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Microwave sounding unit temperature measurements have been obtained from the troposphere since 1979, when they were included within NOAA weather satellites. By comparison, the usable balloon (radiosonde) record begins in 1958 but has less geographic coverage and is less uniform. Satellites do not measure temperature. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature. 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 trends. Among these groups are Remote Sensing Systems (RSS) and the University of Alabama in Huntsville (UAH). The satellite series is not fully homogeneous - the record is constructed from a series of satellites with similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for satellite drift in orbit. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult. To compare to the trend from the surface temperature record (approximately +0.07 °C/decade over the past century and +0.15-0.16 °C/decade since 1979) it is most appropriate to derive trends for the part of the atmosphere nearest the surface, i.e., the lower troposphere. Doing this, through January 2012: * RSS v3.3 finds a trend of +0.137 °C/decade.〔 * UAH v5.4 finds a trend of +0.136°C/decade.〔 An alternative adjustment introduced by Fu ''et al.'' (2004) finds trends (1979–2011) of +0.14 °C/decade when applied to the RSS data set and +0.11 °C/decade when applied to the UAH data set .〔(【引用サイトリンク】title= State of the Climate Upper Air Annual 2011 )〕 Using the T2 channel (which include significant contributions from the stratosphere, which has cooled), Mears et al. of Remote Sensing Systems (RSS) find (through January 2012) a trend of +0.082 °C/decade.〔 Spencer and Christy of the University of Alabama in Huntsville (UAH), find a smaller trend of +0.046 °C/decade.〔 A no longer updated analysis of Vinnikov and Grody found +0.20 °C/decade (1978–2005). Another satellite temperature analysis is provided by NOAA/NESDIS STAR Center for Satellite Application and Research and use simultaneous nadir overpasses (SNO) to remove satellite intercalibration biases yielding more accurate temperature trends. The SNO analysis finds a 1979-2011 trend of +0.128°C/decade for T2 channel. The satellite records have the advantage of greater spatial coverage, whereas the radiosonde record is longer. There have been complaints of data problems with both records, and difficulty reconciling climate model predictions with the observed data. ==Creation of the satellite temperature record== (詳細はmicrowave sounding units (MSUs) on NOAA polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen. The intensity is proportional to the temperature of broad vertical layers of the atmosphere, as demonstrated by theory and direct comparisons with atmospheric temperatures from radiosonde (balloon) profiles. Upwelling radiance is measured at different frequencies; these different frequency bands sample a different weighted range of the atmosphere.〔(Remote Sensing Systems )〕 Channel 2 is broadly representative of the troposphere, albeit with a significant overlap with the lower stratosphere (the weighting function has its maximum at 350 hPa and half-power at about 40 and 800 hPa). In an attempt to remove the stratospheric influence, Spencer and Christy developed the synthetic "2LT" product by subtracting signals at different view angles; this has a maximum at about 650 hPa. However this amplifies noise, increases inter-satellite calibration biases and enhances surface contamination. The 2LT product has gone through numerous versions as various corrections have been applied. Records have been created by merging data from nine different MSUs and AMSU data, each with peculiarities that must be calculated and removed because they can have substantial impacts on the resulting trend.〔(The Satellite Temperature Records: Parts 1 and 2 ) May 1996〕 The process of constructing a temperature record from a radiance record is difficult and some of the required corrections are as large as the trend itself:〔(【引用サイトリンク】title=CCSP sap 1.1 )〕 ; Diurnal sampling All the MSU instruments and to a lesser extent AMSU drift slowly from the sun-synchronous equatorial crossing time changing the local time observed by the instrument, therefore the natural diurnal cycle may be aliased into the long term trend. The diurnal sampling correction is in the order of a few hundredths °C/decade for TLT and TMT. ; Orbit decay All Polar orbiting satellite lose height after launch, the orbital decay is stronger during period of elevated solar activity when the enhanced ultraviolet radiation warm the upper atmosphere and increase the frictional drag over the spacecraft. The orbital decay change the instrument view angle relative to the surface and thus the observed microwave emissivity, furthermore the long term time-series is constructed by sequential merging of the inter-calibrated satellite data so that the error is summed up over time, the required correction is in the order of 0.1°C/decade for TLT. ; Calibration changes Once every earth scan MSU instrument use the deep space (2.7K) and on-board warm targets to make calibration measures, however as the spacecraft drifts through the diurnal cycle the calibration target temperature may change due to varying solar shadowing effect, the correction is in the order of 0.1°C/decade for TLT and TMT. One widely reported satellite temperature record, developed by Roy Spencer and John Christy at the University of Alabama in Huntsville (UAH), is current version corrects previous errors in their analysis for orbital drift and other factors. The record comes from a succession of different satellites and problems with inter-calibration between the satellites are important, especially NOAA-9, which accounts for most of the difference between the RSS and UAH analyses.〔(Remote Sensing Systems )〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「MSU temperature measurements」の詳細全文を読む スポンサード リンク
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