ARM TR-030

> Temperature, Humidity, Wind, and Pressure System (THWAPS) Handbook
>
> January 2005
>
> 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 5](#data-quality)

[7. Instrument Details 6](#instrument-details)

**Tables**

[Table 1. 2](#__RefHeading___Toc94663135)

[Table 2. 2](#__RefHeading___Toc94663136)

[Table 3. 3](#__RefHeading___Toc94663137)

[Table 4. 4](#__RefHeading___Toc94663138)

[Table 5. 4](#__RefHeading___Toc94663139)

# General Overview

The temperature, humidity, wind, and pressure systems (THWAPS) provide
surface reference values of these measurements for balloon-borne
sounding system (BBSS) launches. THWAPS are located adjacent to BBSS
launch sites at the Southern Great Plains (SGP) Central Facility and its
four boundary facilities. The THWAPS system is a combination of
calibration-quality instruments intended to provide accurate
measurements of meteorological conditions near the surface. Although the
primary use of the system is to provide accurate surface reference
values of temperature, pressure, relative humidity (RH), and wind
velocity for comparison with radiosonde readings, the system includes a
data logger to record time series of the measured variables.

The THWAPS system is not generally used as a surface meteorological
measurement system. Many of the variables measured do not conform to WMO
standards for surface meteorological measurements. Instead, the THWAPS
system is used to gather reference values for the Balloon Borne Sounding
System (BBSS) at the SGP ACRF sites.

# Contacts

## Mentor

Michael T. Ritsche

Scientific Associate

Argonne National Laboratory

Bldg. 203

Argonne, IL 60439

Phone: (630) 252-1554

Fax: (630) 252-5498

Email: <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

Website: [http://www.campbellsci.com](http://www.campbellsci.com/)

**Aspiration Radiation Shields and Wind Speed/Direction Sensors**

R. M. Young Company

2801 Aero Park Drive

Traverse City, MI 49686

Phone: (231) 946-3980

Fax: (231) 946-4772

Website: <http://www.youngusa.com/>

**Barometer and Temperature/Relative Humidity Probe**

Vaisala

100 Commerce Way

Woburn, MA 01801-1068

Phone: (617) 933-4500

Fax: (617) 933-8029

Website: [http://www.vaisala.com](http://www.vaisala.com/)

# Deployment Locations and History 

THWAPS is located at the SGP site in Oklahoma at the following SGP
facilities:

[]{#__RefHeading___Toc94663135 .anchor}Table 1.

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

  B1-Hillsboro, KS        1998/04/16                      operational

  B4-Vici, OK             1998/04/17                      operational

  B5-Morris, OK           1998/04/21                      operational

  B6-Purcell, OK          1998/04/20                      operational

  C1-Lamont, OK           1996/09/10                      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___Toc94663136 .anchor}Table 2.

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

  Pressure          pres           hPa        1 m             5 min           0.1

  Temperature       temp           C          1 m             5 min           0.1

  RH                RH             \%         1 m             5 min           1

  Vapor Pressure    vap_pres       kPa        1 m             5 min           0.001

  Mean Wind Speed   wspd           m/s        5 m             5 min           0.1
  ----------------- -------------- ---------- --------------- --------------- ----------------

+----------------+----------+-------+-----------+-----------+---------+
| **Table 2.     |          |       |           |           |         |
| (cont'd)**     |          |       |           |           |         |
+----------------+----------+-------+-----------+-----------+---------+
| **Quantity**   | **Va     | **U   | **Me      | **Me      | **Resol |
|                | riable** | nit** | asurement | asurement | ution** |
|                |          |       | Level**   | I         |         |
|                |          |       |           | nterval** |         |
+----------------+----------+-------+-----------+-----------+---------+
| Unit Vector    | wdir     | deg   | 5 m       | 5 min     | 1       |
|                |          |       |           |           |         |
| Wind Direction |          |       |           |           |         |
+----------------+----------+-------+-----------+-----------+---------+
| Standard       | sd_wdir  | deg   | 5 m       | 5 min     | 1       |
| Deviation of   |          |       |           |           |         |
| Wind Direction |          |       |           |           |         |
+----------------+----------+-------+-----------+-----------+---------+

#### 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

None.

### Diagnostic Variables

[]{#__RefHeading___Toc94663137 .anchor}Table 3.

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

  Standard Deviation of Pressure  sd_pres              5 min

  Standard Deviation of           sd_temp              5 min
  Temperature                                          

  Standard Deviation of Relative  sd_rh                5 min
  Humidity                                             

  Standard Deviation of Vapor     sd_vap_pres          5 min
  Pressure                                             

  Battery Voltage                 vbat                 5 min
  ------------------------------- -------------------- ------------------

### Data Quality Flags

Quality Check Results on:

[]{#__RefHeading___Toc94663138 .anchor}Table 4.

  ---------------------------------------------------------------------------------------
  **Quantity**           **Variable**     **Measurement   **Min**   **Max**   **Delta**
                                          Interval**                          
  ---------------------- ---------------- --------------- --------- --------- -----------
  Sample Time            qc_time          5 min                               

  Pressure               qc_pres          5 min           800       1100      n/a

  Temperature            qc_temp          5 min           -40       50        n/a

  Relative Humidity      qc_rh            5 min           -2        104       n/a

  Vapor Pressure         qc_vap_pres      5 min           0         10        n/a

  Mean Wind Speed        qc_wspd          5 min           0         45        n/a

  Unit Vector Wind       qc_wdir          5 min           0         360       n/a
  Direction                                                                   

  Standard Deviation of\ qc_sd_wdir       5 min           0         90        n/a
  Wind Direction                                                              

  Standard Deviation of  qc_sd_pres       5 min           0         N/A       n/a
  Pressure                                                                    

  Standard Deviation of  qc_sd_temp       5 min           0         2         n/a
  Temperature                                                                 

  Standard Deviation of\ qc_sd_rh         5 min           0         20        n/a
  Relative Humidity                                                           

  Standard Deviation of\ qc_sd_vap_pres   5 min           0         N/A       n/a
  Vapor Pressure                                                              

  Battery Voltage        qc_vbat          5 min           9.6       16        n/a
  ---------------------------------------------------------------------------------------

### Dimension Variables

[]{#__RefHeading___Toc94663139 .anchor}Table 5.

+---------------------+-------------+-----------+---------------------+
| **Quantity**        | *           | **Me      | **Unit**            |
|                     | *Variable** | asurement |                     |
|                     |             | I         |                     |
|                     |             | nterval** |                     |
+---------------------+-------------+-----------+---------------------+
| Base time in Epoch  | base_time   | 5 min     | seconds since       |
|                     |             |           | YYYY-mm-dd          |
|                     |             |           |                     |
|                     |             |           | XX:XX:XX X:XX       |
+---------------------+-------------+-----------+---------------------+
| Time offset from    | time_offset | 5 min     | seconds since       |
| base_time           |             |           | YYYY-mm-dd          |
|                     |             |           |                     |
|                     |             |           | XX:XX:XX X:XX       |
+---------------------+-------------+-----------+---------------------+
| Time offset form    | time        | 5 min     | seconds since       |
| midnight            |             |           | YYYY-mm-dd          |
|                     |             |           |                     |
|                     |             |           | XX:XX:XX X:XX       |
+---------------------+-------------+-----------+---------------------+

  ---------------------- -------------- --------------- ----------------------
  **Table 5. (cont'd)**                                 

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

  north latitude         lat            5 min           degrees

  east longitude         lon            5 min           degrees

  Altitude               alt            5 min           meters above sea level
  ---------------------- -------------- --------------- ----------------------

NOTE: lat/lon/alt refers to the ground where the instrument is sited,
NOT the height of the sensor.

## Annotated Examples

None.

## User Notes and Known Problems

Currently, the THWAPS systems at the four boundary facilities (BF 1, 4,
5, and 6) have incorrect multipliers in the Datalogging program and
incorrect calibrations in the Vaisala electronics and data display. The
systems at these sites will not record RH% values greater than 100%.

The boundary facility calibrations and datalogging program were changed
on the following dates to correct for the incorrect claibrations and
multipliers on:

B1 on 08/01/2005 @ 2034 GMT

B4 on 07/30/2005 @ 1722 GMT

B6 on 07/30/2005 @ 2355 GMT

B5 on 07/31/2005 @ 1714 GMT

The program correction was made to the vapor pressure multiplier from
.2241 to .2441. This error in multiplier only translates to an error of
0.01 kPa which is well within the uncertainty of the sensor.

The calibration error forced the probe to output a maximum of 1V
translating to 100%. This did not allow the sensor to overrange as is
possible with this sensor and accuracy. Removal of this artificial
ceiling will allow for an increased ability to determine a failing
sensor.

## Frequently Asked Questions

None.

# 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

None.

## 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 Atmospheric Radiation Measurement
(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 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
to fill unmet measurement needs, but 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. Instead, a QME adds value to the
input data streams 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 web page at <http://www.arm.gov/data/vaps.stm>.

# Instrument Details

## Detailed Description

### List of Components

**Wind speed and direction sensor:** Propeller anemometer and wind vane,
R.M. Young Model 05103 Wind Monitor

**Temperature and relative humidity sensor:** Vaisala HMP233 Series
Transmitters

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

**Data logger:** Campbell Scientific Model CR10 Measurement & Control
Module and Model SM716 Storage Module, Precision: A function of input
type and range, Uncertainty: 0.2% of Full-Scale Range for Analog Inputs.

### System Configuration and Measurement Methods

The THWAPS system is intended to be used as a ground reference point for
radiosonde launches. Therefore, displays are required for the radiosonde
operators in addition to the data logger. The temperature and relative
humidity (T/RH) sensor is mounted at a height of 1 m. The analog outputs
(i.e., T/RH) of the display module are connected to digital displays
mounted in the BBSS trailer. The PTB201 barometer is also located in the
trailer and is vented to the outside. The wind monitor is mounted on a
mast on the BBSS trailer at a height of 5 m.

The wind monitor propeller anemometer produces a magnetically controlled
AC output whose frequency is proportional to the wind speed. The Wind
Monitor direction vane drives a potentiometer, which is part of a
resistance bridge.

The T/RH sensor head is mounted in an R.M. Young Model 43408 Gill
Aspirated Radiation Shield. The T/RH electronics, power, and display
module (HMP233) is mounted in an enclosure nearby. The temperature RTD
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 barometric pressure sensor uses a silicon capacitive pressure sensor
and is housed in a weatherproof enclosure along with a data logger, a
storage module, and serial communications equipment; all are mounted at
a height of 1 m.

The data logger measures each input once every 3 s. The vapor pressure
is computed from the air T/RH. The data logger produces 5-min averages
of wind speed, vector-averaged wind speed, vector-averaged wind
direction, air temperature, RH, vapor pressure, and barometric pressure.
The standard deviations of wind direction, temperature, RH, barometric
pressure, and vapor pressure are also calculated.

### Specifications

**Wind speed at 5 m**, Precision: 0.01 m/s; Uncertainty: +/-1% for 2.5
to 30 m/s

**Wind direction at 5 m**, Precision: 0.1°; Uncertainty: +/-5°

**Air temperature at 1 m**, Precision: 0.01 C; Uncertainty: a function
of wind speed

**RH at 1 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

**Data Acquisition Errors**

The Campbell Scientific CR10 A/D converter accuracy is +/-0.2 % of
full-scale range. The time base accuracy is +/-1 min per month, or about
23 ppm. The Site Data System checks the time-of-day clock once per day
and corrects the THWAPS clock if it is off by more than a minute.

**Wind Speed**

The National Institute of Standards and Technology (NIST) calibration
uncertainty is specified as +/-1% 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:

  --------------------- -------------------------------------------------
  +/- 1%                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°. The Analog to Digital
Converter (A/D) conversion accuracy is equivalent to +/- 0.7° over a
temperature range of 0 to 40°C for a period of one year. The sensor
alignment to true north has been estimated to be accurate within +/-3°.
The uncertainty with 95% confidence is, therefore, approximately +/-5°.

**Temperature**

The accuracy of the temperature measurement is specified as +/-0.4 C.
Included in this accuracy are sensor interchangeability, bridge resistor
precision, and polynomial curve fitting errors. 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 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.

The uncertainty with at least 95% confidence is, therefore,

  -----------------------------------------------------------------------
  +/-2.06 % RH, 0 to 90 % RH

  +/-3.04 % RH, 90 to 100 % RH
  -----------------------------------------------------------------------

**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 Campbell data logger.

The specified uncertainty with 95% confidence is +/-0.035 kPa.

## Theory of Operation

The THWAPS system is a combination of calibration-quality instruments
intended to provide accurate measurements of meteorological conditions
near the surface. Although the primary use of the system is to provide
accurate surface reference values of temperature, pressure, RH, and wind
velocity for comparison with radiosonde readings, the system includes a
data logger to record time series of the measured variables.

## Calibration

### Theory

The THWAPs have not been calibrated. Work is in progress on creating a
6-month calibration procedure.

### Procedures

This section is not applicable to this instrument.

### History

This section is not applicable to this instrument.

## Operation and Maintenance

### User Manual

This section is not applicable to this instrument.

### Routine and Corrective Maintenance Documentation

This section is not applicable to this instrument.

### Software Documentation

ARM netCDF file header descriptions may be found for THWAPS at
http://science.arm.gov/tool/dod/showdod.php?Inst=thwaps.

### Additional Documentation

This section is not applicable to this instrument.

## Glossary

**Barometric pressure:** Local station pressure measured at the THWAPS
station at a height of 1 m.

**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 which are computed for each
three-second sample of wind speed and direction. The wind directions
reported by the THWAPS are determined from the vector-averaged winds.

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

See the ARM Glossary at <http://www.arm.gov/about/glossary.stm>.

## Acronyms

AC alternating current

A/D Analog to Digital converter

BBSS balloon-borne sounding system

DQA Data Quality Assessment

NIST National Institute of Standards and Technology

QME Quality Measurement Experiment

RH Relative Humidity

rms root mean square

SGP Southern Great Plains

THWAPS Temperature, Humidity, Wind, and Pressure System

T/RH temperature/relative humidity (sensor)

VAP value-added product

Also see the ARM Acronyms and Abbreviations at
<http://www.arm.gov/about/acronyms.stm>.

## Citable References

None.