Radiation exposure mapped at flight altitudes

For several years, PTB has performed measurements at flight altitudes to investigate the global distribution of the ambient equivalent dose rate created by cosmic radiation at cruising altitudes. Between December 2003 and September 2004, a first long-term measurement was performed. The measuring system, which merely has the size of a flight case, was installed on board a Lufthansa Airbus A340. In more than 250 flights over the northern hemisphere, a great number of measurement data was collected. From these measurement data, easily manageable mathematical functions were obtained which describe the dependence of the ambient equivalent dose rate on latitude and altitude. This allows a calculation to be performed at least at cruising altitudes between 9 km and 12 km in the northern hemisphere. A comparison with measurements from the years 1997 to 1999 – in which time, however, only 39 individual measurement flights were carried out – allowed determining the functional relationship between a neutron measurement station on the ground – as a measure of solar activity,– and the radiation exposure at flight altitudes. Solar activity was found to influence the dose rate by up to ±30 %. The results of these measurements are contained in the “FDOScalc” (Flight Dose Calculator) program and are available to the public via the web pages of PTB (http://www.ptb.de/flugdosisrechner.html). PTB itself will use FDOScalc to check other dose determination programs which calculate the radiation exposure at flight altitudes and which must have the Federal Office of Civil Aviation (Luftfahrtbundesamt) approval.