Relations between SMMR 37 GHz polarization difference and rainfall, and atmospheric carbon dioxide concentration

Abstract

Rainfall and the atmospheric carbon dioxide (CO₂) concentration may be considered as proxy variables for spatial and temporal changes of vegetation. Together with theoretical analysis, correlations between these meteorological data and 37 GHz polarization difference (PD) have been studied to test a hypothesis that PD is an indicator of vegetation characteristics. Previously published relations between PD and rainfall, and atmospheric CO₂ concentration are discussed in response to issues raised in Tucker (1992) that: (1) the relation between rainfall and PD was based upon selective information, and (2) winter conditions in the more northern latitudes (e.g. snow, low atmospheric water vapour, etc.) result in the appearance of a relation between PD and CO₂ concentration. It is shown that: (1) the previously published relation between PD and rainfall is valid at a high level of statistical significance when rainfall stations are screened objectively, and (2) a relationship between PD and CO₂ concentration does exist that is not tied to conditions or relationships existent in the winter at northern latitudes. Highly significant correlations between PD and rainfall, and between PD and CO₂ concentration would suggest that the hypothesis being tested is true.