UMARS - Z_probe

The Z_probe is a sensor boom to be used in boundary layer research and alike the well-known “BAT-Probe”. The basic idea is that a relatively large hemisphere (80 mm diameter) of a five-hole-probe contains all the other sensors needed. That ensures a compact unit with all the instruments collocated. Also the probe is less sensitive to little disturbances like droplets or insects.

The design with fife holes, with an absolute pressure sensor for the centred hole, and four differential pressures from there to the top, bottom, left and right ports has three advantages (compared with differential pressure reading between top and bottom, left and right):

• non-linear treatment for large angles
• some redundancy when one hole should be blocked
• the four holes at 45° can also be used for measuring the static pressure (otherwise, nine holes are necessary)

The empirical corrections of the theoretical aerodynamic parameters, integrated in the post-processing software which also contains methods for in-flight calibration, are important parts of the system.

The fast temperature is measured with an ultra-fine thermo-couple (7.5 micrometer diameter copper-constantan) against a slower reference temperature (thermistor). The humidity is measured with a dew point mirror. Even though the method is known to be very accurate but also slow, the device “Snow White” from Meteolabor AG in Switzerland is also fast. Limited only by the data acquisition to 10 Hz, it is even faster than the backup sensor (small, low-cost capacitive sensor).

For measuring wind, which is the vector difference between the flow towards the five-hole hemisphere, and the speed and orientation of this sensor in the earth-fixed system, we are using an IMU xsense MTi-G.

The next step will be to integrate other existing sensors. This will start with an aerosol counter, a fast NO2 sensor and a CO2 sensor head. Of course also other sensors are possible to integrate. However, our approach is not to build what might seem possible, and then looking for applications. We are rather focusing on known scientific questions and then try to tailor a system for the specific purpose. This might include remote sensing and also optical methods (absorption) for faster in-situ measurements.