Detecting Aloft Winds Using RADAR
RADAR stands for Radio Detection And Ranging. It is a remote sensing technique that can be deployed on a radar wind profiler (RWP) to measure vertical profiles of horizontal winds using electromagnetic (EM) signals. A typical configuration for a RWP requires five antenna beams. One is aimed vertically and the other four are tilted orthogonal to one another away from vertical. The RWP transmit EM pulses at fixed intervals into the atmosphere along each of the antenna's pointing direction. Small amounts of EM are scattered back to the antennas from fixed discrete altitudes. The Doppler frequency shift from the scattered signals is determined and used to calculate the radial velocity of the air toward or away from the radar along the antenna's pointing direction at different altitudes. Using the radial wind components measured from four orthogonal beams, the horizontal wind vector can be derived through trigonometry and corrections for vertical motions detected from the vertical beam.
RWP can measure hourly or sub-hourly wind profiles starting at about 100 m above ground level (agl) at various vertical resolutions (ranging from 40 m to 400 m) and can capture data up to about 3-5 km agl. Measuring winds at these heights has provided valuable information on the planetary boundary layer (PBL) related to air quality including the detection of the nocturnal low level jet (NLLJ). The NLLJ is a fast moving stream of air that flows from the south/southwest into Maryland and continues north/northeastward. It forms between the Appalachian Mountains and the Atlantic Ocean during the late night and early morning hours under certain meteorological conditions and is responsible for transporting ozone and its precursors at the altitudes of roughly 200 meters to about 1 kilometer above the surface into Maryland.
RWP is often deployed with a Radio Acoustic Sounding System (RASS) which can be used to measure virtual temperature profiles generally from 0.1-1.5 km agl. The RASS unit works by sending out pulses of acoustic (sound) wave vertically from four speaker drums. The propagation speed of sound wave depends on the temperature and the moisture of the atmosphere (hence, the term virtual temperature). The backscattered RASS wave can be used to determine the Doppler shifted frequency and finally to calculate virtual temperature profiles aloft.
Besides winds and (virtual) temperatures, characteristics about atmospheric structure, mixing, and turbulence can also be derived. This information can be used to provide additional information about the atmospheric stability which is crucial in air quality analysis and forecasting. For instance, mixing depth can be obtained to estimate the impact of aloft pollutants on ground-level pollutant concentrations.
MDE operates three RWP and RASS instruments in Maryland. One is deployed at Howard University Field Laboratory in Beltsville, the second is at the Piney Run monitoring site in Frostburg, and the third is at the Horn Point monitoring site in Cambridge. All three RWPs are part of a Cooperative Agency Profiler (CAP) network. Near real-time data from MDE RWPs and approximately 100 CAP sites from over 35 different agencies around the world are being acquired by NOAA's Earth System Research Laboratory (ESRL) Global System Division (GSD). After GSD applies its additional data quality control algorithms, it makes these value-added data available on the web for the research community, university, the National Weather Service, etc.
Real-time wind profiler data are provided below. Note that graphics are provided directly from NOAA ESRL-GSD/MADIS CAP Profiler Graphical Data Displays website. If graphic(s) do(es) not show up, use the "Reload" button on your browser or "Right-click" on the blank image and select "Show Picture" from the menu. You can also visit the CAP website directly to get operational status or archive data from HU-Beltsville, Piney Run, or other stations in the CAP network.
Latest wind profiles at HU-Beltsville
Latest wind profiles at Piney Run
Latest wind profiles at Horn Point
Ambient Air Monitoring Network
Assessing Visibility Using Haze Cams
Detecting Aloft Winds Using RADAR
Measuring Air Pollution Using Balloons
Measuring Aloft Aerosol Using LIDAR
Measuring Aloft Regional Air Pollution Using Aircraft
Monitoring Interstate Pollutant Transport Using Mountaintop Measurements