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The UAH satellite temperature dataset, developed at the
University of Alabama in Huntsville The University of Alabama in Huntsville (UAH) is a public research university in Huntsville, Alabama. The university is accredited by the Southern Association of Colleges and Schools and comprises nine colleges: arts, humanities & social science ...
, infers the temperature of various atmospheric layers from
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
measurements of the oxygen
radiance In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Radiance is used to characterize diffuse emission and reflection of electromagnetic radiatio ...
in the microwave band, using Microwave Sounding Unit temperature measurements. It was the first global temperature datasets developed from satellite information and has been used as a tool for research into surface and atmospheric temperature changes. The dataset is published by
John Christy John Raymond Christy is a climate scientist at the University of Alabama in Huntsville (UAH) whose chief interests are satellite remote sensing of global climate and global climate change. He is best known, jointly with Roy Spencer, for the firs ...
et al. and formerly jointly with Roy Spencer.


Satellite temperature measurements

Satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
s do not measure
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...
directly. They measure
radiance In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Radiance is used to characterize diffuse emission and reflection of electromagnetic radiatio ...
s in various
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
bands, from which temperature may be
inferred Inferences are steps in reasoning, moving from premises to logical consequences; etymologically, the word ''infer'' means to "carry forward". Inference is theoretically traditionally divided into deduction and induction, a distinction that in ...
. The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. As a result, different groups that have analyzed the satellite data have obtained different temperature data (see Microwave Sounding Unit temperature measurements). Among these groups are Remote Sensing Systems (RSS) and the
University of Alabama in Huntsville The University of Alabama in Huntsville (UAH) is a public research university in Huntsville, Alabama. The university is accredited by the Southern Association of Colleges and Schools and comprises nine colleges: arts, humanities & social science ...
(UAH). The satellite series is not fully homogeneous - it is constructed from a series of satellites starting with the 1978
TIROS-N TIROS-N satellite is the first of the TIROS-N series. It is a weather satellite launched on 13 October 1978. It was designed to become operational during 2 years. Its mass is 734 kilograms. Its perigee to Earth is 829 kilometers. Its apogee is ...
, where different satellites had similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for satellite drift and orbital decay. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult.


Description of the data

The UAH dataset is produced by one of the groups reconstructing temperature from radiance. UAH provide data on three broad levels of the atmosphere. *The Lower
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
- TLT (originally called T2LT). *The mid troposphere - TMT *The lower stratosphere - TLS Data are provided as temperature anomalies against the seasonal average over a past basis period, as well as in absolute temperature values. The baseline period for the published temperature anomalies was changed in January 2021 from 1981-2010 to 1991-2020. All the data products can be downloaded from the UAH server.


Recent trend summary

To compare to the trend from the
surface temperature record The instrumental temperature record is a record of temperatures within Earth's climate based on direct, instrument-based measurements of air temperature and ocean temperature. Instrumental temperature records are distinguished from indirect rec ...
(+0.1610.033 °C/decade from 1979 to 2012 according to NASA GISS) it is most appropriate to derive trends for the part of the atmosphere nearest the surface, ''i.e.'', the lower
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
. Doing this, through December 2019, the UAH linear temperature trend 1979-2019 shows a warming of +0.13 °C/decade. For comparison, a different group, Remote Sensing Systems (RSS), also analyzes the MSU data. From their data: the RSS linear temperature trend shows a warming of +0.208 °C/decade.Remote Sensing Services, Earth Microwave Data Center
MSU & AMSU Time Series Trend Browse Tool
Retrieved 15 Jan. 2020.


Geographic coverage

Data are available as global, hemispheric, zonal, and gridded averages. The global average covers 97-98% of the earth's surface, excluding only latitudes above +85 degrees, below -85 degrees and, in the cases of TLT and TMT, some areas with land above 1500 m altitude. The hemispheric averages are over the northern and southern hemispheres 0 to +/-85 degrees. The gridded data provide an almost global temperature map.


Temporal coverage

Daily global, hemispheric and zonal data are available. Monthly averages are available in gridded format as well as by hemisphere and globally. Each set has data back to December 1978.


Comparison with other data and models

In comparing these measurements to surface temperature models, it is important to note that values for the lower troposphere measurements taken by the MSU are a weighted average of temperatures over multiple altitudes (roughly 0 to 12 km), and not a surface temperature (see figure in Microwave Sounding Unit temperature measurements article). The results are thus not precisely comparable to surface temperature records or models. Pre-1998 results published by UAH showed no warming of the atmosphere. In a 1998 paper, Wentz and Schabel showed this (along with other discrepancies) was due to the orbital decay of the NOAA satellites. With these errors corrected, the UAH data showed a 0.07 °C/decade increase in lower troposphere temperature. Some discrepancies between the UAH temperature measurements and temperatures measured by other groups remain, with (as of 2019) the lower troposphere temperature trend from 1979-2019 calculated as +0.13 °C/decade by UAH, and calculated at +0.208 °C/decade by RSS.Remote Sensing Services, Earth Microwave Data Center
MSU & AMSU Time Series Trend Browse Tool
Retrieved 15 Jan. 2020.
A more detailed discussion can be found in the Comparison with surface trends section of the Microwave Sounding Unit temperature measurements article.


Corrections made

The table below summarizes the adjustments that have been applied to the UAH TLT dataset. The 'trend correction' refers to the change in global mean decadal temperature trend in degrees Celsius/decade as a result of the correction. NOAA-11 played a significant role in a 2005 study by Mears ''et al.'' identifying an error in the diurnal correction that leads to the 40% jump in Spencer and Christy's trend from version 5.1 to 5.2. Christy ''et al.'' asserted in a 2007 paper that the tropical temperature trends from
radiosondes A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calcula ...
matches more closely with their v5.2 UAH-TLT dataset than with RSS v2.1. Much of the difference, at least in the Lower troposphere global average decadal trend between UAH and RSS, had been removed with the release of RSS version 3.3 in January 2011, at which time the RSS and UAH TLT were now within 0.003 K/decade of one another. Significant differences remained, however, in the Mid Troposphere (TMT) decadal trends. However, in June 2017 RSS released version 4 which significantly increased the trend from 0.136 to 0.184 K/decade substantially increasing the difference again. A beta version of 6.0 of the dataset was released on April 28, 2015 via blog post. This dataset has higher spatial resolution and uses new methods for gridpoint averaging.


References


External links

* ''Climate Algorithm Theoretical Basis Document (C-ATBD), UAH MSU Mean Layer Temperature (MLT)'' (no longer available
archived version
. {{DEFAULTSORT:Uah Satellite Temperature Dataset Climatological research Satellite meteorology University of Alabama in Huntsville es:Mediciones de temperatura por satélite