4.1. VIIRS SDR Reader¶
The VIIRS SDR Reader operates on Sensor Data Record (SDR) HDF5 files from the Suomi National Polar-orbiting Partnership’s (NPP) and/or the NOAA20 Visible/Infrared Imager Radiometer Suite (VIIRS) instrument. The VIIRS SDR reader ignores filenames and uses internal file content to determine the type of file being provided, but SDR are typically named as below and have corresponding geolocation files:
SVI01_npp_d20120225_t1801245_e1802487_b01708_c20120226002130255476_noaa_ops.h5
The VIIRS SDR reader supports all instrument spectral bands, identified as
the products shown below. It supports terrain corrected or non-terrain corrected
navigation files. Geolocation files must be included when specifying filepaths to
readers and polar2grid.sh. The VIIRS reader can be specified to the polar2grid.sh script
with the reader name viirs_sdr.
This reader’s default remapping algorithm is ewa for Elliptical Weighted
Averaging resampling. The --weight-delta-max parameter set to 40 and the
--weight-distance-max parameter set to 2.
Product Name |
Description |
|---|---|
i01 |
I01 Reflectance Band |
i02 |
I02 Reflectance Band |
i03 |
I03 Reflectance Band |
i04 |
I04 Brightness Temperature Band |
i05 |
I05 Brightness Temperature Band |
i01_rad |
I01 Radiance Band |
i02_rad |
I02 Radiance Band |
i03_rad |
I03 Radiance Band |
i04_rad |
I04 Radiance Band |
i05_rad |
I05 Radiance Band |
m01 |
M01 Reflectance Band |
m02 |
M02 Reflectance Band |
m03 |
M03 Reflectance Band |
m04 |
M04 Reflectance Band |
m05 |
M05 Reflectance Band |
m06 |
M06 Reflectance Band |
m07 |
M07 Reflectance Band |
m08 |
M08 Reflectance Band |
m09 |
M09 Reflectance Band |
m10 |
M10 Reflectance Band |
m11 |
M11 Reflectance Band |
m12 |
M12 Brightness Temperature Band |
m13 |
M13 Brightness Temperature Band |
m14 |
M14 Brightness Temperature Band |
m15 |
M15 Brightness Temperature Band |
m16 |
M16 Brightness Temperature Band |
m01_rad |
M01 Radiance Band |
m02_rad |
M02 Radiance Band |
m03_rad |
M03 Radiance Band |
m04_rad |
M04 Radiance Band |
m05_rad |
M05 Radiance Band |
m06_rad |
M06 Radiance Band |
m07_rad |
M07 Radiance Band |
m08_rad |
M08 Radiance Band |
m09_rad |
M09 Radiance Band |
m10_rad |
M10 Radiance Band |
m11_rad |
M11 Radiance Band |
m12_rad |
M12 Radiance Band |
m13_rad |
M13 Radiance Band |
m14_rad |
M14 Radiance Band |
m15_rad |
M15 Radiance Band |
m16_rad |
M16 Radiance Band |
dnb |
Raw DNB Band (not useful for images) |
histogram_dnb |
Histogram Equalized DNB Band |
adaptive_dnb |
Adaptive Histogram Equalized DNB Band |
dynamic_dnb |
Dynamic DNB Band from Steve Miller and Curtis Seaman. Uses erf to scale the data. |
hncc_dnb |
Simplified High and Near-Constant Contrast Approach from Stephan Zinke |
ifog |
Temperature difference between I05 and I04 |
i_solar_zenith_angle |
I Band Solar Zenith Angle |
i_solar_azimuth_angle |
I Band Solar Azimuth Angle |
i_sat_zenith_angle |
I Band Satellite Zenith Angle |
i_sat_azimuth_angle |
I Band Satellite Azimuth Angle |
m_solar_zenith_angle |
M Band Solar Zenith Angle |
m_solar_azimuth_angle |
M Band Solar Azimuth Angle |
m_sat_zenith_angle |
M Band Satellite Zenith Angle |
m_sat_azimuth_angle |
M Band Satellite Azimuth Angle |
dnb_solar_zenith_angle |
DNB Band Solar Zenith Angle |
dnb_solar_azimuth_angle |
DNB Band Solar Azimuth Angle |
dnb_sat_zenith_angle |
DNB Band Satellite Zenith Angle |
dnb_sat_azimuth_angle |
DNB Band Satellite Azimuth Angle |
dnb_lunar_zenith_angle |
DNB Band Lunar Zenith Angle |
dnb_lunar_azimuth_angle |
DNB Band Lunar Azimuth Angle |
true_color |
Ratio sharpened rayleigh corrected true color |
false_color |
Ratio sharpened rayleigh corrected false color |
4.1.1. Command Line Arguments¶
usage: polar2grid.sh -r viirs_sdr -w <writer> [-h] [--i-bands] [--m-bands] [--dnb-angle-products] [--dnb-saturation-correction] [--i-angle-products] [--m-angle-products] [--m-rad-products] [--i-rad-products] [--awips-true-color] [--awips-false-color]
4.1.1.1. VIIRS SDR Reader¶
- --i-bands
Add all I-band raw products to list of products
- --m-bands
Add all M-band raw products to list of products
- --dnb-angle-products
Add DNB-band geolocation ‘angle’ products to list of products
- --dnb-saturation-correction
Enable dynamic DNB saturation correction (normally used for aurora scenes)
- --i-angle-products
Add I-band geolocation ‘angle’ products to list of products
- --m-angle-products
Add M-band geolocation ‘angle’ products to list of products
- --m-rad-products
Add M-band geolocation radiance products to list of products
- --i-rad-products
Add I-band geolocation radiance products to list of products
- --awips-true-color
Add individual CREFL corrected products to create the ‘true_color’ composite in AWIPS.
- --awips-false-color
Add individual CREFL corrected products to create the ‘false_color’ composite in AWIPS.
Examples:
polar2grid.sh -r viirs_sdr -w geotiff -f <path to files>/<list of files>
polar2grid.sh -r viirs_sdr -w geotiff -h
polar2grid.sh -r viirs_sdr -w geotiff --list-products -f ../sdr/*.h5
polar2grid.sh -r viirs_sdr -w geotiff --fill-value 0 -f ../sdr/*.h5
polar2grid.sh -r viirs_sdr -w geotiff -p true_color false_color --num-workers 8 --tiled -f ../sdr/*.h5
polar2grid.sh -r viirs_sdr -w awips_tiled -p i04 adaptive_dnb dynamic_dnb --awips-true-color --awips-false-color --sza-threshold=90.0 --letters --compress --sector-id Polar -g polar_alaska_1km --dnb-saturation-correction -f <path to files>
polar2grid.sh -r viirs_sdr -w hdf5 --compress gzip --m-bands -f ../sdr/*.h5
polar2grid.sh -r viirs_sdr -w binary -g lcc_fit -p m15 --num-workers 8 -f ../sdr/SVM15*.h5 ../sdr/GMTCO*.h5
4.1.2. Product Explanation¶
4.1.2.1. True Color¶
The VIIRS SDR “true_color” composite produced by Polar2Grid provides a view of the Earth as the human eye would see it; or as close as we can come to with satellite data and the channels we have available. This means things like trees and grass are green, water is blue, deserts are red/brown, and clouds are white. The True Color GeoTIFF 24 bit image is an RGB (Red, Green, Blue) image consisting of a combination of Red: VIIRS M-Band 5, Green: VIIRS M-Band 4, and Blue: VIIRS M-Band 3 reflectance channels. Each channel goes through a series of adjustments to produce the final high quality image output by Polar2Grid.
Creation of true color RGBs includes the following steps:
Atmospheric Rayleigh Scattering Correction of the RGB visible reflectances.
Combining the 3 channels into a 24 bit output file.
Sharpening of the image to full 350m resolution if the VIIRS I-Band 1 is provided as input.
Application of a non-linear enhancement.
See the Creating VIIRS SDR GeoTIFF Files example to see how Polar2Grid can be used to make this product as a GeoTIFF and KMZ file.
4.1.2.2. False Color¶
A false color image is any combination of 3 bands outside of those used to create a “true color” image (see above). These combinations can be used to highlight features in the observations that may not be easily identified in individual band imagery. Polar2Grid can readily create a preconfigured legacy false color (product false_color) GeoTIFF 24 bit image that consists of a combination RGB (Red, Green, Blue) image using uses Red:VIIRS M-Band 11 (2.25 μm), Green:VIIRS M-Band 7 (.87 μm) and Blue:VIIRS M-Band 5 (.67 μm). This band combination is very effective at distinguishing land/water boundaries as well as burn scars.
Creation of VIIRS legacy false color RGBs includes the following steps:
Atmospheric Rayleigh Scattering Correction of the RGB visible reflectances.
Combining the 3 channels into a 24 bit output file.
Sharpening of the image to full 350m resolution if the VIIRS I-Band 2 is provided as input.
Application of a non-linear enhancement.
See the Creating VIIRS SDR GeoTIFF Files example to see how Polar2Grid can be used to make this product as a GeoTIFF and KMZ output file.
4.1.2.3. Fog - Temperature Difference¶
The VIIRS SDR reader can also produce a “ifog” product which is a simple difference of the infrared brightness temperatures between the I05 (11.45 μm) and I04 (3.74 μm) bands (I05 - I04). The result is scaled linearly between -10.0 and 10.0 Kelvin before being saved to an output image.
4.1.2.4. Day Night Band¶
Polar2Grid allows the user to create images from the VIIRS Day/Night Band, which contains observations of visible radiances for both day and night. Polar2Grid provides 4 options for enhancing and scaling the DNB data. A full description of these options are described in detail in the Scaling of the VIIRS Day/Night Band in Polar2Grid appendix.
4.1.2.5. Reflectance I-Bands 01-03 and M-Bands 01-11¶
The I01-I03 and M01-M11 bands are visible reflectance channels on the VIIRS instrument. Besides the basic calibration necessary to convert the radiance values to reflectances, the data is passed through a square root function before being written to a grayscale image. The square root operation has the effect of balancing the bright and dark regions of the image.
4.1.2.6. Infrared I-Bands 04-05 and M-Bands 12-16¶
The I04-I05 and M12-M16 bands are all brightness temperature (infrared (IR)) channels. To produce a grayscale image with dark land and white clouds, the data is inverted and scaled linearly in two segments. The first segment is from 163K to 242K, the second 242K to 330K. This is a common scaling used by the National Weather Service (NWS) for their AWIPS visualization clients.
