5.1 Radar Systems  [Table of Contents]

5.1.1 NCAR S-Pol Research Radar

The NCAR S-Pol research radar is a polarimetric Doppler radar developed at NCAR/ATD. The radar system is designed to be transported to the research field campaign location. The entire system is packaged into standard sized sea containers that are used as the antenna support structure at the research site. The structure and pedestal are designed to work properly in winds up to 30 m/s. If needed, a CP-2 inflatable radome can be used to enclose the radar.

The S-Pol radar uses a high performance modern transmitter, low sidelobe parabolic antenna, modern dual channel receiver, and a NCAR designed VME data system. The transmitter, built by Westinghouse, is an ASR-9 based unit using an air-cooled klystron and produces a one-Megawatt, one-microsecond pulse. Polarization switching is accomplished using a NCAR built mechanical switch that provides 49 dB transmit isolation, which is comparable to a dual transmitter configuration. Dual receivers, each providing 40 dB isolation is required for cross-polar measurements. The 8.5 m reflector is a high compliance aluminum structure providing –30 dB first sidelobes and at least –35 dB integrated cross-polar isolation. Pulse pair and dual polarization processing is performed by a NCAR designed VME-based Integrated Radar Acquisition system (VIRAQ). The VIRAQ processor uses a dual range 90 dB digital IF system with multiple C44 DSP chips that are controlled by a 486 CPU host running DOS. Refer to Table 5.1 for a detailed list of component specifications.

Between 100-128 samples are need to obtain accurate, reliable polarimetric measurements. Thus, it is recommended to use a PRF of 960 Hz at a scan rate of 6 deg/sec.  This scan rate is needed to utilize the ground clutter filter.  

Table 5.1. Technical specifications for the NCAR S-Pol radar.

 
5.1.2 CSU-CHILL Research Radar   [Table of Contents]

The CSU-CHILL research radar is a portable polarimetric, Doppler radar system stationed at Colorado State University. The system is packaged into shipping crates and assembled similarly to the S-Pol radar. The antenna for the system is housed inside a CP-2 inflatable radome.

The CSU-CHILL radar utilizes modern dual transmitters, high performance parabolic antenna, dual receivers, and programmable signal processor. The transmitting system consists of two klystron-based transmitters, each producing ~1.0 megawatt, one microsecond pulse. The antenna is an 8.5 meter, parabolic antenna with a half-power beamwidth of one degree. The main beam and sidelobe patterns at horizontal and vertical polarizations are well matched. The matched dual receivers have noise power levels of approximately -115 dBm. Information processing is handled by a programmable Lassen SP20 signal processor and recorded to 8 mm Exabyte cassette tapes. See Table 5.2 for a detailed list of specifications.

Between 100-128 samples are need to obtain accurate, reliable polarimetric measurements. Thus, it is recommended to use a PRF of 960 Hz at a scan rate of 6 deg/sec.  This scan rate is needed to utilize the ground clutter filter and match well with the S-Pol radar measurements.

Table 5.2. Technical specifications for the CSU CHILL radar.

5.1.3 NWS WSR-88D Operational Weather Radar  [Table of Contents]

The WSR-88D (KHGX) radar stationed in League City, TX will provide continuous surveillance scans of the research area. These surveillance scans will consist of scans at a sequence of constant elevation angles of radar reflectivity and radial velocities. Because the radar is an operational radar, the scanning strategies for this radar are not controllable by the research team and limited to three Volume Coverage Patterns (VCPs). See Fig. 5.1 for a graphical representation of scanning levels for the three main VCPs. A data recorder will be installed at this facility during the field campaign.

VCP-11 is a precipitation mode that uses a short radar pulse giving a nominal 250 m range resolution. This mode has two surveillance scans for reflectivity and Doppler velocities. The slow rate of pulsing gives a 460 km unambiguous range and the fast rate of pulsing for a 150 km unambiguous range and high Nyquist or folding velocity exceeding 25 m/s. The fast pulse rate is used only in the low scan angles. The precipitation mode consists of 360-deg-in-azimuth scans at 14 elevation angles to obtain 5 minute updates of full volume scans. The lowest seven elevation angles are contiguous and the remaining steps between elevation angles exceed the nominal radar beamwidth of 0.95 deg, leaving some gaps in the vertical coverage.

VCP-21 is a very similar precipitation mode to the VCP-11 mode. This mode uses a short radar pulse giving a nominal 250 m range resolution. This mode has two surveillance scans for reflectivity and Doppler velocities. The slow rate of pulsing gives a 460 km unambiguous range and the fast rate of pulsing for a 150 km unambiguous range and high Nyquist or folding velocity exceeding 25 m/s. The fast pulse rate is used only in the low scan angles. The precipitation mode consists of 360-deg-in-azimuth scans at 9 elevation angles to obtain 6 minute updates of full volume scans. The lowest five elevation angles are contiguous and the remaining steps between elevation angles exceed the nominal radar beamwidth of 0.95 deg, leaving some gaps in the vertical coverage.

VCP-31 is a clear air mode and is used to detect early formation of convective precipitation, air mass discontinuities, and to obtain wind profiles. It uses a long pulse transmission at 5 elevation angles to obtain a 10 minute update rate. The long pulse is used to provide a greater sensitivity. There are separate surveillance and Doppler scans at the lowest three elevation angles.  

Fig. 5.1. Graphs depicting elevation versus distance from radar for different scan angles of the three different VCPs.

5.1.4 Radar Scanning Strategies  [Table of Contents]

The main priority is for the two research radars to conduct dual polarimetric, dual Doppler radar sampling. Both radars will be performing similar scans and integration times to obtain high quality polarimetric and Doppler measurements. The scanning strategy used by the radars needs to have both broad scale and fine scale measurements of the storm dynamics and microphysics. To achieve this goal a PPI-RHI scanning strategy, which toggles between PPI and RHI mode, will be used. This strategy consists of a ~5 minute storm volume scan across azimuthal sectors at a sequence of constant elevation angles (PPI). Following this, a ~2 min storm volume scan in the elevation angle direction at a sequence of constant azimuth angles (RHI) will be conducted. This will give a repeat cycle of ~7 min for a complete PPI-RHI scan sequence. This scan sequence will be repeated continuously except during aircraft penetrations.

The RHI scan will be focused on the storm section that is of primary interest. In this case, the primary interests would be updrafts and electrically active regions. This can be determined from radar, aircraft, electrical measurements, and field reports. Specific placement of the PPIs and RHIs will be determined with the help of scan optimizers and some "canned" scans determined before the start of the field study.

The NWS Doppler radar (KHGX) will be used for surveillance scans to keep track of the larger scale development of storms in the region. The data from KHGX will also be incorporated into the data set to allow triple Doppler analysis in certain areas of the study region. Additional near real time data from nearby NWS radars will also be available in the operations center for planning purposes.

5.2 Surface Mesonet Systems  [Table of Contents]

5.2.1 TNRCC Measurement Stations

The Texas Natural Resource Conservation Commission (TNRCC) maintains a set of surface air monitoring stations in southeast Texas. These stations are mainly for atmospheric pollution monitoring. There are approximately 40 stations with a majority of them in the Houston metro region. Figure 5.2 shows the location of most of the sites in southeast Texas. Figure 5.3 is the zoomed map of Houston showing the location of the various TNRCC monitoring stations. Each monitoring station does not measure the same atmospheric variables, but many measure trace gas concentrations or aerosol concentrations. The three variables that each station does measure include temperature, moisture, and horizontal wind. To obtain information on the variables monitored at each station, please refer to the following web address: http://www.tnrcc.state.tx.us/cgi-bin/monops/select_month?region12.gif.

TNRCC performs regular maintenance of all monitoring stations and performs thorough quality checks on all data. The data from the stations will be available from TNRCC as an archived set after the finish of the HEAT field campaign. The operations center can obtain access to rough data through TNRCC’s website if needed.  

Fig. 5.2. Map of southeast Texas showing the location of TNRCC air monitoring stations. Houston area denoted in yellow.  

Fig. 5.3. Close up map of Houston depicting the location of air monitoring stations. Houston urban area denoted in yellow.

5.3 Aircraft  [Table of Contents]
 
5.3.1 University of Wyoming King Air  [Table of Contents]

The University of Wyoming King Air aircraft is a research craft with several meteorological instrument packages for boundary-layer, turbulence/flux, cloud physics, and atmospheric chemistry studies. This craft is not armored like the T-28, thus is not capable of penetrating strong convective regions with hail. This craft is still capable of penetrating storms and taking microphysical measurements of various cloud and precipitation particles. The main measurements that will be taken are: pollution concentrations near sea breeze and over Houston and supercooled liquid water content. Table 5.4 is a listing of the instruments that will be included on the aircraft.

Table 5.4. Wyoming King Air instrument packages with instrument measurement range, accuracy, and resolution.