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Dataset

 

RAL Infrared Microwave Sounder (IMS) temperature, water vapour, ozone and surface spectral emissivity

Update Frequency: Not Planned
Status: Completed
Online Status: ONLINE
Publication State: Citable
Publication Date: 2018-09-11
DOI Publication Date: 2018-06-28
Download Stats: last 12 months

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

Citable as:  Siddans, R.; Walker, J.; Latter, B.; Kerridge, B.; Gerber, D.; Knappett, D. (2018): RAL Infrared Microwave Sounder (IMS) temperature, water vapour, ozone and surface spectral emissivity. Centre for Environmental Data Analysis, 28 June 2018. doi:10.5285/489e9b2a0abd43a491d5afdd0d97c1a4. http://dx.doi.org/10.5285/489e9b2a0abd43a491d5afdd0d97c1a4
Abbreviation: Not defined
Keywords: IASI, MHS, AMSU, IMS retrieval, temperature, water vapour, surface emissivity, ozone

Details

Previous Info:
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Previously used record 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.
File Format:
NetCDF

Process overview

This dataset was generated by the computation detailed below.
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: 1e-6
  • long_name: A priori column-averaged dry-air mole fraction of atmospheric methane (ppmv).
  • var_id: ap_ch4_xvmr
  • names: A priori column-averaged dry-air mole fraction of atmospheric methane (ppmv).
  • units: 1e-6
  • long_name: A priori dry-air mole fraction of atmospheric methane (ppmv).
  • var_id: ap_ch4_vmr
  • names: A priori dry-air mole fraction of atmospheric methane (ppmv).
  • units: 1e-6
  • long_name: A priori error on retrieved dry-air mole fraction of atmospheric methane (ppmv).
  • var_id: ap_ch4_vmr_err
  • names: A priori error on retrieved dry-air mole fraction of atmospheric methane (ppmv).
  • units: K
  • long_name: A priori surface temperature (K).
  • var_id: ap_surface_temperature
  • names: A priori surface temperature (K).
  • units: 1e-6
  • long_name: Averaging kernel for column-averaged mixing ratio (ppmv).
  • var_id: ak_xvmr
  • names: Averaging kernel for column-averaged mixing ratio (ppmv).
  • units: 1e-6
  • long_name: Averaging kernel for profile mixing ratios (ppmv).
  • var_id: ak_vmr
  • names: Averaging kernel for profile mixing ratios (ppmv).
  • units: 1e-6
  • long_name: Column-averaged equivalent N2O (modelled).
  • var_id: xn2o_eql
  • names: Column-averaged equivalent N2O (modelled).
  • var_id: day
  • long_name: Day of the month (1-31).
  • names: Day of the month (1-31).
  • long_name: Errors on residual scale factors.
  • var_id: rsf_err
  • names: Errors on residual scale factors.
  • units: 1e-6
  • long_name: Estimated error on retrieved methane profile (ppmv).
  • var_id: ch4_vmr_err
  • names: Estimated error on retrieved methane profile (ppmv).
  • units: 1e-6
  • long_name: Estimated error on the retrieved column-averaged mixing ratio (ppmv).
  • var_id: ap_ch4_xvmr_err
  • names: Estimated error on the retrieved column-averaged mixing ratio (ppmv).
  • units: 1e-6
  • long_name: Estimated error on the retrieved column-averaged mixing ratio (ppmv).
  • var_id: ch4_xvmr_err
  • names: Estimated error on the retrieved column-averaged mixing ratio (ppmv).
  • long_name: Flag indicating retrieval convergence (1=fully converged). Results with other values should be used with more caution.
  • var_id: conv
  • names: Flag indicating retrieval convergence (1=fully converged). Results with other values should be used with more caution.
  • var_id: pixel_number
  • long_name: IASI detector pixel (0-3).
  • names: IASI detector pixel (0-3).
  • var_id: month
  • long_name: Month of the year (1-12).
  • names: Month of the year (1-12).
  • long_name: Number of scan line (0=start of orbit).
  • var_id: scan_line
  • names: Number of scan line (0=start of orbit).
  • long_name: Position within scan line (0-29).
  • var_id: scan_position
  • names: Position within scan line (0-29).
  • units: hPa
  • long_name: Pressure levels of true state in provided averaging kernels.
  • var_id: mod_plev
  • names: Pressure levels of true state in provided averaging kernels.
  • units: hPa
  • long_name: Pressures of retrieval levels (hPa) for which averaging kernels are provided.
  • var_id: ret_plev_ak
  • names: Pressures of retrieval levels (hPa) for which averaging kernels are provided.
  • long_name: Retrieval cost function value.
  • var_id: chim
  • names: Retrieval cost function value.
  • units: hPa
  • long_name: Retrieval pressure levels (hPa).
  • var_id: ret_plev
  • names: Retrieval pressure levels (hPa).
  • long_name: Retrieved HDO scaling factor (effective HDO amount compared to Hitran assumed ratio of HDO to main water vapour isotope).
  • var_id: hdo_sf
  • names: Retrieved HDO scaling factor (effective HDO amount compared to Hitran assumed ratio of HDO to main water vapour isotope).
  • units: 1e-6
  • long_name: Retrieved column-averaged dry-air mole fraction of atmospheric methane (ppmv).
  • var_id: ch4_xvmr
  • names: Retrieved column-averaged dry-air mole fraction of atmospheric methane (ppmv).
  • units: 1e-6
  • long_name: Retrieved column-averaged mole fraction of atmospheric water vapour in air (ppmv).
  • var_id: h2o_xvmr
  • names: Retrieved column-averaged mole fraction of atmospheric water vapour in air (ppmv).
  • units: 1e-6
  • long_name: Retrieved dry-air mole fraction of atmospheric methane (ppmv).
  • var_id: ch4_vmr
  • names: Retrieved dry-air mole fraction of atmospheric methane (ppmv).
  • units: 1
  • var_id: cloud_fraction
  • long_name: Retrieved effective cloud fraction.
  • names: Retrieved effective cloud fraction.
  • units: hPa
  • long_name: Retrieved effective cloud-top pressure (hPa).
  • var_id: cloud_pressure
  • names: Retrieved effective cloud-top pressure (hPa).
  • units: K
  • standard_name: surface_temperature
  • var_id: surface_temperature
  • long_name: Retrieved surface temperature (K).
  • names: surface_temperature, Retrieved surface temperature (K).
  • long_name: Scale factors for the mean fit and across-track residual patterns.
  • var_id: rsf
  • names: Scale factors for the mean fit and across-track residual patterns.
  • units: degrees
  • standard_name: sensor_zenith_angle
  • long_name: Sensor zenith angle (degrees).
  • var_id: vza
  • names: sensor_zenith_angle, Sensor zenith angle (degrees).
  • units: degrees
  • var_id: sza
  • standard_name: solar_zenith_angle
  • long_name: Solar zenith angle (degrees).
  • names: solar_zenith_angle, Solar zenith angle (degrees).
  • units: km
  • long_name: Spatially interpolated ECMWF surface altitude (km).
  • var_id: ecmwf_alt
  • names: Spatially interpolated ECMWF surface altitude (km).
  • units: km
  • long_name: Surface altitude (km) corresponding to IASI measurement, based on averaging GTOPO30 to 12km resolution and sampling every 0.05 degrees.
  • var_id: iasi_alt
  • names: Surface altitude (km) corresponding to IASI measurement, based on averaging GTOPO30 to 12km resolution and sampling every 0.05 degrees.
  • units: hPa
  • standard_name: surface_air_pressure
  • var_id: surface_pressure
  • long_name: Surface pressure (hPa) used in the retrieval.
  • names: surface_air_pressure, Surface pressure (hPa) used in the retrieval.
  • long_name: The average number of retrieval steps (number of calls to the forward model).
  • var_id: nstep
  • names: The average number of retrieval steps (number of calls to the forward model).
  • units: K
  • long_name: The brightness temperature difference (K) at 12 microns between observations and simulations (based on ECMWF data). Used to initially screen observations for cloud.
  • var_id: bt_diff
  • names: The brightness temperature difference (K) at 12 microns between observations and simulations (based on ECMWF data). Used to initially screen observations for cloud.
  • units: msec
  • long_name: Time of day in msec since midnight (UTC).
  • var_id: time_in_msec
  • names: Time of day in msec since midnight (UTC).
  • var_id: year
  • long_name: Year.
  • names: Year.

Co-ordinate Variables

  • units: degrees_north
  • standard_name: latitude
  • var_id: lat
  • long_name: Latitude (degrees_north)
  • names: latitude, Latitude (degrees_north)
  • units: degrees_east
  • standard_name: longitude
  • var_id: lon
  • long_name: Longitude (degrees east).
  • names: longitude, Longitude (degrees east).
Coverage
Temporal Range
Start time:
2007-05-31T23:00:00
End time:
2016-12-31T23:59:59
Geographic Extent

 
90.0000°
 
-180.0000°
 
180.0000°
 
-90.0000°