TITLE:  Profiler/Sodar ABLE Wind Profilers (915 MHz) [ABLE] 


Richard L. Coulter - ER 203
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439

Voice: 630 252-5833
Fax: 630 252-5498
Email: rl_coulter@anl.gov


This data set contains hourly profiles of wind speed and direction from
the Atmospheric Boundary Layer Experiments (ABLE) 915 MHz Radar Wind
Profilers operated by the Argonne National Laboratory in the Walnut River 
Watershed in Butler County Kansas (east of Wichita).  Both high and low
power data are included in this data set.  During the IHOP period three
915 MHz wind profilers were in operation.  Data cover the period from 13 
May to 25 June 2002 The data are in ASCII format.


2.1  Instrumentation

The ABLE 915 MHz radar wind profiler with RASS: Three of these profiler 
systems are deployed within the ABLE region. Profiler locations are 
Whitewater, Oxford, and Beaumont, KS. 

General Purpose
The radar wind profiler/RASS (RWP) measures wind profiles from (nominally)
0.1 km to 5 km and virtual temperature profiles from 0.1 km to 2.5 km. It 
operates by transmitting electromagnetic energy into the atmosphere and 
measuring the strength and frequency of backscattered energy. Virtual 
temperatures are recovered by transmitting an acoustic signal vertically and
measuring the electromagnetic energy scattered from the acoustic wavefront.
The propogation speed of the acoustic wave is proportional to the square 
root of the virtual temperature. 

Primary Quantities Measured with System
The primary quantities measured with the system are the intensity and Doppler
frequency of backscattered radiation. The wind speed is determined from the 
Doppler frequency of energy scattered from refractive index fluctuations 
(caused primarily by moisture fluctuations but also by temperature 
fluctuations) embedded within the atmosphere; the virtual temperature is 
determined from the Doppler frequency of microwave energy scattered from 
acoustic energy propogating through the atmosphere. 

Detailed Description
List of Components
The 915 MHz radar wind profiler is manufactured by Radian Corp. It consists 
of a single-phased microstrip antenna array consisting of either four 
(Whitewater and Oxford) or nine (Beaumont) "panels". The antenna is 
approximately 2 or 4 m square and is oriented in a horizontal plane so the
"in-phase" beam travels vertically. Other components in the system include 
four stationary acoustic sources located at the corners of the antenna, a 
receiver, an interface module, and a computer for data analysis and processing. 

Description of System Configuration and Measurement Methods
The radar wind profilers operate by transmitting in two different vertical 
planes and receiving backscattered energy from refractive index fluctuations 
that are moving with the mean wind. By sampling in the vertical direction and 
in two tilted planes, the three components of motion can be determined. The 
Beaumont and Whitewater systems consist of a single phased array antenna that 
transmits alternately along five pointing directions: one vertical, two in the 
north-south vertical plane (one south of vertical, one north of vertical), and 
two in the east-west vertical plane (one east of vertical, one west of 
vertical). The non-vertical beams are tilted at about 23 degrees from vertical.
The Oxford system has only three pointing directions (one south of vertical, 
one west). Radial components of motion along each pointing direction are 
determined sequentially. It takes, nominally, 30 - 45 seconds (dwell time) to 
determine the radial components from a single pointing direction. Thus, at 
the Beaumont and Whitewater sites the system cycles through five beams (South,
North, East, West, and vertical) at low power, and then cycles the five beams
again at a high power (longer pulse length) setting. Then the whole process 
is repeated. About five minutes elapse before the system returns to the 
beginning of its sequence. Within an averaging interval, the estimates from 
each beam-power combination are saved (11-12 in a 1-hr period) and these 
values are examined and compared at the end of the period to determine the 
consensus-averaged radial components of motion. The Oxford system is slightly
different. When operating in multipower mode it averages in the low power mode 
for 25 minutes, then in the high power mode for 25 minutes. 

Briefly, consensus averaging consists of determining if a certain percentage
(e.g., 50%) of the values fall within a certain range of each other 
(e.g., 2 m/s). If they do, the median of those values is used to produce the 
radial wind estimate. The radial values are then combined to produce the wind 
profile. The results of this averaging process are what are reported in the 
".cnw" data files produced by the ABLE data system. Included in these files 
are height, speed, direction, radial components, # values in consensus, and 
signal-to-noise ratio (SNR). 

During a single time period during which the system operates in a single 
pointing direction (dwell time), the data that is produced in the ".mod" and 
".spd" files is created. The system transmits pulses at about 1-10 kHz rate 
into the atmosphere.  The backscatter from each transmit pulse is sampled at,
for example, a 1 MHz rate. This results in 1 sample every 150 m in range. The
samples at each range gate are averaged together (time domain integration) 
over some number (e.g., 100) of pulses to produce a phase value for input 
into a FFT. After (e.g., 64) values are produced, the FFT is performed (one 
for each range gate). This process takes on the order of 1 sec. A number 
(about 30) of these spectra are then averaged together during the dwell time.
At the end of the dwell time we have produced a single averaged spectrum from
each range gate along the designated pointing direction. The spectra 
themselves are placed in the ".spd" data files. 

The spectra are analysed by the system before moving to the next pointing 
direction. This analysis produces estimates of the snr, the noise, the mean 
velocity (proportional to frequency), and the first moment (spectral width) 
at each range gate. This is the information that is stored in the ".mod" data
files. Both the ".mod" and ".spd" data files thus have information at about 
(dwell time) intervals; however, the data sequences among pointing directions 
and output powers. 

A note of warning about the mean values in the ".mod" files. The values are 
in % of full scale times 100, where full scale is the nyquist velocity of 
the spectrum. Thus, velocity estimates are determined by multiplying the 
"mdf" column times the full-scale bandwidth and dividing by 10,000. 

RASS operation is essentially the same, except that the averaging time is 
about 10 minutes and only a single pointing direction (vertical) is used. 
Also, the atmosphere is "seeded" with a sound wave; the index of refraction 
changes created by the sound wave are the signal source. In order to sample 
both the sound wave (speed about 340 m/s) and the atmosphere (to remove air
velocity from temperature estimates) a larger FFT is required (2048 points).
This requires a smaller number of points for each time domain integration 
and increases the processor time required to calculate the FFT. The ".spd"
files again are spectra; however, only a portion of the spectra are 
reported, namely a region near 0 Doppler shift to account for atmospheric 
motions and a region around the expected speed of sound. The ".mod" files 
now consist of moments and widths from both the atmospheric portion of the 
spectrum and from the acoustic portion (the main contributor to the 
temperature calculation). The ".cnt" files consist of profiles of 
temperature and number of consensus values. 

In normal operation, temperature profiles are determined during the first 
10 minutes of every hour and the wind profile is averaged over the remaining 
50 minutes. To hear a sound clip of the RASS acoustic signal click here (264KB). 

2.2  Station Locations

                  UTM km (Zone 14)
Site              99 deg Meridan       DEG     dddmmmsss  ddmm.mm   Alt (m)
Beaumont, KS      4167.1 UTMN km       37.627  37 37' 38" 37 37.64'  478
                   717.2 UTME km       96.538  96 32' 19" 96 32.32'

Oxford, KS        4126.7 UTMN km       37.273  37 16' 25" 37 16.41'  360
                   668.8 UTME km       97.095  97 05' 45" 97 05.75'

Whitewater, KS    4189.5 UTMN km       37.841  37 50' 26" 37 51.43'  416
                   659.6 UTME km       97.186  97 11' 10" 97 11.16'

For file names the station IDs are as follows:

Beaumont   be
Oxford     ox
Whitewater wh

Topo maps and aerial photos are available at:


UCAR/JOSS conducted no processing or quality control on these data.


4.1  Data Format

These data are in ASCII format.

Wind Profile File Format:

Line    Description
----    -----------
1       Station
2       Version
3       N_ Lat W_Long Site_elevation_meters
4       yr mo da hr mi sc minutes_to_add_for_UT 
5       Ave_time_min Number_of_beams Number_of_range_gates
6       Samples_required_for_consensus:Total_samples (consensus_window_size-m/s) 
7       Number_of_coherent_averages
8       Full-scale_Doppler_velocity_m/s 
        Vertical_correction_for_oblique_beams <0=N, 1=Y>
9       Azimuth elevation 
11      Range_gate_height_AGL_km
End     $ 

All times are UTC.

4.2  File Naming conventions

        wh is the station ID (here Whitewater)
        low is the power level (either low or high)
        02 is the year (2002)
        06 is the month (June)
        02 is the day of the month




ABLE Home Page: gonzalo.er.anl.gov/ABLE/index.html