OVERVIEW OF NO_DATA TASK
The "no_data" task was developed at BAS as an adaptive sounding task to reduce dependence on the radar operator selecting the optimum frequency for sounding. When incorporated in the radar control programme (RCP) it monitors the amount of scatter being received (usually placed in the RCP to do this at the end of a full scan). If the amount of scatter falls below a threshold ("nodata_bin_threshold" variable, set in the RCP or site.c) then this triggers a frequency search, using frequencies specified in the RCP. At the end of the frequency search one of two actions can occur.
1) If one of the frequencies scanned has a scatter count that exceeds a threshold value (NODATA_MIN_DATA variable) then the radar moves to this frequency and commences the next scan. As long as the scatter count exceeds the "nodata_bin_threshold" variable the radar will continue at this frequency.
2) If no frequency shows a scatter count that exceeds the NODATA_MIN_DATA variable then the radar moves to a default frequency and commences a scan.
Other variable that can be specified at task start up time are:
The parameter that is to be used for determining the count rate, at Halley this is the pwr_l parameter (e.g. -p p_l).
A threshold value for this parameter, at Halley we normally use 3dB (e.g. -t 3.0). Only pwr_l values exceeding 3dB will contribute to the scatter count.
A minimum range for scatter that is to contribute to the scatter count, at Halley we normally use 600 km (e.g. -d 600). We choose to do this in order to bias the radar operation towards collecting F-region scatter.
The no_data task also accesses the ground scatter flag and does not include ground scatter in the scatter count. Operators who are particularly interested in ground scatter must be aware of this. This condition could easily be removed from the code, ask for details.
The frequency search is only done on a subset of beams (not the full 16). These beams can be set in the RCP. In the RCP at Halley we search five frequencies, each frequency with four beams (2,6, 10 and 14). This allows us to complete the frequency search in less than 2 minutes, so that the next scan can be started on a two minute time boundary. IF YOU CHANGE THE NUMBER OF FREQUENCIES AND/OR BEAMS you may lose this synchronisation with two minute time boundaries.
Original code developed by Rob Barnes whilst working at BAS. Modified in light of operating experience by Duncan Smith and Kevin O'Rourke (Halley radar engineers).INSTALLATION