A Short Course on Radar Meteorology

Home , Doppler radar, Meteorology, Weather radar

A T M O S

Tobias Otto Herman Russchenberg

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Radar Meteorology M O S Radar: Radio Detection And Ranging An electronic instrument used for the detection and ranging of distant objects of such composition that they scatter or reflect radio energy.

Radar Meteorology: The study of the atmosphere and weather using radar as the means of observation and measurement.

Meteorology: The study of the physics, chemistry, and dynamics of the Earth's atmosphere.

Reference: AMS Glossary

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Microwaves M O S HF 3 - 30 MHz VHF 30 - 300 MHz mobile phones UHF 300 - 1000 MHz KNMI Windprofiler L1-2 GHz S2-4GHz C4-8GHz

X8-12GHz PARSAX Ku 12 - 18 GHz KNMI WLAN Weather K18-27GHz Radar Ka 27 - 40 GHz V40-75GHz IDRA W 75 - 110 GHz mm 110 - 300 GHz Cloud Radar

Reference: Radar-frequency band nomenclature (IEEE Std. 521-2002)

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Information in microwaves M O S Electromagnetic waves are transversal waves, i.e. their direction of oscillation is orthogonal to their direction of propagation.

1. Amplitude y x can be related to the strength of precipitation / rain rate

A A

1. Amplitude y x can be related to the strength of precipitation / rain rate 2. Frequency Doppler shift, relative radial velocity of the precipitation z

1. Amplitude y x can be related to the strength of precipitation / rain rate 2. Frequency Doppler shift, relative radial velocity of the precipitation z 3. Phase can be used to measure refractive index variations

1. Amplitude y can be related to the strength of x precipitation / rain rate 2. Frequency Doppler shift, relative radial velocity of the precipitation 3. Phase z can be used to measure refractive index variations 4. Polarisation hydrometeor / rain drop shape

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Radar Resolution M O S

antenna beam-width

c range resolution volume r  range R (range-bin) 2B c .. speed of light B .. bandwidth of the transmitted signal

 ∆r is typically between 3m - 300m, and the antenna beam-width is between 0.5° -2° for weather radars

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Radar Equation for Weather Radar M O S  3 2 PG G c 2 1 P  t t r  K D6  r 2  i 2 1024ln 2B unit volume R

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Radar Reflectivity Factor z M O S  mm6   spans over a large range; to compress it into a z  D6    i  3  smaller range of numbers, a logarithmic scale is unit volume  m  preferred

 z  Z 10log10  dBZ 1mm6 / m3 

To measure the reflectivity by the weather radar, we need to: - know the radar constant C,

- measure the mean received power Pr, - measure the range R, - and apply the radar equation for weather radars: 2 z  PrCR

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Raindrop-Size Distribution N(D) M O  N S z  D6  D6 N(D)dD  0 6!  i  7 unit volume 0  where N(D) is the raindrop-size distribution that tells us how many drops of each diameter D are contained in a unit volume, i.e. 1m3. Often, the raindrop-size distribution is assumed to be exponential:

ND N0 exp D concentration (m-3mm-1) slope parameter (mm-1)

Marshall and Palmer (1948):

-3 -1 N0 = 8000 m mm Λ = 4.1·R-0.21 with the rainfall rate R (mm/h)

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Reflectivity – Rainfall Rate Relations M O S reflectivity (mm6m-3) z   D6 N(D)dD D  liquid water content (mm3m-3) LWC  D3N(D)dD 6  D raindrop volume  rainfall rate (mm h-1) R  D3v(D)N(D)dD 6  D terminal fall velocity  the reflectivity measured by weather radars can be related to the liquid water content as well as to the rainfall rate: b power-law relationship z  aR the coefficients a and b vary due to changes in the raindrop-size distribution or in the terminal fall velocity. Often used as a first approximation is a = 200 and b = 1.6

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A nd T 2 Part - Outline M O S

 radar geometry and displays

 Doppler effect

 polarisation in weather radars

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Radar Display M O S PPI (plan-position indicator):

RHI (range-height indicator):

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A nd T 2 Part - Outline M O S

 radar geometry and displays

 Doppler effect

 polarisation in weather radars

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Doppler Effect M O S

http://en.wikipedia.org/wiki/File:Dopplerfrequenz.gif

2vr  fd  vr,max   target  4Ts

fd .. frequency shift caused by the moving target

vr .. relative radial velocity of the target with respect to the radar λ .. radar wavelength

Ts .. sweep time

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Weather Radar Measurement Example (PPI) M O S

Reflectivity (dBZ) Doppler velocity (ms-1)

Data: IDRA (TU Delft), Jordi Figueras i Ventura

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Combining Reflectivity and Doppler Velocity M O S

Doppler Processing (Power Spectrum):

Mapping the backscattered power of one radar resolution volume into the Doppler velocity domain.

Power Doppler Width

Mean Doppler Doppler Velocity Velocity

Figures: Christine Unal

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A nd T 2 Part - Outline M O S

 radar geometry and displays

 Doppler effect

 polarisation in weather radars

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Can Polarimetry add Information M O S  yes, because hydrometeors are not spheres

- ice particles

- hail

Beard, K.V. and C. Chuang: A New Model for the Equilibrium Shape of Raindrops, Journal of the Atmospheric Sciences, vol. 44, pp. 1509 – 1524, June - raindrops 1987. http://commons.wikimedia.org/wiki/Category:Hail

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. Observed shapes of raindrops

ET4169 - Microwaves, Radar and Remote SensingTitel van de Feb-Marchpresentatie 2012 21 21 A T Measurement Principle M O S transmit

Zhh (dBZ) Zhv (dBZ) receive Zvh (dBZ) Zvv (dBZ)

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Measurement Principle M O S transmit

Zhh (dBZ) Zhv (dBZ)

- receive Zvh (dBZ) Zvv (dBZ)

= Zdr differential reflectivity

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Hydrometeor Classification M O S

aggregatesicemelting crystalsrain layer(snow)

Reflectivity Differential Reflectivity

2 Phh Zhh 10logCR Phh dBZ Zdr 10log dB Pvv

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Measurement Principle M O S transmit

Zhh (dBZ) Zhv (dBZ)

- receive Zvh (dBZ) Zvv (dBZ) = LDR (dB) linear depolarisation ratio

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Linear Depolarisation Ratio M O S

meltingground clutterlayer

Reflectivity Linear Depolarisation Ratio

2 Phv Zhh 10logCR Phh dBZ LDR 10log dB Pvv

Data: POLDIRAD (DLR, Oberpfaffenhofen, Germany), Prof. Madhu Chandra

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T Estimation of raindrop-size distribution M O S ND N0 exp D concentration (m-3mm-1) slope parameter (mm-1)

1. the differential reflectivity Zdr depends only on the slope parameter Λ, so Λ can be directly estimated from Zdr

2. once that the slope parameter is known, the concentration N0 can be estimated in a second step from the reflectivity Zhh

Data: IDRA (TU Delft), Jordi Figueras i Ventura

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T M O S

A short course on radar meteorology

Tobias Otto

e-mail [email protected]

web http://atmos.weblog.tudelft.nl http://rse.ewi.tudelft.nl http://radar.ewi.tudelft.nl (for information on PARSAX)

references R. E. Rinehart, “Radar for Meteorologists”, Rinehart Publications, 5th edition, 2010. R. J. Doviak and D. S. Zrnić, “Doppler Radar and Weather Observations”, Academic Press, 2nd edition, 1993. V. N. Bringi and V. Chandrasekar, “Polarimetric Doppler Weather Radar: Principles and Applications”, Cambridge University Press, 1st edition, 2001. http://collegerama.tudelft.nl/mediasite/SilverlightPlayer/Default.aspx?peid=1805993fac954c3fba5855bce7e6a86e1d

Delft University of Technology Remote Sensing of the Environment (RSE) A short course on radar meteorology. A T S/X data: horizontal and vertical profiling M O S

Delft TU Delft Climate Institute University of Technology Remote Sensing of the Environment