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|2930 - QAD - Qaanaaq Greenland Digisonde|
Instrument Type: Instrument > Sounder > IonSonde
Observation Site: QAD - Qaanaaq Greenland Digisonde
Instrument Page: QADDescription:
The Digisonde (DGS-256) located at Qaanaaq, Greenland (77.5N, 290.6E) and operated by the University of Massachusettes Lowell Center for Atmospheric Research, for Phillips Laboratory Hanscom AFB, has produced ion velocity measurements and electron density profiles since 1983. The data are originally collected in local magnetic coordinates, and then converted to geographic coordinates using the declination angle of -71.0 for an altitude of 0 km. The Digisonde generally operates in a 15 minute cycle mode, where the first 2-3 minutes an ionogram is recorded followed generally by 1-2 minutes of drift measurements, with the remaining 10-12 minutes idle. Sometimes the cycle time is 5 minutes. The range of altitudes is about 200-450 km, where the mean is about 300 km. Digisondes transmit HF radio waves illuminating a large ionospheric area of several hundred kilomaters diameter over the sounder. Radio waves are sent up and reflected off orthogonal surfaces. Each reflection point is considered to be a separate source and has associated with it a line- of-sight (los) Doppler velocity measurement. Making the assumption that the main contribution to the measured Doppler shifts results from the uniform horizontal bulk motion of the plasma, the los velocity and source location are used to calculate the velocity vector by least squares fit. The drift mode operated at Qaanaaq during 1989 resulted in up to a maximum of 64 sources in a single integration period of 5 seconds. One minute data is obtained where the error bar is the average of the standard deviations from 12 5-second integrations, while the value of each velocity component is the median from a further velocity distribution found using all the data points in the entire one minute period. The 1 minute results were taken and reported every 15 minutes.