Perfectly diffuse radiator-
A body that emits radiance isotropically.
Perfectly diffuse reflector-
A body that reflects radiance isotropically.
Permeameter-
One of any number of devices used to measure the permeability of porous media.
Pers sunshine recorder-
A sunshine recorder of the type in which the timescale is supplied by the motion of the sun.
Photoelectric photometer-
A device that uses a photoelectric cell to measure electromagnetic radiation in the visible portion of the electromagnetic spectrum.
Photoelectric transmittance meter-
An instrument for measuring the transmissivity of the atmosphere; a type of transmissometer.
Photographic barograph-
A mercury barometer arranged so that the position of the upper or lower meniscus may be measured photographically.
Photometer -
An instrument for measuring the luminance, luminous intensity, or illuminance of a light source.
Photopolarimeter-
A polarimeter operating at optical wavelengths, especially in the band of wavelengths visible to the human eye.
Phytometer-
A device (similar to a potometer) for measuring transpiration.
Piché evaporimeter-
A porous paper wick atmometer. Named for Albert Piché, a French inventor and weather observer.
Piezometer-
A device (tube or pipe) that allows one to determine the elevation of hydraulic head in an aquifer at a given point.
Pitot tube anemometer-
A pressure-tube anemometer, consisting of a Pitot tube mounted on the windward end of a wind vane.
Pitot tube-
A pressure anemometer consisting of two concentric tubes that are oriented parallel to the flow. Named for Henri Pitot, French hydraulic engineer.
Pivot arm anemometer-
An instrument for measuring the wind speed by determining the force (usually by measurement of mechanical deflection)
on a suspended plate exposed to the airstream.
Point gauge-
A device used to measure water levels.
Polarimeter-
An instrument for determining the degree of polarization of light.
Polarimetric radar-
A radar capable of measuring any or all of the polarization-dependent attributes of a target or backscattering medium.
Polariscope -
An instrument for studying, or examining substances in, polarized light.
Polarization diversity radar-
A radar capable of measuring polarization-dependent attributes of a target.
Pole star recorder-
An instrument used to determine approximately the amount of cloudiness at night.
Potentiometer-
An instrument for measuring differences in electric potential.
Potometer-
A device (similar to a phytometer) for measuring transpiration.
Precipitation gauge-
General term for any instrument that measures precipitation, usually meaning a rain gauge or snow gauge.
Pressure altimeter-
An aneroid barometer calibrated to convert atmospheric pressure into altitude. Standard atmospheric conditions with a correction for surface pressure (altimeter setting) is assumed in this calibration.
Pressure jump detector-
A sensor designed to detect the rapid rise in pressure associated with the leading edges of outflow boundaries (pressure jump) or beneath strong downdrafts (pressure nose).
Pressure sphere anemometer-
An anemometer that measures the three components of the wind vector by means of an array of pressure ports bored in a sphere.
Pressure tide gauge-
Instruments that measure the pressure below the sea surface; this pressure may be converted to sea level if the air pressure,
the gravitational acceleration, and the water density are known.
Propeller anemometer-
A rotation anemometer that has a fixed axis upon which a propeller consisting of helicoidal vanes is mounted.
Propeller type current meter-
A device for streamflow measurement, using the rotation rate of a propeller as an indicator of flow velocity.
Propeller vane anemometer-
An instrument for the measurement of both horizontal wind speed and direction, consisting of a propeller anemometer mounted on the windward end of a wind vane.
Protected thermometer-
A reversing thermometer that is encased in a strong glass outer shell that protects it against hydrostatic pressure.
Psychrometer -
An instrument used to measure humidity . It consists of two thermometers exposed side by side, one of which (the dry bulb) is an ordinary glass thermometer, while the other (the wet bulb) has its bulb covered with
a jacket of clean muslin that is saturated with distilled water prior to an observation.
Pulse integrator-
An electronic device for the measurement of the average received power from a target illuminated by a pulsed transmission.
Pulsed light cloud height indicator -
A remote-sensing instrument used for the determination of cloud heights.
Pulsed radar-
A radar that transmits and receives individual pulses of radio energy, as opposed, for example, to a continuous-wave radar.
Pyranometer -
General name for the class of actinometers that measure the combined intensity of incoming direct solar radiation and diffuse sky radiation.
Pyrgeometer-
Instrument for measuring radiation in the longwave range between 2 and 60 mm. As a horizontal downward-facing black surface, it measures the terrestrial radiation,
and as a horizontal upward-facing black surface, it measures the atmospheric radiation.
Pyrheliometer -
General term for the class of actinometers that measure the intensity of direct solar radiation.
Pyrradiometer -
Instrument for measuring the total irradiance (solar and atmospheric) on a horizontal surface from a solid angle of 2?.
