User’s Guide ______________________________________________________________________
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middle to the last sample, or, equally, from the middle to the first
sample. In other words, the window radius indicates how many samples
before and after the corresponding sample will be taken with in the
filtering window. The number of samples where the median is
calculated is as follows (sample radius = window radius):
Filter Window Length = 2
×
Window 1
The sample radius is the value given for the ground equipment. If the
windows radius is defined as an Integer, the filter window is always an
odd integer and the median algorithm is well-defined.
The ozone sensor response time is typically about 20 seconds, as
indicated in the GAW report 201 (see Appendix D
for details). To avoid cutting real ozone values
of the measurement results, the median filtering window length must be
clearly shorter than the sensor’s response time. Note that the length is
defined as the amount of samples. Therefore, different values for
radiosondes with different sample rates must be used. A typical value
for the window radius for RS41 is 4 (filtering window = 9 seconds).
The median filtering algorithm is disabled by setting the window radius
to 0.
Ozone Partial Pressure Calculation
The ozone sensor operating principles are explained in detail in the
sensor manufacturer manuals. To clarify the ozone calculation, the
operation of the SPC ozone sensor ECC6A is explained here in brief.
Ozone Sensor Operating Principle
The ozone sensor used within the ozonesonde is an iodine-iodide redox
electrochemical concentration cell. It is made of two bright platinum
electrodes immersed in potassium iodide solutions of different
concentrations, contained in separate cathode and anode chambers,
fabricated from polytetrafluoroethylene (Teflon TFE resin). The
chambers are linked together with an ion bridge that serves as an ion
pathway and retards mixing of the cathode and anode electrolytes,
thereby preserving their concentrations. Driving emf for the cell is
derived from a difference of potassium iodide concentrations present in
the two half cells. See
