At the beginning of 1999 I spent three months at the Max-Planck-Institute for Meteorology in Hamburg as a trainee. As a physics student I had to do an obligatory traineeship. While studying at UNIS on Spitzbergen, I did some research by internet and asked at several institutes in Germany by email whether they would have a position for a traineeship. I got a couple of offers and applied to them. Finally, I got the place at the Max-Planck-Institute for Meteorology in Hamburg.
My task was to write the control software for an interferometer system. There where a couple of programmes written in QBASIC which where quite complicated to use and far from intuitive. The requirement was to use Microsoft Visual C++ to create a software with GUI that would control the motors moving the mechanics of the instrument setup, perform different automatic measurement cycles and log all important parameters of the system. The actual data acquisition of the interferometric data is done by a software provided with the interferometer.
This picture shows the whole system (viewed from behind with the cover opened). The interferometer (the white/gray box inside) is mounted on a movable table. In front, there is a huge tube mounted with a mirror inside. There are two strong motors to move the system. One moves the tube with the mirror in and out of the housing and the other turns the tube and thus controls the viewing direction of the instrument. The green gas bottle contains nitrogen that is used to flush the interferometer. This is done to get rid of the water vapour inside the interferometer that would hinder the measurements in the infrared. On the right side you can see a box attached to the main housing. This is one of two black bodies that where developped by Dr. L. Fiedler during his Ph.D. work. They are necessary to calibrate the instrument to correct temperature drifts that would otherwise give large errors in the measurements. The temperature of the blackbodies is stabilized to about 10mK.
The instrument was used in several campaigns at the seaside resort of Graal-Müritz on the shore of the Baltic Sea. The interferometer system was mounted at the end of a walk-bridge extending about 100m out into the sea. On this picture, you can see the two blackbodies mounted to both sides of the main housing. To the right, you see a part of the construction trailer that was used as the control room and where all computers where put in. The instrument was used to measure the reflectivity of the sea surface to examine the so-called skin effect. The scientific results are published in the Ph.D. thesis of Dr. L. Fiedler.
At the same time, the usual set of meteorologic observations where carried out by an automated weather station. The data was directly recorded on a small HP notebook (Omnibook 800CT). The sensors for shortwave and longwave radiation are mounted on the lower left bar. On the upper left bar there are sensors for temperature, humidity, wind speed and wind direction. At the right bar there is mounted an acoustic sonic device pointing upward and a device measuring humidity pointing downward.
The special thing about these two instruments is that they can record their measurement quantities - wind speed & direction and humidity, respectively - at up to 20 Hz. Thus it is possible two study the turbulence by directly measuring the quantities with high temporal resolution. The acoustic sonic device (which is shown in detail in the picture to the right) is based on the doppler effect measured in three directions to get three dimensional data on the movement of the air between the arms of the instrument. The device for measuring humidity is based on absorption spectroscopy of water vapour in the infrared. One problem was to write a data logging programme that is very accurately timed to the two devices measure at exactly the same time. This is necessary if one wants to relate wind and humidity to compute fluxes of humidity from the data.
Even after my traineeship I was working a couple of times at the MPIM to extend the software and to accompany the instrument on two excursions on the Baltic Sea in April and June 2000. These trips with the research vessel F/S ALKOR were used to collect more data on the reflectivity of the sea surface and to demonstrate that it is possible to use the instrument even aboard a ship. To achieve a constant viewing angle with respect to the sea surface it was necessary to add a clinometer to the instrument which measures the pointing direction of the instrument. This information is then used to turn the mirror to correct the movement of the ship. This task required some thoughts but in the end it worked very nicely.
If you want to know more about the instrument please contact
Dr. L. Fiedler
who is now working at EUMETSAT in Darmstadt. This project was done in the group
"Physics of the Atmosphere" under supervision of
Dr. S. Bakan.
If you want to know more about the software, please contact me at firstname.lastname@example.org.