Owner  RIVM
Manufacturer  RIVM
Wavelength  1064 nanometer (Nd:YAG laser)
Measurement Range  150 m to 15000 m
Range Resolution  3.75 m
Integration Time  1 s (adjustable)


Lidar stands for Light Detection And Ranging. The technique is sometimes referred to as ``laser radar'', because lidar is conceptually an optical analogon of the more familiar radar. The lidar measurement principle is as follows: a short pulse of laser light is emitted and the very faint reflections of the light on air molecules and particles are observed. The height resolution is obtained through measuring the time lapse between emission of the laser pulse and the reception of the echo. Time and distance are related by the speed of light. Because the optical echoes that are received are so weak, very often signal averaging is applied to increase the signal to noise ratio in the measurements. For most purposes of lidar (for example boundary layer studies and trace gas concentration measurements) averaging is allowed since the observed quantities vary slowly with time. In other words: the atmosphere can be considered frozen over the time of the measurement. For clouds, however, the frozen atmosphere concept does not apply, since the variations of the structure of a cloud are rapid and large. In order to capture the richness of detail in clouds and aerosol layers, a non-averaging measurement scheme has been implemented into the RIVM backscatter lidar. This type of measurement is denoted by HTRL: High Temporal Resolution Lidar.

The RIVM lidar at CESAR operates at 1064 nm only and collects elastically backscattered light. The system is fully automated and measures day and night. The measurement range is from ca. 150 m up to 15 km.

To date two modes of operation have been implemented:
1. Continuous mode of operation with adjustable time resolution (campaign mode). For example, lidar echoes from 20 laser shots are averaged (2 seconds time resolution).
2. Sampling mode of operation (PBL mode) In this scheme a measurement is taken every 5 minutes. This measurement consists of ten average profiles that are obtained from averaging 25 laser shots each. The rationale behind this scheme is the automatic retrieval of the height of the planetary boundary layer by simultaneous analysis of the vertical aerosol gradient and the temporal variability of the gradient over the sample.


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Backscatter profiles  raw backscatter
# gates  5000 (800 pre-trigger)
unit  Arbitrary units
resolution  3.75 m
Cloud base  up to 10 cloud bases
unit  m
resolution  3.75 m
File format  Proprietary


Operational at Cesar since May 2001 in campaign mode and since May 2002 in PBL mode.


PO Box 1
3720 BA Bilthoven
the Netherlands
Telephone: +31 30 2742678


Apituley, A., A.C.A.P.v. Lammeren, and H.W.J. Russchenberg, High Time Resolution Lidar measurements of Clouds, Physics and Chemistry of the Earth, 25 (1), 113 - 117, 2001.

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This site is maintained by Henk Klein Baltink