The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research. NASA was established in 1958; the new agency was to have a distinctly civilian orientation, encouraging peaceful applications in space science. Since its establishment, most US space exploration efforts have been led by NASA, including the Apollo Moon landing missions, the Skylab space station, the Space Shuttle. NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the Space Launch System and Commercial Crew vehicles; the agency is responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA science is focused on better understanding Earth through the Earth Observing System. From 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1.
In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year. An effort for this was the American Project Vanguard. After the Soviet launch of the world's first artificial satellite on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts; the US Congress, alarmed by the perceived threat to national security and technological leadership, urged immediate and swift action. On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever. On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology" stating: It is of great urgency and importance to our country both from consideration of our prestige as a nation as well as military necessity that this challenge be met by an energetic program of research and development for the conquest of space... It is accordingly proposed that the scientific research be the responsibility of a national civilian agency...
NACA is capable, by rapid extension and expansion of its effort, of providing leadership in space technology. While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency was created in February 1958 to develop space technology for military application. On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA; when it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact. A NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA. A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernher von Braun, now working for the Army Ballistic Missile Agency, which in turn incorporated the technology of American scientist Robert Goddard's earlier works. Earlier research efforts within the US Air Force and many of ARPA's early space programs were transferred to NASA.
In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology. The agency's leader, NASA's administrator, is nominated by the President of the United States subject to approval of the US Senate, reports to him or her and serves as senior space science advisor. Though space exploration is ostensibly non-partisan, the appointee is associated with the President's political party, a new administrator is chosen when the Presidency changes parties; the only exceptions to this have been: Democrat Thomas O. Paine, acting administrator under Democrat Lyndon B. Johnson, stayed on while Republican Richard Nixon tried but failed to get one of his own choices to accept the job. Paine was confirmed by the Senate in March 1969 and served through September 1970. Republican James C. Fletcher, appointed by Nixon and confirmed in April 1971, stayed through May 1977 into the term of Democrat Jimmy Carter. Daniel Goldin was appointed by Republican George H. W. Bush and stayed through the entire administration of Democrat Bill Clinton.
Robert M. Lightfoot, Jr. associate administrator under Democrat Barack Obama, was kept on as acting administrator by Republican Donald Trump until Trump's own choice Jim Bridenstine, was confirmed in April 2018. Though the agency is independent, the survival or discontinuation of projects can depend directly on the will of the President; the first administrator was Dr. T. Keith Glennan appointed by Republican President Dwight D. Eisenhower. During his term he brought together the disparate projects in American space development research; the second administrator, James E. Webb, appointed by President John F. Kennedy, was a Democrat who first publicly served under President Harry S. Truman. In order to implement the Apollo program to achieve Kennedy's Moon la
MetOp is a series of three polar orbiting meteorological satellites developed by the European Space Agency and operated by the European Organization for the Exploitation of Meteorological Satellites. The satellites form the space segment component of the overall EUMETSAT Polar System, which in turn is the European half of the EUMETSAT/NOAA Initial Joint Polar System; the satellites carry a payload comprising 11 scientific instruments and two which support Search and Rescue services. In order to provide data continuity between MetOp and NOAA Polar Operational Satellites, several instruments are carried on both fleets of satellites. MetOp-A, launched on October 19, 2006, is Europe's first polar orbiting satellite used for operational meteorology. With respect to its primary mission of providing data for Numerical Weather Prediction, studies have shown that MetOp-A data are measured as having the largest impact of any individual satellite platform on reducing 24 hour forecasting errors, accounts for about 25% of the total impact on global forecast error reduction across all data sources.
Each of the three satellites were intended to be operated sequentially, however good performance of the Metop-A and Metop-B satellites mean a period of 3 satellite operations are now expected. In 2022 a second generation of MetOp satellites will be deployed, called MetOp-SG. MetOp has been developed as a joint undertaking between the European Space Agency and European Organisation for the Exploitation of Meteorological Satellites. Recognising the growing importance of Numerical Weather Prediction in weather forecasting, MetOp was designed with a suite of instruments to provide NWP models with high resolution global atmospheric temperature and humidity structure. Data from MetOp are additionally used for atmospheric chemistry and provision of long term data sets for climate records; the MetOp satellites have a modular construction, comprising a Service Module, a Payload Module and a suite of Instruments. A SPOT heritage service module provides power and orbit control, thermal regulation and Tracking and Command.
An Envisat heritage payload module provides common command and control and power buses for the instruments along with science data acquisition and transmission. The suite of instruments are derived from precursors flown on the European Space Agency's European Remote-Sensing Satellite /Envisat satellites or are recurrent units developed for NOAA's Television Infrared Observation Satellite series of polar-orbiting satellites. With the exception of Search and Rescue, a purely local mission with its own dedicated transmitter, all data from the MetOp Instruments are formatted and multiplexed by the Payload Module and either stored on a solid state recorder for transmission via an X-Band antenna, or directly transmitted to local users via High Rate Picture Transmission VHF antenna; the main Command and Data Acquisition head is located at Svalbard Satellite Station in Norway. The high latitude of this station allows the global data stored in the solid state recorder of each satellite to be dumped via X-Band once per orbit.
Each MetOp satellite produces 2 GB of raw data per orbit. Additionally, in order to improve timeliness of products, one of the operational satellites dumps the data from the descending part of the orbit over the McMurdo groundstation in Antarctica. Data are trickle fed from the ground stations to EUMETSAT Headquarters in Darmstadt, where they are processed and disseminated to various agencies and organisations with a latency of 2 hours without the McMurdo ground station and 1 hour with Svalbard. HRPT is used to provide a real-time direct readout local mission via a network of receivers on ground provided by cooperating organisations. Data from these stations is transmitted to EUMETSAT and redistributed to provide a regional service with 30 minutes latency. Due to radiation sensitivity of the HRPT hardware, the MetOp-A HRPT does not operate over the polar regions or South Atlantic Anomaly. Command and Control of MetOp is performed from the EPS Control Room at EUMETSAT Headquarters in Darmstadt, Germany.
The control center is connected to the CDA in Svalbard, used for S-Band ranging and doppler measurements, acquisition of real-time house keeping telemetry and uplink of telecommands. The CDA at Svalbard, located at 78 degrees North, provides TT&C coverage on each orbit. Commands for routine operations are uplinked at each CDA contact 36 hours in advance of on-board execution. Orbit determination can be performed using data from the GNSS Receiver for Atmospheric Sounding instrument. An independent back-up control center is located at Instituto Nacional de Técnica Aeroespacial, near Madrid, Spain; the MetOp and NOAA satellites both carry a common set of core instruments. In addition, MetOp carries a set of new European instruments, which measure atmospheric temperature and humidity with unprecedented accuracy along with profiles of atmospheric ozone and other trace gases. Wind speed and direction over the oceans will be measured, it is expected that these new instruments will herald a significant contribution to the ever-growing need for fast and accurate global data to improve numerical weather prediction.
This in turn will lead to more-reliable weather forecasts and, in the longer-term, help with monitoring changing climates more accurately. In addition to its meteorological uses, it will provide imagery of land and ocean surfaces as well as search and rescue equipment to aid ships and aircraft in distress. A data
The troposphere is the lowest layer of Earth's atmosphere, is where nearly all weather conditions take place. It contains 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols; the average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, 6 km in the polar regions in winter. The total average height of the troposphere is 13 km; the lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. This layer is a few hundred meters to 2 km deep depending on the landform and time of day. Atop the troposphere is the tropopause, the border between the troposphere and stratosphere; the tropopause is an inversion layer, where the air temperature ceases to decrease with height and remains constant through its thickness. The word troposphere is derived from the Greek tropos and sphere, reflecting the fact that rotational turbulent mixing plays an important role in the troposphere's structure and behaviour.
Most of the phenomena associated with day-to-day weather occur in the troposphere. By volume, dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, small amounts of other gases. Air contains a variable amount of water vapor. Except for the water vapor content, the composition of the troposphere is uniform; the source of water vapor is at the Earth's surface through the process of evaporation. The temperature of the troposphere decreases with altitude. And, saturation vapor pressure decreases as temperature drops. Hence, the amount of water vapor that can exist in the atmosphere decreases with altitude and the proportion of water vapor is greatest near the surface of the Earth; the pressure of the atmosphere decreases with altitude. This is because the atmosphere is nearly in hydrostatic equilibrium so that the pressure is equal to the weight of air above a given point; the change in pressure with altitude can be equated to the density with the hydrostatic equation d P d z = − ρ g n = − m P g n R T where: gn is the standard gravity ρ is the densityz is the altitude P is the pressure R is the gas constant T is the thermodynamic temperature m is the molar massSince temperature in principle depends on altitude, one needs a second equation to determine the pressure as a function of altitude as discussed in the next section.
The temperature of the troposphere decreases as altitude increases. The rate at which the temperature decreases, is called the environmental lapse rate; the ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The ELR assumes that the air is still, i.e. that there is no mixing of the layers of air from vertical convection, nor winds that would create turbulence and hence mixing of the layers of air. The reason for this temperature difference is that the ground absorbs most of the sun's energy, which heats the lower levels of the atmosphere with which it is in contact. Meanwhile, the radiation of heat at the top of the atmosphere results in the cooling of that part of the atmosphere; the ELR assumes as air is heated it becomes buoyant and rises. The dry adiabatic lapse rate accounts for the effect of the expansion of dry air as it rises in the atmosphere and wet adiabatic lapse rates includes the effect of the condensation of water vapor on the lapse rate.
When a parcel of air rises, it expands. As the air parcel expands, it pushes the surrounding air outward, transferring energy in the form of work from that parcel to the atmosphere; as energy transfer to a parcel of air by way of heat is slow, it is assumed to not exchange energy by way of heat with the environment. Such a process is called an adiabatic process. Since the rising parcel of air is losing energy as it does work on the surrounding atmosphere and no energy is transferred into it as heat from the atmosphere to make up for the loss, the parcel of air is losing energy, which manifests itself as a decrease in the temperature of the air parcel; the reverse, of course, will be true for a parcel of air, sinking and is being compressed. Since the process of compression and expansion of an air parcel can be considered reversible and no energy is transferred into or out of the parcel, such a process is considered isentropic, meaning that there is no change in entropy as the air parcel rises and falls, d S = 0.
Since the heat exchanged d Q = 0 is related to the entropy change d S by d Q = T d S, the equation governing the temperature as a function of height for a mixed atmosphere is d S d z = 0 where S is the entropy. The above equation states; the rate at which temperature decreases with height u
Atmospheric infrared sounder
The atmospheric infrared sounder is one of six instruments flying on board NASA's Aqua satellite, launched on May 4, 2002. The instrument is designed to improve weather forecasting. Working in combination with its partner microwave instrument, the Advanced Microwave Sounding Unit, AIRS observes the global water and energy cycles, climate variation and trends, the response of the climate system to increased greenhouse gases. AIRS uses infrared technology to create three-dimensional maps of air and surface temperature, water vapor, cloud properties. AIRS can measure trace greenhouse gases such as ozone, carbon monoxide, carbon dioxide, methane. AIRS and AMSU-A share the Aqua satellite with the Moderate Resolution Imaging Spectroradiometer and the Earth's Radiant Energy System, the Advanced Microwave Scanning Radiometer-EOS. Aqua is part of NASA's "A-train," a series of high-inclination, Sun-synchronous satellites in low Earth orbit designed to make long-term global observations of the land surface, solid Earth and ocean.
AIRS data is free and available to the public through the Goddard Earth Sciences Data Information and Services Center. NASA's Jet Propulsion Laboratory in Pasadena, manages AIRS for NASA's Science Mission Directorate in Washington, D. C; the term "sounder" in AIRS's name refers to the fact that the instrument measures temperature and water vapor as a function of height. AIRS measures the infrared brightness coming up from the atmosphere, its scan mirror rotates around an axis along the line of flight and directs infrared energy from the Earth into the instrument. As the spacecraft moves along, this mirror sweeps the ground creating a scan swath that extends 800 kilometers on either side of the ground track. Within the instrument, an advanced, high-resolution spectrometer separates the infrared energy into wavelengths; each infrared wavelength is sensitive to temperature and water vapor over a range of heights in the atmosphere, from the surface up into the stratosphere. By having multiple infrared detectors, each sensing a particular wavelength, a temperature profile, or sounding of the atmosphere, can be made.
While prior space instruments had only 15 detectors, AIRS has 2378. This improves the accuracy, making it comparable to measurements made by weather balloons. Thick clouds act like a wall to the infrared energy measured by AIRS. However, microwave instruments on board Aqua can see through the clouds with limited accuracy. Using a special computer algorithm, data from AIRS and the microwave instruments are combined to provide accurate measurements in all cloud conditions resulting in a daily global snapshot of the state of the atmosphere. AIRS and its companion microwave sounder AMSU observe the entire atmospheric column from Earth's surface to the top of the atmosphere; the primary data they return is the infrared spectrum in 2378 individual frequencies. The infrared spectrum is rich in information on numerous gases in the atmosphere. AIRS primary scientific achievement has been to improve weather prediction and provide new information on the water and energy cycle; the instrument yields information on several important greenhouse gases.
Weather and climate forecasting AIRS data are used by weather forecasting centers around the world. By incorporating AIRS measurements into their models, forecasters have been able to extend reliable mid-range weather forecasts by more than six hours. AIRS data have improved forecasts of the location and magnitude of predicted storms. AIRS temperature and water vapor profiles are available in real time to regional weather forecasters, providing twice-daily weather measurements for the entire Pacific Ocean, once in the morning and once in the evening. AIRS measurements form a "fingerprint" of the state of the atmosphere for a given time and place that can be used as a climate data record for future generations, they have become important tools for understanding current climate and increasing the ability to predict the future. Atmospheric Composition, Greenhouse Gases, Air Quality AIRS maps the concentration of carbon dioxide and methane globally, its ability to provide simultaneous observations of the Earth's atmospheric temperature, water vapor, ocean surface temperature, land surface temperature and infrared spectral emissivity, as well as humidity and the distribution of greenhouse gases, makes AIRS/AMSU a useful space instrument to observe and study the response of the atmosphere to increased greenhouse gases.
The instrument can detect carbon monoxide emissions from the burning of plant materials and animal waste by humans in rainforests and large cities. It can follow giant plumes of this gas moving across the planet from these large burns, allowing scientists to better monitor pollution transport patterns. AIRS provides a global daily 3-D view of Earth's ozone layer; the instrument gives scientists their best view of atmospheric ozone in the Antarctic region during the polar winter. AIRS is able to identify concentrations of sulphur dioxide and dust; this article incorporates public domain material from the National Aeronautics and Space Administration document "How Airs Works". AIRS homepage at JPL AIRS/AMSU/HSB on the Aqua mission NASA's Earth Observing System Aqua Project Science Page Global Climate Change: NASA's Eyes on the Earth NASA Earth Observatory
Joint Polar Satellite System
The Joint Polar Satellite System is the latest generation of U. S. polar-orbiting, non-geosynchronous, environmental satellites. JPSS will provide the global environmental data used in numerical weather prediction models for forecasts, scientific data used for climate monitoring. JPSS will aid in fulfilling the mission of the U. S. National Oceanic and Atmospheric Administration, an agency of the Department of Commerce. Data and imagery obtained from the JPSS will increase timeliness and accuracy of public warnings and forecasts of climate and weather events, thus reducing the potential loss of human life and property and advancing the national economy; the JPSS is developed by the National Aeronautics and Space Administration for the National Oceanic and Atmospheric Administration, responsible for operation of JPSS. Three to five satellites are planned for the JPSS constellation of satellites. JPSS satellites will be flown, the scientific data from JPSS will be processed, by the JPSS - Common Ground System.
The first satellite in the JPSS is the Suomi NPP satellite, which launched on October 28, 2011. This was followed by JPSS-1, launched on November 18, 2017, three years than stated when the contract was awarded in 2010. On November 21, 2017, after reaching its final orbit, JPSS-1 was renamed NOAA-20. Three more JPSS satellites will be launched between 2022 and 2031. In addition, the TSI Calibration Transfer Experiment was launched on the U. S. Air Force Space Test Program Satellite-3 on November 19, 2013, it is part of JPSS. The United States has had two main polar orbiting satellite programs. NOAA's POES series and the USAF's DMSP. JPSS was created by the White House in February 2010 following the restructuring dissolution of the National Polar-orbiting Environmental Satellite System program; the original satellite orbit concept from the NPOESS program was divided between two sponsor agencies: NOAA was given responsibility for the afternoon orbit, while environmental measurements from morning orbit were to be obtained from the Defense Weather Satellite System.
DWSS was cancelled in April 2012. The military will continue to rely on the Air Force Defense Meteorological Satellite Program constellation of satellites until the Weather System Follow-on satellites are operational. An independent review team was assigned to provide an independent assessment of the total NOAA satellite enterprise, including JPSS, its findings were published in 2012. Data imagery obtained from the Joint Polar Satellite System will increase timeliness and accuracy of public warnings such as predictions of climate and natural hazards, thus reducing the potential loss of human life and advancing the national economy. JPSS will replace the current Polar-orbiting Operational Environmental Satellites, managed by NOAA and the ground processing component of both POES and the Defense Meteorological Satellite Program. Operational environmental requirements from polar-orbit are met by the NPOESS Preparatory Project, which launched October 28, 2011. Data from the JPSS system shall be made available, by the United States Government, to domestic and international users, in support of U.
S. commitments for the Global Earth Observing System of Systems. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic and solar-geophysical observations of the earth land, oceans and near-earth space; the JPSS Common Ground System converges the NOAA-NASA civil polar environmental satellite program, NPOESS Preparatory Project, the Air Force’s Defense Weather Satellite System ground systems into a single, common system that will satisfy both U. S. and partner international environmental monitoring satellite needs from polar orbit. NOAA-20 is based upon the design of the NPP satellite, with a different communications design for downlinking the raw, unprocessed data back to Earth. JPSS Sensors/Instruments: Visible Infrared Imaging Radiometer Suite takes global visible and infrared observations of land and atmosphere parameters at high temporal resolution. Developed from the MODIS instrument flown on the Aqua and Terra Earth Observing System satellites, it has better performance than the AVHRR radiometer flown on NOAA satellites.
Cross-track Infrared Sounder will produce high-resolution, three-dimensional temperature and moisture profiles. These profiles will be used to enhance weather forecasting models, will facilitate both short- and long-term weather forecasting. Over longer timescales, they will help improve understanding of climate phenomena such as El Niño and La Niña; this is a brand-new instrument with breakthrough performance. CrIS represents a significant enhancement over NOAA's legacy infrared sounder—High Resolution Infrared Radiation Sounders and is meant to be a counterpart to the Infrared Atmospheric Sounding Interferometer. Advanced Technology Microwave Sounder a cross-track scanner with 22 channels, provides sounding observations needed to retrieve profiles of atmospheric temperature and moisture for civilian operational weather forecasting as well as continuity of these measurements for climate monitoring purposes, it is a lighter-weight version of the previous AMSU and MHS instruments flown on previous NOAA and NASA satellites with no new performance capabilities.
Ozone Mapping and Profiler Suite an advanced suite of three hyperspectral instruments, extends the 25-plus
European Organisation for the Exploitation of Meteorological Satellites
The European Organisation for the Exploitation of Meteorological Satellites is an intergovernmental organisation created through an international convention agreed by a current total of 30 European Member States: Austria, Bulgaria, the Czech Republic, Estonia, France, Greece, Ireland, Italy, Lithuania, the Netherlands, Poland, Romania, Slovenia, Sweden, Switzerland and the United Kingdom. These States are the principal users of the systems; the convention establishing EUMETSAT was opened for signature in 1983 and entered into force on 19 June 1986. EUMETSAT's primary objective is to establish and exploit European systems of operational meteorological satellites. EUMETSAT is responsible for the launch and operation of the satellites and for delivering satellite data to end-users as well as contributing to the operational monitoring of climate and the detection of global climate changes; the activities of EUMETSAT contribute to a global meteorological satellite observing system coordinated with other space-faring nations.
Satellite observations are an essential input to numerical weather prediction systems and assist the human forecaster in the diagnosis of hazardous weather developments. Of growing importance is the capacity of weather satellites to gather long-term measurements from space in support of climate change studies. EUMETSAT is not part of the European Union, but became a signatory to the International Charter on Space and Major Disasters in 2012, thus providing for the global charitable use of its space assets; the national mandatory contributions of member states are proportional to their gross national income. However, the cooperating countries contribute only half of the fee they would pay for full membership. Two generations of active Meteosat geostationary satellites, Meteosat Transition Programme and Meteosat Second Generation, provide images of the full Earth disc, data for weather forecasts. More detail can be found on the Meteosat wiki. While geostationary satellites provide a continuous view of the earth disc from a stationary position in space, the instruments on polar-orbiting satellites, flying at a much lower altitude, provide more precise details about atmospheric temperature and moisture profiles, although with less frequent global coverage.
The lack of observational coverage in certain parts of the globe the Pacific Ocean and continents of the southern hemisphere, has led to the important role for polar-orbiting satellite data in numerical weather prediction and climate monitoring. EUMETSAT Polar System Metop mission consists of three polar orbiting Metop satellites, to be flown successively for more than 14 years; the first, Metop-A, was launched by a Russian Soyuz-2.1a rocket from Baikonur on October 19, 2006, at 22:28 Baikonur time. Metop-A was controlled by ESOC for the LEOP phase following launch, with control handed over to EUMETSAT 72 hours after lift-off. EUMETSAT's first commands to the satellite were sent at 14:04 UTC on October 22, 2006; the second EPS satellite, Metop-B, was launched from Baikonur on 17 September 2012, the third, Metop-C, was launched from Kourou on 7 November 2018. Positioned at 817 km above the Earth, special instruments on board Metop-A can deliver far more precise details about atmospheric temperature and moisture profiles than a geostationary satellite.
The satellites ensure that the more remote regions of the globe in Northern Europe as well as the oceans in the Southern hemisphere, are covered. The EPS programme is the European half of a joint program with NOAA, called the International Joint Polar System. NOAA has operated a continuous series of low earth orbiting meteorological satellite since April 1960. Many of the instruments on Metop are operated on NOAA/POES satellites, providing similar data types across the IJPS. A/DCS AMSU-A1 and AMSU-A2 ASCAT Advanced Scatterometer AVHRR GOME-2 — instrument to monitor ozone levels GRAS HIRS IASI MHS SARP-3 and SARR SEM The Jason-2 programme is an international partnership across multiple organisations, including EUMETSAT, CNES, the US agencies NASA and NOAA. Jason-2 was launched from Vandenberg Air Force Base aboard a Delta-II rocket on 20 June 2008, 7:46 UTC. Jason SatellitesJason-2 reliably delivers detailed oceanographic data vital to our understanding of weather forecasting and climate change monitoring.
Jason-2 provides data on the decadal oscillations such as the Atlantic Ocean. Jason-2 measurements contribute to the European Centre for Medium-Range Weather Forecasts satellite data assimilation, helping improve global atmosphere and ocean forecasting. Altimetric data from Jason-2 have helped create detailed decade-long global observations and analyses of the El Niño and La Niña phenomena, opening the way to new discoveries about ocean circulation and its effects on climate, providing new insights into ocean tides, turbulent ocean eddies and marine gravity; the next step is the Jason-3 Programme, approved. It will ensure continuation of the series of measurements made by the Jason-2 satellite, i
The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is the base unit of temperature in the International System of Units; until 2018, the kelvin was defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. In other words, it was defined such that the triple point of water is 273.16 K. On 16 November 2018, a new definition was adopted, in terms of a fixed value of the Boltzmann constant. For legal metrology purposes, the new definition will come into force on 20 May 2019; the Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin, who wrote of the need for an "absolute thermometric scale". Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or written as a degree; the kelvin is the primary unit of temperature measurement in the physical sciences, but is used in conjunction with the degree Celsius, which has the same magnitude.
The definition implies that absolute zero is equivalent to −273.15 °C. In 1848, William Thomson, made Lord Kelvin, wrote in his paper, On an Absolute Thermometric Scale, of the need for a scale whereby "infinite cold" was the scale's null point, which used the degree Celsius for its unit increment. Kelvin calculated; this absolute scale is known today as the Kelvin thermodynamic temperature scale. Kelvin's value of "−273" was the negative reciprocal of 0.00366—the accepted expansion coefficient of gas per degree Celsius relative to the ice point, giving a remarkable consistency to the accepted value. In 1954, Resolution 3 of the 10th General Conference on Weights and Measures gave the Kelvin scale its modern definition by designating the triple point of water as its second defining point and assigned its temperature to 273.16 kelvins. In 1967/1968, Resolution 3 of the 13th CGPM renamed the unit increment of thermodynamic temperature "kelvin", symbol K, replacing "degree Kelvin", symbol °K. Furthermore, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM held in Resolution 4 that "The kelvin, unit of thermodynamic temperature, is equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."In 2005, the Comité International des Poids et Mesures, a committee of the CGPM, affirmed that for the purposes of delineating the temperature of the triple point of water, the definition of the Kelvin thermodynamic temperature scale would refer to water having an isotopic composition specified as Vienna Standard Mean Ocean Water.
In 2018, Resolution A of the 26th CGPM adopted a significant redefinition of SI base units which included redefining the Kelvin in terms of a fixed value for the Boltzmann constant of 1.380649×10−23 J/K. When spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm; when reference is made to the "Kelvin scale", the word "kelvin"—which is a noun—functions adjectivally to modify the noun "scale" and is capitalized. As with most other SI unit symbols there is a space between the kelvin symbol. Before the 13th CGPM in 1967–1968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time, it was distinguished from the other scales with either the adjective suffix "Kelvin" or with "absolute" and its symbol was °K. The latter term, the unit's official name from 1948 until 1954, was ambiguous since it could be interpreted as referring to the Rankine scale. Before the 13th CGPM, the plural form was "degrees absolute".
The 13th CGPM changed the unit name to "kelvin". The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales, but rather an absolute unit of measure which can be manipulated algebraically. In science and engineering, degrees Celsius and kelvins are used in the same article, where absolute temperatures are given in degrees Celsius, but temperature intervals are given in kelvins. E.g. "its measured value was 0.01028 °C with an uncertainty of 60 µK." This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing relative temperatures, the magnitude of the degree Celsius is equal to that of the kelvin. Notwithstanding that the official endorsement provided by Resolution 3 of the 13th CGPM states "a temperature interval may be expressed in degrees Celsius", the practice of using both °C and K is widespread throughout the scientific world; the use of SI prefixed forms of the degree Celsius to express a temperature interval has not been adopted.
In 2005 the CIPM embarked on a programme to redefine the kelvin using a more experimentally rigorous methodology. In particular, the committee proposed redefining the kelvin such that Boltzmann's constant takes the exact value 1.3806505×10−23 J/K. The committee had hoped tha