DOE/SC-ARM/TR-031

> Surface Meteorological Observation System (SMOS) Handbook
>
> March 2008
>
> 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 3](#near-real-time-data-plots)

[5. Data Description and Examples 3](#data-description-and-examples)

[6. Data Quality 9](#data-quality)

[7. Instrument Details 10](#instrument-details)

# Tables {#tables .Heading-Front}

[Table 1. 2](#__RefHeading___Toc94685941)

[Table 2. 3](#OLE_LINK2)

[Table 3. 5](#__RefHeading___Toc94685943)

[Table 4. 6](#__RefHeading___Toc94685944)

Table
5.....................................................................................................................7

Table
6.....................................................................................................................7

Table
7.....................................................................................................................8

# General Overview

The Surface Meteorological Observation System (SMOS) mostly uses
conventional in situ sensors to obtain 1-minute, 30-minute, and
1440-minute (daily) averages of surface wind speed, wind direction, air
temperature, relative humidity (RH), barometric pressure, and
precipitation at the Central Facility and many of the extended
facilities of the Southern Great Plains (SGP) climate research site. The
SMOSs are not calibrated as systems. The sensors and the data logger
(which includes the analog-to-digital converter, or A/D) are calibrated
separately. All systems are installed using components that have a
current calibration. SMOSs have not been installed at extended
facilities located within about 10 km of existing surface meteorological
stations, such as those of the Oklahoma Mesonet.

The Surface Meteorological Observation Systems are used to create
climatology for each particular location, and to verify the output of
numerical weather forecast and other model output. They are also used to
"ground-truth" other remote sensing equipment.

![](media/image1.png){width="2.265972222222222in"
height="3.089583333333333in"}

# 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 and Temperature/Relative Humidity (T/RH) Probe**

Campbell Scientific Inc.

815 W. 1800 N.

Logan UT 84321

Phone: (801) 753-2342

Fax: (801) 750-9540

Web: http://www.campbellsci.com

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

R.M. Young Company

2801 Aero Park Drive

Traverse City, Michigan 49686 USA

Phone: (231) 946-3980

Fax: (231) 946-4772

Web: http://www.youngusa.com/

**Barometer**

Vaisala

100 Commerce Way

Woburn, MA 01801-1068

Phone: (617)933-4500

Fax: (617)933-8029

Web: http://www.vaisala.com

**Precipitation Gauge**

NovaLynx Corporation

PO Box 240

Grass Valley, CA 95945-0240

Phone: (530) 823-7185

USA Toll Free: (800) 321-3577

Fax: (530) 823-8997

Web: http://www.novalynx.com

# **Deployment Locations and History**

Fully operational SMOSs are installed at the following locations:
([**SGP Overview Map**](http://www.arm.gov/sites/sgp/maps.stm))

[]{#__RefHeading___Toc94685941 .anchor}Table 1.

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

  E1-Larned, KS           1995/08/29                      operational

  E3-LeRoy, KS            1995/12/12                      operational

  E4-Plevna, KS           1995/03/28                      operational
  ----------------------- ---------------- -------------- ----------------

  ----------------------- ---------------- -------------- ----------------
  **Table 1.** (cont'd)                                   

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

  E5-Halstead, KS         1996/05/30                      operational

  E6-Towanda, KS          1995/12/14                      operational

  E7-Elk Falls, KS        1995/03/09                      operational

  E8-Coldwater, KS        1993/03/30                      operational

  E9-Ashton, KS           1993/03/31                      operational

  E11-Byron, OK           1995/06/23                      operational

  E13 (CF)-Lamont, OK     1993/03/29                      operational

  E15-Ringwood, OK        1993/04/01                      operational

  E20-Meeker,OK           1993/04/02                      operational

  E21-Okmulgee,OK         1999/07/27                      operational

  E24-Cyril, OK           1995/08/23                      operational

  E25-Seminole, OK        1996/12/13       2002/04/08     

  E27-Earlsboro, OK       2003/05/02                      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

[]{#OLE_LINK2 .anchor}

Table 2.

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

  Wind Speed     wspd             m/s        10m             1 & 30 min      0.01

  Vector Average wspd_va          m/s        10m             1 & 30 min      0.01
  Wind Speed                                                                 

  Wind Direction wdir             deg        10m             1 & 30 min      0.1

  Standard       sd_deg           deg        10m             1 & 30 min      0.1
  Deviation of                                                               
  Wind Direction                                                             

  Temperature    temp             C          2m              1 & 30 min      0.01
  -------------- ---------------- ---------- --------------- --------------- ----------------

  --------------- ------------------- ---------- --------------- --------------- ----------------
  **Table 2.**                                                                   
  (cont'd)                                                                       

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

  RH              rh                  \%         2m              1 & 30 min      0.1

  Vapor Pressure  vap_pres            kPa        2m              1 & 30 min      0.001

  Barometric      bar_pres            kPa        1m              1 & 30 min      0.1
  Pressure                                                                       

  Snow Depth      snow                mm         sfc             30 min          0.1

  Precipitation   precip              mm         sfc             1 & 30 min      0.001
  Total                                                                          

  Maximum Wind    max_wspd            m/s        10m             1440 min        0.01
  Speed                                                                          

  Time of Maximum time_max_wspd       HHMM       10m             1440 min        N/A
  Wind Speed                                                                     

  Minimum Wind    min_wspd            m/s        10m             1440 min        0.01
  Speed                                                                          

  Time of Minimum time_min_wspd       HHMM       10m             1440 min        N/A
  Wind Speed                                                                     

  Maximum         max_temp            C          2m              1440 min        0.01
  Temperature                                                                    

  Time of Maximum time_max_temp       HHMM       2m              1440 min        N/A
  Temperature                                                                    

  Minimum         min_temp            C          2m              1440 min        0.01
  Temperature                                                                    

  Time of Minimum time_min_temp       HHMM       2m              1440 min        N/A
  Temperature                                                                    

  Maximum RH      max_rh              \%         2m              1440 min        0.1

  Time of Maximum time_max_rh         HHMM       2m              1440 min        N/A
  RH                                                                             

  Minimum RH      min_rh              \%         2m              1440 min        0.1

  Time of Minimum time_min_rh         HHMM       2m              1440 min        N/A
  RH                                                                             

  Maximum Vapor   max_vap_pres        kPa        2m              1440 min        0.001
  Pressure                                                                       

  Time of Maximum time_max_vap_pres   HHMM       2m              1440 min        N/A
  Vapor Pressure                                                                 

  Minimum Vapor   min_vap_pres        kPa        2m              1440 min        0.001
  Pressure                                                                       

  Time of Minimum time_min_vap_pres   HHMM       2m              1440 min        N/A
  Vapor Pressure                                                                 

  Maximum         max_bar_pres        kPa        1m              1440 min        0.01
  Barometric                                                                     
  Pressure                                                                       

  Time of Maximum time_max_bar_pres   HHMM       1m              1440 min        N/A
  Barometric                                                                     
  Pressure                                                                       

  Minimum         min_bar_pres        kPa        1m              1440 min        0.01
  Barometric                                                                     
  Pressure                                                                       
  --------------- ------------------- ---------- --------------- --------------- ----------------

  -------------- ------------------- ---------- --------------- --------------- ----------------
  **Table 2.**                                                                  
  (cont'd)                                                                      

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

  Time of        time_min_bar_pres   HHMM       1m              1440 min        N/A
  Minimum                                                                       
  Barometric                                                                    
  Pressure                                                                      

  Maximum Snow   max_snow            mm         sfc             1440 min        0.1
  Depth                                                                         

  Time of        time_max_snow       HHMM       sfc             1440 min        N/A
  Maximum Snow                                                                  
  Depth                                                                         

  Minimum Snow   min_snow            mm         sfc             1440 min        0.1
  Depth                                                                         

  Time of        time_min_snow       HHMM       sfc             1440 min        N/A
  Minimum Snow                                                                  
  Depth                                                                         
  -------------- ------------------- ---------- --------------- --------------- ----------------

#### 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

This section is not applicable to this instrument.

### Diagnostic Variables

[]{#__RefHeading___Toc94685943 .anchor}Table 3.

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

  Snow Depth Sensor                     snow_sen       30 min

  Battery Voltage                       vbat           30 min

  Standard Deviation of Wind Speed      sd_wspd        30 min

  Standard Deviation of Temperature     sd_temp        30 min

  Standard Deviation of RH              sd_rh          30 min

  Standard Deviation of Vapor Pressure  sd_vap_pres    30 min

  Standard Deviation of Barometric      sd_bar_pres    30 min
  Pressure                                             
  ------------------------------------- -------------- ---------------------

### Data Quality Flags

Quality Check Results on:

[]{#__RefHeading___Toc94685944 .anchor}Table 4.

  ---------------- ---------------- ------------------ --------- ----------- -----------
  **Quantity**     **Variable**     **Measurement      **Min**   **Max**     **Delta**
                                    Interval**                               

  sample time      qc_time          1 min, 30 min &                          
                                    1440 min                                 

  Wind Speed       qc_wspd          1 min & 30 min     0         45          N/A

  Wind Speed       qc_wspd_va       1 min & 30 min     0         45          N/A
  (vector                                                                    
  averaged)                                                                  

  Wind Direction   qc_wdir          1 min & 30 min     0         360         N/A

  Standard         qc_sd_deg        1 min & 30 min     0         90          N/A
  Deviation of                                                               
  wind direction                                                             

  Temperature      qc_temp          1 min & 30 min     -40       60          N/A

  RH               qc_rh            1 min & 30 min     -2        104         N/A

  Vapor Pressure   qc_vap_pres      1 min & 30 min     0         10          N/A

  Snow Depth       qc_snow          30 min             -25       1500        N/A

  Snow Depth       qc_snow_sen      30 min             0         1           N/A
  Sensor                                                                     

  Precipitation    qc_precip        1 min & 30 min     0         10 for 1    N/A
  Total                                                          min, 150    
                                                                 for 30 min  

  Battery Voltage  qc_vbat          30 min             9.6       16          N/A

  Standard         qc_sd_wspd       30 min             0         9           N/A
  Deviation of                                                               
  Wind Speed                                                                 

  Standard         qc_sd_temp       30 min             0         2           N/A
  Deviation of                                                               
  Temperature                                                                

  Standard         qc_sd_rh         30 min             0         20          N/A
  Deviation of RH                                                            

  Standard         qc_sd_vap_pres   30 min             0         N/A         N/A
  Deviation of                                                               
  Vapor Pressure                                                             

  Standard         qc_sd_bar_pres   30 min             0         N/A         N/A
  Deviation of                                                               
  Barometric                                                                 
  Pressure                                                                   
  ---------------- ---------------- ------------------ --------- ----------- -----------

### Dimension Variables

**Table 5.**

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

  Base time in     base_time      1 min, 30 min & 1440  seconds since
  Epoch                           min                   YYYY-mm-dd XX:XX:XX
                                                        X:XX

  Time offset from time_offset    1 min, 30 min & 1440  seconds since
  base_time                       min                   YYYY-mm-dd XX:XX:XX
                                                        X:XX

  Time offset form time           1 min, 30 min & 1440  seconds since
  midnight                        min                   YYYY-mm-dd XX:XX:XX
                                                        X:XX

  north latitude   lat            1 min, 30 min & 1440  degrees
                                  min                   

  east longitude   lon            1 min, 30 min & 1440  degrees
                                  min                   

  altitude         alt            1 min, 30 min & 1440  meters above sea level
                                  min                   
  ---------------- -------------- --------------------- -----------------------

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

## Annotated Examples

This section is not applicable to this instrument.

## User Notes and Known Problems

Incorrect Alignment of Towers

Some of the SMOS towers were incorrectly aligned to true north. Offsets
were determined and changes to the data logger programs were made to
correct for the misalignment. Subsequent measurements of alignment
errors showed the original assessment to be in error. The following
table lists the correction and dates to apply the correction to return
the wind measurements to a no offset state. A request for reprocessing
of the improperly corrected data has been made.

**Table 6.**

  ---------- ------------ ----------------------------------------------------
  **SITE**   **OFFSET**   **DATE**

  EF3        +7^o^        3/9/2005 @ 1705 thru 2/7/2007 @ 1815

  EF4        +7^o^        3/9/2005 @ 1739 thru 2/21/2007 @ 1737

  EF6        +7^o^        3/10/2005 @ 1610 thru 2/8/2007 @ 1700

  EF7        +6^o^        3/8/2005 @ 2015 thru 2/6/2007 @ 1745

  EF27       +7^o^        3/2/2005 @ 1635 thru 4/26/2006 @ 1635

  EF27       -7^o^        4/26/2006 @ 1636 thru 2/12/2007 @ 1940
  ---------- ------------ ----------------------------------------------------

Additionally all SMOS towers were auditied and the following table
represents our best estimate for the deviation of each tower from true
north. Data users are encouraged to correct the data on their own the
necessary. No corrections to the data are currently made.

**Table 7.**

  ---------------------------------------- ------------------------------
  **SITE**                                 **Deviation from True North**

  EF1                                      +1^o^

  EF3                                      +2^o^

  EF4                                      0^o^

  EF5                                      -2^o^

  EF6                                      +4^o^

  EF7                                      +1^o^

  EF8                                      0^o^

  EF9                                      -2^o^

  EF11                                     -2^o^

  EF13                                     -3^o^

  EF15                                     -1^o^

  EF20                                     1^o^

  EF21                                     0^o^

  EF24                                     -3^o^

  EF27                                     +6^o^
  ---------------------------------------- ------------------------------

**Snow Depth Sensors Removed**

In the summer of 2002, the Snow Depth Sensors were removed from service.
The variable remains in the data stream as a placeholder. All data
should be --9999.

**Error Flags During Routine Maintenance**

When maintenance occurs, error flags are generated when the technicians
disable intermediate processing.

The following is a description of what happens when intermediate
processing is disabled.

No data is sent to the intermediate storage area, which is where values
are accumulated for output instructions such as average, min, and max.
Any values that were put there before disabling intermediate processing
will be used in calculations. Therefore, if a tech disables intermediate
processing at 30 s past a minute, the 1-min average will only use 30
values to calculate the 1-min average. During maintenance, the 30-min
average value will only use the seconds during which the intermediate
processing was not disabled. Therefore, if maintenance takes 5 min
during which the intermediate processing was disabled the 30-min average
will only use 1500 1-sec values instead of 1800. The reason 6999 is
output for 1-min values is because output instructions for the 1-min are
not disabled for the rain gage tiptest. When the intermediate storage
location has accumulated no values and the logger must output something-
-it puts out 6999. If the values are high resolution, the value output
is 99999. Both of these values are positive. Negative values such as
-6999 and -99999 are output when there is a problem with the sensor
(i.e., overranging or no data from the sensor). This allows for a
differentiation on what the logger is collecting. If values of 6999 and
99999 are output then the intermediate processing has been disabled and
no values are collected but the logger is still required to have an
output. If values of -6999 and -99999 are output then intermediate
processing is enabled but there is something wrong with the data being
collected (out of range, missing, etc). This differentiation allows for
a known state during maintenance. If values at anytime are positive 6999
or 99999 then maintenance is probably occurring.

## Frequently Asked Questions

**1. What is the accuracy (quality) of the RH measurements?**

The UNCERTAINTY of ± 2.06% RH (0% to 90% RH) or ± 3.04% RH (90% to 100%
RH) is for a calibrated probe. The RH values reported by the probe
normally drift slowly upward over time. Whenever a probe falls outside
the range of uncertainty for a SIX-MONTH SENSOR VERIFICATION or reports
values exceeding 104% RH, the probe is replaced by one that has been
recently calibrated. Occasionally, a sensor will report values that are
suspiciously low. A work order is then issued to perform a verification
check and replacement if needed. A data quality report is issued for
known erroneous data.

**2. What is the accuracy (quality) of the snow depth measurements?**

As the snow depth sensor and data logger were initially configured, the
snow depth data are quite noisy. Sonic echos were often received from
waving grass below the sensor and only a single reading was taken every
30-min. In DEC 95, a PIF, P951219.2 "Noisy Snow Depth data from SMOS"
was issued. During the spring of 1996, the data logger program was
changed to average readings taken every 3 min. The program change
contained an error that was not discovered until the summer of 2001. The
program was corrected and Snow Depth data were collected during the
winter of 2001/2002. It was found that the Snow Depth sensors were not
very stable and they were removed from service in August 2002.

**3. Where can SMOS-like data be obtained for extended facilities that
do not have SMOS data?**

Several sources of surface meteorological data exist and are available
as "external data" to ARM science team members. The Oklahoma Mesonet has
more than 50 surface stations within the boundaries of the SGP site, the
Kansas State network has 4-5 stations, and each of the boundary
facilities has a surface meteorological station associated with the
404-MHz radar wind profiler operated by the National Oceanic and
Atmospheric Administration. The status and contacts for external data
can be found on the Web at location
<http://arm3.das.bnl.gov/sisg/ext.html>.

http://www.mesonet.ou.edu/sites/

# 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

This section is not applicable to this instrument.

## 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
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 web page <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

**T/RH sensor:** Thermistor and Vaisala RH, Campbell Scientific Model
HMP35C Temperature and RH Probe

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

**Precipitation:** Electrically heated, tipping bucket precipitation
gauge, Novalynx Model 260-2500E-12 Rain/Snow Gage

**Snow depth sensor:** Ultrasonic depth gauge, Campbell Scientific Model
UDG01 **Removed from service Summer 2002**

**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

**Description of all SMOS stations except at E21, Okmulgee, OK**

The SMOS sensors are mounted on a 10-m triangular tower, except for the
rain gauge.

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 Wind Monitor is mounted on a cross-arm at a
height of 10 m.

The T-RH probe thermistor 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. For all SMOSs, except the
one at the central facility, the T-RH probe is mounted in a naturally
aspirated R. M. Young Model 41002 Gill Multi-plate Radiation Shield. The
central facilities (E13) T-RH probe is mounted in an R. M. Young Model
43408 Gill Aspirated Radiation Shield. The Radiation Shields are mounted
at a height of 2 m on the southwestern leg of the tower.

The snow depth sensor determines the distance from the sensor to the
surface by measuring the time of travel of a series of ultrasonic
pulses. It is mounted to the tower on a boom at a height of
approximately 1.5 m.

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 mounted on the
tower at a height of 1 m.

The rain-snow gauge has a 12-in. orifice and is located near the tower.
A thermostatically controlled heater melts frozen precipitation. The
water is funneled to a tipping bucket, which triggers a magnetic reed
switch. An Alter Shield is used to increase the reliability of rain
collection in high winds and of snow collection.

The data logger measures each input once per second except for
barometric pressure, which is measured once per minute, and snow depth,
which is measured every 3 min. The vapor pressure is computed from the
air temperature and RH. The data logger produces 1- and 30-min averages
of wind speed, vector-averaged wind speed, vector-averaged wind
direction, air temperature, RH, and vapor pressure. An algorithm
computes the standard deviation of the wind direction. The 1-min output
includes the barometric pressure reading and total precipitation during
the minute. The 30-min output includes the battery voltage, 30-min-total
precipitation, and an average snow depth. The 30-min output also
includes the standard deviations of wind speed, temperature, RH, vapor
pressure, and barometric pressure.

**Description of SMOS at E21, Okmulgee, OK**

The same sensors that are used on the other SMOS stations are used on
the E21 SMOS except no snow depth sensor is included. Since this SMOS is
in a forested site, the sensors are mounted on a 20-m tower that extends
above the top of the forest canopy. During the summer of 1999, the
canopy height was estimated to be 47 ft or 14.3 m. The air temperature
and RH probe is mounted at 17.0 m or approximately 2.7 m above the
average canopy height facing north. The wind speed and direction sensor
is mounted at 18 m or approximately 3.7 m above the average canopy
height on a boom 10ft out from the tower facing north. The barometric
pressure sensor is mounted at 19 m or approximately 4.7 m above the
average canopy height. New booms for sensor mounting were installed in
July 2002. The two sensors affected are the wind speed and direction
sensor and the T/RH probe. The height of the wind speed and direction
sensor did not change; it is still 18 m or approximately 3.7 m above the
average canopy height. The orientation of the wind speed and direction
sensor did change and it is now facing west on a boom 15 ft out from the
tower. The date of the wind speed and direction sensor change was July
16, 2002 at 18:44 GMT. Both the orientation and the height of the T/RH
probe changed. It is now 19.25 m above the surface or 4.95 m above the
average canopy height and is facing northeast. The date of the T/RH
probe change was July 15, 2002 at 22:36 GMT.

### Specifications

**Wind speed at 10 m**, Precision: 0.01 m/s; Uncertainty: ± 2% for 2.5
to 30 m/s

**Wind direction at 10 m**, Precision: 0.1°; Uncertainty: ± 5°

**Air temperature at 2 m**, Precision: 0.01°C; Uncertainty: a function
of wind speed

**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**, Precision: 0.254 mm; Uncertainty: ± 0.254 mm (unknown
during strong winds and for snow)

**Snow depth**, Precision: 0.1 mm, ± 10 mm plus any offset error. Snow
Depth sensors were removed from service in August 2002 (see "Overall
Uncertainties for Primary Quantities Measured").

**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 SMOS clock if it is off by more than a minute.

**Wind Speed**

The NIST 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 zero
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 A/D conversion accuracy is
equivalent to ± 0.7° over a temperature range of 0° to 40°C for a period
of one year. I have estimated sensor alignment to true north to be
accurate within ± 3°. The uncertainty with 95% confidence is, therefore,
approximately ± 5°. Except where otherwise noted in Table 7.

**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 naturally aspirated multi-plate
radiation shield used for all stations, except for the central
facilities SMOS, is specified as ± 0.4°C root mean square (rms) at
3 m/s, ± 0.7°C rms at 2 m/s, and ± 1.5°C rms at 1 m/s.

The uncertainty with 95% confidence of temperature sensors in naturally
aspirated radiation shields is approximately:

  -------------- --------------------------------------------------------
  ± 0.45 C       when the wind speed is 6 m/s or greater

  ± 0.89 C       when the wind speed is 3 m/s

  ± 1.46 C       when the wind speed is 2 m/s

  ± 3.07 C       when the wind speed is 1 m/s
  -------------- --------------------------------------------------------

The radiation error of the aspirated radiation shield used at the
Central Facility 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.

**Precipitation**

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 0.254 mm. For rain rates less
than 75 mm per hour with light to moderate winds, the collection
efficiency of the gauge is 99% to 100%.

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

Although Alter shields are used to increase the efficiency of snow
collection, the efficiency of collection is variable and usually well
below 100%. Furthermore, the heater does not melt snow at temperatures
below -10°C. Thus, the data user should use the water-equivalent
estimates for snowfall with a great deal of skepticism. At best, the
readings are only a rough indicator that snow occurred, for temperatures
above -10°C. If snow occurred at -10°C or below and the temperature
increased to above -10°C hours later, then some melting would occur and
an incorrect time of precipitation would be reported.

**Snow Depth**

The sensor has a digital output, therefore, there is no conversion
error. The snow depth is determined by subtracting the measurement from
the height of the sensor. An error in the latter will result in a bias
error. Since this height is manually entered into the data logger
program, the bias error could be large. The sensor accuracy is specified
as ± 10 mm.

## Theory of Operation

Each of the primary measurements of wind speed, wind direction, air
temperature, RH, barometric pressure, and 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 manufacturer can be contacted for further
information.

## Calibration

### Theory

The SMOSs are not calibrated as systems. The sensors and the data logger
(which includes the analog-to-digital converter) are calibrated
separately. All systems are installed using components that have a
current calibration. The sensor calibrations are checked every six
months in the field by SGP site operations personnel by comparison to
calibrated references. The mentor is contacted whenever a sensor fails
the 6-month calibration. A determination is then made as to whether to
retest the sensor during the next maintenance trip or to replace it and
send it back to the manufacturer for repair. Earlier 6-month
calibrations were done without an aspirated shield. It caused many T/RH
failures due to the check set being influenced by solar radiation and
the effects of being in a hot vehicle. Natural aspiration was not
sufficient to overcome the artificial heating. Newer procedures enacted
in 2000 along with an aspirated shield have led to lower incorrect
failure determinations. The Wind Monitors are returned to the
manufacturer for recalibration after two years of use per manufacturer
suggestion and given adequate funding. Therefore, it is possible that in
some years the wind monitors are not sent back to the manufacturer for
the 2-year recalibration and preventative maintenance. Overall, this
should not lead to a problem, as the sensors rarely go out of
calibration and are checked every 6 months.

### 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 RH calibrations are checked by comparison with a
reference Vaisala Model HMI31 Digital RH and Temperature Meter and HMP35
Probe. If the reported temperature and RH 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.

Precipitation calibration is checked by allowing 500 ml of water to pass
slowly through the sensor. If the reported number of tips varies by more
than one from the expected value, the rain gauge is replaced by one with
a current calibration.

Snow depth calibration is checked by placing an object with a known
height under the sensor. If the reported depth varies by more than the
sensor uncertainty of 10 mm from the known height, the offset in the
data logger program is adjusted to produce the correct height. If
adjustment of the offset does not produce the correct height within 10
mm, the sensor is replaced by one with a current calibration.

### History

Calibration checks of SMOS sensors are conducted every six months in the
field. Because the data flow is interrupted and the 10-m tower must be
lowered for these checks, a data quality report (DQR) is usually issued
to note the loss of data. A list of field calibration checks and/or
sensor replacements follows.

**SMOS E1, Larned KS**

Data available beginning on 5 SEP 1995

Field calibration check on 3 OCT 1995

T-RH probe replaced on 29 NOV 1995 (PIF No. P951207.5)

Field calibration check on 18 APR 1996

Rain gauge replaced on 24 JUL 1996

Field calibration check on 30 OCT 1996 (PIF No. P961210.1)

Field calibration check on 30 APR 1997 (DQR No. D970718.2)

Wind monitor replaced on 6 AUG 1997 for 2-year factory PM and
calibration.

Failed barometer replaced on 20 AUG 1997.

Field calibration check on 29 OCT 1997 (DQR No. D971112.1)

Field calibration check on 29 APR 1998 (DQR No. D980601.1

Field calibration check on 24 NOV 1998

Field calibration check on 13 APR 1999

T-RH probe replaced on 6 JUL 1999

Field calibration check on 29 SEP 1999

Field calibration check on 25 APR 2000

Field calibration check on 24 OCT 2000

Wind monitor replaced on 13 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 24 APR 2001

T-RH probe replaced 17 JUL 2001

Field calibration check on 6 NOV 2001

Field calibration check on 21 MAY 2002

Field calibration check on 5 NOV 2002

Field calibration check on 6 MAY 2003

Field calibration check on 21 OCT 2003

Field calibration check & T-RH probe replaced on 20 APR 2004

Field calibration check on 19 OCT 2004

Field calibration check on 5 APR 2005

Field calibration checks on 16 NOV 2005

Wind monitor replaced on 29 NOV 2005

Wind monitor replaced on 13 DEC 2005

Field calibration check on 18 APR 2006

Field calibration check on 3 OCT 2006

T-RH probe replaced/upgraded on 20 FEB 2007

Field calibration check on 3 APR 2007

T-RH probe replaced on 26 June 2007

Field calibration checs on 17 OCT 2007

T-RH probe replaced on 11 DEC 2007

Wind Monitor replaced on 19 FEB 2008

**SMOS E3, LeRoy KS**

Data available beginning on 12 DEC 1995

Field calibration check on 1 MAY 1996 (PIF No. P960523.2)

Field calibration check on 14 NOV 1996 (PIF No. P961210.5)

Field calibration check on 16 APR 1997 (DQR No. D970718.3)

Wind monitor replaced on 6 AUG 1997 for 2-year factory PM and
calibration.

Field calibration check on 15 OCT 1997 (DQR No. D971112.2)

Field calibration check on 13 MAY 1998 (DQR No. D990601.6

Field calibration check on 11 NOV 1998

Field calibration check on 31 MAR 1999 (not wind sensor)

Field calibration on wind sensor 12 MAY 1999

Field calibration check on 8 DEC 1999

Field calibration check on 10 MAY 2000

T-RH probe replaced on 7 JUL 2000

Field calibration check on 27 SEP 2000

Wind monitor replaced on 14 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 11 APR 2001

Field calibration check on 24 OCT 2001

Field calibration check on 8 MAY 2002

T-RH probe replaced on 25 SEP 2002

Field calibration check on 20 NOV 2002

Field calibration check on 23 APR 2003

Field calibration check on 5 NOV 2003

Field calibration check on 7 APR 2004

Field calibration check on 6 OCT 2004

Field calibration check on 20 APR 2005

Field calibration check on 6 NOV 2005

Wind monitor replaced on 16 NOV 2005

Field calibration check on 3 MAY 2006

Field calibration check on 18 OCT 2006

T-RH probe replaced/upgraded on 7 FEB 2007

Field calibration check on 18 APR 2007

Field calibration re-check on barometer 26 JUL 2007

Field calibration checks on 31 OCT 2007

Wind monitor replaced 5 MAR 2008

**SMOS E4, Plevna KS**

Data available beginning on 30 MAR 1995

Wind speed calibration corrected on 18 APR 1995

Field calibration check on 3 OCT 1995

Field calibration check on 18 APR 1996

Field calibration check on 31 OCT 1996 (PIF No. P961210.7)

Field calibration check on 30 APR 1997 (DQR No. D970718.4)

Field calibration check on 30 OCT 1997 (DQR No. D971112.3)

Field calibration check on 29 APR 1998 (DQR No. D9780601.7)

Field calibration check on 24 NOV 1998

Field calibration check on 14 APR 1999

T-RH probe replaced on 12 MAY 1999

Field calibration check on 29 SEP 1999

Wind monitor replaced on 12 APR 2000 for 2-year factory PM and
calibration.

Field calibration check on 26 APR 2000

Failed barometer replaced 1 AUG 2000

Field calibration check on 8 NOV 2000

Field calibration check on 25 APR 2001

Field calibration check on 7 NOV 2001

Field calibration check on 22 MAY 2002

Field calibration check on 6 NOV 2002

Field calibration check on 7 MAY 2003

Field calibration check on 22 OCT 2003

T-RH probe replaced on 22 OCT 2003

Field calibration check & T-Rh probe replaced on 21 APR 2004

T-RH probe replaced 6 MAY 2004

Field calibration check on 20 OCT 2004

Field calibration check on 6 APR 2005

Field calibration check on 17 NOV 2005

Field calibration check on 19 APR 2006

Field calibration check on 4 OCT 2006

Wind Monitor replaced on 6 FEB 2007

T-RH probe replaced/upgraded on 21 FEB 2007

Field clalibration check on 4 APR 2007

Field calibration check on 17 OCT 2007

Wind Monitor replaced on 5 MAR 2008

**SMOS E5, Halstead KS**

Data available beginning on 20 JUN 1996

Field calibration check on 31 OCT 1996 (PIF No. P961210.8)

Field calibration check on 1 MAY 1997 (DQR No. D970718.5)

Field calibration check on 30 OCT 1997 (DQR No. D971112.5)

Field calibration check on 30 APR 1998 (DQR No. D980601.2)

Field calibration check on 25 NOV 1998

Field calibration check on 14 APR 1999

Field calibration check on 30 SEP 1999

Wind monitor replaced on 12 APR 2000 for 2-year factory PM and
calibration.

Field calibration check on 25 APR 2000

Field calibration check on 8 NOV 2000

Field calibration check on 25 APR 2001

Field calibration check on 7 NOV 2001

Field calibration check on 22 MAY 2002

Field calibration check on 6 NOV 2002

Field calibration check on 7 MAY 2003

Field calibration check on 21 OCT 2003

Field calibration check on 21 APR 2004

T-RH probe replaced 14 JUL 2004

Field calibration check on 20 OCT 2004

Field calibration check on 6 APR 2005

Field calibration check on 17 NOV 2005

Field calibration check on 19 APR 2006

Field calibration check on 4 OCT 2006

T-RH probe replaced/upgraded on 21 FEB 2007

Rain Gauge replaced on 7 MAR 2007

Field calibration check on 5 APR 2007

Wind Monitor replaced on 18 APR 2007

Rian Gauge replaced on 18 MAY 2007

Field calibration checks on 16 OCT 2007

**SMOS E6, Towanda KS**

Data available beginning on 21 DEC 1995

Wind Monitor replaced on 3 APR 1996 (PIF No. P960523.5)

Field calibration check on 1 MAY 1996 (PIF No. P960523.4)

Field calibration check on 14 NOV 1996 (PIF No. P961210.11)

Field calibration check on 29 APR 1997 (DQR No. D970718.6)

Field calibration check on 14 OCT 1997 (DQR No. D971112.7)

Last field calibration check revealed that the barometer had drifted out
of tolerance. It was replaced on 24 NOV 1997.

Field calibration check on 13 MAY 1998 (DQR No. D980601.8)

Field calibration check on 12 NOV 1998

Field calibration check on 1 APR 1999 (no wind sensor check)

Field calibration check on wind sensors only 12 May 1999

Field calibration check on 8 DEC 1999

Wind monitor replaced on 29 MAR 2000 for 2-year factory PM and
calibration.

Field calibration check on 10 MAY 2000

Field calibration check on 28 SEP 2000

Wind monitor replaced on 15 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 12 APR 2001

Field calibration check on 23 OCT 2001

T-RH probe replaced on 24 APR 2002

Field calibration check on 8 MAY 2002

T-RH probe replaced on 4 JUN 2002

Field calibration check on 21 NOV 2002

Field calibration check on 24 APR 2003

T-RH probe replaced on 11 SEP 2003

T-RH probe replaced on 15 SEP 2003

Field calibration check on 6 NOV 2003

Field calibration check on 8 APR 2004

Barometer replaced on 24 SEP 2004

Field calibration check on 17 OCT 2004

Field clalibration check on 21 APR 2005

T-RH probe replace 30 JUN 2005

Field calibration check on 3 NOV 2005

Wind monitor replaced on 3 NOV 2005

Field calibration check on 4 MAY 2006

Field calibration check on 19 OCT 2006

T-RH probe replaced/upgraded on 18 FEB 2007

Rain Gauge replaced on 22 MAR 2007

Field calibration check on 19 APR 2007

Field calibration checks on 1 NOV 2007

Wind Monitor replaced on 20 FEB 2008

**SMOS E7, Elk Falls KS**

Data available beginning on 24 FEB 1995

Field calibration check and T-RH probe replaced on 9 MAR 1995

Wind monitor ground repaired on 22 MAR 1995

T-RH probe replaced on 17 MAY 1995 (PIF No. P950814.1)

Field calibration check on 4 OCT 1995 (PIF No. P951009.2)

Field calibration check on 2 MAY 1996 (PIF No. P960523.6)

Field calibration check on 13 NOV 1996 (PIF No. P961210.19)

T-RH probe replaced on 4 FEB 1997

Field calibration check on 16 APR 1997 T-RH probe replaced (DQR No.
D970718.7)

Field calibration check on 16 OCT 1997 (DQR No. D971112.8)

Field calibration check on 12 MAY 1998 (DQR No. D980601.9)

Field calibration check on 11 NOV 1998

T-RH probe replaced on 8 JUN 1999

T-RH probe replaced on 6 JUL 1999

Field calibration check on 30 MAR 1999

Field calibration check on 7 DEC 1999

Field calibration check on 9 MAY 2000

Field calibration check on 26 SEP 2000

Wind monitor replaced on 5 DEC 2000 for 2-year factory PM and
calibration

Wind monitor replaced on 13 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 10 APR 2001

Field calibration check on 25 OCT 2001

Field calibration check on 7 MAY 2002

T-RH probe replaced on 6 JUN 2002

Field calibration check on 19 NOV 2002

Barometer replaced on 22 NOV 2002

Field calibration check on 22 APR 2003

Field calibration check on 4 NOV 2003

Field calibration check on 6 APR 2004

T-RH probe replaced 13 JUL 2004

Field calibration check on 5 OCT 2004

Field calibration check on 19 APR 2005

Field calibration check on 1 NOV 2005

Field calibration check on 2 MAY 2006

Field calibration check on 17 OCT 2006

T-RH probe replaced/upgraded on 6 FEB 2007

Rain Gauge replaced on 6 MAR 2007

Field calibration check on 17 APR 2007

Wind Monitor replaed on 29 MAY 2007

Datalogger replaced on 18 SEP 2007

Field calibration checks on 30 OCT 2007

Wind Monitor replaced on 31 OCT 2007

**SMOS E8, Coldwater KS**

Data available beginning on 28 JUL 1993

Field calibration check on 3 NOV 1993

Field calibration check on 15 JUN 1994

Field calibration check on 16 NOV 1994 (PIF No. P941128.4)

Field calibration check and wind monitor replaced on 19 APR 1995 (PIF
No. P950509.7)

Field calibration check on 2 OCT 1995 (PIF No. P951009.5)

Field calibration check and T-RH probe replaced on 17 APR 1996 (PIF No.
P960523.7)

Field calibration check on 30 OCT 1996 (PIF No. P961210.12)

Field calibration check on 29 APR 1997 (DQR No. D970718.8)

Wind monitor replaced on 5 AUG 1997 for 2-year factory PM and
calibration.

Wind monitor wires corrected 30 SEP 1997 due to install error 5 AUG 1997

Field calibration check on 29 OCT 1997, rain gauge replaced(DQR No.
D971112.9)

T/RH probe had drifted out of tolerance. It was replaced on 24 NOV 1997.

Field calibration check on 28 APR 1998 (DQR No. D980601.10)

Field calibration check on 23 NOV 1998

T/RH probe had drifted out of tolerance. It was replaced on 30 MAR 1999

Field calibration check on 27 APR 1999

Field calibration check on 28 SEP 1999

Field calibration check on 25 APR 2000

T-RH probe replaced on 23 MAY 2000

Field calibration check on 24 OCT 2000

Wind monitor replaced on 5 DEC 2000 for 2-year factory PM and
calibration.

T-RH probe replaced on 10 APR 2001

Field calibration check on 24 APR 2001

Field calibration check on 6 NOV 2001

Wind monitor replaced on 12 MAR 2002

Field calibration check on 21 MAY 2002

Field calibration check on 5 NOV 2002

Field calibration check on 20 MAY 2003

Field calibration check on 21 OCT 2003

Field calibration check & T-RH probe replaced on 20 APR 2004

Field calibration check on 19 OCT 2004

T-RH probe replaced on 25 JAN 2005

T-RH probe replaced on 8 FEB 2005

Field calibration check on 5 APR 2005

Field calibration check on 16 NOV 2005

Field calibration check on 18 APR 2006

T-RH probe replaced on 30 MAY 2006

Field calibration check on 3 OCT 2006

T-RH probe replaced on 17 OCT 2006

T-RH probe replaced/upgraded on 20 FEB 2007

Rain Gauge replaced on 6 MAR 2007

Field calibration check on 3 APR 2007

Wind Monitor replaced on 21 AUG 2007

Field Calibration checks on 17 OCT 2007

**SMOS E9, Ashton KS**

Data available beginning on 1 JUL 1993

Field calibration check on 1 NOV 1993

Field calibration check on 13 JUN 1994

Field calibration check on 14 NOV 1994 (PIF No. P941128.5)

Field calibration check and wind monitor replaced on 18 APR 1995 (PIF
No. P950509.8)

Field calibration check and T-RH probe replaced on 5 OCT 1995 (PIF No.
P951009.4)

Field calibration check on 30 APR 1996 (PIF No. P960523.9)

Field calibration check on 15 NOV 1996 (PIF No. P961210.13)

Field calibration check and wind monitor replaced on 1 MAY 1997 (DQR No.
D970718.9)

Field calibration check on 16 OCT 1997 (DQR No. D971112.11)

Field calibration check on 14 MAY 1998 (DQR No. D980601.3)

Field calibration check on 12 NOV 1998

Field calibration check on 1 APR 1999

T-RH probe replaced on 13 MAY 1999

Field calibration check on 9 DEC 1999

Field calibration check on 11 MAY 2000

T-RH probe replaced on 25 MAY 2000

Field calibration check on 26 SEP 2000

Wind monitor replaced on 5 DEC 2000 for 2-year factory PM and
calibration.

T-RH probe replaced on 27 FEB 2001

T-RH probe replaced on 13 MAR 2001

Field calibration check on 10 APR 2001

Field calibration check on 23 OCT 2001

T-RH probe replaced on 28 MAR 2002

Field calibration check on 9 MAY 2002

Field calibration check on 19 NOV 2002

T-RH probe replaced on 7 FEB 2003

Field calibration check on 24 APR 2003

Field calibration check on 4 NOV 2003

Field calibration check on 6 APR 2004

Field calibration check on 5 OCT 2004

Field calibration check on 9 APR 2005

Field calibration check on 1 NOV 2005

Field calibration check on 2 MAY 2006

Field calibration check on 17 OCT 2006

T-RH probe replaced/upgraded on 6 FEB 2007

Rain Gauge replaced on 6 MAR 2007

Field calibration check on 17 APR 2007

Wind Monitor replaced on 17 APR 2007

Field calibration checks on 30 OCT 2007

**SMOS E11, Byron OK**

Data available beginning on 28 JUN 1995

T-RH probe replaced on 22 AUG 1995 (PIF No. P950828.4)

Field calibration check on 17 OCT 1995 (PIF No. P951101.11)

T-RH probe wiring repaired on 31 OCT 1995 (PIF No. P951103.1)

T-RH probe replaced on 12 DEC 1995 (PIF No. P951219.1)

Field calibration check on 16 APR 1996 (PIF No. P960523.10)

Field calibration check on 29 OCT 1996 (PIF No. P961210.14)

Field calibration check on 29 APR 1997 (DQR No. D970718.10)

Wind monitor replaced on 5 AUG 1997 for 2-year factory PM and
calibration.

Field calibration check on 28 OCT 1997 (DQR No. D971112.12)

Field calibration check on 5 MAY 1998 (DQR No. D980601.4)

Field calibration check on 3 DEC 1998

Field calibration check on 20 APR 1999

Field calibration check on 5 OCT 1999

T-RH probe replaced on 13 JAN 2000

T-RH probe had drifted out of tolerance. Probe replaced on 24 MAR 2000

Field calibration check on 18 APR 2000

T-RH probe replaced on 6 JUN 2000

T-RH probe replaced on 25 JUL 2000

Field calibration check on 17 OCT 2000

Wind monitor replaced on 6 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 17 APR 2001

Field calibration check on 2 OCT 2001

Field calibration check on 14 MAY 2002

Rain gauge replaced on 17 MAY 2002

T-RH probe replaced on 25 JUN 2002

Field calibration check on 12 NOV 2002

Field calibration check on 29 APR 2003

Field calibration check on 14 OCT 2003

Field calibration check & T-RH probe replaced on 13 APR 2004

T-RH probe replaced 13 JUL 2004

Barometer replaced on 20 JUL 2004

Field calibration check on 26 OCT 2004

Field calibration check on 12 APR 2005

Field calibration check on 21 NOV 2005

Field calibration check on 25 APR 2006

Field calibration check on 10 OCT 2006

T-RH probe replaced/upgraded on 12 FEB 2007

Rain Gauge replaced on 16 MAR 2007

Wind Monitor replaced on 27 MAR 2007

Field calibration check on 20 APR 2007

Field calibration checks on 10 OCT 2007

Field calibration checks on 23 OCT 2007

**SMOS E13, Central Facility, Lamont OK**

Data available beginning on 1 JUL 1993

Instrument replaced due to lightning damage on 10 MAY 1993

Field calibration check on 26 OCT 1993 (PIF No. P931101.6)

T-RH probe replaced on 6 MAY 1994

Field calibration check on 17 JUN 1994

Field calibration check on 18 NOV 1994 (PIF No. P941128.1)

T-RH multi-plate radiation shield replaced by aspirated shield on 14 APR
1995

Field calibration check on 5 MAY 1995 (PIF No. P950509.3)

T-RH probe replaced on 30 JUN 1995 (PIF No. P950707.4)

Wind monitor and rain gauge replaced on 18 JUL 1995

Field calibration check on 6 OCT 1995 (PIF No. P951009.6)

Field calibration check on 3 MAY 1996 (PIF No. P96052313)

Field calibration check on 18 NOV 1996 (PIF No. P961210.15)

T-RH probe replaced on 30 JAN 1997

T-RH probe replaced on 14 MAR 1997

T-RH probe replaced on 9 APR 1997

Field calibration check on 20 APR 1997 (DQR No. D970721.3)

T-RH probe replaced on 14 MAY 1997

Wind monitor replaced on 1 AUG 1997 for 2-year factory PM and
calibration.

Field calibration check and Wind monitor replaced on 10 OCT 1997 (DQR
No. D971112.13)

Field calibration check on 7 MAY 1998 (DQR No. D980601.11)

Field calibration check on 4 DEC 1998

Field calibration check on 9 APR 1999

Field calibration check on 7 OCT 1999

Field calibration check on 4 MAY 2000

Field calibration check on 19 OCT 2000

Wind monitor replaced on 8 MAR 2001 for 2-year factory PM and
calibration.

Field calibration check on 20 APR 2001

Field calibration check on 4 OCT 2001

Field calibration check on 16 MAY 2002

T-RH probe replaced on 14 JUN 2002

Field calibration check on 14 NOV 2002

Field calibration check on 1 MAY 2003

Field calibration check on 16 OCT 2003

Field calibration check on 15 APR 2004

T-RH probe replaced on 27 MAY 2004

Field calibration check on 28 OCT 2004

T-RH probe replaced on 1 APR 2005

Field calibration check on 15 APR 2005

Field calibration check on 23 NOV 2005

Field calibration check on 1 MAY 2006

Wind monitor replaced on 1 MAY 2006

Field calibration check on 13 OCT 2006

T-RH probe replaced/upgraded on 3 NOV 2007

Field calibration check on 16 APR 2007

T-RH probe replaced on 18 JUN 2007

Field calibration check on 9 OCT 2007

Wind Monitor replaced on 29 FEB 2008

**SMOS E15, Ringwood OK**

Data available beginning on 13 JUL 1993

Field calibration check on 2 NOV 1993

Field calibration check on 14 JUN 1994

Field calibration check on 21 NOV 1994 (PIF No. P941128.2)

Field calibration check and Wind monitor replaced on 24 APR 1995 (PIF
No. P950509.4)

T-RH probe replaced on 31 JUL 1995 (PIF No. P950808.1)

Field calibration check on 10 OCT 1995 (PIF No. P951101.5)

Field calibration check on 23 APR 1996 (PIF No. P960523.14)

T-RH probe replaced on 7 MAY 1996 (PIF No. P960523.16)

T-RH probe replaced on 15 AUG 1996

Field calibration check on 5 NOV 1996 (PIF No. P961210.16)

Field calibration check on 22 APR 1997 (DQR No. D970718.11)

Wind monitor replaced on 6 MAY 1997 for 2-year factory PM and
recalibration

Field calibration check on 7 OCT 1997 (DQR No. D971112.14)

T-RH probe replaced on 24 FEB 1998 (DQR No. D980401.5)

Field calibration check on 5 MAY 1998 (DQR No. D980601.5)

T-RH probe replaced on 20 OCT 1998

Field calibration check on 3 DEC 1998

Field calibration check on 20 APR 1999

Field calibration check on 5 OCT 1999

Field calibration check on 18 APR 2000

T-RH probe replaced on 13 JUN 2000

Field calibration check on 17 OCT 2000

Wind monitor replaced on 12 DEC 2000 for 2-year factory PM and
calibration.

Field calibration check on 17 APR 2001

Field calibration check on 2 OCT 2001

Wind speed sensor replaced 27 NOV 2001

Field calibration checks on 14 MAY 2002

Wind Monitor replaced on 11 JUN 2002

Field calibration check on 12 NOV 2002

Field calibration check on 29 APR 2003

Field calibration check on 14 OCT 2003

Field calibration check & T-RH probe replaced on 13 APR 2004

Field calibration check on 26 OCT 2004

Field calibration check on 12 APR 2005

Field calibration check on 21 NOV 2005

Field calibration check on 25 APR 2006

Field calibration check on 10 OCT 2006

T-RH probe replaced/upgraded on 13 FEB 2007

Rain Gauge replaced on 14 MAR 2007

Field calibration check on 20 APR 2007

Wind Monitor replaced on 8 MAY 2007

Field calibration checks on 10 OCT 2007

**SMOS E20, Meeker OK**

Data available beginning 8 JUL 1993

T-RH probe replaced on 10 JUN 1993 (PIF No. P930602.2)

Wind Monitor replaced on 8 JUL 1993

Field calibration check on 28 OCT 1993

Field calibration check on 9 JUN 1994

Field calibration check on 25 NOV 1994 (PIF No. P951128.3)

Field calibration check on 27 APR 1995 (PIF No. P950509.6)

T-RH probe replaced on 11 MAY 1995

Field calibration check on 13 OCT 1995 (PIF No. P951101.8)

T-RH probe replaced on 26 OCT 1995 (PIF No. P951101.8)

Field calibration check and Wind monitor replaced on 10 APR 1996 (PIF
No. P960523.17)

T-RH probe replaced on 20 JUN 1996

T-RH probe replaced on 15 AUG 1996

Field calibration check on 23 OCT 1996 (PIF No. P961210.18)

Field calibration check on 9 APR 1997 (DQR No. D970718.12)

Field calibration on wind sensors 21 MAY 1997

Field calibration check on 22 OCT 1997 (DQR No. D980407.1)

Field calibration check on 20 MAY 1998 (DQR No. D980601.12)

Field calibration check on 20 NOV 1998

Field calibration check on 7 APR 1999

T-RH probe replaced on 8 SEP 1999

Field calibration check on 15 DEC 1999

T-RH probe had drifted out of tolerance. It was replaced on 12 JAN 2000

Wind monitor replaced on 22 MAR 2000 for 2-year factory PM and
calibration.

Field calibration check on 17 MAY 2000

Wind monitor replaced on 28 JUN 2000

Field calibration check on 4 OCT 2000

Field calibration check on 4 APR 2001

Field calibration check on 17 OCT 2001

Wind monitor replaced on 23 JAN 2002

Wind monitor replaced on 17 APR 2002

Field calibration check on 1 MAY 2002

T-RH probe replaced on 12 SEP 2002

Field calibration check on 26 NOV 2002

Field calibration check on 16 APR 2003

Field calibration check on 29 OCT 2003

Field calibration check on 28 APR 2004

Field calibration check on 29 SEP 2004

T-RH probe replaced on 8 DEC 2004

T-RH probe replaced on 2 FEB 2005

Field calibration check on 27 APR 2005

Wind monitor replaced 17 AUG 2005

Field calibration check on 9 NOV 2005

Field calibration check on 10 MAY 2006

Field calibration check on 25 OCT 2006

T-RH probe replacement/upgrade on 14 FEB 2007

Rain Gauge replaced on 11 APR 2007

Field calibration check on 25 APR 2007

Wind Monitor replaced on 15 AUG 2007

Field calibration checks on 24 OCT 2007

**SMOS E21, Okmulgee OK**

Data available beginning on 25 AUG 1999

T-RH probe replaced on 27 JUL 1999

Field calibration check on 10 AUG 1999

T-RH probe replaced 5 OCT 1999

T-RH probe replaced on 2 NOV 1999

Barometer replaced on 30 NOV 1999

Field calibration check on 14 DEC 1999

Barometer replaced on 19 APR 2000

Field calibration check on 17 MAY 2000

T-RH probe replaced 26 on JUL 2000

Wind monitor orientation corrected on 17 AUG 2000

Fine tune wind monitor orientation 20 SEP 2000

Field calibration check on 4 OCT 2000

Field calibration check on 3 APR 2001

Rain gauge replaced on 18 SEP 2001

Field calibration check on 11 DEC 2001

Barometer replaced on 17 APR 2002

Field calibration check on 1 MAY 2002(not wind speed and direction)

Field calibration check of wind speed and direction 7 AUG 2002

Field calibration check on 26 NOV 2002

T-RH probe replaced on 5 Mar 2003

Field calibration check on 16 APR 2003

Field calibration check on 29 OCT 2003

Field calibration check on 28 APR 2004

Barometer replaced 23 JUN 2004

Barometer replaced on 26 OCT 2004

Field calibration check on 8 NOV 2004

T-RH probe replaced on 17 DEC 2004

T-RH probe replaced on 18 JAN 2005

Field calibration check on 26 APR 2005

T-RH probe replaced 27 SEP 2005

Barometer replaced 13 OCT 2005

Field calibration check 9 NOV 2005

T-RH probe replaced 4 JAN 2006

T-RH probe replaced on 15 FEB 2006

Field calibration check on 10 MAY 2006

Wind monitor replaced on 23 MAY 2006

Wind monitor replaced on 19 JUL 2006

Field calibration check on 24 OCT 2006

T-RH probe replaced/upgraded on 27 FEB 2007

Rain Gauge replaced on 28 MAR 2007

Field calibration check on 25 APR 2007

Field calibration checks on 24 OCT 2007

**SMOS E24, Cyril OK**

Data available beginning 27 AUG 1995

Field calibration check on 12 OCT 1995 (PIF No. P951101.9)

Field calibration check on 24 APR 1996 (PIF No. P960523.18)

Field calibration check on 7 NOV 1996 (PIF No. P961210.20)

T-RH probe replaced on 11 FEB 1997

Field calibration check on 23 APR 1997 (DQR No. D970718.13)

Field calibration check and Wind monitor replaced on 21 OCT 1997 (DQR
No. D980407.2)

T-RH probe replaced on 10 FEB 1998 (DQR No. D980401.6)

T-RH probe replaced on 10 MAR 1998 (DQR No. D980401.6)

Field calibration check on 19 MAY 1998 (DQR No. D980601.13)

T-RH probe replaced on 3 NOV 1998

Field calibration check on 19 NOV 1998

T-RH probe replaced on 17 DEC 1998

Field calibration check on 23 MAR 1999

Field calibration check on 16 DEC 1999

Field calibration check on 7 MAR 2000

Field calibration check on 18 MAY 2000

Field calibration check on 5 OCT 2000

Wind monitor replaced on 14 DEC 2000 for 2-year factory PM and
calibration.

Field calibration check on 5 APR 2001

T-RH probe replaced 23 AUG 2001

Field calibration check on 16 OCT 2001

Field calibration check on 2 MAY 2002

T-RH probe replaced on 14 JUN 2002

T/RH probe replaced on 17 OCT 2002

Field calibration check on 27 NOV 2002

T/RH probe replaced on 27 NOV 2002

Field calibration check on 17 APR 2003

Field calibration check on 30 OCT 2003

Field calibration check on 29 APR 2004

Field calibration check on 30 SEP 2004

T-RH probe replaced on 9 DEC 2004

Field calibration check on 28 APR 2005

Field calibration check on 10 NOV 2005

Wind monitor replaced 10 NOV 2005

Field calibration check on 11 MAY 2006

Field calibration check on 26 OCT 2006

T-RH probe replaced/upgraded on 15 FEB 2007

Rain Gauge replaced on 12 APR 2007

Field calibration check 26 APR 2007

Barometer replaced on 24 APR 2007

Field calibration checks on 25 OCT 2007

Wind Monitor replaced on 28 FEB 2008

**SMOS E25, Seminole OK**

Data available beginning on 16 DEC 1996

Field calibration check on 9 APR 1997 (DQR No. D970718.14)

Field calibration check on wind sensors only 21 MAY 1997

Field calibration check on 22 OCT 1997 (DQR No. D980407.3)

T/RH probe had drifted out of tolerance. It was replaced on 3 DEC 1997.

Replacement T/RH probe not functioning properly. It was replaced on 16
DEC 1997.

Field calibration check on 20 MAY 1998 (DQR No. D980601.14)

T-RH probe replaced on 21 OCT 1998

Field calibration check on 13 JAN 1999

Field calibration check on 25 MAR 1999

Field calibration check on 15 DEC 1999

Field calibration check on 17 MAY 2000

Field calibration check on 4 OCT 2000

Wind monitor replaced on 13 DEC 2000 for 2-year factory PM and
calibration.

T-RH probe replaced on 10 JAN 2001

Field calibration check on 4 APR 2001

Field calibration check on 17 OCT 2001

**Site removed 08 APR 2002 - last data collection at 15:00 GMT**

**SMOS E27, Earlsboro OK**

Data available beginning on 2 MAY 2003 (no rain gage)

Rain gage installed 5 MAY 2003

Field calibration check on 15 MAY 2003

Field calibration check on 29 OCT 2003

Field calibration check on 28 APR 2004

Field calibration check on 27 SEP 2004

T-RH probe replaced on 8 DEC 2004

Field calibration check on 27 APR 2005

Field calibration check on 9 NOV 2005

Wind monitor replaced on 9 NOV 2005

Field calibration check on 10 MAY 2006

Wind monitor replaced on 30 AUG 2006

Field calibration check on 25 OCT 2006

T-RH probe replaced/upgraded on 12 FEB 2007

Rain Gauge replaced on 28 MAR 2007

Field calibration check on 27 APR 2007

Field calibration checks on 24 OCT 2007

## Operation and Maintenance

### User Manual

This section is not applicable to this instrument.

### Routine and Corrective Maintenance Documentation

<http://www.ops.sgp.arm.gov/pm_proc/smospm.htm>

### Software Documentation

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

### Additional Documentation

## 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, which 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.

**ARM Glossary[:]{.underline}** <http://www.arm.gov/about/glossary.stm>

## Acronyms

A/D analog-to-digital converter

ARM Atmospheric Radiation Measurement (Program)

DQA Data Quality Assessment

RH relative humidity

RMSE root-mean-square error

SGP Southern Great Plains

SMOS Surface Meteorological Observation System

T/RH Temperature/Relative Humidity

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

## Citable References

This section is not applicable to this instrument.