PATMOS-x AVHRR Pathfinder Atmospheres - Extended

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Level 2b Data

The Level-2b data is a new format for the PATMOS-x output.  It consists of a smaller number of products than available in the Level-3 data but at a much finer spatial resolution.  Level-2b data is generated by spatially sampling the Level-2 output.  Each point in a Level-2b file therefore represents if information from one pixel and no averaging of pixels was done.  The current resolution of Level-2b data is 0.1 degree which means the points are separated by approximately 11 km.  

The specific goals of the Level-2b data is to:

  • allow for study of cloud processes not well represented by large-scale averages.
  • give flexibility to generate Level-3 products that are optimized for their application

Level-2b contents are described below and consist of the AVHRR radiances, viewing geometries,  cloud properties and a few selected non-cloud properties.  Level-2b files are computed for each satellite for each day and for each orbital node (ascending or descending).

We have made 30+ year series of Level-2b data over small regions of interest and we hope to get some feedback on the utility of this dataset.

What's New!

We have made many improvements to PATMOS-x based on your feedback and lessons learned during the GOES-R AWG and NPOESS projects.  Here is a list of the major ones.

  • Adoption of the GOES-R Daytime Cloud Optical Properties Algorithm which includes use of the atmospheric correction and surface reflectance information taken from the MODIS Atmospheres Science Team.
  • A Naive Bayesian cloud mask derived from colocated NOAA-18/AVHRR and CALIPSO/CALIOP measurements.
  • Adoption of new reflectance calibration.
  • Implementation of new clock correction procedure that fixed a major bug in the previous version during some periods  of the NOAA-11 record.
  • Addition of meta-data for  CF compliance.
  • HDF4 and NETCDF versions of the data.

Whats in the Data

  • Observations: 0.63, 0.86 micron reflectances, 3.75, 11 and 12 micron brightness temperatures.
  • Angles: sensor zenith, solar zenith, solar azimuth, relative azimuth
  • Geolocation: latitude and longitude
  • Cloud Properties: probability of cloud, cloud mask, type,  pressure, temperature, optical depth, effective radius, 11 micron emissivity and ir-microphysical index (beta) from 11 and 12 microns, quality flags
  • Surface Properties: land type, surface temperature, atmospherically corrected NDVI, remote sensing reflectance
  • Atmospheric Properties: 0.63 micron aerosol optical depth, 11 micron emissivity referenced to the Tropopause, dust mask, smoke mask
  • Example images of all products in one file can be seen here.

How to Read the Data

We have achieved CF compliance so that many HDF and NETCDF applications should be able to read this data.  We have IDL tools available for those interested.  A list of the global attributes is here.  A list of the variable names is given here. A full dump of the headers can be found here.

How to Get the Data

Please note our data policy. The Level-2b products are available for a few selected geographical regions and can be downloaded at these links:

If there is a need for another region, let us know.  Global Level-2b data is coming once we are certain that our format and products are bug-free.

Details

  • Because the Level-2b grid is equally spaced in latitude and longitude, latitude and longitude are stored as 1d vectors.
  • Cloud type value key (0=clear,1=probably clear, 2 = fog, 3 = water, 4 = supercooled water, 5 = mixed, 6 = opaque ice, 7 = cirrus, 8 = overlapped cirrus, 9 = overshooting convection, 10 = unknown, 11 = dust, 12 = smoke)
  • cloud mask value key (0 = clear, 1 = probably clear, 2= probably cloudy, 3= cloudy)
  • quality flag key (0=invalid, 1 = degraded, 2 = fair, 3 = high)
  • land type key (0=shallow ocean, 1=land, 2=coastline,3=shallow_inland_water, 4= ephemeral water, 5 = deep_inland water, 6 = moderate ocean, 7 = deep ocean)
  • Packed Land Cover bits (0 = land cover, 1 = snow mask, 2 = coast mask )
  • 1st packed QF bits (0 = Cloud Temp QF, 1 = Cloud Emissivity QF, 2 = beta ratio QF, 3 = Cloud Optical Depth QF )
  • 2nd packed QF bits (0 = Cloud Effective Radius QF, 1 = Aerosol Optical Thickness QF, 2 = RSR QF, 3 = Cloud Mask )

References

Bayesian Cloud Mask: Coming Soon!

Cloud Type:
Pavolonis, Michael J.; Heidinger, Andrew K. and Uttal, Taneil. Daytime global cloud typing from AVHRR and VIIRS: Algorithm description, validation, and comparisons. Journal of Applied Meteorology, Volume 44, Issue 6, 2005, pp.804-826

Heidinger, Andrew K. and Pavolonis, Michael J.. Global daytime distribution of overlapping cirrus cloud from NOAA's Advanced Very High Resolution Radiometer. Journal of Climate, Volume 18, Issue 22, 2005, pp.4772-4784.

Cloud Height:  
Heidinger, Andrew K. and Pavolonis, Michael J.. Gazing at cirrus clouds for 25 years through a split window, part 1: Methodology. Journal of Applied Meteorology and Climatology, Volume 48, Issue 6, 2009, pp.110-1116.

Cloud Optical and Microphysical Properties:
Heidinger, Andrew K.. Rapid daytime estimation of cloud properties over a large area from radiance distributions. Journal of Atmospheric and Oceanic Technology, Volume 20, Issue 9, 2003, pp.1237-1250.   [A new reference from Andi Walther is coming soon]

Calibration:
Heidinger, Andrew K.; Cao, Changyong and Sullivan, Jerry T.. Using Moderate Resolution Imaging Spectrometer (MODIS) to calibrate advanced very high resolution radiometer reflectance channels. Journal of Geophysical Research, Volume 107, 2002, Doi:10.1029/2001JD002035, 2002.