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Remote Sensing of the Earth

1985 Diploma in solid state physics at the University of Kassel;
1989 Doctorate in surface science at the University of Kassel;
1999 Habilitation at the FU Berlin;
Professor in Bremen since 2002

1990 – 91 Post-Doc Stipend at the Environment Institute of the European Joint Research Centre, Ispra/Italy;
1991 – 92 Research scientist at the Alfred Wegener Institute Bremerhaven;
1992 Move to the Alfred Wegener Institute in Potsdam

Family: Married, three children

email: notholt@uni-bremen.de

Spectroscopic remote sensing methods have been established as a valuable tool in environmental research for many years. All satellite instruments as well as ground-based, aircraft, or balloon-borne instruments are based on spectroscopic methods. The aim of our research is the development of new spectroscopic measurement and analysis methods and their application in atmospheric research. The methods are used for several projects in Bremen and in cooperation with the AWI in the Arctic, the tropics and during expeditions on research vessels. The main foci of our research are:

Composition of the free troposphere

The global transport of the air masses occurs mainly in the free troposphere, i.e. at altitudes between 2 km and 15 km. The upper troposphere is the entry point for tropospheric trace gases into the stratosphere. The knowledge of the composition of the upper troposphere is therefore necessary for the understanding of, the stratospheric ozone chemistry, for example. Up to now the free troposphere has not been studied in detail. Satellites are observing the atmosphere typically above the clouds, i.e. above 10 km to 15 km. Measurements at the ground are only recording the concentration locally at the measuring site. The infrared spectroscopy in absorption, where the sun or the moon serves as a light source, or in emission, where the direct emission of the molecules is being measured, allow the study of the composition of the free troposphere. As an example, Figure 1 shows the mixing ratio of CO, a trace gas resulting from combustion processes. The measurements were performed in 1999/2000 on board the German research vessel Polarstern.

Development of new measurement and analysis methods

We are planning a further development of existing measurement methods, e.g. with the help of imaging spectroscopy with infrared cameras instead of using single detectors. In this way the trace gas concentration profiles can be measured with a much better altitude resolution as required, for example, for the examination of the troposphere. Furthermore, in the case of emission measurements, the imaging spectroscopy might allow the study of tropospheric aerosols and quantify their radiation properties, which are still uncertain. The radiation properties of aerosols are one of the main uncertainties in the determination of the greenhouse effect.

Long-term changes of the atmosphere

One main focus of today's climate research is the study of any long-term change in the atmosphere due to anthropogenic and natural influences. The difficulty in these studies is to differentiate between the human influence and the natural variability of the climatic system. Observations of the atmospheric composition have been made over the years in co-operation with the AWI in the high Arctic on Spitsbergen at 79° N. The main research foci are (i) detection of the change in the stratospheric ozone depletion as a function of the total chlorine loading, stratospheric temperature and circulation, (ii) the long-term trend of water vapour in the stratosphere and mesosphere and (iii) changes in the composition of the troposphere. The observations are performed using infrared and microwave spectrometry. Both methods permit the detection of different trace gases and complement each other quite well. As an example, Figure 2 shows the measured long-term increase of HCl measured at Spitsbergen. HCl is the most important stratospheric chlorine reservoir, and chlorine is mainly responsible for the stratospheric ozone depletion.

Fig. 1 Mixing ratio of CO in winter 1999 as function of latitude and altitude
Fig. 2 Long-term trend of HCl for Spitzbergen