Radar and Satellites AOS 101 Discussion Sections 302 and 303

Satellite History  First satellite in space  Sputnik 1  Launched on 4 October 1957 by the Soviet Union  Orbited in the ionosphere  Helped measure the density of the upper atmosphere layer  Showed meteorologists the usefulness of using satellites for data  Transmitter died after 22 days

Weather Satellite History  First weather satellite in space  Vanguard 2  Launched on 17 February 1959 by the United States Navy  Designed to measure cloud cover  Considered unsuccessful because of a poor rotation axis  TIROS- 1  First successful weather satellite  Launched on 1 April 1960 by NASA  Lasted 78 days  Surveyed atmospheric conditions from space

Current Satellite Information  Now satellites can run for many years  Satellites that are no longer function still remain in orbit around the Earth  These are called space debris  Two basic types of weather satellites  GOES  Geostationary Operational Environmental Satellites  POES  Polar Operational Environmental Satellites  Also called LEO  Low Earth Orbit  Defined by their orbital characteristics

Geostationary vs. Polar Orbiting

GOES  Geostationary Orbiting Environmental Satellite  Geostationary means that the satellite is stationary with respect to one point on the ground  Orbits as fast as the Earth spins  Orbits the Earth at about 36,000 km high  Designed by NASA  Once in orbit, operations are managed by NOAA  Nomenclature  GOES is given a letter before placed in orbit  Example: GOES-M or GOES-G  Once successful, is given a number  Example: GOES-11 or GOES-12

GOES  Takes visible, infrared, and water vapor images  Cons  Poor spatial resolution  Pros  Imagery is obtained approximately every 15 minutes  Can change the temporal resolution if an important meteorological event is unfolding  Good for viewing large scale phenomena

GOES  Currently two operational GOES in orbit  GOES-11  Also called GOES-West  135 W  GOES-12  Also called GOES-South  75 W  GOES-13  Also called GOES-East  105 W

GOES Coverage

POES  Polar Orbiting Environmental Satellite  Rotates around the Earth from pole to pole  Closer to the Earth than GOES  About 850 km above the Earth surface  Sees the entire planet twice in a 24-hour period

POES  Cons  Poor temporal resolution  Only captures two images a day  Pros  Good spatial resolution  Because so close to Earth  Best resolution is over the poles

POES  More then a few in orbit currently  Two examples are TERRA and AQUA  Have different viewing instruments on them  One example is MODIS: Moderate Resolution Imaging Spectroradiometer  Acquires data in 36 spectral bands (groups of wavelengths)  As a result, MODIS can create a true color visible image, which can:  Show changes in vegetation during fall/spring  Show smoke plumes, dust plumes, etc.

MODIS  February 15, 2011  Tropical Cyclone Bingiza (13S) approaching Madagascar

MODIS  February 18, 2011  Dust storm off Oman  gallery/individual.php?db_ date=

MODIS Composite Hurricane Dennis

Types of Satellite Imagery  Three Main Types of Satellite Imagery VisibleInfrared Water Vapor

Visible Satellite Imagery  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 Satellite Imagery  Pros:  Seeing basic cloud patterns and storm systems  Monitoring snow cover  Shows nice shadows of taller clouds (has a 3-D look to it)  Cons:  Only useful during the daylight hours  Difficult to distinguish low clouds from high clouds since all clouds have a similar albedo (reflect a similar amount of light)  Hard to distinguish snow from clouds in winter

Infrared (IR) Satellite Imagery  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

Water Vapor (WV) Satellite Imagery  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

RADAR  What does Radar mean?  Radio Detection and Ranging  During World War II, this Radio Detection and Ranging technique was developed to track enemy ship and aircraft  However, it was soon noted that precipitation of any kind would obstruct this remote detection

RADAR Products  Reflectivity  What most people think of a radar image  Shows power returned to the antenna at some tilt angle (usually base reflectivity at 0.5°)  Radial velocity  Shows the velocity of an echo using the Doppler effect  Only available with Doppler radars  Radar estimated precipitation  Based on amount and duration of reflectivity, estimates precipitation hourly, weekly, or some other time interval  Radar summaries

RADAR - Reflectivity  Radar uses electromagnetic radiation to sense precipitation.  Sends out a microwave pulse (wavelength of 4-10 cm) and listens for a return echo.  If the radiation pulse hits precipitation particles, the energy is scattered in all directions  The RADAR has a “listening” period  When it detects radiation scattered back, the radiation is called an “echo”

RADAR - Reflectivity  The RADAR beam is typically 0.5 o above the horizon  This ensures that the beam is not immediately blocked by nearby trees, buildings, etc.  It rotates in a full circle, with a radius of ~200 miles

RADAR  Time difference between transmission and return of signal is the distance to the storm  The intensity of precipitation is measured by the strength of the echo  Units of decibels (dB)  Just like intensity of sound waves

Reflectivity Image  An image showing precipitation intensity is called a “reflectivity image”

Types of RADAR  Conventional Radar  Echoes are simply displayed on radar screen.  Only produces reflectivity images.  Can identify storm structure, locations of tornadoes, and even non-meteorological objects

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

Conventional Radar  Pros:  Seeing bands/location of precipitation and their intensity  Hook echoes  Bow echoes  Cons:  Ground clutter, bouncing off things other than precipitation  Overestimation/Underestimation of precip Overestimation/Underestimation of precip  Cannot tell type of precipitation by radar alone (Have to use temperatures, actual observations, etc.)

Doppler RADAR  One of the most advanced versions of radar  Does everything a conventional radar can do and more  In addition to conventional techniques, it has a scan that operates on principle of the Doppler Effect  Usually described using sound waves  Definition  The change in the observed frequency of waves produced by the motion of the wave source

Doppler RADAR Locations (NEXRAD)

RADAR – Radial Velocity  Measures changes in wavelength of the RADAR beam after it is scattered from a travelling object  Wavelength of the beam changes after it “strikes” the object  Thus, wind direction AND speed can be measured by RADAR

Doppler RADAR  Useful in detecting tornado signals  Can measure wind speed and direction in a storm  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

RADAR – Radar Estimated Precipitation

RADAR Summary  A product mostly intended for aviation that gives a wide variety of information depending on the source  Typically, at minimum, is a mosaic of base reflectivity with overlays of echo tops and echo movement  Can have other information 

RADAR Summary  Cell movement:  Arrow pointing towards the direction of movement or a wind staff (just like station model) pointing into the direction of movement  Number adjacent the arrow indicates the speed in knots.  Wind barbs/flags indicate speed on a wind staff  Height of echo tops given in hundreds of feet  (550 means 55,000 feet)

RADAR Summary  SIGMETs/AIRMETs  Mesocyclone (abbreviated MESO)  Computer algorithms detect large rotating echo  Tornadic vortex signature (abbreviated TVS)  Compact intense rotation is detected by computer algorithms  Hail  Algorithms are detecting the probability of hail within the storm  Watch Boxes  Thunderstorm and tornado watches issued by the Storm Prediction Center in Norman, OK.  Blue box for thunderstorm watch, Red box for tornado watch

Radar Issues  Not everything on the reflected radar image is precipitation, there can be many other things that create echoes  Cars  Birds and Insects  Ground Clutter  Buildings  Hills  Trees  Anomalous propagation

VIPIR Radar  Volumetric Imaging and Processing of Integrated Radar  Used by television stations to see a three dimensional view of the radar echoes