The data are presently displayed in 90 s panels (corresponding to four ISIS 2 (0.1 to 20 MHz) ionograms) and data displays from 10 s to a full pass (about 13 minutes) can be presented. If a time interval corresponding to only one ionogram is entered, the ionogram will be displayed full width on the screen. The time required to obtain the requested images varies from less than a minute for one ionogram to many minutes for the maximum time interval. The regular pattern of vertical lines on the ionograms are frequency markers that are imbedded in the sounder-receiver video output data. The frequencies of these markers are given in the ISIS 2 SOUNDER OPERATING MODES TEXT. If "interpolated fixed and swept frequencies" are requested, the lower panel will display this information for the entire time interval requested. A lack of data in this panel indicates that automatic frequency interpolation could not be performed due to a problem in the pcm data or due to a problem encountered by the software routine while attempting to extract information from the pcm file. Another indication of a problem associated with the pcm data is a flat AGC trace at the bottom of the ionogram (note: it is possible to have good AGC values even in some cases where no automatic frequency interpolation was performed). Some of these problems are due to noise bursts in the pcm data. In addition, invalid ionogram start times occasionally encountered during the A/D operation can produce problems with CDAWeb viewing of the ISIS 2 digital ionograms, e.g., a message indicating that no data are available in a selected interval when, in fact, data are available. These problems, which occur most frequently at the beginning of a pass over a telemetry station, can often be circumvented by choosing another time interval (even one that includes the problem area). Please inform Bob Benson ( ) or Dieter Bilitza ( of problems encountered.

Go to the ISIS/Alouette Data Restoration Home Page

For more information about the Alouette/ISIS missions, please contact Dieter Bilitza

NASA Official: J. H. King,
Last Updated: 3 November 1999, DKB