The purpose of this project is to provide students with the opportunity to use state-of-the-art meteorological equipment to measure temperature, humidity, radiation, and wind values at two sites. Comparisons of accuracy and response time are made between electronic and hand-held instruments. Data comparisons can also be made between the two sites, one adjacent to a flowing creek and pond and the other located on top of a small hill, above a busy road, and far from a body of water.
In teams of two, you will take weather observations for a three hour period, on the hour, at the Burd Run Bio Pond or at the weather station near the Little Red School House adjacent to Route 696. In addition to using the datalogger to read the weather data, you will use a sling psychrometer to compute temperature and relative humidity values, and a Kestrel weather meter to measure wind speed, temperature, wind chill, relative humidity and dew point. You should make immediate comparisons between the output of all of the sensors taken during your observations. A discussion of all readings will be held in class upon completion of the exercise. This exercise will enable you to determine the controls that produce unique microclimates at two different places on campus and will reveal the differences between using expensive electronic equipment and less expensive hand-held instrumentation.
- Campbell Scientific, Inc. tripod with datalogger and probes to measure temperature, relative humidity, wind speed, wind direction, incoming and reflected solar radiation, and net radiation.
- Sling psychrometer to manually measure temperature, relative humidity, and dew point.
- Kestrel hand-held instrument to measure temperature, relative humidity, dew point, wind speed, and wind chill.
- Compass to determine wind direction.
Readings to be taken on Wednesday, February 28 at
0600, 0700, 0800 (before and after sunrise and around coldest time of day);
1100, 1200, 1300 (before and after the time of maximum solar intensity);
1400, 1500, 1600 (before and after time of warmest daily temperature);
1700, 1800, 1900 (before and after sunset);
2200, 2300, 2400 (complete darkness).
Access the correct key for your location at the campus police station (Reed Operations Center). You will need to leave your student ID when borrowing the key. Take the key to the proper site, unlock the gate (close gate temporarily if at the Bio Pond site), and walk to the weather station.
Procedure #1: Open, or unlock and open (only at the Bio Pond), the white waterproof box and proceed to take readings using the hand-held keypad (with the enclosed flashlight, if necessary). Write down the time and date. Press *6A to read data, press A to advance, B to backup. Using the clipboard and pencil attached to the inside of the white cover, write down all readings. After completing your readings using the datalogger, press *0 to put the datalogger in log mode.
Procedure #2: Take the sling psychrometer out of the bag on the top of the datalogger, wet the wick with the distilled water in the small container, and mark down your dry-bulb temperature. Sling the psychrometer around for 20 seconds keeping the instrument out of direct sunshine. Take your wet-bulb reading, remember it, and sling the psychrometer for another 20 seconds. Continue with this procedure until two consecutive readings result in the same value. Write down the last wet-bulb reading. Calculate the wet-bulb depression (dry minus wet bulb temperature). Using the charts on the clipboard, figure out the relative humidity and dew point temperature. Read down from the wet-bulb depression and to the right from the dry-bulb (or ambient air) temperature. Interpolate between values if the exact numbers are not located on the chart. Write down the correct values on the table on the clipboard. Carefully replace the sling psychrometer on the top of the datalogger box and the container of water inside the shelter.
Procedure #3: Take out the Kestrel weather instrument. Place the lanyard around your neck, slide the cover off the instrument, and press the ON button. Hold the instrument facing into the wind and allow to equilibrate (adjust to the current conditions) for a few minutes. Write down the wind speed in mph and m/s as well as all other readings. To change units, press and hold the ON button and then press the MODE button. Release the ON button to determine the appropriate value. Continue pressing the MODE button and write down maximum wind (mph & m/s), average wind (mph & m/s), temperature (C and F), wind chill (C and F), relative humidity (%), skip the next value (with the little thermometer, rain drop and % sign), and finally, the dew point (C and F). When done, press the ON button to turn off the instrument, slide the cover back on, remove the lanyard, and place back in the white shelter.
Procedure 4: Replace the clipboard in its location. Leave the flashlight in the box (if you're taking readings at night). Lock the shelter (at the Bio Pond only). Do not forget to lock the outside gate when leaving. After completing your three separate readings on the hour, RETURN THE KEY TO THE POLICE STATION!!! PLEASE DON'T FORGET TO DO THIS.
Complete the following questions for your site. Type on a separate piece of paper and bring to class for discussion. Print out graphs and attach to your answers.
1. After the data collection is complete, work together to enter all data into an Excel spreadsheet. Create graphs comparing all weather variables using different instruments at both stations.
2. Did all three types of instrumentation give you similar values for temperature, relative humidity, and dew point? If not, what do you think caused the differences?
3. Describe how you think the site features (e.g., proximity to water) modified the readings that you have taken? Can you see or think of anything that might cause the values to be in error?
4. Describe how the readings taken at the other site were different than yours for the three hours during which you took readings. For instance, what might cause a difference in temperature, wind speed, relative humidity, and dew point between the Bio Pond site and the station near Route 696?
Meteorological Instrumentation Description
Datalogger: This is a 12-volt, solar-powered measurement and control system that can be programmed to read and store meteorological data. It delivers accurate, reliable measurements in a variety of applications for day-to-day operations such as microclimatology, plant water research, canopy energy balance, machinery performance, plant pathology, crop management decisions, food processing/storage, frost prediction, irrigation scheduling, and pest management.
Net Radiometer: This sensor calculates the incoming total hemispherical radiation minus outgoing total hemispherical radiation including both shortwave and longwave radiation. Net radiation is the energy retained by the surface for heating soil and air, plant growth and evaporation of water. Evaporation of water is the largest heat sink when water is available. Evapotranspiration is closely related to net radiation in humid conditions. Therefore, net radiation is the most useful radiative term in evapotranspiration research. This instrument is sensitive to wavelengths from 0.25 to 60 micrometers.
Radiometer: This instrument outputs a low level voltage for shortwave radiation from the sun. Inverted, it measures reflected shortwave radiation.
Relative Humidity Probe: This probe contains a relative humidity sensor and a thermistor configured for use with a datalogger. It is designed for long-term, unattended applications. A switching circuit is installed to supply power only during measurement. Separate input/output instructions are used to read each sensor despite both sensors acting as one probe. The sensor can be programmed to read vapor pressure, a more realistic measure of water content of the air.
Sling Psychrometer: A device used to determine temperature and humidity that consists of a dry-bulb thermometer and a wet-bulb thermometer. After wetting the wick, the instrument is rotated to determine the amount of moisture evaporating from the wet wick. Using the resulting temperatures, charts are used to estimate the relative humidity and dew point.
Soil Heat Flux Probe: Energy transfer within the soil is critical to determine heat availability to plants. Energy storage occurs during the transition stage of the day between periods of positive flow into the soil with sunlight available, to negative flow (out of the soil) during nighttime cooling.
Thermistor Probe: This is a water resistant electronic temperature sensor designed for use in air or soil. It consists of a thermistor encapsulated in an epoxy-filled aluminum housing which protects the thermistor allowing the probes to be buried or submerged. It provides temperature measurements to tenths of a degree (degrees C or F).
Wind Speed Sensor: Wind speed is a critical component of the atmosphere to assist with evapotranspiration measurements. Higher values allow for more mixing of air offsetting conditions that cause frost and stagnant cold air.
Wind Vane: Wind direction is important to determine air mass origin. Cold, more polar air tends to originate in the north while warmer, moist conditions tend to prevail and originate in the south.