Chapter 5: Remote Sensing

Satellites

Wind Profiler

Radar

Lidar

Satellites: Geostationary vs. Polar Orbiting

•What does geostationary mean?•Resolution determined by distance and wavelength

Satellites: Visible, Infrared, and Water Vapor

•Sensing devices are called radiometers

•Sensitive at different wavelengths

•Difference wavelengths reveal different information about weather

•It take practice to use satellites to infer information about clouds and weather

http://cimss.ssec.wisc.edu/satmet/modules/index.html

Satellites: Visible

ADVANTAGES

•High resolution (1 km and less)

•Intuitive interpretation (like a photo)

•Can see more than clouds when clear

•Easy to distinguish different cloud types

DISADVANTAGES

•Blind at night

•No information about temperature

Visible Satellites: what is this?

Visible Satellites: Why are the lakes clear?

Visible satellites: More than clouds

http://modis.gsfc.nasa.gov/gallery/

Satellites: Infrared

ADVANTAGES

•Direct information about temperature

•Can provide vertical profile of Temp. when clear

•Equally effective at night

DISADVANTAGES

•Lower resolution (4+ km)

•Interpretations non-intuitive

Infrared Satellites: Sensitive to temperature

Infrared Satellites: “False Color” and cloud top temp

Bright= cold=high=strong storms (maybe)

Doppler Radar

ADVANTAGES

•Direct Measurement of falling precipitation

•Strong indication of precipitation intensity

•Can detect hail and indicate likely tornados

•Doppler Effect can help determine wind patterns

•Can “see” birds, insects, dust

DISADVANTAGES

•Hard to distinguish between rain and snow

•Useless when clear (no wind info)

•Range and resolution are limited

http://www.srh.noaa.gov/srh/jetstream/doppler/doppler_intro.htm

NEXRAD 88-D radar locations

http://water.weather.gov/

NEXRAD 88-D radar locations

Beams cover about 250 mile diamter

NEXRAD 88-D radar beams:

•Radar beam covers about 1 degree angle

•The further away from the radar you are, the wider the beam spreads

•This causes decreased resolution at long distance

Radar Beam Geometry

•These are the direction that the radar beam is sent out and received

•These 16 angles are rotated through a full 360 degrees

•The entire sky volume is scanned in 5 minutes

•This output can give a 3-D dimensional view of a storm, though usually we only look at the “base” reflectivity.

•The base reflectivity represents a higher height further from the radar

Doppler Radar: Thunderstorm closeup

Doppler wind speeds

•The returned radiation is shifted in frequency by the motion of the target•This can be used to calculate drop speed along the radial path•This path is basically horizontal toward or away from the radar•Green = INBOUND; RED=OUTBOUND

Doppler Radar: Tornadic hook echo and velocity couplet

Doppler winds: only toward or away from radar

http://www.spc.noaa.gov/coolimg/cape_may.htm

Lidar measurements of ice crystals falling on Mars?

Wind Profiler sample data