Intercalibration of 183 GHz sounding channels

Author: Vivienne H. Payne, Jean-Luc Moncet, Pan Liang and Eli J. Mlawer
December 4, 2012
AGU Fall Meeting 2012

Vivienne Payne; Alison Chase; Jean-Luc Moncet; Pan Liang; Eli J. Mlawer (2012) Intercalibration of 183 GHz sounding channels. AGU Fall Meeting, San Francisco, CA.

Radiometer intercalibration is a critical component of obtaining accurate precipitation retrievals from satellite constellations. The assessment and removal of inter-instrument differences between the passive radiometers that will be used in the constellation for the Global Precipitation Measurement (GPM) mission will be of vital importance for the success of the mission. Here we present an approach for intercomparison between 183 GHz channels for currently-flying radiometers. We compare brightness temperature measurements from a range of existing sounders with radiative transfer model simulations over Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) sites. In order to avoid issues related to uncertainty in the surface emissivity, comparisons are limited to atmospheric conditions with sufficient water vapor to obscure the surface for these channels. We compare both absolute differences between model and measured brightness temperatures for individual instruments and inter-instrument differences.
In order to assess the sensitivity of the intercomparison results to the quality of the estimate of the atmospheric state used as input to the radiative transfer model, comparisons have been performed using temperature and water profiles from radiosonde-based “Merged Sounding” products over the ARM sites and from Global Forecast System (GFS) fields. We conclude that the impact of the choice of input profiles is larger for sites where the atmospheric conditions exhibit greater variability in space and time.
An important feature of our approach is the use of well-validated radiative transfer modeling tools, using consistent physics across spectral regions and up-to-date water vapor spectroscopy to accurately model the water vapor absorption. We also assess the sensitivity of the results of the intercomparison to the uncertainties in the water vapor absorption model used within the radiative transfer code.