Post project analysis of sonic anemometer data

The post-project analysis of the sonic anemometer data to correct for bias and tilt was carried out using the two functions: fun.sonic.bias.plot and fun.sonic.tilt.plot which were composed by T. Horst and subsequently modified by G. Maclean. These functions are available on request.

Specified values for parameters which were utilized in this analysis were:

prop.corr = 65.75 degrees for ops1

flagmax = 0.1 for ops1, 2, and 3

wmax = 1.0 ms-1 for ops1, 2, and 3.

(With the exception of ops2, atiS.50.10m, 172:174 when a value of wmax = 5.0 ms-1 was used.)

Operations: ops1, ops2, and ops3

Three configuration were specified during the FOOTPRINT92 deployment.
  1. ops1 from jday 154:157
  2. ops2 from jday 157:174 (Although this was designated as a single ops, two different sonics were deployed on the 50m tower; the atiK from jday 157:163 and the atiS from jday 167:174)

    N.B. atiS.50.10m underwent a radical change on jday 171 when a transducer failed and was replaced. The period 167:174 as been split into two periods, 167:170 and 172:174
  3. ops3 from jday 174:181


These routines use linear regression.

For all sonic anemometers for each ops the sonic anemometer azimuths were determined with a theodolite. These values of sonic.azm are the nominal values. The first step in processing the sonic anemometer data was to determine the true values for sonic.azm. This was done by comparing the difference between the prop-vane and the sonic anemometer as the wind direction varied. The value of the function,

was plotted as a function of the assumed azimuth of the sonic. A minimum in the curve was assumed to correspond to the true azimuth of the sonic anemometer.These true sonic.azm's were then used as input to the bias program which plots u and v wind components as measured by the sonic anemometer and the prop-vane. The gains and intercepts of these lines are given as:

u.gain, v.gain,, and

These gains and intercepts were then used as input to the tilt program, which calculates for each sonic for each ops the offset, pitch and roll.

Table 3 summarizes the sonic anemometer data for FOOTPRINT92.