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President's Corner

On 3 April 1995, a Pegasus rocket launched a small research satellite into a circular orbit of about 750 kilometers altitude. The disk-shaped satellite, which circles the earth every 100 minutes, carries a laptop-sized GPS (Global Positioning System) radio receiver to demonstrate sensing of the terrestrial atmosphere by a limb sounding technique. Each time this receiver rises and sets relative to the 24 operational GPS satellites, the GPS radio waves transect and are bent (refracted) by successive layers of the atmosphere before they reach the receiver. Thus, during each occultation, a vertical profile of refractivity is obtained. The refractivity is a function of pressure, temperature, and water vapor; GPS/MET (GPS/Meteorology) thus provides information on these variables that has the potential to be useful in weather prediction and weather and climate research.

The GPS/MET story is being told elsewhere; in this essay I describe one aspect of this program that touched me personally. GPS/MET was responsible for a renewal of my friendship and collaboration with the pioneer of satellite meteorology, Verner Suomi, who died at the age of 79 on 30 July 1995.

My first significant interaction with Vern was in 1965 at the University of Wisconsin-Madison in a graduate seminar in satellite meteorology. In those days satellite photographs from the TIROS series of satellites were mailed to Madison from Washington; they usually arrived a day or two after they were taken. But even with this delay and the relatively poor quality of the photographs, Vern's enthusiasm and vision about the future of satellites and their unique role in studying the atmosphere were contagious and compelling.

Over the next 30 years our paths crossed from time to time, especially during Vern's tenure as a UCAR trustee from 1983 to 1988. My last interactions with Vern began in January 1995, when I visited him in Madison to discuss the GPS/MET experiment. Even before the successful launch, Vern was a strong and effective advocate of the experiment, and was planning far ahead for his participation in the development of improved retrieval algorithms and the analysis of the data.

We continued our discussions over the next few months, and in May Vern participated in the production of a video describing GPS/MET and its potential. His excitement and enthusiasm came across strongly in this video, in spite of his deteriorating health.

My last contact with Vern was by telephone on 25 July, when he was in the hospital and was not expected to live for more than a few more days. He had asked that there be no further treatment or extraordinary measures taken to prolong his life. In our conversation, which lasted almost an hour, Vern was way ahead of me, as usual.

After expressing warm greetings and thanks for calling him, he jumped into a discussion of GPS/MET, saying the first results were extremely exciting and encouraging to him. He was, however, concerned about the loss of signal in the lower troposphere due to water vapor creating multiple radio wave paths. He thought we could make a guess at the water vapor and temperature structure, compute the ray path that would occur given this structure, and then select, based on this guess, the nearest path from the several that might be the actual one.

He then launched into a minilecture on how his experimental floating instrument to measure heat-flux over the ocean was working--very well, he said, measuring the fluxes with an accuracy of 2-3 Watts per square meter. The only problem was that birds used the instrument to rest on and this adversely affected the measurements.

Finally, he returned to a topic of lifetime interest to him: the hydrologic cycle. He reminded me of how important water vapor and evaporation are in the earth's surface energy budget by telling me of his experience in Nebraska many years ago. On 21 June, with the sun as high in the sky as it gets, the daily temperature range over a dark green, wet cornfield was 15íC. Later that season, in September, when the sun was much lower in the sky but after the field and atmosphere had dried out, the daily temperature range was 30íC--twice the June value.

Enthusiastic and positive to the end, Vern's voice was strong and his confidence and intellect as great as ever. He closed by saying that he had enjoyed his life immensely, had no regrets, was leaving many other competent scientists behind to carry on, and was ready to say good-bye.


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