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