WX RADAR & SATELLITES

Question 1

How many Metservice wx radar sites?
Radius in normal vs doppelar mode?

Answer 1

9
300km
150km

Question 2

How do wx radars work?

Answer 2

Emit microwaves at a wavelength of 3-10cm, that reflect back off of precipitation. Intensity is therefore relative to rainfall rate

Question 3

7 issues with wx radar?

Answer 3

1. attenuation (weakening by heavy precip at close range - shadows rainfall echoes further out)
2. ground echoes (topography cluttering image - effect enhanced by inversion)
3. sea clutter (when radar is located near coast, side lobes pick up waves in high sea states)
4. radar elevation (radar horizon)
5. false echoes at sunrise & sunset (sun emits radiation in every frq, when sun is at the right angle, it will be picked up by radar)
6. bugs on radar
7. other interference lines (caused by broadcasts on the same frq)

Question 4

How does Doppler radar work?

Answer 4

By measuring the phase shift between transmitted & received signals. Target motion as well as reflectivity can be assessed

Question 5

What can Doppler radar capture?

Answer 5

Sev storms, microbursts, downdrafts & tornadoes if within radar range.
Upper winds can be determined if sufficient particles to analyse (dust/droplets etc)

Question 6

How do wx satellites work generally?

Answer 6

Passive, have radiometers used as scanning devices, sensitive to wavelengths in the IR & VIS spectrums.
Results in info on ozone, water vapour, emissions and cloud/wx patterns

Question 7

Polar orbiting Satellites;
- Alt
- FoV
- Time period
-Res
- Wx functions

Answer 7

• 850km
• 3000km
• poles every 105mins, complete coverage every 12hrs
• 375m to 750m per pixel
• IR/VIS imagery, sea SFC temps, vertical temp & moisture profiles

Question 8

Polar orbiting Satellites; Advantages (3)

Answer 8

1. Freq coverage at high latitudes obtained
2. high res with low orbit
3. Accurate data with satellite overhead

Question 9

Polar orbiting Satellites; Disadvantages (2)

Answer 9

1. At lower latitdues (incl) NZ, it takes 12hrs to recieve updated imagery. (but with 2 sats = 4 passes a day)
2. Cannot provide continuous view of one area

Question 10

Geostationary Satellites;
- Alt
- FoV
- Time period
-Res
- Wx functions

Answer 10

• 36,000km
• Full hemisphere (images near edges not good)
• every 10-15mins
• 1-2km per pixel
• IR/VIS imagery, sea SFC temps, rx & tx data from buoys & remote AWS etc, tracking of CLD & water vapour to give upper winds.

Question 11

Geostationary Satellites; Advantages (1)

Answer 11

Frequent coverage at low and mid latitudes

Question 12

Geostationary Satellites; disadvantages (3)

Answer 12

1. Distortion at high latitudes due angle of viewing
2. Lower res
3. Costlier to deploy

Question 13

How does IR imagery work?

Answer 13

IR imagery is obtained by a sensor tuned into IR atmospheric windows. (day and night)
Radiance at a particular wavelength is proportional to temp of the emitting SFC.
White = cold (High CLD)
Grey = warm (low CLD)

Question 14

How does CT imagery work?

Answer 14

Another type of IR imagery.
raw satellite data is fed into a global model of the atmosphere. colour is added to the clouds within specific temp bands

Question 15

How does VIS imagery work?

Answer 15

Relies on light reflected to produce an image. (only available during daylight hours).
Intensity of radiation depends on albedo of object