# Presentation: 084121

## SATELLITE INTERPRETATION

**SATELLITE INTERPRETATION**

- UPDATED: 28 Feb 2000

## VIEWING CONSIDERATIONS

_**VIEWING CONSIDERATIONS**_

_**RESOLUTION**_:   THE SMALLEST INDIVIDUAL ELEMENT THAT A SATELITE SENSOR CAN
-                                DETECT
_**ATTENUATION:**_ THIS PROCESS REDUCES THE AMOUNT OF ENERGY REACHING THE
-                                SATELLITE SENSOR SO CLOUD TOPS APPEAR HIGHER AND COLDER THAN
-                                THEY ACTUALLY ARE. DEPENDS UPON THE VIEWING ANGLE OF THE
-                                SATELLITE.
_**CONTAMINATION**_: THIS OCCURS WHEN ENERGY REACHES THE SATELLITE SENSOR FROM
-                                 TWO OR MORE SOURCES. THE TYPICAL SITUATION FOR CONTAMINATION
-                                 TO OCCUR INVOLVES A HIGH CLOUD WHICH IS NOT THICK ENOUGH TO
-                                 COMPLETELY BLOCK OUT RADIATION FROM ANOTHER SOURCE.
_**FORESHORTENING**_: A LOSS OF RESOLUTION CAUSED BY AN OBLIQUE VIEWING ANGLE
-                                  RESULTING IN DISTORTION NEAR THE EDGE OF THE EARTH’S SURFACE
-                                  ON ANY TYPE OF SATELLITE IMAGERY.  THE RESULT IS AN
-                                  OVERESTIMATION OF CLOUD COVERAGE.
_**OTHER FACTORS**_: GRIDDING ERRORS, SUN ANGLE, LATITUDE, SUN GLINT

## FOG AND STRATUS

- CAN BE EASILY SEEN ON VISUAL IMAGERY BECAUSE OF
- THE SHARP CONTRAST BETWEEN THE FOG/STRATUS AND
- THE TERRAIN.
_**VISUAL IMAGERY**_: APPEARS WHITE TO LIGHT GREY, IN  A
- UNIFORM SHEET.
_**INFRARED IMAGERY**_: DARK GRAY SHADES APPEAR WITH
- LITTLE OR NO CONTRAST BETWEEN THE CLOUDS AND
- LAND SINCE THEY ARE ABOUT THE SAME TEMPERATURE.
- OCCASIONALLY, FOG AND STRATUS FORMING
- UNDERNEATH A RADIATION INVERSION IN THE EARLY
- MORNING HOURS WILL APPEAR DARKER THAN THE
- SURROUNDING CLOUD-FREE REGION.

## Slide 4

## STRATOCUMULUS: VIS: APPEARS LIGHT GRAY TO WHITE WITH A TEXTURED LOOK. HAS

-  CONTINUOUS CLOUD SHEETS COMPOSED OF PARALLEL ROLLS OR CELLULAR  ELEMENTS
- .                                      _IR:_ APPEARS DARK GRAY.  THE CELLULAR OR TEXTURED APPEARANCE
-                                              MAY NOT BE OBSERVED DUE TO THE SENSOR RESOLUTION.
_**CUMULUS:**_                 _VIS_: APPEARS AS A SMALL WHITE  CLOUD USUALLY SEEN AS A FIELD                                  OF UNORGANIZED “POPCORN” CUMULUS.
-                                       _IR:_  INDIVIDUAL CLOUD ELEMENTS USUALLY ARE NOT DESCERNIBLE DUE TO THE RESOLUTION.  ONLY LARGE CONCENTRATED AREAS OF CUMULUS ARE DISCERNIBLE AND THEY APPEAR AS A DARK GREY SINCE THE CLOUD TEMP IS AVERAGED WITH THE WARMER TEMP OF THE UNDERLYING SURFACE AROUND THE CLOUDS.
_**TOWERING CUMULUS**_: _VIS:_ CLOUDS ARE CIRCULAR WHICH APPEAR LIGHT TO BRIGHT WHITE.                                 _IR_: APPEAR LIGHT GRAY AND ARE LIGHTER THAN CUMULUS

_**VIS**_

_**IR**_

## CUMULONIMBUS: VIS: APPEAR BRIGHT WITH A ROUND OR ELONGATED ANVIL PLUME.  THEY HAVE A SHARP UPSTREAM CLOUD EDGE AND A THIN, DIFFUSE ANVIL WHICH SPREADS OUT DOWNSTREAM. INDIVIDUAL UPDRAFT CELLS KNOWN AS OVERSHOOTING TOPS ARE OFTEN VISIBLE AS A BULGE ABOVE THE OTHERWISE, SMOOTH ANVIL TOP.  THIS NORMALLY INDICATES SEVERE WEATHER BELOW THE OVERSHOOTING TOPS.

_**CUMULONIMBUS**_: _VIS:_ APPEAR BRIGHT WITH A ROUND OR ELONGATED ANVIL PLUME.  THEY HAVE A SHARP UPSTREAM CLOUD EDGE AND A THIN, DIFFUSE ANVIL WHICH SPREADS OUT DOWNSTREAM. INDIVIDUAL UPDRAFT CELLS KNOWN AS OVERSHOOTING TOPS ARE OFTEN VISIBLE AS A BULGE ABOVE THE OTHERWISE, SMOOTH ANVIL TOP.  THIS NORMALLY INDICATES SEVERE WEATHER BELOW THE OVERSHOOTING TOPS.
-                                      _IR_: APPEAR BRIGHT WHITE.  A TIGHT GRAY SHADE IS OFTEN PRESENT ON THE UPSTREAM EDGE OF THE ANVIL CIRRUS AND LOOSENS RAPIDLY DOWNSTREAM. THIS TIGHT GRADIENT INDICATES STRONG UPDRAFTS RESISTING THE UPPER LEVEL FLOW.
-             _WATER VAPOR:_ APPEAR AS A BRIGHT WHITE AREA IN A REGION OF DARKER SHADES.  CUMULONIMBUS ANVILS ARE NORMALLY THE BRIGHTEST FEATURES ON A WATER VAPOR IMAGE.  OFTEN THERE IS A DARKENING UPWIND OF A SEVERE THUNDERSTORM .  TIS INDICATION OF STRONG SUBSIDENCE IMPLIES STRONG VERTICAL MOTION NEARBY.

- VIS

## Slide 7

## Slide 8

## Closed-cell SC is cellular, closely packed SC that forms mostly

-             over ocean areas. The individual elements vary in size from 5 to 50km.. They're typically found
-             in large sheets associated with the anticyclonic flow of the subtropical high or with high
-             pressure systems behind cold fronts. Clouds typically are located in the southern half of the
-             high.Closed-cell SC is formed due to low-level instability or convective mixing with a
-             subsidence inversion capping the mixing. The instability or mixing is due to either
-             surface heating, radiative cloud-top cooling, or weak cold-air advection over a warmer water
-             surface. _**VIS imagery**_: closed-cell SC appears as gray shades ranging from white in the center
-             to medium gray to white on the edges. They will have a large quilt-like pattern with a slight
-             separation between the elements. _**IR imagery:**_ closed-sell SC will usually appear similar to
-             ST with a very uniform, medium gray to dark gray shade due to resolution problems.

- IR

## Open-cell cumulus - These are CU clouds that usually form over water behind mid-latitude

-             cyclones and are caused by strong cold air advection over warmer water. They are associated
-             with cyclonic or straight line flow. There is a sharp transition between cellular clouds, showing
-             a separation between stable (closed-cell SC) and unstable (open-sell CU) air. Their vertical
-             development is typically capped by a weak inversion above the cloud layer. The elements vary
-             in size from 5 to 50 km. _**VIS imagery**_: Open-cell CU appears as open and closed ringlets of CU with
-             clear centers like chicken wire. In strong low-level winds, these ringlets will
-             become distorted and line up. Individual elements may be difficult to detect due to the sensors
-             resolution. _**IR imagery**_: open-cell CU appears medium to dark gray due to contamination
-             and resolution problems. Parts of the open-cell CU field may appear as a uniformly darker gray
-             shade than the rest of the field. Although open-cell CU is higher than closed-cell SC, open-cell
-             CU will look lower due to contamination and sensor resolution.

- IR

- VIS

## Actiniform Clouds - These are skeletal remains of closed-cell SC, which are easily confused

-             with open-cell Cu. Actiniform clouds are found in or along the western side of the closed-cell
-             SC. On VIS imagery, actiniform clouds are light gray, due to contamination, with a fish bone or
-             chicken wire appearance. Actiniform clouds are medium gray to dark gray, showing up slightly
-             warmer than open-cell CU on IR imagery. Individual elements are not identifiable. If too much
-             contamination is present, the area will show up as a dark spot or hole in the clouds.

- Rope Clouds - This is a very narrow line of CU/TCU usually found over water and
-             occasionally over very moist coastal land areas. Rope clouds range from several hundred miles
-             in length to several thousand. They are very representative of the surface cold front over water.
-             The rope cloud has the same appearance as CU/TCU in the VIS and IR imagery.

## Slide 12

## Cirrus streaks

_**IR imagery**_: They will appear as a medium gray to white shade. Again, the imagery is very susceptible to contamination. On enhanced IR imagery, gray shade contouring is limited due to contamination problems.

_**Cirrus streaks**_

_**VIS**_

## Anvil Cirrus VIS- Anvil cirrus or thunderstorm blow off has a sharp upwind edge with a fuzzy,

-             diffuse downstream edge. The blow off from numerous thunderstorms combines to form an
-             extensive CS canopy. Anvil cirrus appears on _**VIS imagery**_ as bright white on the upstream edge
-             gradual darkening on the downstream side as it thins and becomes translucent. Unless
-             overshooting tops are present, anvil cirrus is very smooth.

_**Anvil Cirrus IR**_ - On IR and WV imagery, they appear as bright white patches. On enhanced IR imagery, you'll have a contouring of the cloud tops helping you define the height.

- IR

- VIS

## Leeside Cirrus - Lee-of-the-mountain cirrus, or leeside cirrus, is a multi-layered CI cloud shield on the lee of a mountain chain. A sharp, stationary upwind cloud edge, along the ridge line, shows the presence of standing mountain waves. They tend to form late at night and dissipate in the afternoon. There is an inversion or isothermal layer above the mountain tops. The cloud tops range from 25,000-35,000 ft with bases from 10,000 - 15,000 ft. Their occurrence appears highly dependent on the presence of a high-level moisture source in a strong wind zone. It's typically located with and just south of the PFJ but does not have to be near the jet stream. WV imagery helps identify areas of moist air where leeside cirrus may occur while other imagery will show the area as cloud free. Leeside cirrus will affect the temperatures by blocking out incoming solar radiation. Leeside cirrus appears bright white with a sharp edge along the ridge line on VIS imagery. It can appear as thick CS, becoming more diffuse downstream. Contamination is a problem on the downstream edge. On IR imagery, leeside cirrus is a bright white gray shade.. Enhanced IR imagery will show contouring of the cloud tops.

- VIS

- IR

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## CONCEPTS OF INTERPRETING WEATHER SATELLITE IMAGERY

_**LOOK AT THE SYNOPTIC SITUATION**_: WHEN INTERPRETING SPECIFIC FEATURES, ENSURE
- YOU LOOK AT THE WHOLE IMAGE TO DETERMINE WHAT THE FEATURE IS AND HOW IT FITS INTO THE SYNOPTIC SITUATION. DON’T GET TUNNEL VISION AND JUST LOOK AT ONE FEATURE.
_**USE AVAILABLE IMAGERY**_: USE THE DIFFERENT IMAGERY TOGETHER  WHENEVER POSSIBIBLE TO TAKE ADVANTAGE OF EACH ONES UNIQUE PROPERTIES.  THE VISUAL WILL DEFINE SMALL-SCALE FEATURES SUCH AS TERRAIN, CLOUD SHADOWS, TEXTURE, SMALL LOW CLOUDS, ETC.  THE INFARED IMAGERY MAKES RELATIVE CLOUD HEIGHT ANALYSIS POSSIBLE, AND THUS, SPECIFIC CLOUD TYPES.
_**CONTINUITY**_:  ANOTHER EXCELLENT WAY TO FOLLOW CLOUD FEATURES AND SHOULD BE USED AT ALL TIMES. AT NIGHT WHEN NO VISUAL IMAGERY IS AVAILABE, LOOK AT THE LAST VISUAL AND INFARED IMAGERY OF THE DAY.  THEN FOLLOW THE FEATURES ON THE INFRARED THROUGH THE NIGHT KEEPING IN MIND WHAT THEY WOULD LIKE ON THE VISUAL.
_**TERRAIN**_: ALWAYS USE AN ATLAS OR LOCAL TERRAIN MAP WHEN INTERPRETING THE IMAGERY.  THIS ENSURES THAT YOU DON’T MISTAKE TERRAIN FEATURES FOR CLOUDS.  FOR EXAMPLE, LOW LYING FOG/STRATUS VERSUS SNOW COVERED TERRAIN.

## RESOURCES

- BASIC SATELLITE IMAGERY INTERPRETATION
- WEATHER TRAINING FLIGHT SATELLITE ANALYSIS
- THE WORLD WIDE INTERNET

- THANKYOU!