BAO Site Information

Location: Erie, CO, USA

  • Latitude: 40 03 00.10028(N)
  • Longitude: 105 00 13.80781(W)
  • Elevation: 1584 m
  • Time Zone: GMT-7
  • Height: 985 ft (300 m)
  • NGS Benchmark Data

Instrumentation: 4 levels (Surface, 10, 100, 300 meters)

  • Surface Pressure, precipitation
  • 10m T, RH, Wind Speed and Direction (prop-vane)
  • 100m T, RH, Wind Speed and Direction (prop-vane)
  • 300m T, RH, Wind Speed and Direction (2-D sonic anemometer)

How to Access Current BAO Tower Data: Via FTP
cd psd3/bao/Tower/Processed/daily (Daily processed files can be found in this directory)

Files contain both uncorrected and corrected wind directions (see formats below)

  • BAO_010_YYYYDDD.dat
  • BAO_100_YYYYDDD.dat
  • BAO_300_YYYYDDD.dat
  • YYYY = Year DDD = Year day (UTC)

Daily plots of the data like those shown in the Data Browser can be found at:  cd et6/archive/BAO/Tower/Processed_Images/daily

Wind directions are corrected for boom orientation.

300m PRT temperature is also corrected

  • BAO_300_YYYYDDD_Tall  300m temperatures
  • BAO_300_YYYYDDD_WS  300m wind speed and direction
  • BAO_300_YYYYDDD_TRH  300m temperature and relative humidity
  • BAO_010_YYYYDDD_PP  Surface pressure and precipitation
  • BAO_010_YYYYDDD_WS  10m wind speed and direction
  • BAO_010_YYYYDDD_TRH  10m temperature and relative humidity
Composite Plots:
  • BAO_PPall Surface pressure and precipitation for all data
  • BAO_010100300_YYYYDDD_TRH Combined 10, 100, 300m temperature and relative humidity
  • BAO_010300_YYYYDDD_WS Combined 10, 300m wind speed and direction

Monthly data files and plots are also available at:

  • cd et6/archive/BAO/Tower/Processed/monthly:
  • cd et6/archive/BAO/Tower/Processed/monthly:

Format for the Daily and Monthly Processed files are:

As of Oct 2, 2007 ~ 1600 UTC there was a change in the output format for the 10m and 100m data. For data before Oct 2, 2007 ~ 1600 UTC the vector WS and DIRsd are set to -999.0.f On Sept 14, 2010 at 1818 UTC a wind sensor was placed at the 100 m level of the BAO.

Using Campbell Scientific P69 formulas:
WSs = wind speed scalar average wind:
WSv = wind speed vector average wind:
DIR = average wind direction true:
DIRsd = standard deviation of the wind direction:

Surface Data:
ID YR Day hhmm Press Precip :

10m Data:
ID YR Day hhmm T RH WSs WSv DIR DIRsd VDC TrueWindDir(Vector):

100m Data:
ID YR Day hhmm T RH WSs WSv DIR DIRsd VDC TrueWindDir(Vector):

300m Data:
"TOA5","CR1000", "CR1000","2846", "CR1000.Std.11", "CPU:060516b_Met.CR1","10044", "wkt30m":
"TIMESTAMP", "RECORD", "SE1_SONICWS_Avg","SE2_SONICWD_Avg","SE2_SONICWD_Std","SE1_SONICWS_Std", "SE3_SONICTEMP_Avg", "D3_PRTRES_Avg","D3_PRTTEMPAPPROX_Avg", "SE4_HMPTEMP_Avg","SE9_HMPRH_Avg", "P1_AIRFLOW_Avg", "SE10_ACPOWER", "BT_BATVOLT_Min","PRT_AVG","SONICWDT_AVG": "TS", "RN", "ms", "Deg", "Deg", "ms", "mV", "", "Deg C", "Deg C", "%", "Counts", "ms", "Volts", "DegC", "Deg True": "", "", "WVc", "WVc", "WVc", "Std", "Avg", "Avg", "Avg", "Avg", "Avg", "Avg", "Smp", "Min", "Avg", "Avg": "2007-12-31 00:00:30", 574334, 7.723,6.177,5.485, 1.166,2.137,98.82967, -3.682, -2.398,72.77,0, 109.3, 13.64, -2.94,328.2, "2007-12-31 00:01:00", 574335,9.37,351.2,7.864, 1.3,2.046,98.84432,-3.645, -2.394, 72, 0, 109.3, 13.64, -2.91, 313.2 "2007-12-31 00:01:30", 574336,9.42, 3.177, 4.47, 1.356,2.572,98.86556, -3.59, -2.395, 68.39, 0, 109.3, 13.64, -2.85,325.2

Variable Description
TIMESTAMP Date and time of beginning of averaging period (UTC)
RECORD_NUMBER Serial record number of the averaging period
SE1_SONICWS_Avg Sonic wind speed (m/s)
SE2_SONICWD_Avg Sonic wind direction relative to tower boom (deg)
SE2_SONICWD_Std Standard deviation of Sonic wind direction
SE1_SONICWS_Std Standard deviation of Sonic wind speed
SE3_SONICTEMP_Avg Sonic temperature (C) (not to be used as an acurate mean temp)
D3_PRTRES_Avg Precision Resistant Temperature resistence (Ohms) (not corrected)
D3_PRTTEMPAPPROX_Avg Precision Resistant Temperature (C) (not corrected)
SE4_HMPTEMP_Avg Vaisala HMP temperature (C)
SE9_HMPRH_Avg Vaisala HMP Relative humidity (%)
P1_AIRFLOW_Avg Vaisala radiation shield air flow
BT_BATVOLT_Min Campbell datalogger battery voltage (VDC)
PRT_AVG Precision Resistant Temperature (C) (corrected)
SONICWDT_AVG Sonic wind direction True (deg)


The Boulder Atmospheric Observatory (BAO) tower was owned and operated by what is now the NOAA Earth System Research Laboratory's (ESRL) Physical Sciences Division (PSD) for almost 40 years. Constructed in 1976-1977 at a cost of $1.3M, the BAO sat on State of Colorado land just west of I-25, and just east of the town of Erie, along the I-25 corridor. At a height of 300 m (with structural strength capable of supporting an additional 200 m extension), the BAO was a very unique observational platform situated on the gently rolling plains of eastern Colorado.

The BAO was originally constructed to support atmospheric boundary layer probes (e.g., temperature, humidity, wind, and turbulence sensors). Data from these sensors was used in a number of fundamental boundary layer studies and to assess the performance of a wide variety of ground- based remote sensing systems developed by PSD (e.g., radar, lidar, sodar). The dozens of publications that resulted from these studies have established the BAO tower as a premier boundary layer observation facility.

Over the years use of the BAO expanded. NOAA ESRL's Global Monitoring Division began to make measurements from the top the BAO tower in 1985 in an effort to extend NOAA's radiation observational network and to take advantage of the unique opportunity presented by the tower. That opportunity was to be able to view a relatively large surface area and make extended quantitative observations of solar and infrared radiation that is either reflected or emitted from that portion of the earth's surface. The size of the area sampled from the top of the BAO approaches that sampled by satellite or simulated in numerical weather and climate models. The land surface area surrounding the BAO was representative of an area whose complexities make it a challenge to interpret in satellite data or to properly model numerically, but which is similar to a significant portion of the earth's land surface. This defining test for the satellite observations and General Circulations Models (GCM) made the data particularly valuable. The data collected on the BAO tower have been used in multiple satellite global radiation budget studies and by various GCM groups, including NOAA's Geophysical Fluid Dynamics Laboratory and European Center for Medium-Range Weather Forecasting.

Additionally the BAO tower site was a participant in the World Climate Research Program's Baseline Surface Radiation Network (BSRN) that requires that the data meet certain high standards. The BSRN collects the data and provides it through its central high-visibility archive in Zurich, Switzerland. Data are also available directly from the ESRL/GMD radiation group in Boulder. The radiation data collected at the BAO tower were continuous, sampling once per second, 24 hours a day for the last 16 years with only minimal loss so that data are available for nearly any time frame of interest to the diverse user community. Also, such a long-term data set has become valuable in its own right as an important record of the local and regional climate as driven by and reflected in the energy budget obtained from such a uniquely representative vantage point.

The BAO sat on 100 acres of State of Colorado land located in Erie, CO. This land is primarily agricultural and consists of natural grass and wheat fields.