Wyoming Cloud Radar (WCR) 1Hz Data (February 2002) PI: Gabor Vali (others: Samuel Haimov, David Leon) Department of Atmospheric Science University of Wyoming PO BOX 3038 Laramie WY 82071 (307) 766-3245 (307) 766-2635 (Fax) http://www-das.uwyo.edu/wcr email vali@uwyo.edu, haimov@uwyo.edu, leon@uwyo.edu Data Set Overview: This dataset is a subset of the Wyoming Cloud Radar (WCR) data. The WCR was mounted onboard the C130 in a downward looking configuration. Reflectivity and Doppler velocity were recorded for a nadir beam and a slanted beam. In this dataset the recorded data has been averaged to 1 sps, and only the data from the nadir beam is included. Investigators wanting the full-rate or dual-beam data should contact a member of the WCR group. The WCR was operated nearly continuously during the DYCOMS-II research flights (from July 10, 2001 to July 27, 2001.). However, there are small gaps in the radar data due starts/stops in the radar data recording (for changing the radar operating modes, keeping the file sizes manageable, or due to radar crashes). In addition, the WCR was generally not operated during the lowest of the subcloud legs. Combining the radar data with other measurements from the C130 should be done using the C130 data files and aligning the time stamps for each file. Instrument Description: The WCR is a 95Ghz Doppler radar. During DYCOMS-II the WCR was installed in a dual-beam configuration. Two 25 cm diameter antennas were used: one nadir-looking and the second pointed about 35 degrees back of nadir. The radar beams corresponding to these antennas are referred to as "nadir" and "trailing" respectively. Each beam had a beamwidth of approximately 0.7 degrees. A 250 ns pulse was used for the research legs. Pulses of either 250 ns or 500 ns were used for the inbound/outbound ferry legs. Generally a pulse repetition frequency of 5 kHz was used for the nadir beam and a 20 kHz prf was used for the trailing beam. These prfs result in unambiguous velocity widths of 7.9 m/s and 31.6 m/s. Additional technical information on the WCR can be found at http://www-das.uwyo.edu/wcr. Data Processing: There are a number of processing steps, as briefly summarized in the following. The WCR sends out pulses in bursts of four or six. The return signal is sampled at either 15 or 30 meter intervals. Between 50 and 100 (roughly) bursts of pulses are averaged by the WCR data acquisition system; this averaged return is referred to as a profile. The WCR data acquistion system records roughly 20 - 25 profiles per second (in the configurations used for DYCOMS). This 'raw' WCR data is first converted to NetCDF format. The C130 INS data is then used to compute the orientation of the radar beams in ground relative coordinates and to calculate the component of platform motion along the radar beams. The component of aircraft motion along the radar beams is then added to the measured Doppler velocities in order to convert the Doppler velocities into a ground-relative frame. For the low-rate datasets, such as this one, profiles within a given second are averaged. Finally, an estimate of the mean noise is subtracted from the received powers, which are then range corrected and converted to dBZ. Data Format: The data are stored in NetCDF format files with two key dimensions: "time" and "range". Time is not an unlimited dimension in these files. The key variables in these files are: base_time and time_offset -- which have the same meaning as in the C130 data. Note that the naming convention of the data files is "WppYY-MM-DD-HH-MM-SS.MODE.cdf" where YY,MM,DD,HH,MM,SS are the year, month, day, hour, minute, and second that the data file was started (slightly before the first actual data in the file). MODE is the mode of the file -- either 'PPmag' (most of the time) or 'PPmag6'. radar_range -- The range, in meters to the center of the radar gate. Znadir_1hz -- The measured reflectivity, in dbZ. This has been averaged for one second, the estimated noise has been subtracted and the remaining value corrected for range. Values less than the mean noise are set to a number equal to or smaller than the 'badvalue' of -999. nadir_noise1hz -- The estimated value of the mean noise converted to equivalent dBZ at 1km range. sig_nadir1hz -- The estimated standard deviation of the noise converted to equivalent dBZ at 1km. This variable is useful for thresholding the data when combined with the range correction -- 20*log10(radar_range/1000). vel_nadir_1hz -- The Doppler velocity for the nadir beam in m/s. Note that the sign convention is +ve upwards (i.e. in same direction as altitude). grndbeam_nadir_1hz -- A unit vector in ground-relative coordinates aligned along the center of the nadir beam. Useful for determining where the radar is pointing. acbeam_nadir_1hz -- The component of aircraft motion along the nadir beam. This amount has been added to the raw Doppler velocity to give the corrected (ground relative) velocity. windbeam_nadir_1hz -- The component of aircraft measured winds parallel to the nadir radar beam. This value is used to unfold the corrected Doppler velocity -- that is, the velocity is unfolded to between windbeam_nadir_1hz unambiguous velocity/2 to windbeam_nadir_1hz + unambiguous velocity/2. For DYCOMS-II this should eliminate most (if not all) folding problems. In the PPmag6 mode files, the velocities will have the numbers of the pulses (within the burst) appended after vel, thus the parameter names become vel45_nadir_1hz, vel56_nadir_1hz instead of vel_nadir_1hz. Remarks: The Doppler velocity data has been corrected for aircraft motion. This correction is accurate within, roughly, +-0.5 m/s with additional biases that vary from one leg of the flight to another. If the source of the bias in the Doppler velocity is determined then this data will be reprocessed. Also, because of the 2-3 degree roll of the aircraft the nadir beam Doppler velocity contains some component of the horizontal wind, depending on the aircraft heading relative to the wind. The magnitude of this component is normally not greater than 0.04 times the horizontal wind.