One is an official National Weather Service site that is maintained by Oregon State University and is read every morning at eight o'clock. The data collected from this station is reported to the National Weather Service and is the weather information heard on the radio or read in the papers from the Pendleton Experiment Station. This data is used by a variety of people who are interested in agriculture and weather.

The sensors used to collect this data are mechanical sensors, meaning they have to be read manually to collect information. They are calibrated and cleaned periodically by the National Weather Service to make sure they are accurate and in good working order.

Air temperatures are measured from two separate thermometers. Both are alcohol-filled thermometers inside a louvered instrument shelter that protects them from direct sun, rain and condensation. The louvered shelter permits air to circulate freely around the thermometers so that ambient air temperature can be measured. The maximum thermometer has a mercury-filled bulb which expands as the air temperature rises and then stays at the maximum point until it is reset. The minimum thermometer has an index made of glass within the alcohol that retreats with falling temperatures and stays at the lowest point until it is reset.


Both thermometers are positioned nearly horizontal on a bracket. To reset the minimum thermometer, the bracket clamp that holds the thermometer is released and the top end is tipped downward so the glass index can slide toward the current temperature. Spinning the maximum thermometer on the bracket until the mercury is adjusted downward to the current temperature resets the maximum thermometer.

Also inside the instrument shelter is a device called a hygrothermograph. It comes from two Greek words hygros meaning wet and therme meaning heat. It measures relative humidity and air temperature. This is a spring-wound clock instrument that records on a chart the relative humidity and air temperature. Only the relative humidity from this instrument is used. It measures relative humidity by stretching a human hair bundle between mechanical linkages and through expansion and contraction moves a pen on a calibrated chart recording relative humidity in percent. Expansion occurs when the hair bundle absorbs water vapor. This makes the hair bundle heavier and moves the pen up the chart. When the hair bundle loses water vapor it contracts. This makes the hair bundle lighter and moves the pen lower on the chart.

The rain gauge used to collect precipitation is an eight-inch, non-recording gauge that consists of an overflow can, measuring tube, rainfall funnel, and measuring stick. All of this is mounted on a support. Precipitation is measured with the graduated measuring stick, meaning the stick is scaled so that it shows the correct amount (in hundredths). Soil temperatures are recorded at one, four and eight inches beneath bare soil. A spring-wound clock driven recorder uses pen traces on a chart to show the soil temperature changes. The chart has to be changed weekly and the maximum and minimum temperatures are derived by reading the values from the chart for each day. Evaporation is measured from a standard 48-inch evaporation pan installed on a wooden support.

A micrometer hook gauge and stilling well is used to measure daily evaporation. An anemometer is located by the pan to measure wind movement across the water surface. This anemometer is a totalizing anemometer, which means that it records on a dial the total wind movement for a period of time. It records these units in miles and when divided by the hours since it was read, will determine an average wind speed in miles per hour. The evaporation pan operates from March to November and is cleaned and stored over winter during freezing weather. Snow accumulations are recorded by hand measurements. Sky conditions at the time of the readings (cloudy, partly cloudy, etc.) and any other observations are also recorded. This weather station was installed in 1929 and has been read daily since then. It became an official National Weather Service site in 1956.

The second weather station is automated, using electronic sensors and a data acquisition system to record weather parameters hourly. ARS installed this station in 1982 near the OSU weather station to provide more detailed weather information. This station is used for research purposes, although the public can also request and use this data.

The data acquisition system (datalogger) is an AC power-operated system enclosed in a weatherproof, climate-controlled shelter. It takes one-minute readings of each sensor, stores those values for the hour, and then processes the readings and outputs to a computer the maximum, minimum, average and/or total value of those 60 one-minute readings for each sensor.

The computer has direct communication with the datalogger via modems and a phone line between the computer lab and the weather station over 1000 feet away. The electronic sensors output analog signals (in millivolts) to the datalogger and the datalogger converts these readings to digital format which a computer can then read.

Air temperature is recorded using an air temperature and relative humidity probe that is located in the louvered instrument shelter with the OSU thermometers. Air temperature is determined by a thermistor whose electrical output changes according to the rise and fall of the air temperature.

Relative humidity is measured in the same probe, using a chip whose electrical output varies with the moisture content on the chip. An 8-inch orifice, recording rain gauge records its output on a battery-driven chart and uses a potentiometer to send a voltage output to the datalogger to measure precipitation. The more weight in the bucket of the rain gauge, the higher the voltage output.

This rain gauge is protected during freezing weather with an anti-freeze and mineral oil mix. The mineral oil is used to retard evaporation to make a more stable voltage output. In the winter months a wind shield is installed around the rain gauge to more accurately collect snowfall. A tipping bucket rain gauge is also on site to provide more accurate summertime rainfall. It has a mercury-filled switch that, when it accumulates one hundredth of an inch of moisture, will tip, ejecting the moisture and sending a signal to the datalogger. The datalogger will then record how many times the switch tips to determine total rainfall for the hour.

Soil temperatures under a bare soil surface at one, four, and eight inches are recorded using a thermistor at the probe tip. Evaporation is measured by using a standard 48-inch stainless steel evaporation tank. This evaporation tank has an automated fill system. A valve controls the water level between one and three inches from the top of the tank. When the water level evaporates to the 3-inch level, the valve opens and fills the tank to the 1-inch level. Evaporation is measured through a connected stilling well in which a pressure transducer measures the height difference in the tank.

An anemometer is located nearby to record the air movement across the water surface. A second anemometer is located at a 2-meter height to record air movement. As the anemometer spins in the wind, it sends an output frequency (pulses/second) to the datalogger which can then determine the speed in miles per hour.

This anemometer is set to record only those wind gusts sustained over one minute, so its readings tend to be lower than peak wind gusts which last for only a few seconds. A wind direction sensor is also mounted at a 2-meter height and records wind direction in degrees. True north is 0 degrees, south is 180 degrees.

Solar radiation is measured with a pyranometer or radiometer. Its voltage output depends on the amount of sunlight striking its surface. A shadow band (a device that screens the sensor from the sun as it travels across the sky) is located on another radiometer to provide two kinds of measured solar radiation. The radiometer with the shadow band measures diffuse radiation, radiation that reflects off natural surfaces, while the other radiometer measures sun and sky radiation.

These electronic sensors are calibrated and maintained by ARS. Some sensors are returned to the manufacturer to be factory calibrated. Electronic weather stations require less maintenance than mechanical weather stations but need to be watched weekly to ensure accurate and timely data.

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