SAFESEAS Workshop

1
SAFESEAS Workshop

• Wednesday, August 04
• and
• Thursday, August 05
• 2004
• National Weather Service Headquarters
• Silver Spring, Maryland

2
SAFESEAS Overview

• Key Terms
• Localization
• Customizing Your Monitoring Area
• Customizing Your Monitor Thresholds
• The SAFESEAS Monitor
• Customizing Your Display Thresholds
• The SAFESEAS Display

3
SAFESEAS OverviewKey Terms

• Area of Responsibility
• An offices area of responsibility (AOR)
  consists of all the zones and counties for which
  it normally has the responsibility of issuing
  forecasts, watches, and warnings.
• Monitoring Area
• An offices monitoring area (MA) consists of its
  AOR plus the AOR of each adjacent office having
  marine responsibilities. For offices along the
  borders with Canada and Mexico, the MA also
  includes all Canadian/Mexican area within 125
  statute miles of the centroid of any
  zone/county in the MA. Finally, for moving
  platforms (ships and drifting buoys), the MA
  includes all area within 200 nautical miles of
  the centroid of any marine zone in the MA.
• Nominal Hour
• The nominal hour is the whole hour with which a
  report is associated. Reports associated with a
  nominal hour are those from 30 minutes before the
  hour to 29 minutes after the hour. As an
  example, all reports from 1430 to 1529 are
  considered 15Z nominal hour reports.

4
SAFESEAS OverviewLocalization

• determines the default MA.
• which zones and counties are included in the
  MA.
• which fixed stations are in the MA.
• in which zone/county is each fixed station
  located.
• generates the default (factory setting) monitor
  thresholds.
• generates the default (factory setting) display
  thresholds.
• (starting with OB-4) merges previously done
  customizations with the results of the above.

5
SAFESEAS OverviewLocalization (continued)

• SAFESEAS localization uses
• US county shape files,
• marine zone shape files,
• (OB-5 and beyond, oconus site only) forecast zone
  shape files,
• the metarStationInfo.txt file, and
• the maritimeStationInfo.txt file.
• It is the responsibility of each office to make
  sure it has the current
• versions of these files before localization is
  run.

6
SAFESEAS OverviewLocalization (concluded)

• (OB-3 and OB-4)
• In addition, for mesonet stations, SAFESEAS
  localization uses the following files in
  directory /awips/fxa/ldad/data/
• LDADinfo.txt.
• one location information file for each external
  data source. these files have names
• of the form xxxStation.txt, where xxx is a
  data_root value from LDADinfo.txt.
• one dataset information file for each external
  data source. these files have names of
• the form yyy.desc, where yyy is a data_type
  value from LDADinfo.txt.
• It is the responsibility of each office to make
  sure these files are correct and up-to-date
  before localization is run. See the
  documentation in file /awips/fxa/data/localizatio
  n/scripts/SS_mesonetStationInfo.sh for more
  information.
• (OB-5 and beyond)
• Current OB-5 SAFESEAS localization code for
  mesonet, maritime, and METAR stations is the same
  as OB-4. But we are seriously considering using
  .spi files instead of the metarStationInfo.txt
  , maritimeStationInfo.txt, LDADinfo.txt,
  xxxStation.txt, and yyy.desc files.

7
SAFESEAS OverviewCustomizing Your Monitoring Area
SAFESEAS provides a GUI for customizing the MA.
Specifically, the office can

• add and delete zones and counties.
• add and delete fixed stations.
• customize the association of fixed stations with
  zones and counties, that is, which stations are
  monitored to determine each zones / countys
  threat level.

8
SAFESEAS OverviewCustomizing Your Monitor
Thresholds

• SAFESEAS provides a GUI for customizing the
  monitor thresholds. Thresholds are
  zone-specific, and so may be customized for each
  zone individually.

9
SAFESEAS OverviewThe SAFESEAS Monitor

• The SAFESEAS monitor is a persistent background
  process, much like the SCAN and FFMP processors.
  Currently, it monitors METARs, C-MAN reports,
  buoy reports, ship reports, and mesonet reports.
  Only reports from within the MA are monitored.
  From these reports, wind speed, wind direction,
  wave height, and visibility are monitored.
  Starting with OB-4, swell height, swell
  direction, and swell period are also monitored.
• Once every four minutes, it gets all new point
  observation reports. Based on the observation
  values and the monitor thresholds, an overall MA
  threat level is determined. The result is the
  threat level of the most severe observation from
  within the MA during the past two hours. The
  threat level is written to the file read by the
  SAFESEAS D-2D threat level button (the anchor).
  Finally, the anchor and the SAFESEAS display are
  signaled to update themselves.

10
SAFESEAS OverviewCustomizing Your Display
Thresholds

• SAFESEAS provides a GUI for customizing the
  display thresholds. Thresholds are
  zone-specific, and so may be customized for each
  zone individually.

11
SAFESEAS OverviewThe SAFESEAS Display

• the SAFESEAS Plot.
• consists of D-2D METAR, fixed buoy, moving
  buoy, and mesonet plots bundled together.
• includes reports for stations within the MA
  only.
• report plotted for the nominal hour is that
  which is closest to the top of the hour.
• the Zone Table.
• observation values and threat levels for each
  zone and county.
• values shown are from the most recent reports
  for the nominal hour for each station
• associated with the zone.
• sorted by user-selected product/variable
  (default is zone ID).
• the Station Table.
• observation values and threat levels for each
  station within a zone.
• values shown are from the most recent report
  for the nominal hour .
• sorted by user-selected product/variable
  (default is station ID).
• the Trends
• (OB-3) shows all observation values for most
  recent three hours.
• (OB-4 and beyond) shows all values for a
  variable for most recent 24 hours.
• the Single-Station 24-Hour Observation Table.
• new to OB-5.
• shows observations from all reports for the
  most recent 24 hours.

12
Fog Monitor Overview

• Theory and Method
• Localization
• Customizing Your Monitoring Area
• Customizing Your Monitor Thresholds
• The Fog Monitor
• Customizing Your Display Thresholds
• The Fog Monitor Display

13
Supporting theory
Fog monitoring is a kind of object-oriented
processing All we have to know is how to
describe a fog object its properties and its
behaviors
Spectral feature of fog in multiple satellite
channels 1. Scattering radiation feature
(Daytime) (a) VIS Channel (b) 10.7
(3.9) µm Channel 2. Emitting radiation feature
(Nighttime) (a) 3.9 µm Channel (b) 10.7
µm Channel Kinematic feature of fog
properties
behaviors
14
Scattering/Reflecting Radiation(1) 1
According to Mie scattering theory In the VIS
channel, reflectivity mainly is related to the
depth of the cloud/fog. In channel 3.9µm,
fog/stratus has maximum scatter rate with its
size equivalent to 3.9 µm.

• Comments
• Here two differences can be used to distinguish
  fog and cloud 1) VIS difference 2) 3.9 µm IR
  difference.
• The fog region in satellite image should be
  smooth, edge-clearregular.
• Snow cover and sea ice are bad reflectors in
  channel 3.9 µm, while fog and stratus are good.

15
Scattering/Reflecting Radiation(2)12
Data Normalization of the VIS satellite data
16
Normalization with fine tuning
Scattering/Reflecting Radiation(3)
17
Scattering/Reflecting Radiation(4) 21314
Assumed that all objects are black bodies so
TBemit3.9 TB11 Treal , and according to the
Planck radiation law,
This is how reflective product of RAMSDIS ONLINE
is generated . Because of the assumption of
black body and TBemit3.9 TB11 , it is an
approximated reflective product and it does not
take the angular correction into consideration
So in our algorithms, it is not adopted for fog
detection but for sea ice/snow cover
exclusion. http//www.cira.colostate.edu/RAMM/Rmsd
sol/main.html http//www.nrlmry.navy.mil/turk/int
ro.html Allen, R.C., P.A. Durkee, and C.H. Wash,
1994 Snow-cloud discrimination with
multispectral satellite images. J. Appl. Meteor
18
Emitting Radiation(1)2
?0 means can be ignored ?1 means major
Without the presence of sun light, in fog region,
a positive value with 10.7 µm channel - 3.9 µm
channel. This difference is caused by the
emissivity difference of fog between 10.7 um and
3.9 µm. Above will be good only during the night
time Other water/ice clouds like AC/AS also look
similar to Fog in fog product 7. But in 10.7
µm channel , the brightness temperature of fog is
higher than that of higher water/ice cloud
(AC/AS). This can in a degree help distinguish
them.
19
Emitting Radiation(2) 23
R(satellite) R(ground) - R(absorbed)
R(cloud) Different emissivities of different
cloud types Absorptivity is related to emissivity
and the depth of the cloud/fog Planck radiation
law
Thin cloud (night) TB(10.7 µm ) -
TB(3.9 µm ) lt 0 Thick cloud (night)
TB(10.7 µm ) - TB(3.9 µm ) 0 Fog
(night) TB(10.7 µm ) - TB(3.9 µm ) gt
0 ice cloud (night) TB(10.7 µm )
- TB(3.9 µm ) lt 0 Water/ice cloud (night)
TB(10.7 µm ) - TB(3.9 µm ) gt 0
Comment So fog product should be checked to
eliminate other higher water/ice cloud (AC/AS) by
using TB derived from 10.7 µm channel.
Sea Fog Discrimination Chart from Gary Elrod
20
SAFESEAS Fog Monitor

• process only those parts of the images that cover
  the monitoring area.

• Daytime
• use the visible image
• Based on thresholds, apply feature extraction
  algorithm to identify fog areas.
• apply smoothness filter to eliminate noise.
  (optional)
• Apply a filter to eliminate snow/ice (optional)

Twilight No Detection

• Nighttime
• use 3.9 and 10.7 um infra-red images to produce
  night time fog product.
• Apply feature extraction to identify fog area
  based on night time fog product threshold

• Filter out high cloud using channel 10.7 um
• Apply a filter to eliminate very tiny size area
  as noise. (optional)
• Apply a filter to eliminate edge-irregular
  detected area (Optional)

21
SAFESEAS Fog Monitor
Smoothness Definition
Smoothness (1- deviation/mean) 100

X denotes the gray value at the VIS pixel and n
is the number of pixels
22
SAFESEAS Fog Monitor Fog Monitor D2D display
23
SAFESEAS Fog Monitor Fog Monitor D2D Display
(Twilight)
24
Limitations (1)

• When the sky is overcast with high level (thick)
  cloud, fog can not be seen through by satellite.
• During the transition of daytime and nighttime,
  neither VIS product nor fog product is good. And
  twilight is exactly the time when fog mostly
  affects marine interests.
• Lack of observations in marine zones causes
  problem for verification
• No effective approach to distinguish fog from
  stratus just using satellite data

25
Limitations (2)Data normalization
At very low solar elevation, in the clear air
region , there will still be small brightness
values. After normalization, they will be
enhanced to look like fog areas and will be
detected by the Fog Monitoring Processor.
26
Limitations (3)
Radiation from the ground goes through thin
cirrus/high cloud ,which makes cirrus look like
fog in VIS
27
Limitations (3) (continue) 14
Use fractal dimension to try to reduce the
detection of the irregular area This is still not
a good solution but supplied as an optional
filter for user
FD 2ln(P/4)/ln(A) P perimeter A Area

• Count the outside edges of the grid boxes as the
  perimeter
• Amount of the grid boxes as the area.

28
Limitations (3) (continue)
After
Before
Application of Fractal Dimension to filter out
irregular area
29
Limitations (4)
30
Limitations (4) (continue)
31
References

• 1 Liu Jian, Xu Jianmin, Fang Zongyi Analysis
  of the particle sizes at the top of cloud and fog
  with NOAA/AVHRR data Quarterly Journal of
  Meteorology
• 2 http//www.cira.colostate.edu/ramm/visit/fog.h
  tml fog product tutorial
• 3 http//meted.ucar.edu/topics_fog.php
  Fog/stratus tutorials
• 4 Chen Weimin, Satellite Meteorology (Chinese
  version) Beijing Meteorological publishing house
• 5 Ellrod G P. Advances in Detection and
  Analysis of Fog at night Using Advanced Very
  High Resolution Radiometer(AVHRR) Imagery J
  Meteo. Magazine
• 6 http//meted.ucar.edu/topics_satellite.php
  satellite products on METED
• 7 http//meted.ucar.edu/satmet/goeschan/ GOES
  channel selection on METED
• 8 http//www.ssd.noaa.gov/ satellite service
  division homepage
• 9 http//aviationweather.gov/awc/aviation_weathe
  r_center.html Aviation Weather Center
• 10 http//www.cira.colostate.edu/ Cooperative
  Institute for Research in the Atmosphere,
  Colorado State University
• 11 http//www.nrlmry.navy.mil/ Naval Research
  Laboratory Monterey
• 12 ALBERS S. 1992 Photometric correction of
  GOES visible satellite images. Preprints, Sixth
  conf. on Satellite Meteorology and Oceanography,
  Atlanta, GA, Amer. Meteor. Soc., 223-225.
• 13 Allen, R.C., P.A. Durkee, and C.H. Wash,
  1994 Snow-cloud discrimination with
  multispectral satellite images. J. Appl. Meteor
• 14 Olsen, E.R., R.D. Ramsey and D.S.Winn. 1993.
  A modified fractal dimension as a measure of
  landscape diversity.Photogram. Eng. Remote Sens.
  59 1517-1520
• 15 http//www.cira.colostate.edu/RAMM/Rmsdsol/m
  ain.html RAMSDIS ONLINE

32
Fog Monitor OverviewKey Terms

• Area of Responsibility
• An offices area of responsibility (AOR) will
  consist of all the zones and counties for which
  it normally has the responsibility of issuing
  forecasts, watches, and warnings.
• Monitoring Area
• An offices monitoring area (MA) will consist of
  its AOR plus the AOR of each adjacent office.
• Channel 2
• Channel 2 refers to the 3.9 micrometer infra-red
  satellite image.
• Channel 4
• Channel 4 refers to the 10.7 micrometer
  infra-red satellite image.
• Fog Product
• The fog product is the image derived by
  subtracting 10.7 micrometer image brightness
  temperatures from 3.9 micrometer image brightness
  temperatures.

33
Fog Monitor OverviewLocalization

• will determine the default MA.
• which zones and counties are included in the
  MA.
• (OB-6) which fixed stations are in the MA.
• (OB-6) in which zone/county is each fixed
  station located.
• For the alpha test, the default MA will be based
  on the same shape files used for OB-4 SAFESEAS.
  It is the responsibility of each office to make
  sure its systems have the current versions of
  these files before localization is run.
• will generate the dummy fog threat image to
  display for incomplete image sets.
• will generate the default (factory setting)
  monitor thresholds.
• (OB-6) will generate the default (factory
  setting) display thresholds.

34
Fog Monitor OverviewCustomizing your Monitoring
Area

• The Fog Monitor will provide a GUI for
  customizing the MA. Specifically, the office
  will be able to

• add and delete zones and counties.
• (OB-6) add and delete fixed stations.
• (OB-6) customize the association of fixed
  stations with zones and counties, that is, which
  stations are monitored to determine each zones /
  countys threat level.

35
Fog Monitor OverviewCustomizing Your Monitor
Thresholds

• The Fog Monitor will provide a GUI that will
  enable offices to
• customize the range of
• normalized brightness values that should be
  considered fog in visible images.
• temperature differences that should be considered
  fog in fog product images.

36
Fog Monitor OverviewCustomizing Your Monitor
Thresholds (continued)

• The customization GUI will also allow offices to
  enable/disable filters in the
• fog recognition algorithm
• in channel 2 images, each pixel colder than a
  customizable threshold temperature should be
  considered snow/ice.
• in channel 2 images, each pixel having a
  brightness temperature colder than a
  customizable threshold temperature should be
  considered cloud.
• in channel 2 images, each pixel having a
  brightness temperature warmer than a customizable
  threshold temperature should be considered ground
  or water surface.
• in visible images, a group of contiguous pixels
  having a brightness variation greater than a
  customizable threshold cannot be considered fog.
• in visible images, a group of contiguous pixels
  having fewer than a customizable number of pixels
  cannot be considered fog.
• a pixel within a configurable number of degrees
  from the terminator should not be monitored.

37
Fog Monitor OverviewCustomizing Your Monitor
Thresholds (concluded)

• In OB-6, a GUI will also be provided that will
  enable offices to customize the thresholds used
  for monitoring point observations (METARs, C-MAN
  reports, ship reports, buoy reports, and mesonet
  reports) for fog. We will negotiate details
  for this tomorrow!

38
Fog Monitor OverviewThe Fog Monitor

• The fog monitor will be a persistent background
  process, much like the SAFESEAS, SCAN, and
• FFMP processors. The alpha test version will
  monitor
• visible imagery at those times and in those
  places that the sun is sufficiently above the
  horizon
• the fog product at those times and in those
  places that the sun is sufficiently below the
  horizon.
• In all cases, channel 2 images are used for
  certain kinds of filtering (unless the office has
  disabled
• the filters).
• The OB-6 fog monitor will also monitor point
  observations. The details of this will be
  negotiated
• tomorrow.
• The fog monitor will determine a fog threat level
  for each zone/county in the MA, and an overall
• fog threat level for the entire MA. The threat
  level is the most severe of all the individual
  pixel
• (OB-6 and point observation fog) threat levels
  for the past two hours.
• The fog monitor generates a fog threat level
  image and a zone fog threat file for use by the
  Fog
• Monitor display. Finally, the Fog Monitor threat
  level indicator and the Fog Monitor display are
• signaled to update themselves.

39
Fog Monitor OverviewThe Fog Monitor Display

• the Fog Monitor fog threat level image
• black this location is not within the MA.
• gray insufficient data is available for
  determining
• the fog threat level for this location.
• green there probably is not fog at this
  location.
• yellow there may be fog at this location.
• red there probably is fog at this location.
• (OB-6) the Fog Monitor station plot
• only reports from within the MA are plotted.
• variables to be plotted will be negotiated
  tomorrow.

40
Fog Monitor OverviewThe Fog Monitor Display
(concluded)

• the alpha test Fog Monitor zone fog threat table
• two columns zone ID and fog threat level
  (color).
• click column header to sort by that column.
• the OB-6 Fog Monitor zone/station fog threat
  tables and trends
• except for variables, same as SAFESEAS.
• variables to be included will be negotiated
  tomorrow.