306 Flashcards
Role of Satellite imagery in PBS:
Weather Watch
- Provides a coherent view of cloud patterns, a picture from above, of a wide area. Large scale and small.
- Pressure patterns and other features met products to be inferred from distribution,motion and shape.
- Satellite can help to identify mesoscale systems tht are not easily identifiable in any other way.
Role of Satellite imagery in PBS:
During the briefing
- Imagery is often an excellent visual aid
- helps fill in data sparse areas
- it is a source of real time information
- good tool to update analysis of charts and alphanumerics
Role of Satellite imagery in PBS:
Forecasting
- Analysis tool, especially data sparse areas
- Direct aid in short term forecasting
- Input into numerical weather products
- a means of monitoring performance in the early stages of a forecast
GOES
- Geostationary orbit
- exactly matches earth’s rotation
- at 38500km
- over equator
- always points in the same direction
- 2 satelites, GOES W and GOES E
- Satellite subpoints-135 degrees W, 75 degrees W
- areas N of 70 degrees latitude are inconsistent due to the angle of incidence
- Worldwide network of 6 GOES at equator
- Scans every 15 minutes
- CMC Dorval produces images
POES
-Polar orbiting Satelite
-at 850 km
-100 minute orbital period
-Twice daily coverage of the every portion of the earth
-must wait 12 hours to get two consecutive images
-2700 km swath
-
2 types of radiation measured by satellite
-Solar (visible), reflected shortwave radiation 0.2 - 4 micrometers with peaks at 0.5 micrometers, 0.3 to 0.8 for VIS
-Terrestrial (infrared) radiated longwave from earth
3-100 micrometers, maximum intensity 11 micrometers
10-13 for IR
Water Vapour Spectral band (WV)
- Strongly absorbs radiation at very specific wavelengths of 6-7 micrometers
- poor resolution
Sensor Resolution
- The smallest area that can be distinguished from the surrounding areas by the satellite sensor.
- Radiation intensity
- Distance from source
- Radiometer Characteristics
- Distance from subpoint
Image resolution
- The smallest area that can be distinguished from surrounding areas on a satellite image
- Number of KM/Pixel
Resolution at subpoint
Geostationary Polar
- VIS: 1km 1km
- IR: 4 km 1km
- WV: 8km 1km
Disadvantages of the two satellite systems
- Distance from earth
- availability of images
- Resolution at subpoint
- Resolution at high latitude
- Cost
- Life expectancy
- Solar Eclipses
4 spectral bands used by Nav Canada
- Visable (VIS)
- Infrared (IF)
- Near Infrared (NIR)
- Water Vapour (WV)
VIS
- 1 km resolution
- black and white picture
- brightness depends on albedo and sun angle
- shadows add dimensions
- daytime use only
Albedo values
- White=high albedo
- Black=low albedo
- Couds 44-95%
- Fresh Snow 85%
- Desert land 30-40%
- land Surface 8-40%
- grass land
- cities
- forest
- water
Shadows a textures in VIS
- Helps identify cloud structure/edges
- helps identify cloud types
Problems interpreting VIS imagery
- Distinguishing clouds from snow covered ground
- if clouds are smaller than sensor resolution they will appear different than normal convective cloud
- Small clouds-over sea, Cu will appear lighter grey
- Thin Cloud
Advantages of VIS
- unambiguous representation
- important for daytime cloud and surface mapping
- brightness is proportional to solar reflection
- the atmosphere is transparent to this type of radiation
- image can be enhanced to bring out fringe areas
Disadvantages OF VIS
- only available during daylight hours
- brightness of surfaces, orientation and sharpness vary diurnally and seasonally
- surfaces with similar albedo are difficult to distinguish
NIR
- POES
- 1 km resolution
- similar to visible/interpretation is the same
- mostly albedo, small amount from temperature
- good for land/water differentiation
- Daytime only
Advantages and disadvantages of NIR
- Essentially the same as for VIS
- good for high albedo/warm vs low albedo/cold contrast
- Essentially the same as for VIS
- Only available on POES
WV
- 8km resolution
- Displays high and mid level moisture
- no clouds required
- black =dry=high flux
- upper tropospheric humidity appears cold (light)
- lower tropospheric humidity appears warm(dark) {not depicted well in WV}-Jet stream have sharp moisture gradients with dry air on the poleward side.
Advantages of WV
- Good representation of moisture distribution in mid/high levels
- representation of mid/high level circulation
- Cold upper lows, jet streams, Dry air intrusions, deformation zones
Disadvantages of WV
- Low water vapour concentrations are semi-transparent
- Surfaces with similar grey tone are hard to interpret
- Difficult to interpret moisture height and low level moisture
- measure water vapour concentrations through a layer, not at a specific level
- course resolution
- only on GOES
IR
- 4 km resolution
- displays temperature
- white =flux=cold
- good day and night
- thin cloud may be contaminated
- poor representation for ST/FG
- usually requires enhancement
- displays 10.7 micrometers radiation
Characteristics affecting cloud albedo:
-Clouds with high albedo have
- Large vertical depth
- High cloud-water content
- small average cloud droplet size
Characteristics affecting cloud albedo:
Clouds with Low albedo have
- Shallow depth
- Low cloud-water content
- Large average cloud droplet size.
IR interpretation
-shows good contrast between clouds at different levels. esp. a cold low.
-Coastlines - show well in contrast (winter, summer), when water and land are the same temp, greys will blend (spring, autumn).
during the day land may appear darker, and lighter during the night.
-Thin cirrus shows well
-No shadows
-White - low temps -high cloud, convective tops
-black - warm temps - ocean ground - low cloud
IR interpretation: Problems
- Low clouds and fog is difficult to see because there is a low temperature differential.
- cloud is not a black body
- Thin or small clouds may be contaminated and appear lower than they are
- Surface temperature vs air temperature
IR Advantages
- provides a temperature representation of the earth atmosphere system
- Available continuously
- important for day and night
- atmosphere transparent to this wavelength
IR disadvantages
- Surfaces with same temp cannot be distinguished (ST, FG - water surface.
- Contamination of thin cloud from below
- non-enhance dimages are hard to interpret
- resolution is not as good as VIS (4km vs 1km)
factors of greyscale
- 256 shades of grey, each is assigned a temperature
- White is cold dark is warm
- high albedo is white, low albedo is dark
- No image manager curve can be assigned,cannot be remapped into image manager.
- GOES - greyscale code on left side
- POES - side
POES regions
- hsb -hudson bay
- ont- ontario
- pry- Praries
- wel- norman wells
- yzf yellowknife
- yrb- resolute bay
- ykn - yukon
- bci - british columbia interior
- Pac- pacific
- can- canada
GOES regions
-AZO - azores
-ECA- eastern canada
-HUR - great lakes region
-ENA-Eastern North America
-NWC- Northwest Canada
WNA- Western North America
-EPA- Eastern Pacific
