Observatoire Haute Provence


The Observatory de Haute-Provence (OHP) in France. OHP (44°N, 6°E) is located near the town of Forcalquier on a plateau at 650 meter altitude in the southern French pre-Alps. First dedicated to astronomical observations, the Observatory accommodated geophysical observations from the beginning of the 1970s. A geophysical station devoted to the long term monitoring of the atmosphere was established in 1980. It was one of the first stations to be part of the Network of the Detection of Stratospheric Changes (former designation of NDACC) in 1991.

The first astronomical observations were made at OHP in 1943 and the Observatory was opened to foreign astronomers in 1949. The main facilities include telescopes of 1.93, 1.52 and 1.20 meter diameter. The first planet outside the solar system was discovered in 1995 at OHP by M. Mayor and D. Queloz of the University of Geneva using the radial velocity technique. Presently, the detection of exo-planets is a main research activity at OHP, based on high resolution cross-dispersed spectrometer implemented on the 1.93 m telescope.

The first geophysical observations were taken at OHP in the 1970s, in particular with the pioneering work on lidar by Gérard Mégie. The first lidar system implemented on the site used the resonance-fluorescence technique for the measurement of the sodium layer in the mesosphere. Subsequently other lidar systems for measuring atmospheric parameters such as the temperature and ozone vertical distributions were set up at OHP. Initially based on dye lasers as active radiation source, the lidar instruments became more reliable with the development of commercial solid state or gas lasers. Temperature, ozone and aerosol lidar time series started in 1980 and 1985 respectively and they represent the longest time series worldwide. The OHP site is particularly well suited for lidar observations, with in average 170 clear-sky and 50 partially cloudy nights per year.

During the same period, various instruments for the monitoring of the atmospheric composition were also implemented on the site. A Dobson spectrometer, part of the automated Dobson network and providing measurements of ozone total content and ozone vertical distribution using the Umkehr technique was installed in 1983. Ozone soundings started in 1984 using first Brewer-Mast and then ECC sondes from 1991. A UV-Visible spectrometer for the measurement of ozone and nitrogen dioxide total contents was implemented in 1992. Most recent instruments implemented at OHP include a CIMEL sun photometer as part of the AERONET program for the measurement of the aerosol optical depth, a Max-DOAS UV-Visible spectrometer measuring BrO, a high resolution spectro-radiometer for the measurement of UV radiation, and surface ozone and CO analysers. Tropospheric aerosols lidar measurements are performed as part of the EARLINET network. New lidar techniques continue to be tested and implemented, e.g. Doppler wind, high resolution backscatter and water vapour Raman lidars.

The institutions participating to the NDACC monitoring programme at OHP are the CNRS, UVSQ, ADEME and CNES (France), NOAA (USA) and IASB-BIRA (Belgium). Long term measurements at OHP have been extensively used for the validation of satellite observations, in particular the UARS, Envisat and AURA platforms. Lidar and UV-Visible measurements are currently part of the long term Envisat validation programme. Several NDACC intercomparison campaigns were organised at OHP for lidar (1992 and 1997) and UV-Visible measurements (1996). The next intercomparison campaign involving the NASA-GSFC mobile lidar instrument is scheduled for 2009. Regular training sessions are organized including lidar courses. It concerns mainly master students from French universities and PhD students and postdocs through the ERCA sessions.

Instrument Description

1. Rayleigh-Mie-Raman Lidar:

The first measurements of routine temperature were obtained in 1979 with a preliminary instrument also used for ozone measurements. Several improvements have been made since this date: a second channel for Rayleigh scattering , Raman channels for Nitrogen (1999), and water vapour. The pulse source is a Continuum Neodyme:YAG laser using a harmonic generator for providing the second harmonic at 532 nm. It provides 350 nm at 50 Hz. One receiver is composed by a mosaic of 4 parabolic mirrors of 500 mm diameter dedicated for Rayleigh scattering from high altitude, and a telescope of 800 mm diameter for the Raman signals and 2 telescopes of 200 mm diameter respectively for aerosols and the lower sensitivity Rayleigh channel used for the lower range. The photons were collected, using optical fibers. Photon counting were insured using photomultipliers (PM) of Hamamatsu R1477S.

2. Ozone DIAL lidar for the stratosphere:

This system allows measuring the ozone profile in the stratosphere (10-50 km) using the DIAL technique. Both wavelengths used have been generated with two different lasers. The third harmonic of a Nd/Yag (Neodyme-Yag) at 355 nm (50 Hz, 60 mJ par pulse) have been used for the non-absorbed wavelength. An excimer laser at 308 nm (100 Hz et 200 mJ par pulse) is used for the absorb wavelength. The receiver is composed of a mosaic of 4 telescopes of 500 mm diameter. Optical fibers at each telescope's focal point collect the backscatter light up to the (Jobin Yvon) spectrometer used to separate the different wavelengths including the Raman shifted lines that are used for the lower range where aerosols are present. Glass beam splitters (8% - 92%) are used to provide low sensitive channels for covering the whole dynamic of the signals. Photon counting is insured with a LICEL system. A mechanical chopper made with a rotating disc (24000 rps) is used to prevent the saturation of the photomultiplier by the large initial burst.

3. The tropospheric ozone DIAL lidar:

This system is dedicated to the tropospheric ozone (3-12 km) and has been installed since 1988 and provides routine operation since 1990. As the stratospheric system it is using the DIAL technique. Different wavelengths have been used to provide a higher sensitivity in a region where ozone density is small. The both wavelengths (289 and 316 nm) are performed using the fourth harmonic of a Nd/Yag laser (0,8 W at 266 nm, 20Hz). Both wavelengths have been generated by the Raman shifting technique in a cell containing 30 bar of a gas including Helium (289 nm) and Deuterium (316 nm). The receiving telescope has a diameter of 800 mm and the wavelength separation is done using a spectrometer similar to the one used for the stratosphere. Analog channels are also used for the lower altitude channels.


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