6.3 DOWs

6.3.1 Introduction

The University of Oklahoma's Doppler on Wheels (DOW) radars will gather data of high spatial and temporal resolution, for the study of orographic and lake-effect precipitation structure and kinematics.

The DOWs are pulsed, 3-cm wavelength, Doppler radars mounted on the back of small, flatbed trucks. The characteristics of each radar are described in Table X and also by Wurman et al. (1997). One DOW has been committed to IPEX for the entire duration of the project. The other DOW is scheduled to arrive in Salt Lake City on 5 February and be available thereafter for the collection of dual-Doppler radar data.

A DOW crew will consist of a radar operator and a scribe/driver (who must be a University of Oklahoma employee with a valid driver's license). Operators will be trained by the DOW technician or other qualified personnel. The scribe will make notes on truck orientation, the begin/end time of specific scan sequences, hardware or software problems, etc.

Besides the radar operations, each crew also will be responsible for three-hourly observations of snow depth at the DOW site. There are no time restrictions on crew duty (although some operational limitations are described below). However, if an IOP is expected to last more than 15-18 hrs, substitute crews will be shuttled to the sites.

Communication -- either DOW-to-DOW, for scan coordination, or DOW-to-Ops center, for operations updates -- will be via cell phone.
Frequency9.370 GHz9.380 GHz
Transmitter TypeMagnetron Magnetron
Peak Power250 kW250 kW
Pulse Length200-2000 ns 150-2000 ns
PRFup to 3200 Hz and staggered up to 5000 Hz and staggered
Nyquist Intervalup to 160 ms/ up to 160 m/s
Diameter2.44 m parabolic 2.44 m parabolic
Beam Width0.93 deg0.93 deg
Peak Scanning Rate30 deg/sec 50 deg/sec
PolarizationH or VH or V
Controller SoftwareNCAR SPOL NCAR SPOL
Noise Power
Min Det Sig @3 km
Min Det Sig @50 km
Dynamic Range
Bistatic CompatibleYes Yes
Clutter Filtering35 dB 35 dB
Data Acquisition
Gatesup to 1000up to 1000
Gate Lengthas low as 12 m as low as 12 m
Equivalent A/D bits14 14
Clutter Filtering35 dB 4 pole IIR 35 dB 4 pole IIR
Display ProductsV,Z,CZ,SW,NCP,P V,Z,CZ,SW,NCP,P
Recorded ProductsA,B,P A,B,P

Table X. Characteristics of the Doppler on Wheels radars.

6.3.2 Observations

The DOW observing sites have been determined with the following criteria in mind: road accessibility (which includes road surface type), terrain flatness, lack of radar-domain obstructions (trees, telephone and power lines, buildings, etc.), and appropriate dual-Doppler baseline and range to anticipated precipitation region.

Orographic precipitation experiments

North - south baseline of ~20-km length, with bisector distance (in eastern dual-Doppler lobe) to crest of Wasatch ~20 to 25 km.

1. Syracuse (southern site): Rt 108 west to lake edge; site in parking lot off south side of road.

2. West Weber (northern site): near intersection of Rt. 134 and Rt. 39 (N. 4700 West St. and W. 900 South St.; site off south(?) side of 900 South St..

3. West Warren (northern site): near intersection of 8300 West St. and 900 South St.; site off south(?) side of 900 South St. This is the preferred northern site if for scans of orographic and lake-effect precipitation (i.e., if 360° scans) are desired.

Lake-effect precipitation experiments

West-east baseline of ~20-km length, south of GSL, with dual-Doppler lobes extending ~40 km north and south of baseline

1. Saltair Resort (eastern site): near I-80 Exit 104; site in parking lot.

2. Great Salt Lake Marina (alternate eastern site)

3. "View area," near Mile-Marker 101, off I-80 (western site)

4. Stansbury Island, on road past gate (alternate western site)

An example of a radar-scan tilt sequence, suitable for the study of orographic precipitation (and complementing the along-barrier racetrack strategy; see below) is as follows:

0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, and 18°

in a 150° azimuthal sector. With an antenna rotation rate of 30° sec-1 (the maximum rate for DOW2), one volume scan can be collected in 1 min. When the across-barrier racetracks are flown (see below), full 360° scans will be necessary (to provide coverage in both dual-Doppler lobes), thus lengthening the volume-scan collection time to 2 min 24 sec for the tilt sequence above. Note that the 1° elevation steps between the first 7 tilts allows for relatively high resolution (nominally, 500 m in the vertical and horizontal) at altitudes below 2 km, within the ~25-km ranges of interest.

The lake-effect scanning sequences also will require 360° scans, since coverage in both dual-Doppler lobes likely will be necessary. These and the orographic volume-scan sequences can be adapted, as needed, from the example sequence above.

The radars can be operated in an RHI mode, which may be desirable at time when only one of the radars is available. Alternative vertical cross sections can be obtained with the radar(s) operating in vertically pointing mode and traveling down a flat highway (see Wurman et al. 1997).

6.3.3 Radar and truck operations

6.3.4 Post-event analysis

Wurman, J, J. Straka, E. Rasmussen, M. Randall, and A. Zahrai, 1997: Design and deployment of a portable, pencil-beam, pulsed, 3-cm Doppler radar. J. Atmos. Oceanic Technol., 14, 1502-1512.