Radar Imagery Theory Flashcards
What does RADAR stand for?
Radio Detection and Ranging
What does PPI stand for?
Plan Position indicator
What is a PPI?
A display of echoes superimposed over a grid of geography and viewed from overhead
What does CAPPI stand for?
Constant altitude Plan Position Indicator
What are the dimensions of the CAPPI area?
1.5km vertically
130km horizontally
What is an Echo Top?
A representation of the highest altitude where detectable precipitation is observed
In a CAN/US composite what are the significant points?
- Canadian echoes are CAPPI, US echoes are PPI
- resolution is 4.2nm per pixel
- Always set on rain
what type of radar are modern radars and how do they work
- Pulsed RADAR
- Short bursts of energy are transmitted and there are long silent periods to listen for returned energy
Why are those type of radar used?
Only one antenna needed and it uses much less power
List the 5 components of a RADAR system
Transmitter Receiver Antenna Processor Display
Define wavelength
The distance between one crest and the next, or. one trough and the next
Define frequency
The path that the wave travels in one wavelength is called a cycle and the number of cycles in a given unit of time(one second) is the frequency (hz)
What are the advantages and disadvantages of short wavelengths?
- It can detect light precipitation
- It is severely weakened or attenuated by precip
What are the advantages and disadvantages to long wavelengths?
- The greater its capacity to detect heavy precip
- it burns through most light precip
what are the 3 wavelengths and which do we use in Canada? What is its letter band indicator?
-3cm is good for snow
-10cm is good for showers
5cm is the one we use.
C band
What is the pulse length?
The duration of time that the RADAR is radiating
What kind of shape does the radar beam have?
Conical
The horizontal and vertical dimensions of the RADAR beam are referred to as the
Beam Width
What is normal propagation?
4/3 the earth’s curvature
what is anomalous propagation
when the RADAR beam is bent more or less than usual due to unusual temperature or humidity lapse rate.
What are the 2 types of anomalous propagation?
- Sub refraction
- Super refraction
Radar targets will affect return power as a result of 3 factors:
- Number of drops or flakes
- composition
- size
which hydrometeor reflects better, rain or snow?
Rain. Snow reflects gives a return 1/5 that of rain
the reflective capability of hydrometeors listed in order is:
Large Hail Rain Small hail snow clouds
List the 3 types of attenuation
Range
Absorption
scattering
Define attenuation
A lessening of the concentration of energy per unit volume of the beam.
what is the energy that is returned to the radar, and captured by the antenna for processing
Backscatter
Define distortion
The misrepresentation of the target in any of its parameters
What are the 2 categories of distortion
Radar design
Propagation characteristics
What are the 3 distortions due to radar design?
- Beam width
- Pulse length
- processor distortion
What are the 4 propagation characteristic distortions
- Range
- Precip attenuation
- Fringing
- Earth’s curvature
What is used on all canadian radar to help with range distortion?
STC (sensitivity Time Control)
Define extraneous echo
Any echo not derived from clouds or precip
What are the 3 types of extraneous echoes?
- Angel echoes
- Clutter
- Second trip echoes
How many radar sites are there in Canada?
31
What are the 2 types of radar used in the USA?
5 cm (S-band) 10cm (C-band)
