A T M O S A short course on radar meteorology 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 z 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 2. Frequency Doppler shift, relative radial velocity of the precipitation z 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 2. Frequency Doppler shift, relative radial velocity of the precipitation z 3. Phase can be used to measure refractive index variations 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 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 θ 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: ND 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 depolar- isation 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 ND 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.