Samenvatting

Kipp & Zonen, based in Delft manufactures and develops atmospheric measurement instruments, including a scintillometer. Kipp & Zonen currently manufactures the large aperture scintillometer (LAS) MkII and previously manufactured the extra large aperture scintillometer (XLAS) MkI. A scintillometer can measure the sensible heat flux, the amount of warm rising warm due to the solar radiation. A LAS or XLAS consists of a transmitter and a receiver, measuring over a long open path. The XLAS, a scaled up version of the LAS, allows measurements over even longer paths up to 10 km, on the scale of satellite pixels or atmospheric models. In this bachelor thesis a XLAS MkII was built and tested and a LAS was compared with other scintillometers to verify the quality of the measurements.

The frequency spectrum was investigated to see if the scintillometers were responding to the typical scintillation spectrum. The frequency spectrum of a reference LAS, a control LAS, an upgraded old LAS and two XLAS were found similar to the typical spectrum. A LAS from Wageningen University, of different design, showed a strong noise spike.

A XLAS with a reduction ring in front of it was compared with a LAS. The reduction ring has the same aperture diameter as the aperture of the LAS, making the two instruments comparable. A LAS transmitter was placed on the roof of the University of Delft and receivers were placed on the roof of Kipp & Zonen. Reference LAS 120001, control LAS 120002, XLAS 140001 and 140002, were placed on the Kipp & Zonen roof. The measurements from the scintillometers were compared in the form of the structure parameter of the refractive index of air (C_"n" ^2). Control LAS 120002 measured 2.8 ± 0.5 % higher C_"n" ^2 than reference LAS 120001. The XLAS measured lower C_"n" ^2 values than reference LAS 120001, 6.3 ± 0.7 % lower for XLAS 140001 and 4.2 ± 0.9 % lower for XLAS 140002. The two XLAS agreed very well, with XLAS 140002 measuring C_"n" ^2 values 1.3 ± 0.9 % higher than XLAS 140001.

The Kipp & Zonen LAS was compared with a LAS developed by Wageningen University, with a reversed path. The Wageningen LAS transmitter was placed on the Kipp & Zonen roof and the Wageningen LAS receiver was placed on the TU Delft roof. The Wageningen LAS measured 23 ± 2 % higher C_"n" ^2 than reference LAS 120001. This was due to a peak in the frequency spectrum, which leads to an offset in the measured C_"n" ^2. This is probably due to noise from the electronics.

The Kipp & Zonen LAS was also compared with a LAS from Scintec (BLS900), replacing the Wageningen LAS again in a reversed path configuration. The BLS900 has a low pass filter of 150 Hz, as opposed to the Kipp & Zonen LAS 120001 and 120002, which have a band pass filter from 0.5 to 400 Hz. For this comparison LAS 040007 has a band pass filter set to 0.1 Hz to 400 Hz, which more closely matches the BLS900.
The BLS900 measures 8 ± 1 % higher C_"n" ^2 than reference LAS 120001, and only 2 ± 1 % higher C_"n" ^2 than LAS 040007 with the different band pass filter setting of 0.1 Hz to 400 Hz. If the band pass filter of LAS 040007 is changed back to 0.5 Hz to 400 Hz, to match, then the measured C_"n" ^2 values agree extremely well with reference LAS 120001, within an uncertainty of 0.8 %.

To summarise, the Kipp & Zonen LAS agreed very well with each other and with the BLS900 if the same band pass filter range was used. The XLAS with a reduction ring agreed very well with the LAS.