Abstract
Abstract. Representative parameters of the scan geometry are empirically determined for the Global Precipitation Measurement (GPM) Microwave Imager (GMI). Effective fields of view (EFOVs) are computed for the GMI's 13 channels, taking into account the blurring effect of the measurement interval on the instantaneous fields of view (IFOVs). Using a Backus–Gilbert procedure, coefficients are derived that yield an approximate spatial match between synthetic EFOVs of different channels, using the 18.7 GHz channels as a target and with due consideration of the tradeoff between the quality of the fit and noise amplification and edge effects. Modest improvement in resolution is achieved for the 10.65 GHz channels, albeit with slight ringing in the vicinity of coastlines and other sharp brightness temperature gradients. For all other channels, resolution is coarsened to approximate the 18.7 GHz EFOV. It is shown that the resolution matching procedure reduces nonlinear correlations between channels in the presence of coastlines as well as enables the more efficient separation of large brightness temperature variations due to coastlines from the much smaller variations due to other geophysical variables. As a byproduct of this work, we report accurate EFOV resolutions as well as a self-consistent set of parameters for modeling the scan geometry of the GMI.
Highlights
Since the 1970s, satellite passive microwave imagers have played a major role in observing the global environment
As found previously by Bauer and Bennartz (1998) for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager, the improvement is somewhat better in the along-scan direction due to more oversampling in that direction
Because the 89.00 GHz channels are badly undersampled in the cross-scan direction, the synthetic FOV fit to the target effective field of view (EFOV) is poor in that direction
Summary
Since the 1970s, satellite passive microwave imagers have played a major role in observing the global environment. In adapting the algorithm of Petty and Li (2013a) to GMI, the concern arose that the noise associated with unmatched EFOVs would degrade the efficiency with which precipitation signatures could be separated from background variability, especially in the vicinity of coastlines and other sharp brightness temperature gradients. These concerns are the primary motivation for undertaking the work described in this paper. While these are not a substitute for the detailed ephemeris and navigation data provided with the imagery for each orbit, they may be useful for the realistic simulation of GMI images from atmospheric and terrestrial models
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