Improved Alignment and Testing of LAS MkII
Published: Friday, April 5, 2013
A new alignment and calibration facility for the Large Aperture Scintillometer (LAS) has recently been commissioned on the roof of Kipp & Zonen in Delft.
A large aperture scintillometer is an instrument that consists of a transmitter and receiver, spaced from a hundred metres to several kilometres apart, that measures heat fluxes from the Earth’s surface. Using an internal data logger the LAS MkII receiver records intensity fluctuations of the light beam emitted by the transmitter. These fluctuations are caused by refraction of the light beam as it passes through the turbulent surface layer of air.
To obtain the best quality measurements, the alignment of optical components within the transmitter and receiver to the axis of the Fresnel focussing lens must be optimised. We have now designed and installed equipment that allows new LAS MkII, and instruments returned for service, to be tested at the factory by a single operator.
A reference transmitter is located 890 m away on top of the Electrical Engineering, Mathematics and Computer Science building of the Delft University of Technology, and points at the Kipp & Zonen roof. The infra-red light beam from the transmitter spreads out slightly with distance, so we can place several test receivers alongside a reference receiver for optical alignment and we can compare the data from them for performance checks.
The university’s roof also has a reference receiver with a radio data link so that the received signal strength can be monitored whilst a test transmitter on the Kipp & Zonen roof is optically aligned and the beam power checked.
This new facility enables easy and repeatable alignment and testing of our Large Aperture Scintillometers and comparison with reference instruments.
