Cooperative observers use a variety of equipment types. The type used will depend on what services are needed at a particular station. Most observers report at least 24-hour precipitation; some will also report snowfall, high and low temperature. Fewer observers report evaporation measurements, river stages, soil temperatures, or solar readings.
(Rain gage at station Athens 2SW. Click to enlarge.)
This rain gage is what most observers use. It is called a "Standard Rain Gage" (SRG), and consists of a funnel 8 inches in diameter, leading to a tube inside the gage. The inside tube can hold up to 2 inches of rain; any excess will flow into the main container to be measured after the inside tube is emptied. The rainfall is measured using a specially calibrated dipstick. During the winter, the funnel and inside tube are removed; snow falls into the main container, and then is melted to determine the liquid equivalent of the snowfall.
(Recording rain gage at station Flora 5NW. Click to enlarge.)
Selected stations have a recording rain gage. Inside the gage is a bucket on a scale. Every 15 minutes, a punch block inside punches a hole onto a paper tape, indicating the level of the bucket's contents. Using this tape, hourly amounts of precipitation can later be determined. Each month, the observer removes the tape, and mails it in for processing. Upgrades to this gage are beginning, to replace the tape punch feature with an electronic data logger.
(Thermometer shelter at the University of Illinois. Click to enlarge.)
Some stations use mercury and alcohol thermometers to register high and low temperatures. The thermometers are kept inside a ventilated box called a Cotton Region Shelter (CRS, so named because of the location where they were first used). The maximum thermometer pushes the mercury to the highest temperature observed that day, where it stays until it is reset by the observer. The minimum thermometer has a small pin inside, which marks the low temperature.
(Electronic temperature shelter at station Loami 3SSW. Click to enlarge.)
Many temperature-reporting stations use electronic thermometers in place of the mercury thermometers. This particular system is called a Maximum-Minimum Temperature System (MMTS). The sensor is mounted outside, and cables are routed to a digital display inside a nearby building. The digital readout logs the high and low temperatures until reset by the observer. The next generation of MMTS will log high and low temperatures from midnight to midnight (some stations log high and low temperatures currently from 7 am to 7 am, or 6 pm to 6 pm) and keep the last 30 days of observations in memory.
(Staff gage at Havana. Click to enlarge.)
Some observers read river levels using a staff gage. These gages are basically large rulers mounted or painted onto objects such as bridge supports, walls, etc. River levels are read from this gage to the nearest tenth of a foot.
(Wire weight gage. Click to enlarge.)
At some locations, river levels are read using a wire weight gage. This type of gage has cable wound around a drum; a brass or bronze weight is attached to the end of the cable. A crank is used to lower the weight to the surface of the water; a counter and disk on the crank handle indicates the river reading, usually to a hundredth of a foot.
(Data Collection Platform at Allenville, IL. Click to enlarge.)
Many river levels are read using automated methods. Data Collection Platforms (DCP) collect the river level readings, and relay them via satellite or telephone lines. Inside the DCP houses, river levels may be determined using nitrogen gas, voltmeters, or electrical tapes. Many of these DCP sites also have a staff or wire weight gage for backup purposes, especially if river forecasts are issued.