Scientific Goal     Scientific Program     Meeting Format     Meeting dates


Over the last 10-15 years, our understanding of the Earth's atmosphere and its influence on astronomical observations has been dramatically improved. A sound physical basis for the measurement and interpretation of the atmospheric parameters of key importance for astronomical research at all wavelengths has been established and translated into working field equipment. This development has happened in increasingly close collaboration with the meteorological and atmospheric sciences, drawing on atmospheric modeling, and a better knoledge on turbulence parametrization. As a result, the evaluation and intercomparison of existing and potential observing sites has reached a level of sophistication, detail, and reliability which was hardly dreamed of only 25 years ago.
The experience over this period has led to dramatic improvements in delivered image quality at existing observatories, both with conventional telescope optics in suitable mountings and enclosures and through the development of adaptive optics and optical interferometry to the operational stage. These advances greatly increase the demands on the atmospheric quality of potential future sites for optical telescopes. At the same time, the wavelength range covered from a single observatory has increased dramatically: At observatories initially established for optical astronomy, optical and (sub)mm astronomy have become of increasing importance. In addition, the existence of multi-year cycles of climate variation makes it necessary to extend measurements over long periods. Finally, diagnostics of the rapid rise in man-made perturbation of the environment must also be included, such as potential airborne pollution from (natural and) artificial sources, interference from urban development and airline traffic, and radio noise from ground and space based radar or communications installations. These and other factors must be quantified and considered in the selection of future observatory sites.
Together, these developments greatly expand the range of atmospheric and other environmental parameters to be explored when prospecting for potential observatory sites. On the one hand, this implies greater complication and more rational planning of the equipment and analysis techniques to be deployed in future site testing campaigns. On the other hand, the more detailed understanding of the atmosphere that results from these measurements is itself of scientific value that transcends the narror borders of astronomy into the environmental sciences. Finally, the recent commissioning of several very large telescopes on a very small number of sites has highlighted the need to prepare an inventory of the - presumably few - remaining sites on Earth where adequate conditions still exist for future major observatories, so that the options are known and protective measures can be taken in time, if necessary.
We propose to hold an IAU Colloquium - the first on this subject for many years - to review the state of the art in site testing methods and instruments across the entire ground-based optical, infrared, and (sub)mm wavelength ranges. Capabilities, commonalities, and complementarities between methods will be clarified, with a view to establish lists of necessary and sufficient equipment for site testing at various ambition levels as well as the corresponding data reduction, calibration, and standardization procedures. Links and synergisms between ground and space based techniques will be explored with a view to mapping out a strategy for identifying additional high-quality observatory sites, suitably distributed in geographical longitude and latitude.


Monday, November 13

Session I: Physical mechanism of atmospheric turbulence
Chairperson: S. Radford
Review paper: Mechanism of formation of optical turbulence   J. Vernin
-Generation of atmospheric turbulence 
-Optical turbulence in the visible: The temperature field 
-In the Radio range: water vapor, long baseline 
-In the IR: Temperature and water vapor 

Session II: Measuring Instruments in the visible
Chairperson: M. Sarazin
Review paper: Observational methods for the study of optical turbulence  R. Avila
-Remote sensing (G-Scidar, DIMM, Radiometer, Scintillometer, GSM ...) 
-In situ sensing (Balloon, mast ...) 
1st Large Audience Conference 

Tuesday, November 14

Session III: Site characterization and atmospheric transparency in the mm/submm range
Chairperson: M. Ishiguro
Review paper: Site characterization for mm/submm astronomy  S. Radford
-Tropospheric constituents  
-Atmospheric transparency  
-Radiometers and photometers  
-Spectrometers (submm FTSs) 
-In situ measurements, i. e., radiosondes, etc.  
-Transparency models 
Cultural Activities 

Wednesday, November 15

Session IV: Tropospheric phase stability and compensation schemes
Chairperson: L.F. Rodriguez
Review paper: Compensation schemes for tropospheric phase instability  D. Woody
-Water vapor turbulence 
-Radio and optical seeing 
- Interferometry decorrelation 
- Test interferometers 
- Sky brightness fluctuations 
- Fast switching 
- Water vapor radiometry 

Session V: Forecasting
Chairperson: J. Vernin
Review paper: What can meteorological numerical models do for the astronomers  E. Masciadri
- Weather  
- Seeing 
- Cloud cover 
- Extinction 
2nd Large Audience Conference 

Thursday, November 16

Session VI: Site Surveys
Chairperson: R. Giovanelli
Review paper: The 'ideal' site revisited by future ground-based telescope projects  M. Sarazin
- Existing sites 
- New sites (High altitude, Antarctic...)  
- Radio and light pollution  
- Dust pollution  

Friday, November 17

Session VII: Astroclimatic Stations
Chairperson: Z. Benkhaldoun
Review paper: What an astronomer might expect from an astroclimatic station?   C. Muñoz-Tuñon
- Existing stations 
- Standards to apply 
- Networking, Database  

Session VIII: Phase correction: Adaptive Optics and Interferometry
Chairperson: M. Chun
Review paper: Atmospheric limitations to adaptive image compensation   F. Roddier
- Relevant atmospheric parameters 
- New ideas for integrated parameters 
- Monitoring (Differential water vapor, G-Scidar,...) 
Visit to the Astronomical Site of Oukaimeden 


General remarks:
- Each session will be 3-4 hour long with a coffee break.  
- Invited (review) papers will be 30-45 minutes long.  
- Contributed papers will be 15-20 minutes long. 
- Two conferences will be given to a large Moroccan audience. 


Detailed Program is now available.
- Sunday 12, Registration 
- Monday 13, Registration, Session I, Session II, 1st Large Audience Conference before diner. 
- Tuesday 14 Session III, Guided visit of Medina (afternoon), Ceremonial diner and folkloric show. 
- Wednesday 15, Session IV, Session V, 2nd Large Audience Conference before diner. 
- Thursday 16, Session VI, Free afternoon. 
- Friday 17, Session VII, Session VIII, Visit to the astronomical site of Oukaimeden, Diner and "Star Night" with amateur astronomers.  
- Back to Marrakech in the morning of Saturday 18. 

Updated 1999 October 27