Near-Infrared Lunar Absorption Spectroscopy for the Retrieval of Column Averaged CO2 and CH4 - Towards an Interdisciplinary Approach in Earth System Science - page 77

Near-Infrared Lunar Absorption
Spectroscopy for the Retrieval of Column
Averaged CO 2 and CH 4

Matthias Buschmann, Nicholas M. Deutscher, Mathias Palm,
Thorsten Warneke, Tine Weinzierl and Justus Notholt

Abstract High resolution Fourier-Transform InfraRed (FTIR) absorption spec-
troscopic measurements are used to retrieve trace gas abundances in the atmosphere
at a number of sites throughout the world. Typically, the sun is used as an infrared
light source above the atmosphere of the Earth, however, at polar sites, such as our
measurement site at Spitsbergen, sunlight

is not available during polar night

(October March). Instead, the moon can be used as a substitute infrared light

source. In this article we present a proof of concept for the usage of a thermo-
electrically cooled InGaAs (Indium-Gallium-Arsenide) near infrared detector to
measure the column averaged trace gas abundances by lunar absorption spectros-
copy based on trial measurements made in Bremen. These measurements demon-
strate the potential of using lunar measurements for retrieval of atmospheric
columns of CO 2 and CH 4 . The resulting data can be used to

-

fill a crucial gap in the

seasonal cycle at polar sites.

1 Introduction

The measurement of the carbon cycle is important in order to understand the
complex relationships of its sources and sinks [e.g. Ciais et al. ( 2013 )]. Within the
measurement network Total Carbon Column Observing Network (TCCON), solar
absorption spectra are taken with high resolution Fourier-Transform InfraRed
(FTIR) spectrometers. Since the start of the TCCON program in 2004 measure-
ments have been taken at an increasing number of stations around the globe
(approximately 20 sites in the beginning of 2014). The measured spectra provide
information on column-averaged mole fractions of CO 2 ,CH 4 and other gases.