Dear Jim,
I believe attempting to produce one number and regard it as a threshold
could lead to oversimplification and ultimately may create confidence
where judgment and experience need to be applied. Please consider the
GOES-R cloud mask with which I am most familiar. The cloud mask is
produced by applying 8 Infrared tests, using a variety of BT's, 2 short
wave tests, 4 visible band reflectance tests, and finally uniformity
tests are run. If you would like to see the details, you could google
to find the GOES-R ATBD for cloud mask by A. Heidinger of
NOAA/NESDIS/STAR. The smoke and dust mask is much less complicated,
but BT differences are invoked and uniformity tests applied. I do not
see an obvious way to simplify this information by publishing a single
threshold. To publish multiple thresholds requires considering whether
we'll show the thresholds for day, night, ocean, or land.
In another consideration, if we include BT's, wavelengths, and
thresholds used to derive the mask, will we not restrict the standard
name to usefulness for only those programs that compute the masks in a
similar manner?
With respect to the aerosol_binary_mask, GOES-R will set the mask to
true (1) if smoke or dust is detected. Other programs may consider
other particulate matter types, so leaving the mask with a general
definition will allow more flexibility from the user base.
I hope this clarifies our considerations. Thank you for your question.
Regards,
Charles
Jim Biard wrote:
There may be a complex algorithm underlying the binary state to be
represented by these standard names, but there clearly is a threshold
for each binary state. There is some level of each constituent for
which the corresponding algorithm will produce zeros. It seems to me
that it would better to state even a rough estimate of the threshold
in each case than to leave it unstated.
Jim Biard
Research Scholar
Cooperative Institute for Climate and Satellites <http://www.cicsnc.org/>
Remote Sensing and Applications Division
National Climatic Data Center <http://www.ncdc.noaa.gov/>
151 Patton Ave, Asheville, NC 28801-5001
[email protected] <mailto:[email protected]>
828-271-4900
Follow us on Facebook <https://www.facebook.com/cicsnc>!
On May 15, 2013, at 3:34 PM, Charles Paxson <[email protected]
<mailto:[email protected]>> wrote:
Dear CF Metadata Users Group,
Through observations and analysis, GOES-R weather products produce
binary masks for: aerosols, smoke, dust and clouds. No coordinate
value is warranted (i.e. CF Metadata standard
surface_snow_binary_mask) for any of these four proposed quantities,
since a complex set of tests for each case, such as using brightness
temperatures, are used to derive signatures of the four atmospheric
constituents. The proposed masks are analogous and defined in a
similar way as the CF Metadata standard names: land_binary_mask and
sunlit_binary_mask.
aerosol_binary_mask: X_binary_mask has 1 where condition X is met, 0
elsewhere. 1 = aerosols present, 0 = aerosols absent
smoke_binary_mask: X_binary_mask has 1 where condition X is met, 0
elsewhere. 1 = smoke present, 0 = smoke absent
dust_binary_mask: X_binary_mask has 1 where condition X is met, 0
elsewhere. 1 = dust present, 0 = dust absent
cloud_binary_mask: X_binary_mask has 1 where condition X is met, 0
elsewhere. 1 = cloud present, 0 = cloud absent (clear)
Please accept these four mask names for inclusion into the CF
Metadata standard.
Sincerely,
Charles Paxson
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Charles Paxson
System Engineer
Atmospheric and Environmental Research (AER), Inc.
a Verisk Analytics Company
131 Hartwell Avenue, Lexington, MA 02421-3126
office: 781-761-2209
fax:781-761-2299
www.aer.com
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