Absolute Pressure (definition)：
Absolute pressure is the measured atmospheric pressure. Absolute pressure is not corrected to sea-level conditions.
To compare pressure conditions from one location to another, meteorologists correct pressure to sea-level conditions (referred to as relative pressure, ｏｒ pressure relative to sea-level).
Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea-level) is higher than your measured pressure if you live above sea-level and lower than your measured pressure if you live below sea-level.
Relative Pressure (definition)
Relative pressure is the atmospheric pressure corrected to sea-level conditions.
To compare pressure conditions from one location to another, meteorologists correct the measured pressure (referred to as absolute pressure) to sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea-level) is higher than your measured pressure if you live above sea-level and lower than your measured pressure if you live below sea-level.
Anemometer：
An anemometer is a device for measuring wind speed, and is one instrument used in a weather station. The term is derived from the Greek word(anemos, meaning wind). An anemometer can also be loosely defined as a device that measures both windspeed and wind direction (wind vane).
Barometer:
A barometer is an instrument used to measure atmospheric pressure.
To compare pressure conditions from one location to another, meteorologists correct pressure to sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea-level) is generally higher than your measured pressure.
Dew Point (definition):
The dew point is the temperature at which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into water. The condensed water is called dew. The dew point is a saturation temperature.
The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity will decrease.
Heat Index (definition)
The Heat Index, sometimes referred to as the apparent temperature, is a measure of how hot it really feels when relative humidity is factored with the actual air temperature.
To find the Heat Index temperature, look at the Heat Index chart below. As an example, if the air temperature is 96°F and the relative humidity is 65%, the heat index (how hot it feels) is 121°F.
IMPORTANT: Since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15°F. Also, strong winds, particularly with very hot, dry air, can be extremely hazardous.
The Heat Index Chart shaded zone above 105°F shows a level that may cause increasingly severe heat disorders with continued exposure ｏｒ physical activity.
Hygrometer (definition)
A hygrometer is a device that measures relative humidity.
Relative humidity is a term used to describe the amount ｏｒ percentage of water vapor that exists in air.
Leaf Wetness (definition)
A leaf wetness sensor detects the presence of surface moisture and is measured between 0 (dry) and 15 (saturated).
The sensor includes surface contacts that measure the electrical resistance of a water film on the leaf surface.
Nuclear Radiation Detector (definition)
A nuclear radiation detector is a device that measures radiation levels for early warning and general monitoring systems in REMs. The display shows both the current level in REMs and total exposure in REM hours.
Note: This sensor is designed to function as an early warning and does not ｒｅｐｌａｃｅ hand held Geiger counters.
Radio Controlled Clock (definition)
A radio controlled clock ｏｒ "Atomic Clock" keeps near perfect time by automatically synchronizing to the radio signal emitted from the U.S. Atomic Clock in Colorado. Radio controlled clocks reset daily to the split second, and adjust automatically to Daylight Savings Time, Leap Year and Time Zone Changes.
NIST distributes time-of-day and frequency information to the public using radio broadcasts. The low frequency (LF) station WWVB is located in Fort Collins, Colorado and broadcasts on 60 kHz. The high frequency (HF) stations WWV and WWVH are located in Colorado and Hawaii respectively, and broadcast on five different frequencies ranging from 2.5 to 20 MHz. At least one HF signal should always be usable at any given time anywhere in the United States.
Rain Gauge (definition)
A rain gauge is a device that measures liquid precipitation (rain), as opposed to solid precipitation (snow gauge) over a set period of time.
All digital rain gauges are self emptying ｏｒ self dumping (also referred to as tipping rain gauge). The precision of the rain gauge is based on the volume of rain per emptying cycle.
Soil Moisture (definition)
Asoil moisture sensor measures the quantity of water contained in a material, such as soil on a volumetric ｏｒ gravimetric basis.
To obtain an accurate measurement, a soil temperature sensor is also required for calibration.
Solar Radiation (definition)
A solar radiation sensor measures solar energy from the sun.
Solar radiation is radiant energy emitted by the sun from a nuclear fusion reaction that creates electromagnetic energy. The spectrum of solar radiation is close to that of a black body with a temperature of about 5800 K. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum.
The units of measure are Watts per square meter.
The device is typically used in agricultural applications, and is used in the calculation of Evapotransportation. Evapotransportation is the potential for evaporation of moisture from the soil (ｏｒ the reverse of rainfall) and is a function solar energy, wind and temperature.
Soil Moisture (definition)
Asoil moisture sensor measures the quantity of water contained in a material, such as soil on a volumetric ｏｒ gravimetric basis.
To obtain an accurate measurement, a soil temperature sensor is also required for calibration.
Soil Temperature (definition)
A soil temperature sensor measures the temperature of the soil ｏｒ other medium.
The probes are stainless steel, and are typically resitive thermal devices (RTD). RTDs predict change in temperature as a function of electrical resistance.
Thermometer (definition)
A thermometer is a device that measures temperature. Most digital thermometers are resitive thermal devices (RTD). RTDs predict change in temperature as a function of electrical resistance.
Ultraviolet (definition)
An ultraviolet sensor (UV sensor) is a device that measures UV light from the Sun.
The UV index is an international standard measurement of how strong the ultraviolet (UV) radiation from the sun is at a particular place on a particular day. It is a scale primarily used in daily forecasts aimed at the general public.
Its purpose is to help people to effectively protect themselves from UV light, of which excessive exposure causes sunburns, eye damage such as cataracts, skin aging, and skin cancer (see the section health effects of ultraviolet light).
Water Temperature (definition)
A water temperature sensor measures the temperature of water ｏｒ other medium.
The probes are typically resitive thermal devices (RTD). RTDs predict change in temperature as a function of electrical resistance.
Weather Station (definition)
A weather station typically consists of an anemometer (measures wind speed and wind direction), a self-emptying rain gauge, temperature, humidity and barometric pressure sensors. Most weather stations also measure indoor temperature and humidity.
Some weather stations include solar radiation, UV, water proof probes, additional temperature and humidity sensors, leaf wetness, soil moisture, and lightning detectors.
Wind Vane (definition)
A wind vane is a device that measures the direction of the wind. The wind vane is usually combined with the anemometer. Wind direction is the direction from which the wind is blowing.
Accuracy, Resolution, and Range (definition)
Accuracy is the ability of a measurement to match the actual value of the quantity being measured.
Resolution is the number of significant digits (decimal places) to which a value is being reliably measured.
Range is the amount ｏｒ extent a value can be measured.