Photometric Variability of the Disk Integrated Infrared Emission of the Earth

TL;DR

This study analyzes Earth's global mid-infrared emission variability, revealing how rotation, seasons, and geographic features influence the observed thermal flux, with implications for remote sensing and exoplanet studies.

Contribution

It provides new insights into how Earth's infrared emission variability can be interpreted from a point-like observation, considering effects of geography, weather, and orbital position.

Findings

Earth's rotation can be determined from infrared time series despite weather masking.

Seasonal modulation of infrared emission depends on observer's latitude.

Lunar signal dominates phase variations in Earth-Moon infrared observations.

Abstract

We present an analysis of the global-integrated mid-infrared emission flux of the Earth based on data derived from satellite measurements. We have studied the photometric annual, seasonal, and rotational variability of the thermal emission of the Earth to determine which properties can be inferred from the point-like signal. We find that the analysis of the time series allows us to determine the 24 hr rotational period of the planet for most observing geometries, due to large warm and cold areas, identified with geographic features, which appear consecutively in the observer's planetary view. However, the effects of global-scale meteorology can effectively mask the rotation for several days at a time. We also find that orbital time series exhibit a seasonal modulation, whose amplitude depends strongly on the latitude of the observer but weakly on its ecliptic longitude. As no systematic difference of brightness temperature is found between the dayside and nightside, the phase variations of the Earth in the infrared range are negligible. Finally, we also conclude that the phase variation of a spatially unresolved Earth-Moon system is dominated by the lunar signal.