Characterising the FY-3A microwave temperature sounder using the ECMWF model

Characterising the FY-3A microwave temperature sounder using the ECMWF model
Technical memorandum
Date Published
Secondary Title
ECMWF Technical Memoranda
Qifeng Lu
W. Bell
C. Peubey
Abstract China's FY-3A, launched in May 2008, is the first in a series of seven polar orbiting meteorological satellites planned for the next decade by China. The FY-3 series is set to become an important data source for Numerical Weather Prediction (NWP), reanalysis and climate science. FY-3A is equipped with a microwave temperature sounding instrument (MWTS). This study reports an assessment of the MWTS instrument using the ECMWF NWP model, radiative transfer modelling and comparisons with equivalent observations from the Advanced Microwave Sounding Unit-A (AMSU-A). The study suggests the MWTS instrument is affected by biases related to large shifts, or errors, in the frequency of the channel passbands as well as radiometer non-linearity. The passband shifts, relative to pre-launch measurements, are 55 MHz, 39 MHz and 33 MHz for channels 2-4 respectively. Relative to the design specification the shifts are 60 MHz, 80 MHz and 83 MHz with uncertainties of ± 2.5 MHz. The radiometer non-linearity results in a positive bias in measured brightness temperatures and is manifested as a quadratic function of measured scene temperatures. By correcting for both of these effects the quality of the MWTS data is improved significantly, with the standard deviations of (observed minus simulated) differences based on short range forecast fields reduced by 30-50% relative to simulations using pre-launch measurements of the passband, to values close to those observed for AMSU-A equivalent channels. The new methodology could be applied to other microwave temperature sounding instruments and illustrates the value of NWP fields for the on-orbit characterisation of satellite sensors.
DOI 10.21957/tb92c4mj8