¶ Sonic Detection and Ranging Instrument (SODAR)
¶ Instrument Description
The SODAR wind profiler measures wind profiles and backscattered signal strength between 15 meters and 500 meters. It transmits acoustic energy into the atmosphere in several directions and measures the strength and frequency of the energy scattered back to the instrument (backscatter). The strength of this returned signal is determined by the strength of temperature inhomogeneities with size, on the order of 10 cm. By assuming that the scattering elements in the atmosphere are moving with the mean wind, the horizontal wind field can then be derived.
The SODAR instrument consists of a single-phased antenna array that is approximately 1.5 square meters and oriented horizonally, so that the five transmitted signals (transmitted in two different vertical planes) travel vertically. These signals are transmitted alternately along five pointing directions: one vertical, two in the north-south vertical plane (one south of vertical and one north of vertical), and two in the east-west vertical plane (one east of vertical and one west of vertical). Transmitting in these directions allows the three components of motion to be determined. The SODAR cycles through these five beams at multiple pulse lengths and frequencies, taking about five minutes before the system returns to the beginning of its sequence.
¶ Additional Information
Data produced by this instrument comes in two forms: raw spectra data, and time-averaged profiles, similar to the data produced by the radar wind profiler. These time-averaged profiles are what you, the student analyst, will monitor. These data include, for each height: wind speed and direction, vertical wind speed (positive = upward), vertical wind standard deviation, and average backscatter strength. These can be very useful in determining atmospheric structure on time scales as fine as a few minutes. It is important to keep in mind that vertical velocities and signal-to-noise ratios can be affected by rainfall (essentially, the SODAR would register a large downward motion associated with energy from the falling rain rather than from atmospheric structure).
For more information, please see the SODAR Instrument web page.
¶ Expected Operations
¶ Metrics
In the metrics table below, the primary measurement is the backscatter signal. Note that this quantity, however, is not the principle measurement of interest to most climate scientists. Instead, the derived quantities of wind speed, wind direction, and vertical wind speed as a function of height tend to be of most interest to climatologists. The accuracies of these quantities depend on both the accuracy of the frequency measurement as well as various atmospheric affects, and vary considerably according to atmospheric conditions.
It is quite normal to have large portions of these variables missing throughout each day. As long as the plots look reasonable, these missing portions of data should not be an issue.
¶ Plots
SODAR winds
The first plot for SODAR depicts both the wind speed and direction as a function of height and time, and is typically the most useful plot to glean information from, as it can tell you both wind speed and wind direction in one succinct, easy-to-read plot.
Additional SODAR plots
In addition to the SODAR wind plot, there are also plots showing vertical wind speed, vertical wind speed standard deviation, and backscatter as a function of height. The instrument error plot shows when there is no error (a value of 0), versus ground clutter contamination beting detected and removed (a value of 256). This plot should usually only show a value of zero.
¶ Site-Specific Information
The SODAR instrument is currently only deployed with the AMF1.
¶ Known Issues
¶ Known Behaviors
Known behaviors for this instrument that MAY need to be mentioned in your DQAs:
Document some here.
¶ Past Problems
Past problems for this instrument that DO need to be mentioned in your DQAs and possibly requiring a DQPR submittal:
Document some here.