HAB Report

Investigating the Structure of the Atmosphere 

This is the report (right) summarising the results from our high altitude balloon flight on 23rd September.  If you don't want to read the details I have summarised the main figures below.

There were a number of reboots during the flight, this powerpoint shows some analysis done by Neil on why this occurred.

Speed of Sound

The speed of sound was measured using an ultrasonic range finder which reflected a sound pulse from a metal reflector 30cm away. This was done every 10 seconds throughout the flight and the results are shown below. However, at around 10km the sensor stopped recording data, more details on the reasons why are found in the report.

The graph shows how there is a linear correlation between Speed of sound squared and temperature. This is in accordance with the Newton-Laplace equation, proving that speed of sound varies only with temperature through the atmosphere.

Temperature

The Troposphere is defined as the layer where temperature decreases with height, therefore from the graph below this is up to the height of 12050m agreeing with the standard atmospheric model. The Tropopause is therefore found between 12050m and 13700m where the temperature is roughly stable at around −47 Degrees C. The payload extended into the Stratosphere up to a height of 35km, which would put it above the Ozone layer at around 20-30km high. This is also evident from the results, as in the Stratosphere temperature rises with height, as predicted from the absorption of UV radiation in this layer.

Pressure

The pressure in the atmosphere should exponentially decay, as shown in the first graph below. The second graph shows the natural log of Pressure, where a linear correlation confirms that the decay seen is exponential. The minimum pressure seen is 820Pa, compared with 101,000Pa at sea level.

Humidity

The relative humidity varied as expected, with high humidity as the payload passes through the clouds. An unexpected feature was the slight bump at 12km, this turned out to be high altitude ice clouds as seen in the pictures below. The first picture shows a view from inside the low-level clouds. The second and third images show the high-level clouds from below and from inside.

UV intensity

The ozone layer blocks 90% of UVB (particular band of ultraviolet light), so there should be a significant increase in the intensity as the payload travelled past the ozone layer. However, the graph shows that there was only a 17% increase in UVB, and an 8% increase in UVA. This is due to the sensor only measuring the top part of the UVB band, a part that is not blocked as much as I thought it would be. Next time we will try and measure UVC, which is completely blocked on all wavelengths, so there should be a drastic change in readings.