Dataset
RAL Infrared Microwave Sounder (IMS) temperature, water vapour, ozone and surface spectral emissivity
Abstract
The Rutherford Appleton Laboratory (RAL) Infrared Microwave Sounder (IMS) data set contains vertical profiles of temperature, water vapour, and ozone as well as surface spectral emissivity spanning infrared and microwave, surface temperature, cloud fraction and height. Data are retrieved from co-located measurements by the Infrared Atmospheric Sounding Interferometer (IASI), the Microwave Humidity Sounder (MHS) and the Advanced Microwave Sounding Unit (AMSU) on board the Eumetsat Metop satellites.
Development of the IMS scheme and data production were funded by the UK’s National Centre for Earth Observation (NCEO) under the Natural Environment Research Council (NERC), with additional funding from EUMETSAT contract EUM/CO/13/4600001252/THH.
Data were produced by the Remote Sensing Group (RSG) at the Rutherford Appleton Laboratory (RAL).
This first public release consists of a full processing of the Metop A mission from 2007 to the end of 2016, using version 2.1 of the algorithm.
IMS data are produced with the horizontal sampling of IASI, ~25 x 25 km
Details
| Previous Info: |
No news update for this record
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| Previously used record identifiers: |
No related previous identifiers.
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| Access rules: |
Access to these data is available to any registered CEDA user. Please Login or Register for an account to gain access.
Use of these data is covered by the following licence: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/. When using these data you must cite them correctly using the citation given on the CEDA Data Catalogue record. |
| Data lineage: |
Data produced by the Rutherford Appleton Laboratory (RAL) Remote Sensing Group (RSG). The development of the Infrared Atmospheric Sounding Interferometer (IASI) IMS data was funded by the Natural Environment Research Council (NERC) through its National Centre for Earth Observation (NCEO). |
| Data Quality: |
See dataset associated documentation
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| File Format: |
NetCDF
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Process overview
| Title | METOP IMS RAL computation process |
| Abstract | The RAL Infrared Microwave Sounder (IMS) retrieval scheme jointly retrieves height-resolved temperature, water vapour, and ozone, as well as surface spectral emissivity, effective cloud fraction, effective cloud ice fraction, and effective cloud top height, from three instruments on board the MetOp platform: the Infrared Atmospheric Sounding Interferometer (IASI), the Advanced Microwave Sounding Unit (AMSU), and the Microwave Humidity Sounder (MHS). The IMS scheme is a modified version of the EUMETSAT 1DVar IASI L2 retrieval, resulting from the study “Optimal Estimation Method retrievals with IASI, AMSU and MHS measurements” (R. Siddans et al., 2015). The IMS scheme differs from the EUMETSAT L2 scheme through the addition of microwave channels from AMSU and MHS to the measurement vector, and the addition of surface spectral emissivity and cloud to the state vector. There are also differences in the prior assumptions made by the retrieval and RTTOV coefficients used. The IMS scheme measurement vector comprises the same subset of 139 IASI channels as the EUMETSAT L2 scheme (700-1900 cm-1), all (functioning) AMSU channels, and all MHS channels. The forward model used is RTTOV (Matricari, 2009) with v9 coefficients to allow the modelling of spatial and seasonal variation and trends in greenhouse gases. The IMS retrieval state vector is expressed in terms of PC weights of a climatological global zonal mean covariance matrix, with 28 PC weights for the atmospheric temperature profile, 18 for the water vapour profile, 10 for the ozone profile and 20 for surface spectral emissivity. In the output files, profiles are reported on the 101 level RTTOV fixed pressure grid. A climatological zonal mean prior, scaled to match NWP, is used for temperature, water vapour and ozone, and is interpolated linearly to the latitude of each measurement. For the retrieval of surface spectral emissivity, PCs were computed from the global covariance of the RTTOV implementation of the University of Wisconsin global infrared land surface emissivity database (Borbas and Ruston, 2010) and RTTOV microwave spectral emissivity models. Prior covariances for surface spectral emissivity are defined for the first 6 patterns using the combined RTTOV infrared and microwave atlases. Spectral correlations between the infrared and microwave emissivities are included (derived from the RTTOV representation of the spatial covariance of infrared and microwave emissivity). Initial cloud screening of IASI scenes is performed by implementing a threshold on the brightness temperature difference between observations and cloud-free simulations (based on ECMWF) at 11 microns. Scenes containing partial, thin or very-low cloud are processed by the retrieval and characterised by the retrieved cloud variables. see documentations for additional details |
| Input Description | None |
| Output Description | None |
| Software Reference | None |
- units: 1
- var_id: ixt
- long_name: Across-track index.
- units: 1
- var_id: iat
- long_name: Along-track index.
- units: hPa
- var_id: sp
- long_name: Assumed surface pressure in retrieval
- units: 1
- var_id: ak_t
- long_name: Atmospheric temperature averaging kernel.
- units: K
- var_id: t_ap
- long_name: Climatological prior for atmospheric temperature.
- var_id: o_ap
- long_name: Climatological prior for natural logarithm of ozone mixing ratio in pats per million by volumne.
- units: ln(ppmv)
- units: K
- var_id: tsk_ap
- long_name: Climatological prior for surface temperature.
- units: 1
- var_id: bcf_dofs
- long_name: Degrees of Freedom for Bias Correction Factors.
- units: 1
- var_id: cfr_dofs
- long_name: Degrees of Freedom for Signal of Cloud Fraction.
- units: 1
- var_id: cth_dofs
- long_name: Degrees of Freedom for Signal of Cloud Top Height.
- units: 1
- var_id: o_dofs
- long_name: Degrees of Freedom for Signal of ozone
- units: 1
- var_id: em_dofs
- long_name: Degrees of Freedom for Signal of surface emissivity
- units: 1
- var_id: t_dofs
- long_name: Degrees of Freedom for Signal of temperature
- units: 1
- var_id: w_dofs
- long_name: Degrees of Freedom for Signal of water vapour
- units: 1
- var_id: tsk_dofs
- long_name: Degrees of Freedom for Surface Temperature.
- units: 1
- var_id: evecs_t
- long_name: Eigenvectors to reconstruct atmospheric temperature profile from principal component weights.
- units: 1
- var_id: evecs_w
- long_name: Eigenvectors to reconstruct atmospheric water vapour profile from principal component weights.
- units: 1
- var_id: evecs_o
- long_name: Eigenvectors to reconstruct ozone profile from principal component weights.
- units: K
- standard_name: air_temperature
- var_id: t_err
- long_name: Error in retrieved atmospheric temperature profile.
- units: 1
- var_id: o_err
- long_name: Error in retrieved natural logarithm of the atmospheric ozone profile.
- units: 1
- var_id: w_err
- long_name: Error in retrieved natural logarithm of the atmospheric water vapour profile.
- units:
- var_id: bcf_err
- long_name: Estimated error on retrieved bias correction factors.
- units: 1
- var_id: cfr_err
- long_name: Estimated error on retrieved cloud fraction.
- units: km
- var_id: cth_err
- long_name: Estimated error on retrieved cloud top height.
- units: 1
- var_id: em_err
- long_name: Estimated error on retrieved emissivity
- units: K
- var_id: tsk_err
- long_name: Estimated error on retrieved surface temperature.
- units: m
- var_id: ecmwf_altitude
- long_name: Estimated surface altitude from interpolated ECMWF ERA Interim data
- units: m
- var_id: iasi_altitude
- long_name: Estimated surface altitude from interpolated GTOPO30 atlas
- units: 1
- var_id: do_station
- long_name: Flag indicating scenes close to one of a list of predefined ground-stations
- units: 1
- var_id: do_sx_t
- long_name: Flag indicating scenes for atmospheric temperature for which solution error covariance are provided
- units: 1
- var_id: do_ak_o
- long_name: Flag indicating scenes for ozone for which full diagnostics are provided including averaging kernels
- units: 1
- var_id: do_sx_o
- long_name: Flag indicating scenes for ozone for which solution error covariance are provided
- units: 1
- var_id: do_sx_w
- long_name: Flag indicating scenes for water vapour for which solution error covariance are provided
- units: 1
- var_id: do_nwp
- long_name: Flag indicating scenes for which NWP profiles are provided
- units: 1
- var_id: do_resid
- long_name: Flag indicating scenes for which fit residual spectra are provided
- units: 1
- var_id: do_sample
- long_name: Flag indicating scenes forming regular sub-sampling of IASI observations
- units: 1
- var_id: do_retrieval
- long_name: Flag indicating scenes which pass quality control (BTD flag zero)
- units: K
- var_id: btd_flag
- long_name: Flag used as indicator of cloud derived from reported BTD
- var_id: sa_ts
- long_name: Global surface temperature a priori variance.
- units: K^2
- units: 1
- var_id: sa_o
- long_name: Globally averaged ozone a prior covariance in terms of PC weights.
- units: 1
- var_id: sa_t
- long_name: Globally averaged temperature a prior covariance in terms of PC weights.
- units: 1
- var_id: sa_w
- long_name: Globally averaged water vapour a prior covariance in terms of PC weights
- units: 1
- var_id: pixel_number
- long_name: IASI detector pixel (0-3).
- units: 1
- var_id: avhrr_radiance
- long_name: Mean of co-located AVHRR radiances.
- units: 1
- var_id: jy
- long_name: Measurement component of cost.
- units: K
- var_id: bt
- long_name: Measurement vector in terms of brightness temperature.
- units: K
- standard_name: air_temperature
- var_id: t_nwp
- long_name: NWP atmospheric temperature profile.
- units: K
- standard_name: surface_temperature
- var_id: tsk_nwp
- long_name: NWP surface temperature.
- units: ln(ppmv)
- var_id: o_nwp
- long_name: Natural logaritm of the atmospheric ozone profile in parts per million by volume from NWP model
- units: 1
- var_id: ak_o
- long_name: Ozone averaging kernel.
- units: hPa
- var_id: p
- standard_name: air_pressure
- long_name: Pressure grid for retrieved profiles.
- units: K
- var_id: resid
- long_name: Residual spectra
- units: K
- standard_name: air_temperature
- var_id: t
- long_name: Retrieved atmospheric temperature profile.
- units: 1
- var_id: bcf
- long_name: Retrieved bias correction factor.
- units: km
- var_id: cth
- long_name: Retrieved cloud top pressure in z-star scale-height.
- units: 1
- long_name: Retrieved effective cloud fraction.
- var_id: cfr
- units: 1
- var_id: em
- long_name: Retrieved emissivity
- units: ln(ppmv)
- var_id: o
- long_name: Retrieved natural logaritm of the atmospheric ozone profile in parts per million by volume
- var_id: w
- units: ln(ppmv)
- long_name: Retrieved natural logaritm of the atmospheric water vapour profile in parts per million by volume
- units: degree
- standard_name: sensor_zenith_angle
- var_id: satzen
- long_name: Sensor view zenith angle
- units: degree
- long_name: Solar zenith angle
- standard_name: solar_zenith_angle
- var_id: solzen
- units: 1
- var_id: jx
- long_name: State vector component of cost.
- units: 1
- var_id: xt
- long_name: State vector for atmospheric temperature in terms of principal component weights.
- units: 1
- var_id: xo
- long_name: State vector for ozone in terms of principal component weights.
- units: K
- standard_name: surface_temperature
- var_id: tsk
- long_name: State vector for surface temperature.
- units: 1
- var_id: xw
- long_name: State vector for water vapour in terms of principal component weights.
- units: 1
- long_name: The average number of retrieval steps (number of calls to the forward model).
- var_id: n_step
- units: s
- long_name: Time of day in msec since midnight (UTC).
- var_id: sensingtime_msec
- units: 1
- var_id: ak_w
- long_name: Water vapour averaging kernel.
- units: micrometers
- var_id: cwn
- long_name: Wavenumbers associated with measurement vector.
- units: day
- var_id: sensingtime_day
Co-ordinate Variables
- units: degree_north
- standard_name: latitude
- var_id: latitude
- long_name: Latitude
- units: degree_east
- standard_name: longitude
- var_id: longitude
- long_name: Longitude
Temporal Range
2007-05-31T23:00:00
2016-12-31T23:59:59
Geographic Extent
90.0000° |
||
-180.0000° |
180.0000° |
|
-90.0000° |