Open Suomi NPP VIIRS Data

ENVI reads imagery from the Suomi National Polar-orbiting Partnership (NPP) Visible Infrared Imager Radiometer Suite (VIIRS) sensor, specifically the following:

• HDF5 format
• Produced by the Integrated Data Processing Segment (IDPS) and distributed through the NOAA CLASS web site
• Joint Polar Satellite System (JPSS) Common Data Format Control Book (CDFCB)
• Sensor Data Records (SDRs)
• I-bands, M-bands, and Day/Night Band (DNB)
• Active Fires Product (AVAFO*.h5): ENVI displays these files as point vectors.
• Environmental Data Records (EDRs) with Quality, Latitude, and Longitude rasters:
  • Aerosol Optical Thickness (aerosol optical depth, Angstrom exponent)
  • Ice Surface Temperature
  • Land Surface Temperature
  • Ocean Color Chlorophyll (chlorophyll-a, IOP-a, IOP-s, nLw)
  • Sea Ice Characterization (ice age, ice age weight)
  • Sea Surface Temperature (bulk temperature, skin temperature)
  • Snow Cover Depth Binary Map
  • Snow Fraction
  • Surface Type (surface type, vegetation fraction)
  • Suspended Matter
  • Vegetation Index (top-of-atmosphere NDVI and EVI)
• EDRs without Latitude and Longitude rasters:
  • Cloud Base Height
  • Cloud Cover Layers
  • Cloud Effective Particle Size
  • Cloud Optical Thickness
  • Cloud Top Height
  • Cloud Top Pressure
  • Cloud Top Temperature

If an EDR I-band image originally contained gaps (filled with a "missing data" value) between data granules, ENVI automatically removes the gaps and merges the data granules.

Open Files

ENVI does not open NPP VIIRS files that only contain geographic information with no image data. However, you can open these files using the File > Open As > Scientific Formats > HDF5/NetCDF-4 menu option and selecting the desired datasets from the Dataset Browser.

Follow these steps to open NPP VIIRS files:

1. Use the File > Open menu option and select an NPP VIIRS .h5 file. The Select NPP VIIRS Parameters dialog appears.
2. The Select Product drop-down menu lists the available products to choose from. For EDRs, select a specific product to open. For SDRs, select the type of calibration to perform on the imagery. The data type and units for each calibrated image are as follows:

Radiance:

• Day/Night Band: 32-bit floating point in units of W/(cm² * sr)
• I-bands 1-5: unsigned 16-bit integer in units of W/(m² * sr * µm)
• M-bands 3-5, 7, 13: 32-bit floating point in units of W/(m² * sr * µm)
• M-bands 1, 2, 6, 8-12: unsigned 16-bit integer in units of W/(m² * sr * µm)

Reflectance:

• I-bands 1-3: unsigned 16-bit integer
• M-bands 1-11: unsigned 16-bit integer

Brightness temperature (Kelvins)

• I-bands 4-5: unsigned 16-bit integer
• M-band 13: 32-bit floating point
• M-bands 12, 14-16: unsigned 16-bit integer

Albedo

• NCC products only: 32-bit floating point
3. Some products contain bowtie artifacts in the source imagery. Select the Geocorrect and Mitigate Bowtie Effect option if you want to georeference the source imagery, which will also remove the bowtie artifacts. You should georeference NPP VIIRS imagery if you plan to use it in a workflow (for example, Classification or Change Detection Workflow). This process can take several minutes to complete. Georeferencing is only available if the file you selected has Latitude and Longitude bands. A Quality band is further needed to perform bowtie correction.
4. If you do not want to georeference the image and correct for bowtie effects, select the Load Raw Image option. After you click OK, the raw (non-corrected) image will display if the Auto Display Files on Open preference is set to True. If you later decide to georeference an opened image and correct it for bowtie effects, you can perform these steps independently by selecting Geometric Correction > Reproject GLT with Bowtie Correction from the Toolbox.
5. The default Projection Type is Geographic WGS-84. Choose Polar Stereographic WGS-84 if the imagery covers the polar regions.
6. Select an Interpolation Method: The GLT algorithm establishes a regular output grid and finds the best location for each source image pixel. Any output grid point for which a source pixel could not be found will be filled with one of the following methods.
   • Distance Weighted (default): A distance-weighted average of the surrounding valid values. Use this method to create an image with the fewest visible interpolation artifacts.
   • Nearest Neighbor: Select this method when the set of valid pixel values cannot be modified, for example, when values represent the integral values of a classification.
7. Select an output directory for the georeferenced and bowtie-corrected image.
8. Select the Display Geocorrected Image option to display the georeferenced and bowtie-corrected image after processing is complete.
9. Click OK.