The chill radar facility

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THE CHILL RADAR FACILITY: A DESCRIPTION

E. A. Mueller and J. L. Vogel Climate and Meteorology Section

Illinois State Water Survey 2204 Griffith Drive

Champaign, Illinois 61820

March 1988

(The CHILL radar is a National Science Foundation facility)

Table of Contents

INTRODUCTION

TRANSMITTER AND ANTENNA SYSTEM

RECEIVER

ANTENNA-RADAR CONTROLLER

DATA PROCESSING AND RECORDING SP20 Signal Processor SKY320 and MicroVax I MicroVax II Display Controller Recording Format

DISPLAY SYSTEMS ADAGE 3000 Display System TI-990 Display System

USER VAN AND RADAR TRAILER

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THE CHILL RADAR FACILITY: A DESCRIPTION

E. A. Mueller and J. L. Vogel

INTRODUCTION The CHILL radar system was designed and developed jointly by the University of CHicago and the ILLinois State Water Survey from 1968 to 1970. CHILL is a transportable, dual-wavelength (3 and 10 cm), dual polarization, Doppler radar. Between 1971 and 1983 the CHILL Radar Facility was used in many meteorological projects in East Central Illinois and in other locations in the United States. From 1971 though 1983 the CHILL radar had been moved 24 times and had taken data at 7 locations. By 1981 some of the components were becoming unreliable. In particular, the data processor was showing signs of wear and tear as a result of the many moves and the large number of weatherrelated projects which the CHILL had served. A Workshop was convened in 1983 by the National Science Foundation (NSF) to determine the desirability of refurbishing the CHILL. The feeling of the Workshop was that a need existed for a research radar like the CHILL. As a result, in 1984 the NSF awarded a 5year Cooperative Agreement to the Illinois State Water Survey and the University of Illinois to refurbish, upgrade, and operate the CHILL radar as a National Facility. The following is a description of the CHILL system as configured in 1988. The CHILL is designed so that the user can control the antenna scan mode and manage the displays. Some of the general operational characteristics of the CHILL are given in Table 1.

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TABLE 1. OPERATIONAL CHARACTERISTICS OF THE CHILL RADAR SYSTEM

Parameter

10-cm Channel

3-cm and 10-cm Channel

3-cm Channel

Antenna

Shape

Diameter

Half-Power

Beamwidth

Cain

First Side Lobe Level

Polarization

Azimuthal Antenna Rotation Rate

Antenna Controller PPI Capability Sector Scan with Variable Limits Azimuthal Sample Spacing Elevation Increment RHI

Transmitter Wavelength Frequency Peak Power** Pulse Width Pulse Repetition Time-Equispaced* Maximum Unambiguous Range Maximum Unambiguous Velocity

Receiver Noise Figure Transfer Function Dynamic Range** Band Width 3 dB Min. Detectable Signal (SNR=1)**

Parabolic 8.5 m .96 43.3 dB -25 dB Horizontal and vertical on pulse to pulse basis

30 ?/s

Yes

Yes Unlimited Unlimited Yes

10.7 cm 2.73 GHz 1 Mw 0.25, 0.5, or 1.0 ?m

800-2500 ?s 375 Km ?36.4 m/s

4.0 dB linear 90 dB Varies with P.W

-110

Polarization twist Cassegrain feed 2.5 m 1.0 39 dB -30 Horizontal

Same

3.2 cm 9.375 GHz

100 kw 1 usec (150 m) 1056/1230 us

13 dB logarithmic 55 dB 1.2 MHz -98 dBm

Data Acquisition No. of Range Gates Range Cate Spacing Recorded Word Length Velocity Width Intensity Ground Clutter Canceller Number of Samples in Estimate

Tape Recording Format

Tape Density Block Length

Initial Variables Available*** Reflectivity Horizontal Polarization Vertical Polarization Cross Polarization**** Differential Velocity (from pulse pair algorithm) Width (from 2nd lag pulse pair algorithm) Correlation functions with lags of 1 Normalized Coherent power Doppler Spectra from FFT processing

1024-4096 0.25, 0.5, 1.0 ?s 8 bits (2's comp) 8 bits (binary) 8 bits (binary)

Not decided Arbitrary

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

1024-4096 1 ?s

8 bits (binary) No

Arbitrary

Almost Universal Recording

6250 cpi 8192

Yes Yes No No No

No

No

No No

No

* ** *** ****

A pulse repetition staggering is possible permitting larger unambigious ranges Representative value Other variables or variants of these variables can be obtained by reprogramming of the preprocessor With accuracy reservations

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TRANSMITTER AND ANTENNA SYSTEM

The transmitter (figure 1) is essentially the same as the FPS-18 system obtained from the U. S. Air Force with some modernization. The original vacuum-tube, high-voltage rectifiers in the FPS-18 transmitter have been replaced by silicon rectifiers. Also, the rectifiers in the 5,000 volt power supply have been replaced by silicon rectifiers. These changes provide more reliable operations.

A charging diode has been added to the pulse forming network in the FPS-18 transmitter. This allows the pulse repetition time (PRT) to vary from 800 ?s to 2500 ?s, and the PRF from 1200 Hz to 400 Hz without large changes in the amplitude of the transmitting pulse. Software controls provide for a sequence of different PRT's which can vary from pulse to pulse. This feature allows multiple-PRT integration cycles which avoids range ambiguity, while maintaining a high Nyquist velocity. Changes in the PRT are made by the antenna-radar controller in steps of 16 ?s.

The radio frequency chain preceding the transmitter tube (figure 2) is now controlled by a crystal. This provides a more stable local oscillator (STALO) than was possible in the original FPS-18 configuration. The new radio frequency chain allows pulse width to be variable, with sizes of 1/4, 1/2, and 1 ?s. These intervals provide radial resolutions of 37.5, 75, or 150 m. A radial resolution of 37.5 m is obtainable if both the pulse width and receiver resolutions are set to 1/4 ?s.

After the signal is transmitted, it passes through the waveguide and the switchable circulator. The transmission is through a Potter-type dualpolarization horn and is horizontal polarization, or when the polarization switch is activated alternates between horizontal and vertical polarization.

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