EO 307.1 Identify geographical features on satellite
imagery.
IDENTIFY GEOGRAPHICAL FEATURES ON ANY SATELLITE IMAGERY
Geography
When attempting to interpret satellite imagery, it is essential to have a good
knowledge of the geography of the area being examined.
The following can be used to provide accurate geographical references:
Grid lines or latitude and longitude lines
- Lines depicting geographical and geopolitical boundaries
Geographical features substantially influence the formation and dissipation of
cloud, snowfall, rainfall, and vegetation cover.
It is essential to be aware of topography as it greatly influences the weather.
For example:
- Sloping terrain: upslope for orographic lift, downslope for cloud
dissipation.
- Land/water interfaces: sea/land breezes, air mass modification.
- Valley effects: valley fog inversions, snow on the ground.
EO 307.2 List the five characteristics of cloud pattern
recognition on satellite imagery
For proper and informed interpretation of cloud structures on satellite
imagery, the briefer must integrate other available data:
- Surface reports
- Pilot reports
- Radar imagery
- Upper air data
- Surface and upper level analyse
Determination of cloud type is based on the following five basic
characteristics of cloud pattern recognition:
- Size of clouds or cloud groupings
- Shape of clouds or cloud groupings
- Shadow vertical structure (VIS or NIR only)
- Texture of the surface
- Tone or radiation flux (i.e. gray shade) -KNOW THIS
Size
Always evaluate size with respect to:
- Geographical features
- Latitude and longitude lines
The scale of the phenomena is very important in determining the cloud type:
- Frontal wave (synoptic scale)
- Air mass thunderstorm (mesoscale)
Shape
Known shapes of clouds:
explain how the Maturity of system is related to the shape (synoptic evolution):
- TCU (convective with small horizontal coverage)
- AS (stratiform with great horizontal extent)
Maturity of system related to the shape (synoptic evolution):
- Stage of evolution
- Line
- Coma shape
- Spiral
The shadow length of a cloud will be determined by:
- Solar elevation
- Height separation between layers
o Small separation will cast narrow shadows
o Large separation will cast pronounced shadows
Texture
Texture on VIS imagery
Texture on visible satellite imagery depends on the degree of apparent
roughness displayed by the upper surfaces of clouds. Variations in cloud
thickness can also contribute to the texture on images.
Texture is due to a combination of two factors:
- The actual shape of the top of the cloud structure
o Flat, smooth
o Rough, uneven
- The degree of lighting
o Intensity (strong or weak)
o Angle of the sun (high or low)
At low sun angles, texture will be at a maximum, while at high sun angles,
texture will be at a minimum.
Some examples of texture include:
- Smooth
o (ST) Stratiform cloud due to constant thickness
- Mottled
o (SC) Stratocumulus due to variable thickness
- Uneven/bumpy
o (TCU, CB) Cumuliform or convective cloud
- Patterned
o (AC/SC) Orographic cloud (low and mid-levels)
- Fibrous/wispy
o (CI) Cirroform type cloud
Tone
Tone on VIS and NIR images
The brightness on the VIS and NIR images will vary depending on the
following factors:
- The albedo of the surface
o Depends on:
Tone on IR images
The tone of gray will vary depending on the temperature of the body.
Tone
Tone on VIS and NIR images
The brightness on the VIS and NIR images will vary depending on the
following factors:
- Height of the sun
o The quantity of reflected light is more important than the absolute
value of albedo.
- Sensor viewing angle
o Directly overhead at a specific point is the ideal angle.
- The albedo of the surface
Depends on:
▪ Surface composition (water vs snow vs cloud)
▪ Wavelength of reflected light (colour of surface)
▪ Type of surface (smooth vs rough)
Tone on IR images
The tone of gray will vary depending on the temperature of the body.
- Cold = white
- Warm = dark
Tone for all images
The following factors have a direct effect on the tone of gray depicted on all
satellite imagery
- Cloud composition (ice crystals vs water droplets)
- Thickness of cloud
- Resolution of sensor
- Enhancement curve
EO 307.3 Identify the types of clouds from satellite Imagery.
IDENTIFY THE FOLLOWING CLOUDS FROM SATELLITE IMAGERY:
- High level
- Mid-level
- Low level
Cirrus (CI) / Cirrocumulus (CC):
Cirrostratus (CS):
HIGH LEVEL CLOUDS
Cirrus (CI) / Cirrocumulus (CC)
Satellite sensors are unable to resolve individual CC elements. Therefore, the
characteristic signature of cirrocumulus is identical to that of cirrus:
- Size
o Mesoscale to synoptic
▪ Dependent on extent of physical processes
- Shape
o Defined by generating physical processes
▪ Often in elongated streaks
▪ Wispy, fibrous edges
- Shadow
o May cast moderate shadows on lower cloud decks
- Texture and tone
o VIS: Minimal texture, transparent to white
o IR: Minimal texture, gray to white
Cirrostratus (CS)
Cirrostratus has a characteristic signature similar to cirrus except:
- Size
o Generally large (synoptic scale)
- Shape
o Similar to cirrus
- Shadow
o Similar to cirrus
- Texture and tone
o VIS: Little to no texture, uniform light gray
o IR: No texture, white
Identifying MID-LEVEL CLOUDS
Altostratus (AS) and Altocumulus (AC):
- Size
o Generally larger than mesoscale
o Dependent on extent of physical processes
- Shape
o Defined by generating physical processes
o Edges tend to be well defined
o Mountain ranges may induce gravity wave patterns in cloud shield
- Shadow
o May cast shadows on lower cloud deck
- Texture and tone
o VIS images:
▪ AS smooth, no texture, gray to white – usually only seen in warm front
▪ AC minimal texture, gray to white
o IR images:
▪ Minimal to no texture, gray to white depending on temperature
Identifying LOW LEVEL CLOUDS
Stratus (ST) and fog (FG)
- Size
o Generally local phenomena
o Dependent on extent of generating physical processes
- Shape
o Defined by terrain and generating physical processes
o Sharp edges frequently associated with topographical features
- Shadow
o No shadow is cast
- Texture and tone
o VIS: Smooth, minimal texture over land, but sometimes shows a
wispy texture over water, gray to white
o IR: Smooth, no texture, gray to invisible with respect to surrounding
surfaces, sometimes appears dark with an inversion near the surface
Stratocumulus (SC)
Stratocumulus (SC)
- Size
o Generally mesoscale or larger
o Dependent on extent of generating physical processes
- Shape
o Defined by generating physical processes
o Terrain and topography can strongly influence shape
o Edges generally not sharp
- Shadow
o Casts minimal discernible shadow, if any
- Texture and tone
o VIS: Fairly smooth, but lumpiness depends on stability, roughness of
terrain and is very dependent on underlying surface and boundary
conditions.
▪ White to gray tone.
IR: Usually smooth, minimal texture, gray tone
Cumulus (CU) and towering cumulus (TCU)
Cumulus (CU) and towering cumulus (TCU)
- Size
o Individual clouds are mesoscale or smaller
- Shape
o Individual clouds are circular but may be organized into lines or
streets
o Edges are very sharp
o Cloud development influenced by terrain and physical processes
- Shadow
o May cast moderate shadows on lower cloud decks depending on
vertical extent of cumuliform cloud
- Texture and tone
o VIS: Very lumpy, globular, bright white
o IR: Moderate texture, white (depends on enhancement curve)
Cumulonimbus (CB)
- Size
o Individual clouds are mesoscale
- Shape
o Individual clouds are circular except for the cirrus anvil
o Blown downstream if the winds at cloud top level are significant
o Edges are very sharp, except for the cirrus anvil which is fibrous and
wispy downstream
- Shadow
o May cast strong shadows on lower cloud decks
- Texture and tone
o VIS: Very lumpy, globular, bright white
o IR: Strong texture, bright white
IDENTIFY AREAS OF STABILITY FROM SATELLITE IMAGERY
Stable and unstable areas can be recognized by the type of clouds on the
images (stratiform or convective).
Indicators of a stable air mass could be summarized as follows:
- Cloud texture
o Smooth
- Cloud shape
o Uniform, extensive coverage
- Temperature
o Rather uniform
- Cloud types
o ST, SC, AS, AC, CI, CS
IDENTIFY AREAS OF INSTABILITY FROM SATELLITE IMAGERY
Indicators of an unstable air mass could be summarized as follows:
- Cloud texture
o Lumpy
- Cloud shape
o Globular, anvils in shape of a carrot
- Temperature
o Strong contours (on IR only, properly enhanced)
- Cloud types
o CU, TCU, CB, ACC
Identifying unstable areas on satellite imagery is fairly simple due to distinct,
easily recognizable signatures
EO 307.5 Identify synoptic weather features from
satellite imagery.
IDENTIFY THE FOLLOWING SYNOPTIC WEATHER FEATURES:
- Surface features
- Fronts
- Upper air features
- Jet stream axis
Techniques used to determine the position of a high or ridge:
- Pattern recognition
In the absence of cloud near the centre of the ridge, recognition is done with
cloud patterns of low pressure areas situated ahead and behind highs and
ridges.
- Groundtruthing
Surface reports are by far the best confirmation of the ridge position if such
observations are available. Locate the ridge position as analyzed on the last
surface chart and examine the imagery at that time to see if you can make
any correlations between the satellite image and analyzed ridge position.
Jet streams
Techniques used to identify the jet stream:
- A CI baroclinic leaf forms to the south of an anti-cyclonic jet (30% of
cases)
- Maximum wind axis coincides with the dry air intrusion (30% of cases)
- In the absence of high level clouds, the jet axis separates various types of
low clouds. The jet axis location is 1 to 3 degrees north of separation zone
(30% of cases)
- Combination of all of the above (10% of cases)
Identification using water vapour imagery
A jet stream is caused by a strong baroclinic zone, and as such, it separates
a warm air mass from a colder one. The sharp contrast in moisture content
The best imageries for jet stream identification are:
- Water vapour (due to sharp contrast in moisture content).
Which is the best image for identifying the position of the jet stream?
Water vapor satelite
EO 307.6 Identify probable areas of turbulence from
satellite imagery.
Name the five atmospheric processes that indicate the possibility of turbulence on satellite imagery.
ATMOSPHERIC PROCESSES
Strong surface wind
› Convection
› Stationary waves
› Wind shear
› Deformation zone
- What characteristic is indicative of high-level turbulence on satellite
Imagery
Tranverse banding
