ARM-TR-073

> W-band ARM Cloud Radar (WACR) Handbook
>
> April 2006
>
> K. B. Widener
>
> K. Johnson
>
> Work supported by the U.S. Department of Energy,
>
> Office of Science, Office of Biological and Environmental Research

# Contents {#contents .Heading-Front}

[1 General Overview 1](#general-overview)

[2 Contacts 1](#contacts)

[3 Deployment Locations and History
2](#deployment-locations-and-history)

[4 Near-Real-Time Data Plots 2](#near-real-time-data-plots)

[5 Data Description and Examples 2](#data-description-and-examples)

[6 Data Quality 8](#data-quality)

[7 Instrument Details 9](#instrument-details)

# Figures {#figures .Heading-Front}

[1 Plots of copolarization and cross-polarization moments, both for the
SGP WACR. 6](#__RefHeading___Toc133910065)

[2 Plots of copolarization and cross-polarization moments from the AMF
WACR at Niamey. 7](#__RefHeading___Toc133910066)

# Tables {#tables .Heading-Front}

[1 WACR Deployment Locations and Dates 2](#__RefHeading___Toc133910099)

[2 WACR Data Stream Availability 2](#__RefHeading___Toc133910100)

[3 Primary Variables 3](#__RefHeading___Toc133910101)

[4 Secondary Variables 3](#__RefHeading___Toc133910102)

[5 Diagnostic Variables 4](#__RefHeading___Toc133910103)

[6 Dimension Variables 5](#__RefHeading___Toc133910104)

[7 WACR Operation Parameters 10](#__RefHeading___Toc133910105)

# General Overview

The W-band Atmospheric Radiation Measurement (ARM) Program Cloud Radar
(WACR) systems are zenith pointing Doppler radars that probe the extent
and composition of clouds at 95.04 GHz. The main purpose of this radar
is to determine cloud boundaries (e.g., cloud bottoms and tops). This
radar reports estimates for the first three spectra moments for each
range gate up to 15 km. The 0^th^ moment is reflectivity, the 1^st^
moment is radial velocity, and the 2^nd^ moment is spectral width. Also
available are the raw spectra files. Unlike the millimeter wavelength
cloud radar (MMCR), the WACR does not use pulse coding and operates in
only copolarization and cross-polarization modes.

# Contacts

## Mentor

Kevin Widener\
Pacific Northwest National Laboratory\
P.O. Box 999\
Richland, WA 99952\
Phone: 509-375-2487

Fax: 509-375-6736\
[kevin.widener@pnl.gov](../kevin.widener@pnl.gov)

Karen Johnson\
Environmental Sciences Department\
Brookhaven National Laboratory\
Upton, NY 11973\
Phone: 631-344-5952

Fax: 631-344-2060\
<kjohnson@bnl.gov>

## Instrument Developer

James Mead, President\
ProSensing, Inc.\
107 Sunderland Road\
Amherst, MA 01002\
Phone: 413-549-4402\
[mead@prosensing.com](mailto:Ken.Moran@noaa.gov)

# Deployment Locations and History

Table 1 displays the locations and status of each WACR.

  --------------------------------- -------------------- ------------------ ----------------
  []{#__RefHeading___Toc133910099                                           
  .anchor}**Table 1**. WACR                                                 
  Deployment Locations and Dates                                            

  **Location**                      **Date Installed**   **Date Removed**   **Status**

  SGP/C1                            07/01/2005                              Operational

  AMF/M1                            03/16/2006                              Operational
  --------------------------------- -------------------- ------------------ ----------------

The first WACR was installed at the Southern Great Plains (SGP) site in
the same shelter as the 35-GHz MMCR in July 2005. In early August, it
was removed from operation due to a problem with the transmitter.
Reinstallation occurred in December 2005. From late January until
mid-March 2006, the unit was redeployed to the ARM Mobile Facility (AMF)
site. A new WACR was installed at the SGP site in late March 2006. The
AMF WACR was first installed at Niamey in mid-March 2006.

# Near-Real-Time Data Plots

Near-real-time WACR data plots are available from the ARM DQHandS Plot
Browser, at <http://dq.arm.gov/plotbowser/>.

# Data Description and Examples

WACR moments data are available from the ARM Climate Research Facility
(ACRF) Data Archive in data stream "wacr."

Table 2 indicates which data streams are available at each site and time
period:

+--------------+---------------------------+--------------------------+
| []{#__R      |                           |                          |
| efHeading___ |                           |                          |
| Toc133910100 |                           |                          |
| .an          |                           |                          |
| chor}**Table |                           |                          |
| 2**. WACR    |                           |                          |
| Data Stream  |                           |                          |
| Availability |                           |                          |
+--------------+---------------------------+--------------------------+
| **Site**     | **Data Stream**           | **Date Range**           |
+--------------+---------------------------+--------------------------+
| SGP          | sgpwacrC1.b1              | 2005.07.01 -- 2005.07.19 |
|              |                           |                          |
|              |                           | 2005.12.13-- 2006.01.26  |
|              |                           |                          |
|              |                           | 2006.03.24 - Present     |
+--------------+---------------------------+--------------------------+
| NIM          | nimwacrM1.b1              | 2006.03.16 - Present     |
+--------------+---------------------------+--------------------------+

WACR spectra data are also collected continuously at each site.
Approximately 15 GB of raw spectra files are generated per day. Due to
the large volume of data collected, the disks containing spectra files
are mailed to the archive every few weeks so there is a delay in their
availability.

WACR spectra data are not in stored in NetCDF format, but rather in
binary data files. They consist of a header block, with general
information such as pulse repetition frequency, number of range gates,
number of fast Fourier transformation (FFT) points, etc. followed by
data values collected at each time. At each time, there are system
temperature measurements followed by the measured spectrum stored as an
*m* X *n* array, where *m* is the number of range gates and *n* is the
number of FFT points. Detailed information on reading the binary spectra
data format is available by emailing Karen Johnson at
<kjohnson@bnl.gov>.

## Data File Contents

### Primary Variables and Expected Uncertainty

Table 3 shows the primary quantities measured by the WACR for the wacr
data stream.

  --------------------------------- ----------------------------------- -----------------
  []{#__RefHeading___Toc133910101                                       
  .anchor}**Table 3**. Primary                                          
  Variables                                                             

                                    **wacr Data Stream**                

  **Variable**                      **Description**                     **Uncertainty**

  Reflectivity                      WACR Reflectivity (time, height),   0.5dB
                                    in dBZ                              

  MeanDopplerVelocity               WACR Mean Doppler Velocity (time,   0.1 m/s
                                    height), in m/s                     

  SpectralWidth                     WACR Spectral Width (time, height), 0.1 m/s
                                    in m/s                              
  --------------------------------- ----------------------------------- -----------------

The overall uncertainties for the primary quantities measured are as
follows:

-   Measurement accuracy: 0.5 dB over receiver dynamic range

-   Doppler resolution: less than 0.1 m/s.

#### Definition of Uncertainty

We define uncertainty as the range of probable maximum deviation of a
measured value from the true value within a 95% confidence interval.
Given a bias (mean) error *B* and uncorrelated random errors
characterized by a variance *σ^2^*, the root-mean-square error (RMSE) is
defined as the vector sum of these,

$\text{RMSE} = \left( B^{2} + s^{2} \right)^{\frac{1}{2}}$.

(*B* may be generalized to be the sum of the various contributors to the
bias and *σ^2^* the sum of the variances of the contributors to the
random errors). To determine the 95% confidence interval we use the
Student's *t* distribution: *t*~n;0.025~ ≈ 2, assuming the RMSE was
computed for a reasonably large ensemble. Then the *uncertainty* is
calculated as twice the RMSE.

### Secondary/Underlying Variables

Table 4 presents the secondary variables measured by the WACR.

  --------------------------------- ---------------------------------------
  []{#__RefHeading___Toc133910102   
  .anchor}**Table 4**. Secondary    
  Variables                         

  **wacr Data Stream**              

  **Variable**                      **Description**

  Polarization                      0=copol / 1=crosspol
  --------------------------------- ---------------------------------------

### Diagnostic Variables

Table 5 presents the diagnostic variables measured by the WACR.

+-------------------------------+--------------------------------------+
| []                            |                                      |
| {#__RefHeading___Toc133910103 |                                      |
| .anchor}**Table 5**.          |                                      |
| Diagnostic Variables          |                                      |
+-------------------------------+--------------------------------------+
| **wacr Data Stream**          |                                      |
+-------------------------------+--------------------------------------+
| **Variable**                  | **Description**                      |
+-------------------------------+--------------------------------------+
| PowerAmbientLoad              | Ambient load power in dBm            |
+-------------------------------+--------------------------------------+
| Power HotLoad                 | Hot load power in dBm                |
+-------------------------------+--------------------------------------+
| PowerTransmitDriver           | Transmit driver power sampled by     |
|                               | receiver in dBm                      |
+-------------------------------+--------------------------------------+
| txpower                       | Detected pulse (Watts)               |
+-------------------------------+--------------------------------------+
| wacr_status                   | Status flag                          |
+-------------------------------+--------------------------------------+
| Temp_ambient                  | Ambient temperature of radar front   |
|                               | end components (deg. C)              |
+-------------------------------+--------------------------------------+
| Temp_LNA                      | Low noise amplifier temperature      |
|                               | (deg. C)                             |
+-------------------------------+--------------------------------------+
| Temp_Hot                      | Hot load physical temperature (deg.  |
|                               | C)                                   |
+-------------------------------+--------------------------------------+
| Temp_EIKA                     | Extended Interaction Klystron        |
|                               | Amplifier temperature (deg. C)       |
+-------------------------------+--------------------------------------+
| Temp_modulator                | Modulator temperature (deg. C)       |
+-------------------------------+--------------------------------------+
| Temp_Chiller                  | Chiller reservoir temperature (deg.  |
|                               | C)                                   |
|                               |                                      |
|                               | (SGP only)                           |
+-------------------------------+--------------------------------------+
| Temp_Antenna_Top              | Antenna top temperature (deg. C),    |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Antenna_Bottom           | Antenna bottom temperature (deg. C)  |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Modulator_Control        | Modulator control temperature (deg.  |
|                               | C)                                   |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Future                   | For future use                       |
+-------------------------------+--------------------------------------+
| Temp_Outside                  | Outside temperature (deg. C)         |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Computer_Enclosure       | Computer enclosure temperature (deg. |
|                               | C)                                   |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Chiller_Supply           | Chiller supply temperature (deg. C)  |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Temp_Chiller_Return           | Chiller return temperature (deg. C)  |
|                               |                                      |
|                               | (AMF only)                           |
+-------------------------------+--------------------------------------+
| Noise                         | Calculated noise (dB)                |
+-------------------------------+--------------------------------------+

### Data Quality Flags

There are three data quality flags in the wacr data stream:

**qc_time**: Contains the results of quality checks on sample time. This
field has a value at each sample time. The qc_time values are calculated
by comparing each sample time with the previous time. In the table
below, Delta_time = t\[n\] -- t\[n-1\].

**qc_time**:

1 = Delta_time is within expected interval

> 2 = Delta_time is zero: Duplicate sample times

4 = Delta_time is greater than expected

8 = Delta_time is less than expected.

**qc_Reflectivity**: Contains the results of quality checks on
Reflectivity. This field has a value at each sample time and height. The
qc_Reflectivity values are calculated by comparing Reflectivity values
to reasonable maximum and minimum values. The value '0' indicates
acceptable Reflectivity values.

**qc_MeanDopplerVelocity**: Contains the results of quality checks on
MeanDopplerVelocity. This field has a value at each sample time and
height. The qc_MeanDopplerVelocity values are calculated by comparing
MeanDopplerVelocity values to reasonable maximum and minimum values. The
value '0' indicates acceptable MeanDopplerVelocity values.

QC flag values for the above two flags can be interpreted as follows:

0 = Value is within the valid range

1 = value is missing

2 = value is less than the valid minimum

4 = value is greater than the valid maximum

8 = value failed the valid delta check, relative to previous value.

### Dimension Variables

  --------------------------------- ---------------------------------------
  []{#__RefHeading___Toc133910104   
  .anchor}**Table 6**. Dimension    
  Variables                         

  **wacr Data Stream**              

  **Variable**                      **Description**

  alt                               Altitude, meters above mean sea level,
                                    of ground instrument is sited on

  base_time                         Base time for file, in seconds since
                                    1/1/1970 00:00:00 GMT

  heights                           Range heights in meters above mean sea
                                    level of data collection (center of
                                    radar sample volume)

  lat                               North latitude in degrees

  lon                               East longitude in degrees

  time                              Time offset in seconds from midnight on
                                    file's collection date

  time_offset                       Time offset in seconds from base_time
  --------------------------------- ---------------------------------------

Annotated Examples

Below are example plots of copolarization moments (reflectivity, mean
Doppler velocity, and spectral width) from the SGP WACR followed by
plots of cross-polarization moments, both for 20060411.

![](media/image1.png){width="4.389583333333333in"
height="4.0569444444444445in"}

![](media/image2.png){width="4.389583333333333in"
height="4.079861111111111in"}

[]{#__RefHeading___Toc133910065 .anchor}**Figure 1**. Plots of
copolarization (top) and cross-polarization (bottom) moments,\
both for the SGP WACR.

Next are plots from the AMF WACR at Niamey, first copolarization moments
followed by cross-polarization moments for 2006402:

![](media/image3.png){width="4.1in" height="3.8020833333333335in"}

![](media/image4.png){width="3.8895833333333334in"
height="3.779861111111111in"}

> []{#__RefHeading___Toc133910066 .anchor}**Figure 2**. Plots of
> copolarization (top) and cross-polarization (bottom) moments\
> from the AMF WACR at Niamey.

## User Notes and Known Problems

N/A

## Frequently Asked Questions

**What index of refraction for water is used to computer reflectivity
(Kw) at 95 GHz?**

0.84 at 95 GHz vs. 0.93 for 35 GHz

# Data Quality

## Data Quality Health and Status

The [Data Quality Office](http://dq.arm.gov/) website has links to
several tools for inspecting and assessing WACR data quality:

-   [[DQ HandS]{.underline}](http://dq.arm.gov/cgi-bin/dqmenu.pl) (Data
    Quality Health and Status)

-   [[DQ HandS Plot
    Browser]{.underline}](http://dq.arm.gov/plotbrowser/)

-   [[NCVweb]{.underline}](http://dq.arm.gov/ncvweb/ncvweb.cgi):
    Interactive web-based tool for viewing ARM data.

Plots of reflectivity, Doppler radial velocity, and Doppler spectral
width provide a good indicator of whether the system is operational or
not.

## Data Reviews by Instrument Mentor

Data reviews are done weekly. Monthly assessments will be provided here
in the future.

## Data Assessments by Site Scientist/Data Quality Office

All Data Quality Office and most Site Scientist techniques for checking
have been incorporated within [DQ HandS](http://dq.arm.gov/) and can be
viewed there.

## Value-Added Products and Quality Measurement Experiments

At present, no Value-Added Products or Quality Measurement Experiment
exist for the WACR.

# Instrument Details

## Detailed Description

### List of Components

The following is a list of components for the WACR:

-   CPI Extended Interaction Amplifier (EIKA)

-   Pulse Technology modulator

-   Antenna

-   Radio Frequency Section

-   Radar controller

-   Radar computer

-   Chiller

-   Uninterruptible Power Supply.

### System Configuration and Measurement Methods

The WACR system consists of the radar, data acquisition/control
subsystem, enclosures, cables, and accessories so that it will be
operable in a semi-autonomous mode. For the purposes of this
specification, semi-autonomous operation is defined as a mode wherein an
operator is required only to power up and power down the system. Once
powered up, the WACR will automatically enter a standby mode ready to
begin taking data.

### Specifications

**Radar specifications are as follows:**

+----------------------------------+-----------------------------------+
| Frequency                        | 95 GHz (Wavelength 3.16 mm, W     |
|                                  | band)                             |
+----------------------------------+-----------------------------------+
| Peak Transmitted Power           | 1500 W                            |
+----------------------------------+-----------------------------------+
| Maximum Duty Cycle               | 0.1%                              |
+----------------------------------+-----------------------------------+
| Antenna Diameter                 | SGP: 2 ft                         |
|                                  |                                   |
|                                  | AMF: 4 ft                         |
+----------------------------------+-----------------------------------+
| Antenna Gain                     | see table under Calibration       |
|                                  | History                           |
+----------------------------------+-----------------------------------+
| Beam Width (full-width,          | see table under Calibration       |
| half-maximum)                    | History                           |
+----------------------------------+-----------------------------------+
| PRF (max)                        | 20 kHz                            |
+----------------------------------+-----------------------------------+

**WACR Mode Sequence and Characteristics**

The WACR alternates between copolarization and cross-polarization modes
continuously. Table 7 gives operating characteristics at each site.

+------------------------------+-------------------+-------------------+
| []{                          |                   |                   |
| #__RefHeading___Toc133910105 |                   |                   |
| .anchor}**Table 7**. WACR    |                   |                   |
| Operation Parameters         |                   |                   |
+------------------------------+-------------------+-------------------+
| **Radar Parameter**          | **Site**          |                   |
+------------------------------+-------------------+-------------------+
|                              | **SGP**           | **AMF NIM**       |
+------------------------------+-------------------+-------------------+
| ####### Pulse Repetition Fre | 10000             | 10000             |
| quency (Hz) {#pulse-repetiti |                   |                   |
| on-frequency-hz .unnumbered} |                   |                   |
+------------------------------+-------------------+-------------------+
| Pulse Width (microsec)       | 0.3               | 0.3               |
+------------------------------+-------------------+-------------------+
| Gate Spacing (microsec)      | 0.143             | 0.143             |
+------------------------------+-------------------+-------------------+
| Number of Gates              | 348               | 348               |
+------------------------------+-------------------+-------------------+
| Spectral Averages            | 160               | 160               |
+------------------------------+-------------------+-------------------+
| FFT Length                   | 256               | 256               |
+------------------------------+-------------------+-------------------+
| Obs. / Processing Time       | 2.14              | 2.14              |
+------------------------------+-------------------+-------------------+
| Nyquist Velocity (m/s)       | 7.885             | 7.885             |
+------------------------------+-------------------+-------------------+

## Theory of Operation

The WACR works by transmitting a pulse of millimeter-wave energy from
its transmitter through the antenna. The energy propogates through the
atmosphere until it intercepts objects that reflect some of the energy
back to the WACR. These objects can be clouds, precipitation, insects,
spider webs, man-made objects, etc. The same antenna is used to receive
the return signal. The received signal is downconverted into an
intermediate frequency that is then fed to a digital receiver. A digital
receiver processes the signal and ultimately provides the radar spectra.
From the radar spectra, power, Doppler velocity, and spectral width are
calculated. The power measurement is processed by knowing the WACR's
calibration coefficient to provide the radar reflectivity.\
\
Looking at the meteorological radar range equation gives insight as to
how the WACR works and what parameters affect its sensitivity. Any
radar\'s sensitivity is proportional to the transmit power, the square
of the antenna gain, and the square of the radar's wavelength. The
sensitivity is inversely proportional to the square of the range from
the radar to the target.

## Calibration

### Theory

Several systems within the radar require calibration at regular
intervals. The values obtained from these calibrations are stored as
constants, polynomials, or curves in the calibration files or programs.
These are used by the software to convert raw radar moment files to
range-corrected power (dBm) and reflectivity (dBZ) data in netCDF format
and sent to the site data system.

### Procedures

N/A

### History

N/A

## Operation and Maintenance

N/A

### User Manual

N/A

### Routine and Corrective Maintenance Documentation

N/A

### Software Documentation

N/A

### Additional Documentation

N/A

## Glossary

See the [ARM Glossary](http://www.arm.gov/about/glossary.stm).

## Acronyms

AMF ARM Mobile Facility

ARM Atmospheric Radiation Measurement (Program)

EIKA Extended Interaction Klystron Amplifier

FFT fast Fourier transformation

Lidar Light Detection and Ranging

MMCR millimeter wave cloud radar

MMW Millimeter wave (30GHz - 300GHz)

MPL Micropulse LIDAR

NIM Niamey, Niger

NOAA National Oceanic and Atmospheric Administration

NSA North Slope of Alaska

QC quality control

RMSE root-mean-square error

SGP Southern Great Plains

TWP Tropical Western Pacific

WACR Wband ARM Cloud Radar

Also, see [ARM Acronyms and
Abbreviations](http://www.arm.gov/about/acronyms.stm).

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