TOVS PathB Description

Measurements

The TOVS instruments aboard the NOAA Polar Orbiting Environmental Satellites have measured radiation emitted and scattered from different levels of the atmosphere since 1979. The TOVS system consists, in particular, of two sounders: the High resolution Infrared Radiation Sounder (HIRS) with 19 IR spectral channels and the Microwave Sounding Unit (MSU) with 4 microwave channels. The IR channels are clustered near absorption bands of CO2, H2, and O3.
By assuming that CO2 is mixed uniformly in the atmosphere, absorption and emission due to CO2 can be used to sense the temperature and the uppermost cloud level in the atmosphere: measured radiances from near the center of a CO2 absorption band are sensitive only to the upper atmosphere while radiances from the wings of the band see successively lower levels of the atmosphere. Microwave radiation passes through aerosols and most clouds, since these wavelengths are much greater than aerosol and cloud particles.

Local Observation Time and Length of Data Record

7:30 AM and 7:30 PM ; 1987–1994, microphysics available for 1987–1990 (NOAA10);
1:30 AM and 1:30 PM ; 1989–1994

Spatial Resolution

17 km (detection), 100 km (retrieval)

Cloud Detection

multi-spectral, MSU clear sky estimation, snow/ice surface from MW

Retrieval Methodology

CP and CEM are determined from 5 CO2 absorbing channels by a weighted χ2 method based on spectral emissivity coherence. Therefore spectral emissivities are calculated from measured radiance, clear sky radiance and radiance of an opaque cloud for 30 pressure levels. The method takes into account the vertical weigthing of the different channels and the growing uncertainty in the computation of CEM with increasing pressure.
CT is derived from CP using the retrieved atmospheric temperature profiles.
COD = -2 ln ( 1 - CEM ). Ice clouds are defined by CT < 230 K.
The retrieval of CREIH of semi-transparent cirrus ( 0.3 < CEM < 0.85 ) is based on spectral cirrus emissivity difference between 8 and 11 μm, applying a Look-Up Table approach. CIWPH is then deduced from CEMIH and CREIH.

Ancillary Input

  • retrieved T profiles (TOVS Path B) or initial guess from TIGR database
  • spectral atmospheric transmissivities from TIGR database
  • 4A radiative transfer
  • bias adjustment from collocated radiosonde-TOVS data
  • single scattering properties of planar ice polycrystals (Mitchell), bimodal size distribution, Streamer radiative transfer
  • spectral surface emissivities from CERES/SARB
  • References

  • Stubenrauch, C. J., A. Chédin, G. Rädel, N. A. Scott, and S. Serrar, 2006: Cloud properties and their seasonal and diurnal variability from TOVS Path-B. J. Climate, 19, 5531–5553.
  • Stubenrauch, C. J., A. Chédin, R. Armante, N. A. Scott, 1999: Clouds as seen by Infrared Sounders (3I) and Imagers (ISCCP): Part II) A New Approach for Cloud Parameter Determination in the 3I Algorithms. J. Climate, 12, 2214–2223.
  • Stubenrauch, C. J., W. B. Rossow , F. Chéruy, N. A. Scott, and A. Chédin, 1999: Clouds as Seen by Satellite Sounders (3I) and Imagers (ISCCP): I) Evaluation of Cloud Parameters. J. Climate, 12, 2189–2213
  • Stubenrauch, C. J., W. B. Rossow , N. A. Scott, and A. Chédin, 1999: Clouds as Seen by Satellite Sounders (3I) and Imagers (ISCCP): III) Combining 3I and ISCCP Cloud Parameters for better Understanding of Cloud Radiative Effects. J. Climate, 12, 3419–3442
  • Scott, N. A., A. Chédin, R. Armante, J. Francis, C. J. Stubenrauch, J.-P. Chaboureau, F. Chevallier, C. Claud, and F. Chéruy, 1999: Characteristics of the TOVS Pathfinder Path-B Dataset, Bull. Amer. Meteor. Soc., 80, 2679–2701.
  • Rädel, G., C. J. Stubenrauch, R. Holz, and D. L. Mitchell, 2003: Retrieval of Effective Ice Crystal Size in the Infrared:Sensitivity Study and Global Measurements from TIROS-N Operational Vertical Sounder. J. Geophys. Res., 108, 10.1029/2002JD002801.
  • Stubenrauch, C. J., F. Eddounia, and G. Rädel, 2004: Correlations between microphysical properties of large-scale semi-transparent cirrus and the state of the atmosphere. Atmos. Res., 72, 403–423.