Large Aperture Scintillometer (LAS) data at location no. 16 in CASES99 network of 
flux towers

version 1.0

1. Authors and data source:

Wageningen University (the Netherlands)
Oscar Hartogensis, Bas van de Wiel


2. Description of the sensor

2.1. Sensor type
Large Aperture Scintillometer, built by Wageningen University

2.2. Theory in a nutshell:
The Large Aperture Scintillometer (LAS) consists of a transmitter and receiver. The 
transmitter emits a near parallel 15 cm beam of near infra red light. The light intensity  
of this beam is determined at the receiver placed at a distance of 300m to 5000m from 
the transmitter. Following wave propagation theory for strong turbulence intensity 
fluctuations caused by turbulent fields along the path can be evaluated into a value of 
Cn2, the structure parameter of the refractive index. To distinguish the scintillometer 
emitted infra red radiation from ambient radiation, it is modulated at 7kHz. The 
scintillometer is designed such that it outputs both the average received intensity 
signal (the demodulated signal) and Cn2.

2.3. Location:
Location no. 16 in CASES99 network of flux towers; co-ordinates N37’38.611’ 
W096’44.233’

2.4. Set-up:
Receiver was installed at 5.17m height in the flux tower at location no. 16.
Transmitter was installed at 3.40m height on a tri-pod.
Scintillometer path was 420m in a NNE – SSW direction.

A small field survey had been conducted to establish the extend of the sloping terrain 
along the scintillometer path. In the table below the heights are given relative to the 
surface at the scintillometer transmitter, which is indicated by (*); the receiver is 
indicated by (**). The table represents a grid around the scintillometer path with 
intervals of 75 m between the points.

		-1.2		0.05		1.45		2.35
-0.25		-0.6		0 (*)		1.4		2.7
1.65		0.9		0.9		1.9		2.7
2.65		1.55		1.4		2.45		3.7
4.05		2.2		1.25		2.25		3.05
4.1		1.5		1.65 (**)	1.6		2.85
4.2		3		2.5		2.3		2.9
4		3.1		3.75		3		2.95

Data was logged with a micro-world G2 datalogger (12 bits) built-in in the receiver.


3. Description of derived variables

A crude quality control test has been performed based on the following criteria: error 
code is set to 0 (bad data) if demodulated signal is more than –200mV, standard 
deviation of the demodulated signal is more than 25 mV, if  Cn2 < 10^-17 m^-2/3 or 
more than 0.5*10^-11. These are rule of thumb estimations to rule out a distorted  
signal due to misalignment, dew formation on the windows, rain, or any intensity 
fluctuations in the signal caused by something else then turbulence (e.g. tower 
movement, birds flying through the path etc.). Invalid or no data are given as a 
dummy “-9999”.

The columns in the data files are labelled; here follows an overview of all the 
variables with their label names and units:

YYYYMMDDHHMMSS : Time in CASES99 standard time format [UTC]
DOY : Day of Year [CDS]
HH,MMSS : Decimal time, where minutes and seconds are expressed as a fraction of 
an hour [CDS]
error : Flag which is set to 1 for good data, and 0 for bad data; description of error is 
given above [-]
demod: average received demodulated signal intensity [mV]
sd(demod): standard deviation of demod [mV]
Cn2: Structure parameter of the refractive index, scaled with a factor of 10^15 
[10^15m^-2/3]
sd(Cn2): standard deviation of Cn2 [10^15m^-2/3]


4. Sample period

Sample period = 1s
Averaging period = 1 minute averaged data were stored.

All data for the whole experiment are given in one plain ASCII file; the columns are 
space separated


5. Data availability

The LAS has been in continuous operation between 1002 17:30 and 1028 14:00 local 
(CDS) time.