Satellite and RadarSatellite and Radar

Lecture 5Lecture 5

February 25, 2010February 25, 2010

SatellitesSatellites October 4, 1957 – Russia October 4, 1957 – Russia

launched Sputnik 1, the first launched Sputnik 1, the first satellite in historysatellite in history– As a result, space science As a result, space science

boomed in America as it led boomed in America as it led Americans Americans to fear that the to fear that the Soviets would launch missiles Soviets would launch missiles containing nuclear weapons. containing nuclear weapons.

1959 – Scientists at the Space 1959 – Scientists at the Space Science and Engineering Science and Engineering Center (SSEC) at UW-Center (SSEC) at UW-Madison conducted pioneering Madison conducted pioneering meteorological satellite meteorological satellite research, revealing the vast research, revealing the vast benefits of meteorological benefits of meteorological satellites.satellites.

http://burro.astr.cwru.edu/stu/advanced/

20th_soviet_sputnik.html

Evolution Until Today

First weather satellite lasted 79 daysFirst weather satellite lasted 79 days Now many yearsNow many years Two distinct types of weather satellitesTwo distinct types of weather satellites

– GOES - Geostationary Operational Environmental GOES - Geostationary Operational Environmental SatellitesSatellites

- POES - Polar Operational Environmental Satellites POES - Polar Operational Environmental Satellites (also referred to as “LEO” – Low Earth Orbit)(also referred to as “LEO” – Low Earth Orbit)

They are defined by their orbital characteristicsThey are defined by their orbital characteristics There are also many other satellites in orbit, There are also many other satellites in orbit,

some of which are not functioning and those are some of which are not functioning and those are referred to as “space debris”.referred to as “space debris”.

Geostationary Vs. Polar OrbitingGeostationary Vs. Polar Orbiting

http://cimss.ssec.wisc.edu/satmet/modules/sat_basics/images/orbits.jpg

GOESGOES

GOESGOES: Geostationary Operational : Geostationary Operational Environmental SatellitesEnvironmental Satellites

Orbit as fast as the earth spinsOrbit as fast as the earth spins Maintain constant altitudes (~36,000 Maintain constant altitudes (~36,000

km, or 22,300 miles) and momentum km, or 22,300 miles) and momentum over a single point, always over the over a single point, always over the equatorequator

GOESGOES Imagery is obtained approximately every Imagery is obtained approximately every

15 minutes unless there happens to be an 15 minutes unless there happens to be an important meteorological phenomenon important meteorological phenomenon worth higher temporal resolutionworth higher temporal resolution

Generally has Generally has poor spatial resolutionpoor spatial resolution-- sees sees large fixed area and covers polar regions large fixed area and covers polar regions poorly. poorly.

But, good for viewing large scale But, good for viewing large scale meteorological phenomena (cyclones, meteorological phenomena (cyclones, hurricanes, etc.) at lower and middle hurricanes, etc.) at lower and middle latitudeslatitudes

GOESGOES

GOES- EAST (GOES- 12) GOES- WEST (GOES – 11)

GOES COVERAGEGOES COVERAGE

http://goes.gsfc.nasa.gov/pub/goes/global_geosynch_coverage.gif

Sample CompositeSample Composite

http://www.ssec.wisc.edu/data/comp/latest_moll.gif

POESPOES• POESPOES: Polar Operational Environmental Polar Operational Environmental SatellitesSatellites

• Rotates around the earth from pole to pole

• Significantly closer to the Earth than geostationary satellites (879 km above the surface)

• Sees the entire planet twice in a 24 hour period

POESPOES

• Lower altitude gives it a Lower altitude gives it a good spatial good spatial resolutionresolution: Very high resolution images of : Very high resolution images of the atmosphere and Earththe atmosphere and Earth

• Poor temporal resolutionPoor temporal resolution: Over any point : Over any point on Earth, the satellite only captures two on Earth, the satellite only captures two images per day!images per day!

• Best resolution over the polesBest resolution over the poles

POES COVERAGEPOES COVERAGE

POESPOES More then a few in orbit currentlyMore then a few in orbit currently Two examples are TERRA and AQUATwo examples are TERRA and AQUA Have different viewing instruments on themHave different viewing instruments on them One example is MODIS: Moderate Resolution One example is MODIS: Moderate Resolution

Imaging SpectroradiometerImaging Spectroradiometer Acquires data in 36 spectral bands (groups of Acquires data in 36 spectral bands (groups of

wavelengths)wavelengths) As a result, MODIS can create a true color As a result, MODIS can create a true color

visible image, which can:visible image, which can:– Show changes in vegetation during fall/springShow changes in vegetation during fall/spring– Show smoke plumes, dust plumes, etc.Show smoke plumes, dust plumes, etc.

Example MODIS imageExample MODIS image

http://ge.ssec.wisc.edu/modis-today/images/terra/true_color/2010_02_17_048/t1.10048.USA_Composite.143.4000m.jpg

Wildfires Near Los Angeles Using Wildfires Near Los Angeles Using MODISMODIS

Types of Satellite Imagery

• VISIBLE

• Measures visible light (solar radiation, 0.6 m) which is reflected back to the satellite by cloud tops, land, and sea surfaces.

• Thus, visible images can only be seen during daylight hours!

• Dark areas: Regions where small amounts of visible light are reflected back to space, such as forests and oceans

• Light areas: Regions where large amounts of visible light are reflected back to space, such as snow or clouds

Visible Pros/ConsVisible Pros/Cons

Pros:Pros:– Seeing basic cloud patterns and storm systemsSeeing basic cloud patterns and storm systems– Monitoring snow coverMonitoring snow cover– Shows nice shadows of taller clouds (has a 3-D look Shows nice shadows of taller clouds (has a 3-D look

to it) to it) Cons:Cons:

– Only useful during the daylight hoursOnly useful during the daylight hours– Difficult to distinguish low clouds from high clouds Difficult to distinguish low clouds from high clouds

since all clouds have a similar albedo (reflect a similar since all clouds have a similar albedo (reflect a similar amount of light) amount of light)

– Hard to distinguish snow from clouds in winter Hard to distinguish snow from clouds in winter

Soufriere Hills Volcano Eruption in West IndiesSoufriere Hills Volcano Eruption in West Indies

Types of Satellite ImageryTypes of Satellite Imagery• INFRARED (IR)

• Displays infrared radiation (10 to 12 m) emitted directly by cloud tops, land, or ocean surfaces

• Wavelength of IR depends solely on the temperature of the object emitting the radiation

• Cooler temperatures (like high cloud tops) are shown as light gray, or white tones

• Warmer temperatures (low clouds, ocean/lake surfaces) are shown dark gray

• Advantage: You can always see the IR satellite image

Types of Satellite ImageryTypes of Satellite Imagery

• WATER VAPOR (WV)

• Displays infrared radiation emitted by the water vapor (6.5 to 6.7 m) in the atmosphere

• Bright, white shades represent radiation from a moist layer or cloud in the upper troposphere

• Dark, grey or black shades represent radiation from the Earth or a dry layer in the middle troposphere

VISIBLE

IR

WATER VAPOR

Interpreting Visible vs. IRInterpreting Visible vs. IR

Moving on to RADAR….Moving on to RADAR….

RADARRADAR What does Radar mean?What does Radar mean?

– RaRadio dio DDetection etection aand nd RRanginganging

During World War II, this Radio Detection and During World War II, this Radio Detection and Ranging technique was developed to track Ranging technique was developed to track enemy ship and aircraft. However, it was soon enemy ship and aircraft. However, it was soon noted that precipitation, of any kind, would noted that precipitation, of any kind, would obstruct this remote detection.obstruct this remote detection.

At first this was a problem, but the potential At first this was a problem, but the potential benefits were soon seen. This was the birth of benefits were soon seen. This was the birth of weather Radar. weather Radar. 

How does RADAR work?How does RADAR work? Radar uses Radar uses electromagnetic radiationelectromagnetic radiation to sense  to sense

precipitation. precipitation. Sends out a Sends out a microwavemicrowave pulse (wavelength of 4- pulse (wavelength of 4-

10 cm) and listens for a return echo. 10 cm) and listens for a return echo. If the radiation pulse hits precipitation particles, If the radiation pulse hits precipitation particles,

the energy is scattered in all directionsthe energy is scattered in all directions The RADAR has a “listening” period. When it The RADAR has a “listening” period. When it

detects radiation scattered back, the radiation detects radiation scattered back, the radiation is called an “echo.”is called an “echo.”

How does RADAR work?How does RADAR work?• The RADAR beam is The RADAR beam is

typically 0.5typically 0.5oo above the above the horizonhorizon

• This ensures that the This ensures that the beam is not immediately beam is not immediately blocked by nearby trees, blocked by nearby trees, buildings, etc.buildings, etc.

• It rotates in a full circle, It rotates in a full circle, with a radius of ~200 mileswith a radius of ~200 miles

How does RADAR work?How does RADAR work?

• Time difference between Time difference between transmission and return of transmission and return of signal = distance to the signal = distance to the stormstorm

• The intensity of The intensity of precipitation is measured precipitation is measured by the strength of the by the strength of the echo, in units of decibels echo, in units of decibels (just like intensity of (just like intensity of sound waves!)sound waves!)

www.radar.weather.gov/graphics/ridge_sitemap.gifwww.radar.weather.gov/graphics/ridge_sitemap.gif

• An image showing precipitation intensity is called a An image showing precipitation intensity is called a “reflectivity image”“reflectivity image”

Intensity measured in decibels (dBZ)

Thunderstorms over MichiganThunderstorms over Michigan

Types of RADARTypes of RADAR Conventional RadarConventional Radar

– Echoes are simply displayed on radar screen.Echoes are simply displayed on radar screen.– Only produces reflectivity images.Only produces reflectivity images.– Can identify storm structure, locations of Can identify storm structure, locations of

tornadoes, and even non-meteorological tornadoes, and even non-meteorological objects!objects!

Circular and vertical sweeps reconstruct the precipitation type and intensity throughout the atmosphere

Good/Bad of Conventional RadarGood/Bad of Conventional Radar Good forGood for

– Seeing bands/location of precip and their Seeing bands/location of precip and their intensityintensity

– Hook echoes Hook echoes – Bow echoesBow echoes

Bad forBad for– Ground clutter, bouncing off things other than Ground clutter, bouncing off things other than

precipitationprecipitation– Overestimation/Underestimation of precipOverestimation/Underestimation of precip– Cannot tell type of precip by radar alone (Have Cannot tell type of precip by radar alone (Have

to use temperatures, actual observations, etc.to use temperatures, actual observations, etc.

Doppler RadarDoppler Radar One of the most advanced versions of radarOne of the most advanced versions of radar Does everything a conventional radar can do, Does everything a conventional radar can do,

PLUS more...PLUS more... In addition to conventional techniques, the In addition to conventional techniques, the

Doppler Radar has a scan that operates on Doppler Radar has a scan that operates on principle of the principle of the Doppler EffectDoppler Effect– Usually described using sound wavesUsually described using sound waves– Definition: Definition: The change in the observed frequency of The change in the observed frequency of

waves produced by the motion of the wave sourcewaves produced by the motion of the wave source

Doppler Radar in MeteorologyDoppler Radar in Meteorology• Measures changes in wavelength of the Measures changes in wavelength of the

RADAR beam after it is scattered from a RADAR beam after it is scattered from a travelling objecttravelling object

• Wavelength of the beam changes after it Wavelength of the beam changes after it “strikes” the object“strikes” the object

• Thus, wind direction AND speed can be Thus, wind direction AND speed can be measured by RADARmeasured by RADAR

Doppler RADAR in Meteorology• This is VERY useful in detecting tornado signatures!

•Doppler can measure wind speed and direction in a storm and can be viewed in a storm-relative velocity image

• Red: Winds away from RADAR site, Green: Winds toward RADAR site

• This is how the National Weather Service issues tornado warnings

Phased-array radarPhased-array radar Next generation of radar.Next generation of radar. Can scan multiple levels at Can scan multiple levels at

once using multiple radar once using multiple radar beams sent out at one time.beams sent out at one time.

Scanning only takes 30 Scanning only takes 30 secs compared to ~6 secs compared to ~6 minutes for the Dopplerminutes for the Doppler

Gives instantaneous profile Gives instantaneous profile of atmosphere for winds and of atmosphere for winds and precipitation intensity.precipitation intensity.

Cars on IND radarCars on IND radar

ExamplesExamples

Birds on radarBirds on radar– http://www.crh.noaa.gov/images/mkx/radar/http://www.crh.noaa.gov/images/mkx/radar/

birdanimation.gifbirdanimation.gif

http://www.crh.noaa.gov/mkx/?n=using-http://www.crh.noaa.gov/mkx/?n=using-radarradar