DOE/SC-ARM/TR-033

> Surface Meteorology (SMET) Handbook
>
> M.T. Ritsche
>
> January 2009
>
> Work supported by the U.S. Department of Energy,
>
> Office of Science, Office of Biological and Environmental Research

**DISCLAIMER**

This report was prepared as an account of work sponsored by the U.S.
Government. Neither the United States nor any agency thereof, nor any of
their employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed,
or represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial product, process, or service
by trade name, trademark, manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or
favoring by the U.S. Government or any agency thereof. The views and
opinions of authors expressed herein do not necessarily state or reflect
those of the U.S. Government or any agency thereof.

# 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 10](#data-quality)

[7 Instrument Details 11](#instrument-details)

# Figures {#figures .Heading-Front}

[1 Induced voltage in the wind speed data.
7](#__RefHeading___Toc221603656)

[2 Sample data plot of ORG. 9](#__RefHeading___Toc221603657)

**Tables**

[1 Locations and history. 2](#__RefHeading___Toc221603658)

[2 Primary variables. 3](#__RefHeading___Toc221603659)

[3 Removed variables. 4](#__RefHeading___Toc221603660)

[4 Diagnostic variables. 4](#__RefHeading___Toc221603661)

[5 Quality control variables. 5](#__RefHeading___Toc221603662)

[6 Dimension variables. 6](#__RefHeading___Toc221603663)

[7 Dates coefficients were removed. 6](#__RefHeading___Toc221603664)

[8 Dates gauges were installed. 7](#__RefHeading___Toc221603665)

# General Overview

The TWP Surface Meteorology station (SMET) uses mainly conventional *in
situ* sensors to obtain 1‑minute statistics of surface wind speed, wind
direction, air temperature, relative humidity, barometric pressure and
rainfall amount.

# Contacts

## Mentor

Michael Ritsche\
Argonne National Laboratory\
9700 South Cass Avenue\
Argonne, IL 60439\
Phone: 630-252-1554\
Fax: 630-252-5498\
E-mail:
[mtritsche@anl.gov](http://www.arm.gov/instruments/static/mail to: mtritsche@anl.gov)

## Instrument Developer

Data Logger\
Campbell Scientific Inc.

815 W. 1800 N.

Logan, UT 84321

Phone: 801-753-2342

Fax: 801-750-9540

Web page: [http://www.campbellsci.com](http://www.campbellsci.com/)

Wind Monitor & Aspirated Radiation Shield\
R. M. Young Company

2801 Aero Park Drive

Traverse City, MI 49686

Phone: 231-946-3980

Fax: 231-946-4772

Web page: <http://www.youngusa.com/>

Temperature-Relative Humidity Probe & Digital Barometer\
Vaisala\
100 Commerce Way\
Woburn, MA 01801-1068\
Phone: 617-933-4500\
Fax: 617-933-8029

Web page: [http://www.vaisala.com](http://www.vaisala.com/)

Optical Raingauge\
Optical Scientific, Inc.\
205 Perry Parkway, Suite 14\
Gaithsburg, MD 20877-2141\
Phone: 301-948-6070\
Fax: 301-948-4674

Tipping Bucket Raingauge

McVan Instruments

58 Geddes Street

PO Box 298, Mulgrave

Victoria, Australia, 3170

Phone: (+61-3) 9582-7333

Fax: (+61-3) 9560-1164

Web page: [http://www.mcvan.com](http://www.mcvan.com/)

# Deployment Locations and History 

ARCS site C1 was installed on Manus Island, Papua New Guinea in October
1996.

ARCS site C2 was installed on the island of Nauru (republic) in November
1998.

ARCS site C3 was installed at Darwin, Australia in April 2002. In 2004
the data collection system was changed.

[]{#__RefHeading___Toc221603658 .anchor}Table 1. Locations and history.

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

  ARCS C1 Manus       08/2004                              Operational

  ARCS C2 Nauru       07/2004                              Operational

  ARCS C3 Darwin      05/2004                              Operational
  ------------------- ------------------ ----------------- ----------------

# Near-Real-Time Data Plots

Near-real-time data plots can be found at the following locations:

-   <http://www.nsdl.arm.gov/Visualization/quicklook_interface.shtml>

-   <http://www.nsdl.arm.gov/Visualization/ncvweb.shtml>.

# Data Description and Examples

## Data File Contents

### Primary Variables and Expected Uncertainty

[]{#__RefHeading___Toc221603659 .anchor}Table 2. Primary variables.

  --------------- ----------------------- ---------- --------------- --------------- ----------------
  **Quantity**    **Variable**            **Unit**   **Measurement   **Measurement   **Resolution**
                                                     Level**         Interval**      

  Precipitation   precip_mean             mm/hr      1m              1 min           0.1
  Mean                                                                               

  Precipitation   precip_max              mm/hr      1m              1 min           0.1
  Maximum                                                                            

  Precipitation   precip_min              mm/hr      1m              1 min           0.1
  Minimum                                                                            

  Tipping bucket  tbrg_total              mm         sfc             1 min           0.2
  raingauge total                                                                    

  Temperature     temp_mean               C          2m              1 min           0.1
  Mean                                                                               

  Relative        relh_mean               \%         2m              1 min           0.1
  Humidity Mean                                                                      

  Vapor pressure  vappress_mean           kPa        2m              1 min           0.1
  mean                                                                               

  Upper wind      up_wind_spd_arith_avg   m/s        10m             1 min           0.1
  speed                                                                              
  arithmetic                                                                         
  average                                                                            

  Upper wind      up_wind_spd_vec_avg     m/s        10m             1 min           0.1
  speed vector                                                                       
  average                                                                            

  Upper wind      up_wind_dir_vec_avg     deg        10m             1 min           1
  direction                                                                          
  vector average                                                                     

  Upper wind      up_wind_dir_sd          deg        10m             1 min           1
  direction                                                                          
  standard                                                                           
  deviation                                                                          

  Upper wind      up_wind_spd_max         m/s        10m             1 min           0.1
  speed maximum                                                                      

  Upper wind      up_wind_spd_min         m/s        10m             1 min           0.1
  speed minimum                                                                      

  Lower wind      lo_wind_spd_arith_avg   m/s        10m             1 min           0.1
  speed                                                                              
  arithmetic                                                                         
  average                                                                            

  Lower wind      lo_wind_spd_vec_avg     m/s        10m             1 min           0.1
  speed vector                                                                       
  average                                                                            

  Lower wind      lo_wind_dir_vec_avg     deg        10m             1 min           1
  direction                                                                          
  vector average                                                                     

  Lower wind      lo_wind_dir_sd          deg        10m             1 min           1
  direction                                                                          
  standard                                                                           
  deviation                                                                          

  Lower wind      lo_wind_spd_max         m/s        10m             1 min           0.1
  speed maximum                                                                      

  Lower wind      lo_wind_spd_min         m/s        10m             1 min           0.1
  speed minimum                                                                      

  Atmospheric     atmos_pressure          hPa        1m              1 min           0.1
  pressure                                                                           
  --------------- ----------------------- ---------- --------------- --------------- ----------------

The following variables were removed when the systems were changed to
the new data collection system. See *Deployment Locations and History*
for exact dates.

[]{#__RefHeading___Toc221603660 .anchor}Table 3. Removed variables.

  -------------- -------------- ---------- --------------- --------------- ---------------- ------------
  **Quantity**   **Variable**   **Unit**   **Measurement   **Measurement   **Resolution**   **Status**
                                           Level**         Interval**                       

  Temperature    temp_max       C          2m              1 min           0.1              Removed
  Maximum                                                                                   

  Temperature    temp_min       C          2m              1 min           0.1              Removed
  Minimum                                                                                   

  Relative       relh_max       \%         2m              1 min           0.1              Removed
  Humidity                                                                                  
  Maximum                                                                                   

  Relative       relh_min       \%         2m              1 min           0.1              Removed
  Humidity                                                                                  
  Minimum                                                                                   
  -------------- -------------- ---------- --------------- --------------- ---------------- ------------

#### Definition of Uncertainty

This definition should probably be included in a Definitions web page,
and only linked to from here.

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

This section is not applicable to this instrument.

### Diagnostic Variables

[]{#__RefHeading___Toc221603661 .anchor}Table 4. Diagnostic variables.

  --------------------------------- ---------------- --------------------
  **Quantity**                      **Variable**     **Measurement
                                                     Interval**

  Precipitation standard deviation  precip_sd        1 min

  Temperature standard deviation    temp_sd          1 min

  Relative Humidity standard        relh_sd          1 min
  deviation                                          

  Vapor pressure standard deviation vappress_sd      1 min
  --------------------------------- ---------------- --------------------

**Table 4**. (contd)

  --------------------------------- ------------------ --------------------
  Upper wind speed standard         up_wind_spd_sd     1 min
  deviation                                            

  Lower wind speed standard         lo_wind_spd_sd     1 min
  deviation                                            

  Internal Voltage                  internal_voltage   1 min

  Logger Temperature                logger_temp        1 min

  Tipping bucket raingauge count    tbrg_count_total   1 min
  total                                                
  --------------------------------- ------------------ --------------------

### Data Quality Flags

[]{#__RefHeading___Toc221603662 .anchor}Table 5. Quality control
variables.

+--------------------+-----------------------+------------+-----+-----+
| **Quantity**       | **Variable**          | **M        | *   | *   |
|                    |                       | easurement | *Mi | *Ma |
|                    |                       | Interval** | n** | x** |
+--------------------+-----------------------+------------+-----+-----+
| sample time        | qc_time               | 1 min      |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Precipitation mean | qc_precip_mean        | 1 min      | 0   | 500 |
+--------------------+-----------------------+------------+-----+-----+
| Precipitation      | qc_precip_max         | 1 min      | 0   | 500 |
| maximum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Precipitation      | qc_precip_min         | 1 min      | 0   | 500 |
| minimum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Tipping bucket     | qc_tbrg_total         | 1 min      | 0   | 10  |
| raingauge total    |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Temperature mean   | qc_temp_mean          | 1 min      | 0   | 50  |
+--------------------+-----------------------+------------+-----+-----+
| Relative Humidity  | qc_relh_mean          | 1 min      | 0   | 104 |
| mean               |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Upper wind speed   | qc_                   | 1 min      | 0   | 100 |
| arithmetic average | up_wind_spd_arith_avg |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Upper wind speed   | q                     | 1 min      | 0   | 100 |
|                    | c_up_wind_spd_vec_avg |            |     |     |
| vector average     |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Upper wind         | q                     | 1 min      | 0   | 360 |
| direction vector   | c_up_wind_dir_vec_avg |            |     |     |
| average            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Upper wind speed   | qc_up_wind_spd_max    | 1 min      | 0   | 100 |
| maximum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Upper wind speed   | qc_up_wind_spd_min    | 1 min      | 0   | 100 |
| minimum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Lower wind speed   | qc_                   | 1 min      | 0   | 100 |
| arithmetic average | lo_wind_spd_arith_avg |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Lower wind speed   | q                     | 1 min      | 0   | 100 |
|                    | c_lo_wind_spd_vec_avg |            |     |     |
| vector average     |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Lower wind         | q                     | 1 min      | 0   | 360 |
| direction vector   | c_lo_wind_dir_vec_avg |            |     |     |
| average            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Lower wind speed   | qc_lo_wind_spd_max    | 1 min      | 0   | 100 |
| maximum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Lower wind speed   | qc_lo_wind_spd_min    | 1 min      | 0   | 100 |
| minimum            |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+
| Atmospheric        | qc_atmos_pressure     | 1 min      | 850 | 1   |
| pressure           |                       |            |     | 030 |
+--------------------+-----------------------+------------+-----+-----+
| Tipping bucket     | qc_tbrg_count_total   | 1 min      | 0   | 50  |
| raingauge count    |                       |            |     |     |
| total              |                       |            |     |     |
+--------------------+-----------------------+------------+-----+-----+

### Dimension Variables

[]{#__RefHeading___Toc221603663 .anchor}Table 6. Dimension variables.

  -------------------- -------------- --------------- ----------------------------
  **Quantity**         **Variable**   **Measurement   **Unit**
                                      Interval**      

  Base time in Epoch   base_time      1 min           seconds since YYYY-mm-dd
                                                      XX:XX:XX X:XX

  Time offset from     time_offset    1 min           seconds since YYYY-mm-dd
  base_time                                           XX:XX:XX X:XX

  Time offset form     time           1 min           seconds since YYYY-mm-dd
  midnight                                            XX:XX:XX X:XX

  north latitude       lat            1 min           degrees

  east longitude       lon            1 min           degrees

  altitude             alt            1 min           meters above sea level
  -------------------- -------------- --------------- ----------------------------

## Annotated Examples

This section is not applicable to this instrument.

## User Notes and Known Problems

**Induced Voltage on Wind Speed Cable Caused Offsets in Wind Speed
Data**

The marine model of the RM Young wind sensor needs twisted pair shielded
cable. The manufacturer did not originally supply the pigtail with
twisted pair shielded cable. Use of twisted pair shielded cable for the
rest of the cable run to the logger was also not specified. This caused
an induced voltage in the wind speed line from the wind direction
excitation. The induced voltage varied from sensor to sensor and
probably changed anytime the cable was replaced or parts of the wind
sensor were repaired or replaced. The induced voltage has been seen to
vary from 0.15 m/s to as much as 1.08 m/s. To complicate matters until
2006 or 2007 depending upon site, the calibration coefficients of the
wind monitors included an offset. This offset would change with the
sensor. These offsets were not always captured until 2004 when the
System changed over to the Campbell Scientific dataloggers (see Table
1). The following table lists when the various sites stopped using the
sensor specific calibration coefficients.

[]{#__RefHeading___Toc221603664 .anchor}Table 7. Dates coefficients were
removed.

  ----------------------------------- -----------------------------------
  **Site**                            **Date coefficient removed**

  C1                                  09/26/06 @ 1438 GMT

  C2                                  09/26/06/ @ 1400 GMT

  C3                                  09/25/06 @ 1435 GMT
  ----------------------------------- -----------------------------------

The following is a plot of the wind speed and direction data showing the
induced offset caused by the excitation voltage of the wind direction at
TWP C3. This offset does NOT include any calibration coefficient offset.

![](media/image1.png){width="6.498611111111111in"
height="4.079166666666667in"}

[]{#__RefHeading___Toc221603656 .anchor}Figure 1. Induced voltage in the
wind speed data.

**Tipping Bucket Raingauges Added at Different Times**

Tipping bucket raingauges were added at each site at different times.
The following table lists the location and the date the gauge was
installed. Tipping bucket raingague data prior to the installation date
was filled with -9999.

[]{#__RefHeading___Toc221603665 .anchor}Table 8. Dates gauges were
installed.

  ----------------------------------- -----------------------------------
  **Site**                            **Date Installed**

  C1                                  10/16/2006

  C2                                  11/29/2006

  C3                                  09/26/2006
  ----------------------------------- -----------------------------------

**Incorrectly Listed Units for Vapor Pressure in Data Object Design**

The Data Object Design incorrectly listed the units of hPa for Vapor
Pressure. When the new collection system was installed at each site (see
Table 1) the units were actually reported in kPa.

**Naming Convention of the Two Wind Monitors**

The two wind monitors (speed & direction) are mounted such that one
sensor is slightly higher than the other to minimize interference. The
higher wind monitor is designated as sensor #1 or "hi" so that all data
streams associated with wind speed or direction that have a "1" or "hi"
in the name are from the higher of the two sensors. Any variables
associated with wind speed or direction that have a "2" or "lo" in the
name are from the lower of the two sensors.

**Error in Calibration Factors for Wind Speed at ARCS1 Manus**

Calibration factors between wind speed sensor C1 and C2 were reversed
causing a less than 1% error in recorded wind speeds. A correction
factor may be used. For sensor C1 (add) + .03 m/s and for sensor C2
(subtract) - .03 m/s. The errors in calibration factors were for data
from 10/25/1996 - 03/02/1999.

**Optical Rain Gauge (ORG) Reporting Values Less Than 0.1 mm/hr**

For the data prior to installation of the new data collection system the
following incorrect data was ingested. After installation of the new
collection system, this problem was corrected:

During normal operation, the sensor always puts out some voltage
(background noise), even during clear sky conditions. The rain rate
equation that is used to convert voltage to rain rate should only be
applied to voltages equal to or above a certain fixed threshold. This
threshold is different for each model (ORG-815 or ORG-115-DA mini-ORG).
At values below the fixed threshold the equipment will report small
values (some negative) at all times. Currently, the rain rate equation
is used for all voltages reported by the sensor. The rain rates that
correspond to voltages below the thresholds are between -0.1 mm/hr and
+0.1 mm/hr. Therefore, such values should be considered by the data user
to be 0 mm/hr. It is also possible that values between -0.15 mm/hr and
-0.1 mm/hr may be reported as a result of very low voltages. These
values should also be considered as 0 mm/hr. If values less than -0.15
mm/hr are reported then negative voltages are being used and this is an
indication of a problem with the sensor. These values should be
discarded. Any value equal to and above 0.1 mm/hr that are reported are
good values since positive voltages above the thresholds are being
reported and the rain rate equation is valid.

**Optical Rain Gauges Upgraded at Sites C1 and C2**

The Optical Rain Gauges (ORG) at Manus site C1 and Nauru site C2 were
the older model ORG-115. At Darwin site C3 the ORG is the model ORG-815.
For the sake of consistency and due to problems with the aging models
the ORGs at Manus and Nauru were upgraded to the ORG-815 models. Due to
changes and upgrades the rain rate calculation is different for the
ORG-815 and the ORG-115. See the section **System Configuration and
Measurement Methods** for the different formulas used.

Nauru site C2 was upgraded on 12/14/2004.

Manus site C1 was upgraded on 01/19/2005.

**Optical Rain Gauges Reporting Values less that 0.2 mm/hr**

The Optical Rain Gaures make continuous measurements. They are sampled
once a second and the 1-sec values are averaged each minute. Very small
values resulting from dust, dirt, insects are sometimes included in the
averaged values. These values can be recognized when the average
precipitation rate for a minute is less than 0.01 mm/hr. Any value less
than that should be removed from study. Future reprocessing tasks will
remove those from the data record. More importantly it has been
determined that values between 0.01 mm/hr and 0.2 mm/hr are not
necessarily precipitation. Instead values less than 0.2mm/hr likely
represent fog and/or haze and individuals should view the data
critically before assuming all values are precipitation. The below plot
shows the typical response of the ORG to fog situations. However, it
should be noted that the fog may not be visually present and it is
possible that the ORG is responding to the moisture content of the air
during high RH situations.

![](media/image2.png){width="5.950694444444444in"
height="4.988888888888889in"}

[]{#__RefHeading___Toc221603657 .anchor}Figure 2. Sample data plot of
ORG.

## Frequently Asked Questions

This section is not applicable to this instrument.

# Data Quality

## Data Quality Health and Status

Data Quality Health and Status (DQ HandS)
[http://dq.arm.gov](http://dq.arm.gov/)

NCVweb - for interactive data plotting using
<http://dq.arm.gov/ncvweb/ncvweb.cgi>

## Data Reviews by Instrument Mentor

The Instrument Mentor (Michael Ritsche) performs a number of tasks to
assure the quality of AMFMET data. Data quality control procedures for
this system are considered **mature**.

-   **QC frequency**: Weekly

-   **QC delay**: Real-time; weekly

-   **QC type**: Min/max/delta flags; graphical plots; mentor reviews

-   **Inputs**: Collected data

-   **Outputs**: Monthly Mentor Reports, DQR, BCR, ECO, PIF, DQPR (as
    needed)

-   **Reference**: None

Standard AMFMET data are subject to several levels of quality control
and quality assurance. When the data are collected each variable has
various automated QC checks that look for values outside defined
max/min/delta. Any variable outside these parameters are flagged in the
QC variable. The mentor recieves weekly reports, called Data Quality
Assessment Reports (DQAR) from the DQ Office and reviews them for
problems. Any problems listed in the weekly DQAR's are checked and spot
checks are also performed to verify the DQAR's are accurate.

## Data Assessments by Site Scientist/Data Quality Office

The ARM Data Quality Office uses the Data Quality Assessment (DQA)
system to inform the ARM Site Operators, Site Scientists, and Instrument
Team members of instrument and data flow problems as well as general
data quality observations. The routine assessment reports are performed
on the most recently-collected ARM data, and used with the Data Quality
Problem reports tool to initiate and track the problem resolution
process.

<http://dq.arm.gov/weekly_reports/weekly_reports.html>

## Value-Added Procedures and Quality Measurement Experiments

Many of the scientific needs of the ARM Program are met through the
analysis and processing of existing data products into \"value-added\"
products or VAPs. Despite extensive instrumentation deployed at the ARM
CART sites, there will always be quantities of interest that are either
impractical or impossible to measure directly or routinely. Physical
models using ARM instrument data as inputs are implemented as VAPs and
can help fill some of the unmet measurement needs of the program.
Conversely, ARM produces some VAPs not in order to fill unmet
measurement needs, but instead to improve the quality of existing
measurements. In addition, when more than one measurement is available,
ARM also produces \"best estimate\" VAPs. A special class of VAP called
a Quality Measurement Experiment (QME) does not output geophysical
parameters of scientific interest. Rather, a QME adds value to the input
datastreams by providing for continuous assessment of the quality of the
input data based on internal consistency checks, comparisons between
independent similar measurements, or comparisons between measurement
with modeled results, and so forth. For more information, see the [VAPs
and QMEs](http://www.arm.gov/data/vaps_all.php) web page.

# Instrument Details

## Detailed Description

### List of Components

**Wind speed and direction sensors**: A pair of propeller anemometers
and wind vanes, R. M. Young Model 05106 Wind Monitors.

**Temperature and relative humidity sensor**: Platinum RTD and RH,
Vaisala Model HMP45

D Temperature and Relative Humidity Probe.

**Barometric pressure sensor**: Digital barometer, Vaisala Model
PTB201A.

**Precipitation:**

[Optical Raingauge]{.underline}: Optical Scientific, Inc. Model
ORG-115-DA MiniOrg or ORG-815-DA MiniOrg.

Tipping Bucket Raingauge: RIMCO 7499 Series.

**Data logger**: Campbell Scientific, Inc. Model CR23X.

### System Configuration and Measurement Methods

The SMET sensors are mounted on a 10-meter mast, except for the rain
gauge.

The wind monitor propeller anemometers produce a magnetically controlled
AC output whose frequencies are proportional to the wind speed. The Wind
Monitor direction vanes drive potentiometers, which are part of
resistance bridges.

Two Wind Monitors are mounted on a cross-arm at a height of 10 m. One is
mounted slightly above the other in order to minimize interference. The
higher wind monitor is designated sensor #1 and the lower wind monitor
is designated sensor #2.

The T-RH probe 4-lead, platinum resistance thermometer is part of a
resistance bridge. The Vaisala RH circuitry produces a voltage that is
proportional to the capacitance of a water vapor absorbing, thin polymer
film. The T-RH probe is mounted in an R. M. Young Model 43408 Gill
Aspirated Radiation Shield at a height of 2 m.

The barometric pressure sensor uses a silicon capacitive pressure sensor
and is housed in an enclosure along with the data logger.

The optical precipitation gauge detects scintillation of an infrared
beam caused by liquid water in the path. It is located near the tower.
The following equations are used to convert the voltage signal to a
rainrate.

For the ORG-815:

Rainrate (mm/hr) = (25\*(V^1.87^) -- 0.15

For the ORG-115:

Rainrate (mm/hr) = (20\*(V^2^) -- 0.05

The tipping bucket raingauges is a siphon controlled tipping bucket
raingauge. It is designed and constructed for long-term operation with
minimal maintenance required. Any rain falling on the 203mm collecting
funnel is directed through a siphon control unit and discharges as a
steady stream into a two compartment bucket mounted in unsable
equilibrium. As each compartment fills the bucket tilts anternately
about its axis. Each tip forces a momentary contact closure by magnetic
means. The datalogger senses each contact closure and applies 0.2 mm for
each contact closure. At site C3 the raingauge is connected only to the
SMET system and is only part of the SMET system. At sites C1 and C2 the
raingauge is connected to the Bureau of Australina Meteorology (BoM)
Automated Weather Station (AWS) and also the SMET systems at each site.
The raingauges as sites C1 and C2 belong to the AWS system and not to
the SMET system.

The CR23X data logger measures each input once per second except for
barometric pressure, which is measured once per minute, and logs 1-min
averaged data. Vapor pressure is computed from the air temperature and
relative humidity. The data logger produces 1-min averages, minimums,
maximums, and standard deviations of wind speed, air temperature,
relative humidity, and rain rate. It also produces 1-min vector-averaged
wind speed and direction, a 1-min standard deviation of the wind
direction computed by an algorithm, 1-min averages and standard
deviations of vapor pressure, and a reading of the barometric pressure,
logger panel temperature, and the internal supply voltage.

### Specifications

**Wind speed at 10 m**: Precision: 0.01 m/s; Uncertainty: +/-2% for 2.5
to 30 m/s (see *Assessment of System Uncertainties for Primary
Quantities Measured* for wind speeds below 2.5 m/s).

**Wind direction at 10 m**: Precision: 0.1 deg; Uncertainty: +/-5 deg.

**Air temperature at 2 m**: Precision: 0.01 C; Uncertainty: +/-0.57 C.

**Relative humidity at 2 m**: Precision: 0.1% RH; Uncertainty: +/-2.06%
RH (0% to 90% RH), +/-3.04% RH (90% to 100% RH).

**Barometric pressure at 1 m**: Precision: 0.01 kPa; Uncertainty:
+/-0.035 kPa.

**Precipitation**:

**Optical Raingauge:** Precision: 0.1 mm/hr; Uncertainty: +/-0.1 mm/hr.

**Tipping Bucket Raingauge:** Precision: 0.2 mm; Uncertainty +/- 0.2 mm
(unknown during strong winds).

**Overall Uncertainties for Primary Quantities Measured**

All SMET uncertainty analyses are based on manufacturer\'s
specifications. Manufacturers specify accuracies in several ways. Some
give absolute range of error, some give uncertainties as defined above,
while others give rms errors. In this analysis, rms errors are
multiplied by 2. This results in confidence limits of approximately 95%.

**Data Acquisition Errors**

The Campbell Scientific, Inc CR23X datalogger A-D converter accuracy is
+/- 0.025% FSR for 0 -- 40 C, +/- 0.05% FSR --25 to 50 C, +/- 0.075% FSR
--40 to 80 C. The clock accuracy is +/- 1 minute per month --25 to 50 C,
+/- 2 minutes per month --40 to 80 C. The LoggerNet software checks the
clock of the logger once per day and adjusts it if it off by more than 2
seconds. The computer continuously maintains time synchronization with a
GPS based time reference using the NTPD protocol. The GPS based
reference is local to each site.

For the system initially installed, the Coastal Environmental Systems
ZENO-3200 A-D converter accuracy is +/-0.05% of full-scale range. The
time base accuracy is +/-0.005%. The Site Data System checked the
time-of-day clock once per day and corrected the logger clock if it is
off by more than a minute.

**Wind Speed**

The calibration uncertainty is specified as +/-2% for wind speeds from
the sensor threshold to 30 m/s. The conversion error is negligible. The
schedule of routine maintenance and sensor verification is designed to
eliminate any long-term stability error.

The sensor threshold is specified as 1 m/s. The following estimates of
the range of underestimation caused by the threshold assume a normal
distribution of wind speeds about the mean. When the true wind speed is
1.0 m/s, the winds will be below the threshold 50% of the time. This
will result in an underestimate of 0.5 m/s. When the true wind speed is
1.5 m/s, assuming the standard deviation will be between 0.25 and 1.00
m/s, the winds will be below the threshold between 2 and 31% of the
time. This will result in an underestimate between 0.02 and 0.23 m/s.
When the true wind speed is 2.0 m/s with a range of standard deviations
between 0.25 and 1.00 m/s, the winds will be below the threshold between
0 and 16% of the time. This will result in an underestimate between 0
and 0.12 m/s.

If the reported wind speed is 0.5 m/s, an underestimate of 0.5 is
probable. This would bias the measurement by -0.5. If the reported wind
speed is 1.0 m/s, an underestimate of 0.19 to 0.30 m/s is possible. If
the reported wind speed is 1.5 m/s, an underestimate of 0.02 to 0.20 m/s
is possible. If the reported wind speed is 2.0 m/s, an underestimate of
0 to 0.10 m/s is possible.

The uncertainty range with 95% confidence is approximately:

> +/- 2% for a reported wind speed from 2.5 to 30.0 m/s
>
> -0.12 to +0.02 m/s for a reported wind speed of 2.0 m/s
>
> -0.22 to +0.00 m/s for a reported wind speed of 1.5 m/s
>
> -0.31 to -0.20 m/s for a reported wind speed of 1.0 m/s
>
> -0.51 to -0.49 m/s for a reported wind speed of 0.5 m/s

**Wind Direction**

The sensor accuracy is specified as +/-3 deg. The A-D conversion
accuracy is equivalent to 0.7 deg over a temperature range of 0 to 40
deg C for a period of one year. I have estimated sensor alignment to
true north to be accurate within +/-3 deg. The uncertainty with 95%
confidence is, therefore, approximately +/-5 deg.

**Temperature**

The accuracy of the temperature measurement is +/-0.4 C. The long-term
stability is not known. The radiation error of the aspirated radiation
shield is specified as +/-0.2 C rms. The uncertainty with 95% confidence
of temperature sensors in this radiation shield is, therefore, +/- 0.57
C.

**Relative Humidity**

The accuracy of the RH sensor is specified as +/-2% RH for 0 to 90% RH,
and +/-3% RH for 90 to 100% RH. Errors considered in this accuracy are
calibration uncertainty, repeatability, hysteresis, temperature
dependence, and long-term stability over a period of one year. The A-D
conversion accuracy is equivalent to +/-0.5% RH, which is negligible.

**Barometric Pressure**

The manufacturer\'s technical data contains an uncertainty analysis.
Errors included in their analysis are linearity, hysteresis, calibration
uncertainty, repeatability, temperature dependence, and long-term
stability over a period of one year. Because the sensor has a digital
output, no conversion error occurs in the data logger. The specified
uncertainty with 95% confidence is +/-0.035 kPa. Note that the pressure
behaves anomalously during rain events - even very mild ones. Normally,
the pressure undergoes a smooth semi-diurnal oscillation with little
higher frequency variability. However, during and shortly after rain
events, the pressure signal exhibits abrupt changes until the collection
system was changed from the Zeno loggers in a pressure sealed container
to the Campbell Scientific loggers in a fiberglass enclosure. See Table
1 for dates when the Campbell loggers were installed.

**Precipitation/Rainfall Rate**

The Optical raingauge has an uncertainty of +/-0.1 mm/hr. Values that
fall between -0.1 mm/hr and +0.1 mm/hr should be considered 0 mm/hr. In
other words, no rainfall is occurring. See the *User Notes* *and Known
Problems* section for a more comprehensive explanation.

The tipping-bucket rain gauge produces a pulse output. The data logger
counts the pulses for the period of integration. The uncertainty is,
therefore, a minimum of one full bucket or 0.2 mm. For rain rates up to
250 mm/hr the manufacturer states the accuracy is +/- 1% and for
rainrates above 250 mm/hr up to 500 mm/hr the manfacturer states the
accuracy is +/- 3%.

During heavy rain or strong, gusty winds, the collection efficiency is
reduced. Manufacturers have not attempted to specify accuracies for
these conditions.

## Theory of Operation

Each of the primary measurements of wind speed, wind direction, air
temperature, relative humidity, barometric pressure, and rate of
rainfall are intended to represent self-standing data streams that can
be used independently or in combinations. The theory of operation of
each of these sensors is similar to that for sensors typically used in
other conventional surface meteorological stations. Some details can be
found under *System Configuration and Measurement Methods* but further,
greatly detailed description of theory of operation is not considered
necessary for effective use of the data for these rather common types of
measurements. The instrument mentor or the manufacturers can be
contacted for further information.

## Calibration

### Theory

The SMET\'s are not calibrated as systems. The sensors and the data
logger (which includes the A-D converter) are calibrated separately. All
systems are installed using components that have a current calibration.
RESET personnel check the sensor and data logger calibrations in the
field by comparison to calibrated references. Any sensor or data logger
that fails a field check is returned to the manufacturer for
recalibration. The Wind Monitors are returned to the manufacturer for
recalibration after two years of use.

### Procedures

Wind speed calibration is checked by rotating the propeller shaft at a
series of fixed rpm\'s using an R. M. Young Model 18810 Anemometer
Drive. The reported wind speeds are compared to a table of expected
values and tolerances. If the reported wind speeds are outside the
tolerances for any rate of rotation, the sensor is replaced by one with
a current calibration.

Wind direction calibration is checked by using a vane angle fixture, R.
M. Young Model 18212, to position the vane at a series of angles. The
reported wind directions are compared to the expected values. If any
direction is in error by more than 5 degrees, the sensor is replaced by
one with a current calibration.

Air temperature and relative humidity calibrations are checked by
comparison with a reference Vaisala Model HMI31 Digital Relative
Humidity and Temperature Meter and HMP35 Probe and a YSI 4600 Precision
Thermometer. If the reported temperature and relative humidity vary by
more than the sensor uncertainty from the reference, the probe is
replaced by one with a current calibration.

Barometric pressure calibration is checked by comparison with a
reference Vaisala PA-11 Barometer. If the reported pressure varies by
more than the sensor uncertainty from the reference, the sensor is
replaced by one with a current calibration.

The data logger A-D converter is checked by using a Valhalla 2707A
Programmable Precision DC Voltage/Current Standard as an input voltage
reference or they are sent in to the manufacturer for checks and repair.

### History

> [ARCS C1]{.underline}
>
> -10/8/1996 system installed
>
> -04/25/1998 Field Calibration Check
>
> -05/01/1998 Field Calibration Check.
>
> -03/10/1999 Field Calibration Check. Upper wind sensor replaced.
>
> -08/12/1999 T/RH probe replaced.
>
> -04/02/2000 Field Calibration Check.
>
> -04/06/2000 T/RH probe replaced.
>
> -10/21/2001 Field Calibration Check. T/RH probe was replaced.
>
> -10/16/2002 Field Calibration Check. Lower wind sensor and T/RH probe
> replaced.
>
> -12/12/2003 Field Calibration Check.
>
> -08/02/2004 Datalogger changed.
>
> -08/07/2004 Barometer replaced.
>
> -08/09/2004 Barometer replaced.
>
> -11/04/2004 Field Calibration Check.
>
> -01/20/2005 ORG-115 upgraded to ORG-815.
>
> -06/15/2006 Lower wind sensor replaced.
>
> -10/14/2006 Field Calibration Check. Upper wind sensor replaced.
>
> -06/11/2007 Cr23X datalogger 7115 installed.
>
> [ARCS C2]{.underline}
>
> -11/20/1998 System installed.
>
> -03/14/1999 Upper wind sensor replaced.
>
> -08/10/1999 Field Calibration Check.
>
> -07/01/2000 Field Calibration Check.
>
> -01/20/2001 T/RH probe replaced.
>
> -05/11/2001 Field Calibration Check. T/RH probe replaced.
>
> -10/31/2001 Field Calibration Check
>
> -11/01/2001 T/RH probe replaced.
>
> -09/15/2002 Field Calibration Check. T/RH probe replaced.
>
> -02/07/2003 T/RH probe replaced.
>
> -08/14/2003 Both wind sensors replaced.
>
> -09/17/2003 Field Calibration Check.
>
> -04/24/2004 Lower wind sensor replaced.
>
> -07/08/2004 Barometer replaced and Datalogger changed.
>
> -12/13/2004 ORG-115 upgraded to ORG-815.
>
> -03/03/2005 Upper wind sensor replaced.
>
> -04/17/2005 Upper wind sensor replaced.
>
> -07/15/2005 T/RH probe replaced.
>
> -09/19/2005 Field Calibration Check.
>
> -06/15/2006 T/RH probe replaced.
>
> -11/30/2006 Field Calibration Check.
>
> -12/01/2006 Lower wind sensor and barometer replaced.
>
> -01/23/2007 barometer replaced Y1330002 installed.
>
> [ARCS C3]{.underline}
>
> -04/01/2002 System installed.
>
> -08/22/2002 Field Calibration Check.
>
> -03/11/2003 T/RH probe replaced.
>
> -07/22/2003 Field Calibration Check.
>
> -05/17/2004 Barometer(V044001) replaced and Datalogger(5964) changed.
>
> -09/07/2004 Field Calibration Check.
>
> -08/09/2005 Field Calibration Check.
>
> -11/16/2005 T/RH probe replaced. Upper wind sensor replaced.
>
> -11/23/2005 ORG replaced.
>
> -04/27/2006 Lower wind sensor replaced.
>
> -05/18/2006 ORG replaced.
>
> -09/06/2006 Field Calibration Check.
>
> -04/20/2007 CR23X #5972 installed.

## Operation and Maintenance

### User Manual

This section is not applicable to this instrument.

### Routine and Corrective Maintenance Documentation

See the following links:

-   <http://www.twppo.lanl.gov/internal/pages/operations_manus.html>

-   <http://www.twppo.lanl.gov/internal/pages/operations_nauru.html>

-   <http://www.twppo.lanl.gov/internal/pages/operations_darwin.html>.

### Software Documentation

See <http://science.arm.gov/tool/dod/showdod.php?Inst=smet>.

### Additional Documentation

See <http://www.twppo.lanl.gov/internal/pages/operations.html>.

## Glossary

Barometric pressure - Local station pressure measured at the SMOS
station at a height of 1 m.

Precipitation - All forms of water meteors.

Relative humidity - Percentage of saturated vapor pressure at the
specified temperature.

Vector-averaged wind speed - Wind speed computed as the vector sum of
the orthogonal u and v components that are computed for each one-second
sample of wind speed and direction. The wind directions reported by the
SMOS are determined from the vector-averaged winds.

Wind Monitor - Trade name for R. M. Young propeller anemometer and wind
vane.

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

## Acronyms

A-D: Analog to Digital converter

RH: Relative Humidity

SGP: Southern Great Plains

SMOS: Surface Meteorological Observation System

T-RH: Temperature-Relative Humidity

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

## Citable References

None.