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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-252
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Aug 2018

Research article | 27 Aug 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Radiometric correction of observations from microwave humidity sounders

Isaac Moradi1,2,3, Jim Beauchamp1, and Ralph Ferraro2 Isaac Moradi et al.
  • 1ESSIC, University of Maryland, College Park, Maryland, USA
  • 2STAR, NOAA, College Park, Maryland, USA
  • 3NASA Global Modelling and Assimilation Office, Greenbelt, Maryland, USA

Abstract. Advanced Microwave Sounding Unit (AMSU-B) and Microwave Humidity Sounder (MHS) are total power microwave radiometers operating at frequencies near the water vapor absorption line at 183GHz. The measurements of these instruments are crucial for deriving a variety of climate and hydrological products such as water vapor, precipitation, and ice cloud parameters. However these measurements are subject to several errors that can be classified into radiometric and geometric errors. The aim of this study is to quantify and correct the radiometric errors in these observations through intercalibration. Since bias in the calibration of microwave instruments changes with scene temperature, a two-point intercalibration correction scheme was developed based on averages of measurements over the tropical oceans and night-time polar regions. The intercalibration coefficients were calculated on a monthly basis using measurements averaged over each specified region and each orbit, then interpolated to estimate the daily coefficients. Since AMSU-B and MHS channels operate at different frequencies and polarizations, the measurements from the two instruments were not interalibrated. Because of the negligible diurnal cycle of both temperature and humidity fields over the tropical oceans, the satellites with most stable time series of brightness temperatures over the tropical oceans (NOAA-17 for AMSU-B and NOAA-18 for MHS) were selected as the reference satellites and other similar instruments were intercalibrated with respect to the reference instrument. The results show that Channels 1, 3, 4, and 5 of AMSU-B onboard NOAA-16 and Channels 1 and 4 of AMSU-B onboard NOAA-15 show a large drift over the period of operation. The MHS measurements from instruments onboard NOAA-18, NOAA-19, and MetOp-A are generally consistent with each other. Because of the lack of reference measurements, radiometric correction of microwave instruments remain a challenge as the intercalibration of these instruments largely depend on the stability of the reference instrument.

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Short summary
Microwave (MW) satellite instruments are used for a variety of applications such as retrieving geophysical variables such as temperature and humidity as well as assimilated into NWP models to improve the weather forecast. However, MW instruments are subject to errors and uncertainty that can be classified into radiometric and geometric errors. This study evaluate the observations from several MW instruments for radiometric errors and provide correction coefficients for the data that are biased.
Microwave (MW) satellite instruments are used for a variety of applications such as retrieving...
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