MnSGC Ballooning Team Techniques: BalloonSat Easy/Weather data analysis James Flaten Summer 2010

Weather station data, as stored on a BalloonSat Easy flight computer, usually looks about like this when originally stored – 3 channels of raw data containing temperature, relative humidity, and pressure information.

To analyze the data, insert these extra rows and columns and label them.

Put consecutive integers in the “Data point number” column then use them to calculate values for the “Time T min” column. Here the data points were collected 15 seconds (i.e min) apart – see the equation.

The temperature sensor gives values ranging from 1 to 256 (for 8-bit) or from 1 to 1024 (for 10-bit), which correspond to absolute temperatures (i.e. temperature in Kelvin). Limit digits shown using cell formatting. According to the manufacturer (nearsys.com), raw temperature values can be changed to degrees Fahrenheit using the equation “= ((((((+B5/256)*5)*100)-273)+40)*1.8)-40” (for 8-bit). A quick plot of temperature versus time shows the expected shape.

The relative humidity sensor gives values ranging from 1 to 256 (for 8-bit) or from 1 to 1024 (for 10-bit), which correspond to relative humidity in %. Limit digits shown using cell formatting. According to the manufacturer (nearsys.com), raw relative humidity values can be changed to percent relative humidity using “= (((+C5/256)*5)-0.8)/0.031” (for 8-bit). A quick plot of relative humidity versus time suggests possibly-suspect data. Evidence of peaks when passing through clouds. Generally low humidity at altitude, but data is noisy.

The pressure sensor gives values ranging from 1 to 256 (for 8-bit) or from 1 to 1024 (for 10-bit), which correspond to pressure in millibar. Limit digits shown using cell formatting. According to the manufacturer (nearsys.com), raw pressure values can be changed to pressure using “= ((((+D5/256)*5)-0.5)/4)*1013” (for 8-bit). A quick plot of pressure versus time shows initial steady atmospheric pressure, a smooth decrease till burst, then a quick return to the surface.

Launch, Burst, and Touchdown times can now be identified, probably most-easily from the pressure vs time graph. Use them to select an offset (i.e. the flight time t when clock time T is zero (must be negative since the clock is started prior to release). Use the offset to generate a “Flight time t” column – will use absolute referencing. Notice that I moved that column next to the T column, for ease in graphing. BSE clocks aren’t too well calibrated so if time intervals in this data set don’t match those from other sources, consider expanding or contracting the flight time here (by up to 10%). Generate final graphs using the Flight time t column.