NovaLynx Corporation
Weather Monitoring Instruments and Systems
Evaporation Sensors and Stations
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 Evaporation Pan |
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 Evaporation Gauge |
NovaLynx offers a variety of mechanical and electronic systems for measuring the evaporation rate of water into the atmosphere.
255 Series Evaporation Stations
255-100 Evaporation Gauge (3003)
255-110 Evaporation Gauge Tester
255-200 Evaporation Pan (3005) (6821)
255-212 Floating/Submersible Min-Max Thermometer
255-250 Evaporation Pan Platform (PDF 36KB)
255-620 Auto Refill Kit
255-700 ETgage
255-704-A Evaporation Logger
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NWS OBSERVING HANDBOOK NO. 2
SECTION 5: EVAPORATION STATION OBSERVATIONS
5.1 INTRODUCTION
Observations are made of the amount of evaporation to the nearest hundredth inch from an open pan. Other elements recorded include wind movement, water and air temperatures, and precipitation. At some sites, additional parameters will be required, such as dry and wet bulb temperatures, humidity, and the temperature and moisture content of the soil. Section 6 contains instructions on soil temperature measurements.
5.2 SETTING UP THE OBSERVING SITE
5.2.1 EXPOSURE OF EQUIPMENT
The equipment site should be fairly level, sodded, and free from obstructions (exhibit 5.1). It should be typical of the principal natural agricultural soils and conditions of the area. Neither the pan nor instrument shelter should be placed over heat-absorbing surfaces such as asphalt, crushed rock, concrete slabs or pedestals. The equipment should be in full sunlight during as much of the daylight hours as possible, and be generally free of obstructions to wind flow. Obstructions that cannot be moved, such as trees, buildings, and nearby shrubs, should not be closer to the instruments than four times their heights. Shadows are permissible only near sunrise and sunset. Avoid areas subject to flooding or lawn sprinkling.
At reservoirs (flood control, water supply, and irrigation projects) the pan should be placed on the upwind side of the water. This is based on the prevailing direction of the strongest winds. The pan site should be far enough from the water to avoid the chance that water or spray carried from a spillway, or picked up from the reservoir by a strong wind, will be deposited in the pan. The layout of equipment on the plot is shown in exhibit 5.2. The orientation N of the layout should be as indicated by the North arrow. If necessary, the layout can be rotated as much as 45°.
5.2.2 PLOT LAYOUT
Note that the layout is designed to eliminate shadows from instruments at stations in the northern hemisphere. Shadows from small diameter fence posts will occur only briefly in the late afternoon. The minimum distances between instruments are shown in exhibit 5.2. The 10- by 16-foot plot shown is the minimum size. If other equipment is installed, the plot should be enlarged accordingly.
5.2.3 ENCLOSURE
The plot must be enclosed by a fence that will keep out animals. A steel chain link fence (9 or 11 gauge), at least four feet high, with steel posts set in concrete is recommended. Fences of wood or other solid material shall not be used. It may be necessary to bury a barrier under the fence for protection from burrowing animals, or add 18 to 24 inches of one inch galvanized chicken mesh fence along the bottom of the chain link fence to keep out small animals.
5.3 EVAPORATION EQUIPMENT
This section describes the installation, maintenance, and method of taking observations from each instrument. Evaporation measurements are made with an evaporation pan and a fixed-point gage with a measuring tube. Evaporation stations have the following additional instruments:
a) An anemometer to determine the daily wind movement over the pan and a display stand pintle (subsection 5.3.4).
b) An Clinch nonrecording precipitation gage with appropriate measuring stick or in some cases, a weighing-type recording precipitation gage.
c) A water temperature thermometer or thermograph to provide maximum, minimum, and current temperatures of the water in the evaporation pan (subsection 5.3.6).
d) Maximum and minimum thermometers or a thermograph for measuring the air temperature. Some stations have a hygrothermograph in place of these for measuring air temperature and humidity (subsection 5.3.5).
e) An instrument shelter for housing the temperature and humidity measuring instruments.
f) A water storage tank (if necessary) to provide a reserve water supply for the pan (subsection 5.3.3).
Continued... (PDF 1.4MB 94 pages)
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