GeoTIFF format, Geographic projection, and 1-kilometer resolution.
Composite Building Process for the Normalized Difference Water Index (NDWI)
The first step in the eVIIRS composite building process is to create the various geotiff bands required for building an NDWI composite for each of the days and times in the compositing period. In this case for a compositing period of 10 days.
One of the GeoTIFF bands created is the NDWI band. NDWI is created from the equation
NDWI = (green – SWIR) / (green + SWIR)
where green is band M4 and SWIR is band M10. These bands come from the 750-m surface reflectance bands of VNP09 granules.
The minimum NDWI values allowed are -0.1999, and all NDWI values (which normally fall between -1.0 and 1.0) are scaled by 10,000. Thus, the output NDWI values from this application fall between -2000 and 10,000 (with the exception of negative surface reflectance values) to match the LP DAAC MOD09 products.
If either of the green or SWIR pixel values is background fill, then the output NDWI value is set to UNDEF (-2000). The same value applies if the green and SWIR pixels are the same value. If either of the green or SWIR pixels is negative, then the output NDWI value is set to NEG_SR (-3000).
Other bands created for the compositing process are Satellite Zenith Angle and Surface Reflectance Quality Bands 1, 2 and 4.
Composite Calculation for the Normalized Difference Water Index (NDWI)
The software used to create 10-day dekadal NDWI composites was developed by the USGS EROS software development team. The software processes VIIRS 750-m swath granules to produce 1-km composite products.
The software grids the required swath granules (VNP09 and VNP03MOD) for the global bounded region (using upper left and lower right corner coordinates). For each gridded granule, an NDWI band is generated using the green (band M4) and SWIR (band M10) bands.
Once each granule has been gridded to the given coordinate extents and the NDWI has been built, then an enhanced maximum value composite (MVC) is generated. With a straight MVC algorithm, each pixel in the composite (for each band) would be filled using the pixel value of the granule with the highest NDWI for the current pixel. The MVC has been enhanced in the eVIIRS algorithm by incorporating band quality, cloud mask, negative surface reflectance, and view angle into the algorithm for eVIIRS processing.
- The band quality information in the surface reflectance product is used to determine if a certain pixel is of “bad quality.” Bad quality pixels are not used in the final composite product.
- The NDWI algorithm flags negative surface reflectance values so that they will not be used in the output composite if positive values are available. If either the red or NIR band surface reflectance values are negative, then the output NDWI value is flagged with a value of -3000. (NOTE: Undefined or background fill NDWI values are -2000 and that is specified as the lower limit of the “valid” NDWI values.) The composite algorithm then disregards granules with NDWI values of -3000 to omit negative surface reflectance values in the output composite.
- The cloud mask is used to minimize the presence of cloud pixels in the composite product. If the quality flag is probably clear and/or confident clear, then the pixel may be used to fill the current composite pixel.
- The view angle (distance from nadir) determines which of the two highest NDWI pixels is used in the composite. Of the non-cloudy, ideal-quality pixels, the two highest NDWI values are determined from the list of granules. Of these two granules, the pixel value which is closest to nadir is used to fill the composite.
Digital Products
The products are generated and delivered in a compressed (zipped) GeoTIFF format.
The spatial resolution of 1,000 m is available to download individually. These data are available in EarthExplorer as well Machine-to-Machine API. The download product is a .zip file containing 9 files, including six .tif, one jpeg, and two .txt files.
Following is a sample list of files from a Global NDWI 1-km NDWI composite
GN_eVSH_NDWI.2023.091-100.1KM.WI_ACQI.001.2023104131321.tif Acquisition geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_ACQT.001.2023104131321.txt Acquisition text file
GN_eVSH_NDWI.2023.091-100.1KM.WI_M04B.001.2023104131321.tif Band 4 geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_M10B.001.2023104131321.tif Band 10 geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_MASK.001.2023104131321.tif Mask band geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_META.001.2023104211226.met Metadata text file
GN_eVSH_NDWI.2023.091-100.1KM.WI_NDWI.001.2023104131321.jpg NDWI browse JPEG
GN_eVSH_NDWI.2023.091-100.1KM.WI_NDWI.001.2023104131321.tif NDWI geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_QUAL.001.2023104131321.tif Quality geotiff
Acquisition Band (ACQI)
An acquisition band provides the user with a GeoTIFF image that can be overlayed onto the NDWI image so that the user can then identify each granule that provided the value for each NDWI pixel. The DOY and the acquisition number will be used to specify the acquisition. The acquisition number in this case represents not the time of the acquisition, but the order of capture. The output values are represented as an unsigned 16-bit integer using the equation
DOY * 1000 + acq_number
Thus, the first acquisition for DOY 117 would be 117001. The eleventh acquisition for DOY 117 would be 117011. To make it easier for the user to determine which acquisition integer value maps to which granule, an output acquisition table text file is written to match the acquisition values to the granule names.
Acquisition Text File (ACQT)
An acquisition text file provides the user a text file to accompany the Acquisition image, which gives the composite details of the data used to create the product. This list of the acquisition band values is used in the composite acquisition band product and the corresponding acquisition filename for that acquisition value.
160005 MA2RG_2020_160_2120_250m_NDWI.hdf
160004 MA2RG_2020_160_1940_250m_NDWI.hdf
160003 MA2RG_2020_160_1935_250m_NDWI.hdf
160002 MA2RG_2020_160_1800_250m_NDWI.hdf
160001 MA2RG_2020_160_1755_250m_NDWI.hdf
159007 MA2RG_2020_159_2035_250m_NDWI.hdf
159006 MA2RG_2020_159_2030_250m_NDWI.hdf
159005 MA2RG_2020_159_1900_250m_NDWI.hdf
Metadata (META)
The Metadata file provides the details about the composite image, including acquisition time period, publication dates, pixel and row counts, map projection information, datum, pixel resolution, satellite and platform, digital data type, fill values, scaling factors, and center and corner coordinates.
Browse JPEG
A full resolution browse image is provided in JPEG format and is zipped with the product and used to display the image on EarthExplorer. The color mapping is used to create a color image for the browse image and is not the same as the 16-bit single band data delivered in the NDWI GeoTIFF.
Mask GeoTIFF
The mask GeoTIFF provides information on the following attributes for each pixel based on which bits are set.
| Bit Value | Attributes |
|---|---|
| 1 | Water |
| 2 | Cloud Shadow |
| 4 | Adjacent Cloud |
| 8 | Snow / Ice |
| 16 | Thin Cirrus Reflective |
| 32 | Thin Cirrus Emissive |
Thus, the bits for decimal 58 are 111010 which means that the pixel has these attributes (from left bit to right bit)
- thin cirrus emissive
- thin cirrus reflective
- snow / ice
- cloud shadow
NDWI GeoTIFF
The NDWI GeoTIFF is the product created in the compositing process detailed in the above section. All the other files including quality band, acquisition band, as well as the text files and browse are companion files for this NDWI product.
Quality Band (QA) GeoTIFF
A quality assurance (QA) band is 8 bits and produced by the composite software to identify the quality of each composite pixel. Most pixels will be filled with a pixel of good band quality. However, if none of the granules for a particular pixel are of good band quality or all of the pixels are cloudy, then the current pixel is filled with data from the best pixel possible where the preference order is valid NDWI over fill, good quality over bad, snow pixel over cloudy pixel. The following values are used in the QA band:
0 = good quality
1 = cloudy pixel
2 = bad band quality
4 = snow
10 = fill
Surface Reflectance Quality Band 1 is made up of the following bit values. Bit number 0 is the bit in the binary number which is of the lowest numerical value or Least Significant Bit (LSB).
| Surface Reflectance Quality Band 1 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0-1 | Cloud Mask Quality | 00 | Poor |
| 01 | Low | ||
| 10 | Medium | ||
| 11 | High | ||
| 2-3 | Cloud Detection and Confidence | 00 | Confident Clear |
| 01 | Probably Clear | ||
| 10 | Probably Cloud | ||
| 11 | Probably Clear | ||
| 4 | Day / Night | 0 | Day |
| 1 | Night | ||
| 5 | Low Sun Mask | 0 | High |
| 1 | Low | ||
| 6-7 | Sun Glint | 00 | None |
| 01 | Geometry Based | ||
| 10 | Wind Speed Based | ||
| 11 | Geometry and Wind Speed Based | ||
Surface Reflectance Quality Band 2 is made up of the following bit values.
| Surface Reflectance Quality Band 2 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0-2 | Land/Water Background | 000 | Land and Desert |
| 001 | Land No Desert | ||
| 010 | Inland Water | ||
| 011 | Sea Water | ||
| 100 | --- | ||
| 101 | Coastal | ||
| 110 | --- | ||
| 3 | Shadow Mask | 0 | No Cloud Shadow |
| 1 | Cloud Shadow | ||
| 4 | Heavy Aerosol Mask | 0 | No Heavy Aerosol |
| 1 | Heavy Aerosol | ||
| 5 | Snow / ice | 0 | No Snow or Ice |
| 1 | Snow or Ice | ||
| 6 | Thin Cirrus Reflective | 0 | No Cloud |
| 1 | Cloud | ||
| 7 | Thin Cirrus Emissive | 0 | No Cloud |
| 1 | Cloud | ||
Surface Reflectance Quality Band 4 is made up of the following bit values. Bits 1 and 2 from quality band 4 are used to determine if the bits from a given gridded I1 (red) or I2 (near-infrared) band should be used in creating the NDWI band. Surface Directional Reflectance (SDR), Aerosol Optical Thickness (AOT), Ante Meridiem (AM), Precipitable Water (PW)
| Surface Reflectance Quality Band 4 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0 | BAD M11 SDR Data | 0 | No |
| 1 | Yes | ||
| 1 | Bad I1 SDR Data | 0 | No |
| 1 | Yes | ||
| 2 | Bad I2 SDR Data | 0 | No |
| 1 | Yes | ||
| 3 | Bad I3 SDR Data | 0 | No |
| 1 | Yes | ||
| 4 | Overall Quality of AOT | 0 | Good |
| 1 | Bad | ||
| 5 | Missing AOT Input Data | 0 | No |
| 1 | Yes | ||
| 6 | Invalid Land AM Input Data | 0 | Valid |
| 1 | Invalid AM Input Over Land or Over Ocean | ||
| 7 | Missing PW Input Data | 0 | No |
| 1 | Yes | ||
Additional Information
- Land Atmosphere Near Real-time Capability for Earth Observing System (EOS) (LANCE)
- Level 1 and Atmosphere Archive and Distribution System (LAADS)
- VIIRS NASA
- VIIRS NOAA
Access Data
eVIIRS Global NDWI products held in the USGS archive can be searched using EarthExplorer. On EarthExplorer, eVIIRS Global NDWI products can be found under the Vegetation Monitoring category.
Digital Object Identifier (DOI)
The EROS Visible Infrared Imaging Radiometer Suite (eVIIRS) Global Normalized Difference Water Index (NDWI) collection is based on the Visible Infrared Imaging Radiometer Suite (VIIRS) data acquired by the Joint Polar Satellite System (JPSS), a collaborative program between the National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA). The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites.
The EROS Visible Infrared Imaging Radiometer Suite (eVIIRS) Global Normalized Difference Water Index (NDWI) collection uses the Visible Infrared Imaging Radiometer Suite (VIIRS) collection that is available at NASA’s Land Atmosphere Near-real-time Capability for EOS (LANCE) for the expedited product and Level-1 and Atmosphere Archive & Distribution System (LAADS) for the historical products.
Moderate resolution remote sensing provides a means for operational monitoring communities to develop historical trend information and use near real-time deviations from temporal averages to identify areas of change. High quality, consistent and well-calibrated satellite measurements are needed to detect and monitor changes and trends, especially in vegetation patterns useful for drought, crop yield, phenology and fire potential studies.
The eVIIRS Global NDWI collection is based on the Visible Infrared Imaging Radiometer Suite (VIIRS) data acquired by the National Aeronautics and Space Administration's (NASA) Earth Observing System (EOS). Even though VIIRS data are beneficial in vegetation studies, there have been usability issues encountered with the reprojection, file format and sub-setting. Therefore, eVIIRS was developed to specifically address these issues.
The eVIIRS Global NDWI is a 10-day data composited data set using the VIIRS sensor only. Expedited (near real-time) production runs every ten days for the 10-day products. Because each of the composites are created from a varying number of images, the eVIIRS composites include acquisition files to identify which of the possible inputs were used to populate the final composite. Product generation information can be found in the Open File Report – eVIIRS: A User-Friendly Data Source. The metadata accompanying the data files summarize geographic bounds, projection parameters and product contact information. The data has Global coverage and is available in GeoTIFF format, Geographic projection, and 1-kilometer resolution.
Composite Building Process for the Normalized Difference Water Index (NDWI)
The first step in the eVIIRS composite building process is to create the various geotiff bands required for building an NDWI composite for each of the days and times in the compositing period. In this case for a compositing period of 10 days.
One of the GeoTIFF bands created is the NDWI band. NDWI is created from the equation
NDWI = (green – SWIR) / (green + SWIR)
where green is band M4 and SWIR is band M10. These bands come from the 750-m surface reflectance bands of VNP09 granules.
The minimum NDWI values allowed are -0.1999, and all NDWI values (which normally fall between -1.0 and 1.0) are scaled by 10,000. Thus, the output NDWI values from this application fall between -2000 and 10,000 (with the exception of negative surface reflectance values) to match the LP DAAC MOD09 products.
If either of the green or SWIR pixel values is background fill, then the output NDWI value is set to UNDEF (-2000). The same value applies if the green and SWIR pixels are the same value. If either of the green or SWIR pixels is negative, then the output NDWI value is set to NEG_SR (-3000).
Other bands created for the compositing process are Satellite Zenith Angle and Surface Reflectance Quality Bands 1, 2 and 4.
Composite Calculation for the Normalized Difference Water Index (NDWI)
The software used to create 10-day dekadal NDWI composites was developed by the USGS EROS software development team. The software processes VIIRS 750-m swath granules to produce 1-km composite products.
The software grids the required swath granules (VNP09 and VNP03MOD) for the global bounded region (using upper left and lower right corner coordinates). For each gridded granule, an NDWI band is generated using the green (band M4) and SWIR (band M10) bands.
Once each granule has been gridded to the given coordinate extents and the NDWI has been built, then an enhanced maximum value composite (MVC) is generated. With a straight MVC algorithm, each pixel in the composite (for each band) would be filled using the pixel value of the granule with the highest NDWI for the current pixel. The MVC has been enhanced in the eVIIRS algorithm by incorporating band quality, cloud mask, negative surface reflectance, and view angle into the algorithm for eVIIRS processing.
- The band quality information in the surface reflectance product is used to determine if a certain pixel is of “bad quality.” Bad quality pixels are not used in the final composite product.
- The NDWI algorithm flags negative surface reflectance values so that they will not be used in the output composite if positive values are available. If either the red or NIR band surface reflectance values are negative, then the output NDWI value is flagged with a value of -3000. (NOTE: Undefined or background fill NDWI values are -2000 and that is specified as the lower limit of the “valid” NDWI values.) The composite algorithm then disregards granules with NDWI values of -3000 to omit negative surface reflectance values in the output composite.
- The cloud mask is used to minimize the presence of cloud pixels in the composite product. If the quality flag is probably clear and/or confident clear, then the pixel may be used to fill the current composite pixel.
- The view angle (distance from nadir) determines which of the two highest NDWI pixels is used in the composite. Of the non-cloudy, ideal-quality pixels, the two highest NDWI values are determined from the list of granules. Of these two granules, the pixel value which is closest to nadir is used to fill the composite.
Digital Products
The products are generated and delivered in a compressed (zipped) GeoTIFF format.
The spatial resolution of 1,000 m is available to download individually. These data are available in EarthExplorer as well Machine-to-Machine API. The download product is a .zip file containing 9 files, including six .tif, one jpeg, and two .txt files.
Following is a sample list of files from a Global NDWI 1-km NDWI composite
GN_eVSH_NDWI.2023.091-100.1KM.WI_ACQI.001.2023104131321.tif Acquisition geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_ACQT.001.2023104131321.txt Acquisition text file
GN_eVSH_NDWI.2023.091-100.1KM.WI_M04B.001.2023104131321.tif Band 4 geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_M10B.001.2023104131321.tif Band 10 geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_MASK.001.2023104131321.tif Mask band geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_META.001.2023104211226.met Metadata text file
GN_eVSH_NDWI.2023.091-100.1KM.WI_NDWI.001.2023104131321.jpg NDWI browse JPEG
GN_eVSH_NDWI.2023.091-100.1KM.WI_NDWI.001.2023104131321.tif NDWI geotiff
GN_eVSH_NDWI.2023.091-100.1KM.WI_QUAL.001.2023104131321.tif Quality geotiff
Acquisition Band (ACQI)
An acquisition band provides the user with a GeoTIFF image that can be overlayed onto the NDWI image so that the user can then identify each granule that provided the value for each NDWI pixel. The DOY and the acquisition number will be used to specify the acquisition. The acquisition number in this case represents not the time of the acquisition, but the order of capture. The output values are represented as an unsigned 16-bit integer using the equation
DOY * 1000 + acq_number
Thus, the first acquisition for DOY 117 would be 117001. The eleventh acquisition for DOY 117 would be 117011. To make it easier for the user to determine which acquisition integer value maps to which granule, an output acquisition table text file is written to match the acquisition values to the granule names.
Acquisition Text File (ACQT)
An acquisition text file provides the user a text file to accompany the Acquisition image, which gives the composite details of the data used to create the product. This list of the acquisition band values is used in the composite acquisition band product and the corresponding acquisition filename for that acquisition value.
160005 MA2RG_2020_160_2120_250m_NDWI.hdf
160004 MA2RG_2020_160_1940_250m_NDWI.hdf
160003 MA2RG_2020_160_1935_250m_NDWI.hdf
160002 MA2RG_2020_160_1800_250m_NDWI.hdf
160001 MA2RG_2020_160_1755_250m_NDWI.hdf
159007 MA2RG_2020_159_2035_250m_NDWI.hdf
159006 MA2RG_2020_159_2030_250m_NDWI.hdf
159005 MA2RG_2020_159_1900_250m_NDWI.hdf
Metadata (META)
The Metadata file provides the details about the composite image, including acquisition time period, publication dates, pixel and row counts, map projection information, datum, pixel resolution, satellite and platform, digital data type, fill values, scaling factors, and center and corner coordinates.
Browse JPEG
A full resolution browse image is provided in JPEG format and is zipped with the product and used to display the image on EarthExplorer. The color mapping is used to create a color image for the browse image and is not the same as the 16-bit single band data delivered in the NDWI GeoTIFF.
Mask GeoTIFF
The mask GeoTIFF provides information on the following attributes for each pixel based on which bits are set.
| Bit Value | Attributes |
|---|---|
| 1 | Water |
| 2 | Cloud Shadow |
| 4 | Adjacent Cloud |
| 8 | Snow / Ice |
| 16 | Thin Cirrus Reflective |
| 32 | Thin Cirrus Emissive |
Thus, the bits for decimal 58 are 111010 which means that the pixel has these attributes (from left bit to right bit)
- thin cirrus emissive
- thin cirrus reflective
- snow / ice
- cloud shadow
NDWI GeoTIFF
The NDWI GeoTIFF is the product created in the compositing process detailed in the above section. All the other files including quality band, acquisition band, as well as the text files and browse are companion files for this NDWI product.
Quality Band (QA) GeoTIFF
A quality assurance (QA) band is 8 bits and produced by the composite software to identify the quality of each composite pixel. Most pixels will be filled with a pixel of good band quality. However, if none of the granules for a particular pixel are of good band quality or all of the pixels are cloudy, then the current pixel is filled with data from the best pixel possible where the preference order is valid NDWI over fill, good quality over bad, snow pixel over cloudy pixel. The following values are used in the QA band:
0 = good quality
1 = cloudy pixel
2 = bad band quality
4 = snow
10 = fill
Surface Reflectance Quality Band 1 is made up of the following bit values. Bit number 0 is the bit in the binary number which is of the lowest numerical value or Least Significant Bit (LSB).
| Surface Reflectance Quality Band 1 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0-1 | Cloud Mask Quality | 00 | Poor |
| 01 | Low | ||
| 10 | Medium | ||
| 11 | High | ||
| 2-3 | Cloud Detection and Confidence | 00 | Confident Clear |
| 01 | Probably Clear | ||
| 10 | Probably Cloud | ||
| 11 | Probably Clear | ||
| 4 | Day / Night | 0 | Day |
| 1 | Night | ||
| 5 | Low Sun Mask | 0 | High |
| 1 | Low | ||
| 6-7 | Sun Glint | 00 | None |
| 01 | Geometry Based | ||
| 10 | Wind Speed Based | ||
| 11 | Geometry and Wind Speed Based | ||
Surface Reflectance Quality Band 2 is made up of the following bit values.
| Surface Reflectance Quality Band 2 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0-2 | Land/Water Background | 000 | Land and Desert |
| 001 | Land No Desert | ||
| 010 | Inland Water | ||
| 011 | Sea Water | ||
| 100 | --- | ||
| 101 | Coastal | ||
| 110 | --- | ||
| 3 | Shadow Mask | 0 | No Cloud Shadow |
| 1 | Cloud Shadow | ||
| 4 | Heavy Aerosol Mask | 0 | No Heavy Aerosol |
| 1 | Heavy Aerosol | ||
| 5 | Snow / ice | 0 | No Snow or Ice |
| 1 | Snow or Ice | ||
| 6 | Thin Cirrus Reflective | 0 | No Cloud |
| 1 | Cloud | ||
| 7 | Thin Cirrus Emissive | 0 | No Cloud |
| 1 | Cloud | ||
Surface Reflectance Quality Band 4 is made up of the following bit values. Bits 1 and 2 from quality band 4 are used to determine if the bits from a given gridded I1 (red) or I2 (near-infrared) band should be used in creating the NDWI band. Surface Directional Reflectance (SDR), Aerosol Optical Thickness (AOT), Ante Meridiem (AM), Precipitable Water (PW)
| Surface Reflectance Quality Band 4 | |||
| Bit No. | Parameter Name | Bit Combination | Definition |
| 0 | BAD M11 SDR Data | 0 | No |
| 1 | Yes | ||
| 1 | Bad I1 SDR Data | 0 | No |
| 1 | Yes | ||
| 2 | Bad I2 SDR Data | 0 | No |
| 1 | Yes | ||
| 3 | Bad I3 SDR Data | 0 | No |
| 1 | Yes | ||
| 4 | Overall Quality of AOT | 0 | Good |
| 1 | Bad | ||
| 5 | Missing AOT Input Data | 0 | No |
| 1 | Yes | ||
| 6 | Invalid Land AM Input Data | 0 | Valid |
| 1 | Invalid AM Input Over Land or Over Ocean | ||
| 7 | Missing PW Input Data | 0 | No |
| 1 | Yes | ||
Additional Information
- Land Atmosphere Near Real-time Capability for Earth Observing System (EOS) (LANCE)
- Level 1 and Atmosphere Archive and Distribution System (LAADS)
- VIIRS NASA
- VIIRS NOAA
Access Data
eVIIRS Global NDWI products held in the USGS archive can be searched using EarthExplorer. On EarthExplorer, eVIIRS Global NDWI products can be found under the Vegetation Monitoring category.