MET4994_5994_RS_Lec21_S11

MET4994_5994_RS_Lec21_S11 - MET MET 4994 Remote Sensing:...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: MET MET 4994 Remote Sensing: Radar and Satellite Meteorology MET MET 5994 Remote Sensing in Meteorology 2. Lecture 21: February 28, 2011 1. Range and Velocity Folding Interpreting Doppler velocity patterns Doppler Doppler Dilemma Range Folding and Multitrip Echoes Multitrip Recognizing Multitrip Echoes Multitrip Look outside By echo shape: narrow, wedge-like echoes are suspicious. Recognizing Multitrip Echoes Multitrip Look at the echo height displayed by RHI. Recognizing Multitrip Echoes Multitrip Multitrip echoes are weaker than real because return power is proportional to 1/r^2. Change PRF. Velocity Velocity Folding/Aliasing The figure below shows the meausred Doppler velocity as a function of azimuth angle for an environmental wind blowing from the west at 36 m/s. The aliasing process causes the Doppler velocity values offset by 2 Vmax until they fall within +/- Vmax. Thus, +36 m/s is aliased to: 36-2*30=-24 m/s. Recognizing Recognizing Velocity Aliasing/Folding Finding velocity discontinuity (usually in strong reflectivity regions): Doppler velocity changes from max. negative values to max. positive values, or vice versa. Unfolded Interpretation Interpretation of Doppler Velocity Doppler radar viewing configuration (scanning 360 degree at a given elevation angle). An An Example • • • • Get wind profile from Doppler radar VAD display Doppler velocity is negative for toward radar, positive for away from radar Zero value zone means that the wind direction is perpendicular to the radar beam. The wind speed at a given height is the maximum value around a constant slant range circle. Patterns associated with vertical profiles having having constant wind directions Patterns associated with vertical profiles having having constant wind directions Patterns associated with vertical profiles having having constant wind directions Patterns associated with nonuniform nonuniform horizontal wind fields (difluent) Patterns associated with nonuniform nonuniform horizontal wind fields (confluent) Patterns associated with vertical profiles having having constant wind speed Patterns associated with vertical profiles having having constant wind speed Patterns associated with vertical profiles of of varying wind speed and direction Patterns associated with horizontal discontinuities discontinuities in the wind field Patterns associated with a tropical cyclone (Max. real wind speed=60m/s; Doppler Vmax Vmax=30m/s. Velocity Velocity Folding! Folding!) Patterns associated with a mesocyclone mesocyclone For more examples including divergence/convergence, tornados, supercell thunderstorms, supercell, thunderstorms, please read the guide for interpreting Doppler velocity patterns online at the class website. No class on Wednesday March 2 Summary Summary The combination effect of Earth curvature and atmosphere refraction causes the radar rays bend upward relative to the Earth surface under standard refraction condition. Super refraction may cause ducting. Rayleigh regime: σ ~ D6 ; Optical regime: σ= geometric area; Mie regime: complicated For next class, read radar book Ch 5 (Distributed targets). ...
View Full Document

This note was uploaded on 09/13/2011 for the course MET 4994 taught by Professor Haijan during the Spring '11 term at FIU.

Ask a homework question - tutors are online